CN113075183B

CN113075183B - DPA solution relative fluorescence emission intensity standard substance and preparation method and application thereof

Info

Publication number: CN113075183B
Application number: CN202110328139.9A
Authority: CN
Inventors: 尹强; 黄彦捷; 罗思婷; 周瑾艳; 陈玲; 廖泽荣
Original assignee: Guangdong Provincial Institute Of Metrology (south China National Centre Of Metrology)
Current assignee: Guangdong Provincial Institute Of Metrology (south China National Centre Of Metrology)
Priority date: 2021-03-26
Filing date: 2021-03-26
Publication date: 2022-02-22
Anticipated expiration: 2041-03-26
Also published as: CN113075183A

Abstract

The invention discloses a DPA solution relative fluorescence emission intensity standard substance and a preparation method and application thereof. The DPA solution relative fluorescence emission intensity standard substance provided by the invention can provide a standard relative fluorescence emission intensity value with an emission wavelength coverage range of 400-830nm and a wavelength interval of 1nm under the excitation of 380-450nm, and can well meet the calibration requirements of red light and near infrared bands of related instruments. The DPA solution provided by the invention is mainly used as a standard of quantity value transfer relative to a fluorescence emission intensity standard substance, meets the requirements of current research and detection, and can be used for the calibration and analysis method evaluation of detectors and detection modules of fluorescence instruments (such as a spectrometer, a spectrophotometer, an enzyme labeling instrument, a gene amplification instrument, an immunoassay analyzer and the like) and the quality control and other aspects in biology, food, medicines, chemical products and cosmetics.

Description

DPA solution relative fluorescence emission intensity standard substance and preparation method and application thereof

Technical Field

The invention belongs to the technical field of molecular fluorescence analysis and measurement, and particularly relates to a DPA solution relative fluorescence emission intensity standard substance, and a preparation method and application thereof.

Background

In the field of molecular fluorescence analysis and measurement, the most commonly used national standard substances are a GBW (E)130290 liquid phase analyzer detection solution standard substance (naphthalene-methanol solution) and a GBW (E)130100 quinine sulfate fluorescence standard substance. Wherein, the naphthaline methanol solution can only calibrate one excitation wavelength and the corresponding emission wavelength for wavelength calibration. And GBW (E)130100 quinine sulfate fluorescence standard substance has the maximum luminescence position of 450nm (relative emission intensity standard value of 1.000) of bluish green under the excitation of 350nm visible light, and the luminescence efficiency is only 55%. Under 395nm or above 565nm, the standard value of the luminous brightness is under 0.1, which brings great uncertainty. Due to the limitation of the above properties, quinine sulfate standard substances are ineffective in some biological systems, especially in immunoassay of fluorescent markers, mainly because the autofluorescence of many organisms and tissues thereof is in the ultraviolet and visible light regions, such as the ultraviolet light region with the emission fluorescence wavelength range of (325-350) nm of serum proteins in plasma, and the application requirements of red light and near infrared light (600-.

A series of Standard substances (Relative Intensity Correction Standard for Fluorescence Spectroscopy) developed by NIST are mainly used abroad, the serial number is SRM 2940-2944, 5 Standard substances provide values of Relative Intensity Emission Correction (calibration Relative Emission Intensity) covering the range from ultraviolet to near infrared wavelength (320-830 nm) and every 1nm, and the fluorescent calibration Standard has wide application prospect and well meets the calibration requirements of red light and near infrared bands. But related standard substances are still lacked in China.

DPA, IUPAC name: 6- [4- (diphenylamino) phenyl ] coumarin-3-carboxylic acid ethyl ester with CAS number 1056693-13-0 is a coumarin derivative. Coumarin is also called coumarin, is a general name of a class of compounds with benzo alpha-pyrone parent nucleus, and can be structurally regarded as lactone formed by dehydration of cis-o-hydroxycinnamic acid. Low concentration can stimulate plant germination and growth, and high concentration can inhibit. The coumarin compound also has photosensitive effect, antibacterial effect, antiviral effect, smooth muscle relaxation effect and anticoagulant effect, and is a common oral anticoagulant drug. Meanwhile, the coumarin compound is a common fluorescent reagent, is widely applied as a fluorescent dye and a pigment, and has good photoluminescence performance when being externally connected with a D-Pi-A substituent group. At present, no fluorescent dye standard substance exists in the coumarin class or the other classes.

Disclosure of Invention

The invention mainly aims to provide a DPA solution relative fluorescence emission intensity standard substance, under the irradiation of excitation light of 380-450nm, the emission wavelength coverage range is (400-830) nm, the wavelength interval is 1nm, and the calibration requirements of red light and near infrared bands of related instruments can be well met. The standard substance with relative fluorescence emission intensity provided by the invention is mainly used as a standard for quantity value transfer, meets the requirements of current research and detection, and can be used for the calibration and analysis method evaluation of detectors and detection modules of fluorescence instruments (such as a spectrometer, a spectrophotometer, an enzyme labeling instrument, a gene amplification instrument, an immunoassay instrument and the like) and the quality control and other aspects in biology, food, medicines, chemical products and cosmetics.

According to one aspect of the present invention, a DPA solution relative fluorescence emission intensity standard substance is provided, which can provide a standard relative fluorescence emission intensity value with an emission wavelength coverage of 400-830nm and a wavelength interval of 1nm under 380-450nm excitation.

DPA is a good molecular fluorescent probe; the light-emitting range covers red light and partial near infrared region, the fluorescence emission peak has more complete peak type before 830nm, international standard substances can be utilized for tracing, in addition, the DPA has higher luminous intensity and can be used in solvents with moderate polarity, the fluorescence quantum yield (which refers to the utilization of a photon in a photochemical reaction, defined as the number of molecules of the reactant produced per absorbed quantum, which is usually for a particular wavelength, that is, the quantum yield (the number of molecules of the produced product)/(the number of absorbed quanta)) is higher than 70%, has good photoluminescence efficiency, the DPA is used as a raw material to develop a standard substance with relative fluorescence emission intensity, the prepared standard substance with relative fluorescence emission intensity has wide emission wavelength coverage range, can be stable for a long time, is slightly influenced by photobleaching, and has concentration changed within a small range (10).^-6～10^-3) The magnitude does not change.

In some embodiments, the solvent of the DPA solution may be selected from at least one of ortho-xylene, meta-xylene, para-xylene, toluene, benzene. As the polarity of the solvent increases, the maximum absorption and emission wavelengths of the DPA are red-shifted, while the fluorescence intensity decreases. If the polarity of the solvent is too strong, part of fluorescence emission exceeds 830nm and cannot be traced, and the fluorescence intensity is low, and the concentration needs to be increased to cause a fluorescence self-quenching effect, therefore, the solvent with moderate polarity, such as o-xylene, m-xylene, p-xylene, toluene, benzene and the like, is preferably selected to prepare the DPA solution.

In some embodiments, the concentration of the DPA solution may be 10^-7-1 mol/L. When the concentration is too low, the fluorescence intensity is low, and baseline noise can generate large influence on the measurement of an instrument; when the concentration is too high, the fluorescence intensity is higher, on one hand, the fluorescence intensity may exceed the upper limit of the measurement of an instrument, and on the other hand, the self-absorption and self-quenching phenomena are easy to generate.

The excitation wavelength and the emission wavelength coverage range (i.e., emission wavelength range) of the DPA solution prepared by selecting different solvents are different from those of the standard substance with fluorescence emission intensity, as shown in table 17, so that the DPA can be used to prepare the standard substance with fluorescence emission intensity that provides the standard value with fluorescence emission intensity at the wavelength interval of 1nm in the coverage range of 400-830nm under the excitation of 380-450 nm.

In some embodiments, the solvent may be ortho-xylene. The DPA has the best solubility in toluene, but the toluene is a controlled solvent and has hidden danger, the DPA has the better solubility in o-xylene, the maximum emission is 553nm (yellowish green light), and the emission wavelength coverage range is (440-780) nm.

In some embodiments, the concentration of the DPA ortho-xylene solution can be 0.010 mg/mL. When the concentration of the DPA o-xylene solution is 0.010mg/mL (i.e., about 2.17X 10)^-5mol/L), the fluorescence intensity is moderate and stable, and meanwhile, the fluorescence intensity is in the same order of magnitude as that of the fluorescent standard substances SRM2943 and SRM2944 of NIST, and is basically consistent, so that the standard substance with relative fluorescence emission intensity can be traced by using the international standard substance.

The standard relative fluorescence emission intensity values of the DPA o-xylene solution with the concentration of 0.010mg/mL and the wavelength interval of 1nm in the wavelength range of 440-780nm relative fluorescence emission intensity standard substance provided by the invention are shown in Table 16, and can provide the standard relative fluorescence emission intensity values with the emission wavelength coverage range of (440-780) nm and the wavelength interval of 1nm under the excitation of 400 nm.

According to another aspect of the present invention, there is provided a method for preparing a DPA solution relative fluorescence emission intensity standard, comprising the steps of:

preparing DPA into a DPA solution; wherein, the emission spectrum of the DPA solution does not contain impurity fluorescence peaks, namely, the DPA solution does not contain impurities which can quench fluorescence or have fluorescence except the DPA, such as rhodamine, phycobilin, fluorescein, DCM (CAS:51325-91-8) and the like;

carrying out uniformity inspection, stability inspection, value determination and uncertainty analysis on the relative fluorescence emission intensity values of the prepared DPA solution at intervals of 1nm within the corresponding emission wavelength coverage range, and obtaining a DPA solution relative fluorescence emission intensity standard substance if the DPA solution can meet the requirements of the standard substance at intervals of 1nm within the corresponding emission wavelength coverage range;

wherein the step of measuring the relative fluorescence emission intensity value of the DPA solution at intervals of 1nm within the corresponding emission wavelength coverage range comprises the following steps:

(1) under the experimental temperature condition of (25.0 +/-0.5) DEG C, setting the excitation wavelength to be 330.3nm and the emission wavelength detection range to be 350-640nm by using a qualified fluorescence spectrometer under the irradiation of excitation light required by the SRM2943 standard substance certificate specification, setting the excitation side slit and the emission side slit to be 3nm simultaneously or 2.5nm simultaneously, and collecting the spectral emission intensity value at the interval of 1 nm; then dividing the spectral emission intensity under each wavelength by the maximum spectral emission intensity of the SRM2943 standard substance to obtain the relative emission intensity under each wavelength; taking 3 SRM2943 standard substance samples, carrying out parallel measurement on each sample for 3 times, and calculating the average relative emission intensity value under each wavelength; finally, dividing the relative emission intensity value under each wavelength given in the SRM2943 standard substance certificate by the average relative emission intensity value of the corresponding wavelength to calculate the correction factor F value of the SRM2943 standard substance under each wavelength within the wavelength range of 350-640 nm;

(2) under the experimental temperature condition of (25.0 +/-0.5) DEG C, setting the excitation wavelength to be 515nm, the emission wavelength detection range to be 530-830nm, the excitation side slit and the emission side slit to be 3nm simultaneously or 2.5nm simultaneously by using a qualified fluorescence spectrometer under the irradiation of excitation light required by the SRM2944 standard substance certificate, and acquiring the spectral emission intensity value at the interval of 1 nm; then dividing the spectral emission intensity under each wavelength by the maximum spectral emission intensity of the SRM2944 standard substance to obtain the relative emission intensity under each wavelength; taking 3 SRM2944 standard substance samples, carrying out parallel measurement on each sample for 3 times, and calculating the average relative emission intensity value under each wavelength; finally, dividing the relative emission intensity value under each wavelength given in the SRM2944 standard substance certificate by the average relative emission intensity value of the corresponding wavelength to calculate the correction factor F value of the SRM2944 standard substance under each wavelength within the wavelength range of 530-830 nm;

(3) under the experimental temperature condition of (25.0 +/-0.5) DEG C, a qualified fluorescence spectrometer is utilized, a DPA solution is placed in a sample chamber, the corresponding detection ranges of the excitation wavelength and the emission wavelength are set, the excitation side slit and the emission side slit are set to be 3nm or 2.5nm at the same time, and the spectral emission intensity value is acquired at the interval of 1 nm; then multiplying the spectrum emission intensity under each wavelength by the correction factor F value of the corresponding wavelength, and then dividing the product of the maximum spectrum emission intensity of the DPA solution and the correction factor F value of the corresponding wavelength to obtain the relative emission intensity under each wavelength, wherein for each wavelength in the wavelength range of 400-; and (3) selecting 3 DPA solution samples, measuring each sample in parallel for 3 times, and taking the calculated average relative emission intensity value at each wavelength as the measurement result of the relative fluorescence emission intensity value at the corresponding wavelength of the DPA solution.

In the preparation method of the DPA solution relative fluorescence emission intensity standard substance, the intensity calibration is carried out by adopting the SRM2943 or SRM2944 standard substance of NIST when the emission intensity value of the DPA solution is measured every time, so that the measurement result is compared with the international standard substance quality value, the international standard substance can be used for tracing, and meanwhile, the difference of the measurement result of instruments among laboratories (such as accidental errors of the instruments, intensity fluctuation or different sensitivities of detectors and the like) can be avoided, so that the measurement result of each laboratory can be compared.

In some embodiments, the determination of the relative fluorescence emission intensity values of a DPA solution at every 1nm within its corresponding emission wavelength coverage comprises the steps of:

s1, utilizing n laboratories to respectively refer to the measurement steps (1) - (3) of the relative fluorescence emission intensity values of the DPA solution at every 1nm in the corresponding emission wavelength coverage range to determine the relative fluorescence emission intensity values of the DPA solution at every 1nm in the corresponding emission wavelength coverage range; wherein n is more than or equal to 3;

s2, performing normal distribution analysis and suspicious value analysis in groups on the fixed value result of each laboratory respectively; then, performing equal precision analysis between groups and consistency test of data between groups on the fixed value results of all laboratories; finally, combining the fixed value results of all laboratories to perform normal distribution analysis and data abnormal value test; if the following conditions are met simultaneously: the method comprises the steps that the default setting result of each fixed value laboratory accords with normal distribution, no suspicious value exists in the default setting result of each fixed value laboratory, the precision among the constant setting result groups of all fixed value laboratories is equal, the average value of data among all fixed value laboratory groups is consistent, the fixed value results of all fixed value laboratories are combined to accord with normal distribution, no suspicious value exists in the fixed value results of all fixed value laboratories, and then the average value of the fixed value results of all laboratories under the corresponding wavelength is used as the final fixed value of the DPA solution.

The method adopts a method with the same principle to fix the value and a combined value fixing mode of the statistical mean value of experimental big data to the DPA solution relative fluorescence emission intensity standard substance, so that the reliability and the accuracy of the value can be effectively improved.

In some embodiments, the solvent of the DPA solution may be selected from at least one of ortho-xylene, meta-xylene, para-xylene, toluene, benzene.

In some embodiments, DPA solutions formulated with different solvents have excitation wavelength and emission wavelength coverage as shown in table 17.

In some embodiments, the concentration of the DPA solution may be 10^-7-1mol/L。

In some embodiments, the solvent may be ortho-xylene; further, the concentration of the DPA ortho-xylene solution may be 10^-7-1 mol/L; still further, the concentration of the DPA ortho-xylene solution may be 0.010 mg/mL.

In some embodiments, a DPA ortho-xylene solution at a concentration of 0.010mg/mL, as a relative fluorescence emission intensity standard, corresponds to an emission wavelength coverage of 440-780nm under excitation at 400 nm.

The standard substance with relative fluorescence emission intensity provided by the invention can be used for preparing a fluorescence standard substance or can be directly used as the fluorescence standard substance, when the standard substance is used as the fluorescence standard substance, the measurement result of the standard substance is consistent with that of the existing fluorescence standard substance at home and abroad within an uncertainty range, the standard substance is suitable for measuring samples, and the measurement method is stable, convenient and practical. The standard substance with relative fluorescence emission intensity provided by the invention can meet the requirements of research and detection of biology, food, medicine, daily chemicals, environmental protection and chemical products, can be used for the calibration and analysis method evaluation of detectors and detection modules of fluorescence instruments (such as a spectrometer, a spectrophotometer, an enzyme labeling instrument, a gene amplification instrument, an immunoassay analyzer and the like), and plays a due role in unifying relevant quantity values.

Drawings

FIG. 1 is a corrected relative emission spectrum of a DPA o-xylene solution at a concentration of 0.010mg/mL relative to a fluorescence emission intensity standard candidate measured by the Guangdong provincial institute of metrology science using a Nanog spectrometer at all constant wavelengths;

FIG. 2 is a graph of the magnitude of SRM2941 and GBW (E)130100 quinine sulfate fluorescent standards;

FIG. 3 is a graph of corrected relative emission spectra of GBW (E)130100 compared to a standard emission spectrum;

FIG. 4 is a graph of energy correction factor F for calibrating a fluorescence spectrometer at wavelengths (530-640) nm using SRM2943 and 2944, respectively;

FIG. 5 is the emission spectra of DPA ortho-xylene solution relative to fluorescence emission intensity standard substance under the conditions of 3nm grating slit and 2.5nm grating slit of different instruments;

FIG. 6 is the emission spectra of DPA ortho-xylene solution versus fluorescence emission intensity standard under different light source conditions.

Detailed Description

The present invention will be described in further detail with reference to the following embodiments and the accompanying drawings. Experimental procedures, in which specific conditions are not indicated in the examples below, are generally carried out according to conditions conventional in the art or as recommended by the manufacturer. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is familiar to those skilled in the art.

In the preparation method of the standard substance with relative fluorescence emission intensity provided by the invention, the fixed value basis and model method is as follows:

1. SRM2943 and SRM2944 standard substances are selected as calibration substances

The development of the relative fluorescence emission intensity standard substance adopts 8 quality laboratories to jointly determine the value, and a fluorescence spectrometer used by each laboratory is calibrated at the same emission wavelength of the determined value of the SRM2943 and SRM2944 fluorescence standard substances of NIST.

The SRM2943 and SRM2944 standard substances are selected as calibration bases, and the calibration bases comprise: (1) the application fields of the SRM2943, the SRM2944 and the standard substance with relative fluorescence emission intensity to be developed are the calibration of the relative emission intensity of fluorescence emission spectrum, and have the same application prospect; (2) when the SRM2943, the SRM2944 and a standard substance to be developed with relative fluorescence emission intensity are used, the selected excitation wavelengths are similar, and the wavelength ranges corresponding to the emission spectra are the same; (3) the SRM2943 and the SRM2944 are uniform solid crystals with the size of 12.5mm multiplied by 45.0mm, and the standard substance with the relative fluorescence emission intensity to be developed is filled in a quartz cuvette with the size of 12.5mm multiplied by 45.0mm in the form of uniform solution when in use; (4) when the same fluorescence spectrometer is used for measurement, the fluorescence intensities of the NIST standard substance and the standard substance with relative fluorescence emission intensity to be developed are consistent; (5) the SRM2943 and the SRM2944 are solid crystals, and the matrix of the solid crystals is transmission glass; and the DPA uses a quartz cuvette or selected solvents such as o-xylene and the like, and has no fluorescence emission in a fixed wavelength range, so that the fixed value is not interfered.

2. Fixed value model and procedure

The specific value setting steps are as follows:

emission spectra of SRM2943 and SRM2944 Standard substances in a wavelength range within the Certificate range were measured by a fluorescence spectrometer under excitation light irradiation for which specification is required, setting the corresponding excitation wavelength and the excitation side and emission side slits to be 3nm and 3nm, respectively, according to the use requirements in NIST Standard Reference Material 2943 and Standard Reference Material 2944Certificate and the relative description of error P C, et al, characteristics of Standard Reference Material 2944, Bi-ion-doped glass, and spectral correction Standard for which fluorescence is required, J.Lumin 2013,141:9-14, and ensuring that the laboratory temperature is (25.0 + -0.5) ° C. The spectral intensity at each wavelength is divided by the maximum spectral emission intensity to give the relative emission intensity at each wavelength. The relative emission intensity value given in the SRM2943 or SRM2944 standard substance certificate is divided by the relative emission intensity value at the corresponding wavelength to calculate a correction factor F value.

Energy correction factor:

in the formula:

-averaging the relative emission intensity measurements; er-a reference value for relative emission intensity in a certificate;

setting the wavelength of an excitation side at the excitation wavelength of a fluorescence standard substance candidate by using a fluorescence spectrometer, placing the fluorescence standard substance candidate in a sample chamber, setting slits of the excitation side and an emission side to be 3nm and 3nm respectively, collecting an emission spectrum in an emission wavelength range, and multiplying the obtained relative emission spectrum by a correction factor F to obtain the relative emission intensity value of the fluorescence standard substance. 3 bottles of fluorescent standard substance are randomly selected, each bottle is parallelly measured for 3 times, and the relative emission intensity value is calculated. And calculating the average relative emission intensity value as a fixed value result of the fluorescent standard substance.

Taking the fixed value of DPA o-xylene solution with the concentration of 0.010mg/mL relative to the fluorescence emission intensity standard substance at 600nm calculated by Guangdong provincial institute of metrology science as an example:

the fluorescence emission spectrum of the SRM2944 is measured under 515nm excitation by using a Nanolog spectrometer, and the maximum emission wavelength of the fluorescence emission spectrum is 704nm and accords with a certificate. Wherein the fluorescence emission intensity at 704nm in one measurement is 3.136X 10⁶Fluorescence emission intensity at 600nm of 4.065X 10⁵So that the relative emission intensity at 600nm is 4.065X 10⁵/3.136×10⁶＝0.1296。

② 3 samples are respectively calculated by the same method for 3 times of parallel measurement, and the average relative emission intensity at 600nm is 0.1311 in 9 times of experiments.

Searching for the SRM2944 certificate, wherein the relative emission intensity at 600nm is 0.1418. According to the formula (1), the energy correction factor F at 600nm is calculated to be 0.1418/0.1311 to be 1.082. The energy correction factor F at 553nm can be calculated 0.801 in a similar manner.

The emission spectrum of the DPA o-xylene solution relative to the fluorescence emission intensity standard substance candidate under the excitation of 400nm by using a Nanolog spectrometer shows that the maximum emission wavelength is 553nm, wherein the fluorescence emission intensity at 553nm in one measurement is 2.363 multiplied by 10⁶Fluorescence emission intensity at 600nm of 1.269X 10⁶Thus, the relative emission intensity after calibration at 600nm was (1.269X 10)⁶×1.082)/(2.263×10⁶×0.801)＝0.7254。

In the same way, 3 replicates of 3 samples were calculated, and the average relative emission intensity at 600nm was 0.7265 for a total of 9 experiments, and this data was used as a fixed value of the relative emission intensity at 600nm for the fixed value laboratory DPA ortho-xylene solution relative fluorescence emission intensity standard candidate.

The relative emission intensity calculation process for the remaining wavelengths is similar to that described above. The corrected relative emission spectra of DPA ortho-xylene solutions versus fluorescence emission intensity standard candidates at all wavelengths for the values are shown in FIG. 1.

The constant value calculation process for other constant value units is similar to the above process.

3. Evaluation of rationality of traceability rating result

3.1 comparative rationality evaluation of relative emission intensity

At each unit's associated setting, calibration was performed using the relative emission intensity at the same emission wavelength of the fluorescent standard substance SRM2943 or SRM2944 from NIST, i.e., the measured emission intensity of the calibration instrument at the same wavelength. However, it is considered that the emission intensity at the same emission wavelength is greatly different because the SRM2943 or SRM2944 is not the same substance as the DPA in the present invention. In order to prove the rationality of the calibration, several fluorescence standard substances with accurate values are selected for experimental study.

The fluorescence standard substances selected are: SRM2941 from NIST, which can provide relative emission intensity values covering (450-650) nm under 427nm excitation, with a wavelength interval of 1 nm; (E) GBW 130100 quinine sulfate fluorescence standard substance, which can provide relative emission intensity values covering (375-675) nm under the excitation of 350nm, and the wavelength interval is 5 nm. Both magnitudes are shown in figure 2.

As can be seen from FIG. 2, both of them can repeatedly cover the wavelength range of (450 to 650) nm, although the excitation wavelengths are different. Especially at certain wavelengths, there is a large difference in the relative emission intensity values, for example: at 450nm, the relative emission intensity of SRM2941 is only 0.0004, while GBW (E)130100 is 1.000; at 525nm, the relative emission intensity of SRM2941 is 0.9941, while GBW (E)130100 is only 0.303. Therefore, the invention adopts a calibration method similar to that of the standard substance in fixed value, firstly the emission spectrum of the SRM2941 of NIST is measured, and the correction factor F is calculated; the emission spectrum of GBW (E)130100 is then determined and compared with the certificate value of GBW (E)130100 after calibration, the result is shown in FIG. 3.

As can be seen from FIG. 3, the emission spectrum measured in GBW (E)130100, after calibration with the SRM2941 standard substance of NIST, matches well with the relative emission intensity value of the standard spectrum. The relative emission intensity is 0.9977 when measured at 450nm, and meets the requirement of 1.000 +/-0.004 specified by the certificate; the relative emission intensity measured at 525nm is 0.3042, which meets the requirement of 0.303 +/-0.002 specified by the certificate. It is reasonable to use NIST standard substance for calibration of fixed value instrument.

3.2 SRM2943 and SRM2944 repeat wavelength ranges

The excitation and emission wavelengths are generally different for different fluorescent substances, and it is therefore difficult to cover the entire wavelength range with one NIST standard substance as a calibration reference. In the process of valuing the standard substance, two NIST standard substances are selected. The SRM2943 of NIST can provide a relative emission intensity value covering (350-640) nm under the excitation of 330.3nm, and the wavelength interval is 1 nm; ② the SRM2944 of NIST, which can provide relative emission intensity value covering (530-830) nm under 515nm excitation, and the wavelength interval is 1 nm.

When the two substances are used for calibrating a fluorescence spectrometer, a repeated wavelength range, namely (530-640) nm, exists. In order to compare the consistency of the two standard substances to the wavelength calibration, the emission spectra of the two SRM standard substances were measured separately using a fluorescence spectrometer, and the energy correction factor F value was calculated, and the results are shown in fig. 4.

It can be seen from fig. 4 that the energy correction factor F values obtained by calibrating the fluorescence spectrometer with the SRM2943 and the SRM2944, respectively, are substantially consistent, and the maximum deviation of the F values calculated for the two SRM standard substances is not more than 1.0%. The other subject matter measured after correction falls within the uncertainty range given by both certificates. Thus, the relative emission intensities of the SRM2943 or SRM2944 may be arbitrarily chosen as a basis for calibration for the repeated wavelength ranges.

In subsequent calculations, the calibration concept adopted by the invention is as follows: because the energy calibration factors given by the calibration of the SRM2943 and the SRM2944 are basically consistent, the relative emission intensity of the SRM2943 is used as a calibration basis for (440-560) nm, and the relative emission intensity of the SRM2944 is used as a calibration basis for (561-780) nm.

EXAMPLE 1 development of DPA ortho-xylene solution relative fluorescence emission intensity Standard

1. Standard substance sample preparation

1.1 starting materials and reagents

Raw materials: commercially available high purity ethyl 6- [4- (diphenylamino) phenyl ] coumarin-3-carboxylate from TCI taishieii chemical industry development limited (TCI), 1 bottle.

Solvent: chromatographically pure o-xylene (CAS: 95-47-6) from Fisher (Fisher) Inc., 4L package.

1.2 apparatus

1.2.1 Equipment for Standard substance preparation: 2000mL of A-grade volumetric flask; accuracy is one hundred thousand balance (sidoris, germany); electric pipettors (Eppendorf, germany); hundred grades of clean benches and the like are qualified by verification.

1.2.2 Standard substance packaging equipment: 5mL brown ampoule bottle and ampoule melting and sealing machine.

1.2.3 apparatus for standard substance analysis:

(1) homogeneity test and stability investigation equipment: a Nanolog fluorescence spectrometer, HORIBA JOBIN YVON, France, is equipped with a non-chromatic aberration total reflection focusing light path and a mechanically etched planar diffraction grating. Excitation light source: 450W non-ozone continuous xenon lamp, standard low pressure mercury lamp; a detector: and an R928 photomultiplier detector (200-900 nm).

(2) Combining a fixed value unit and a fixed value instrument: as shown in Table 1

TABLE 1 Joint constant value Unit and constant value Instrument

Serial number	Name (R)	Instrument type	Instrument brand
				1	Beijing university analysis and test center	FL3-2iHR	HORIBA
2	Chemical and industrial college of Xiamen university	FLS980	EDINBURGH
				3	Analytical testing center of Guangdong university of industry	Fluorolog3	HORIBA
4	Guangzhou Wondfo Biotech Co.,Ltd.	RF5301PC	SHIMADZU
				5	Guangzhou analytical testing center, China	RF6000	SHIMADZU
6	ZHEJIANG MEASUREMENT SCIENCE Research Institute	FluoroMax-4	HORIBA
				7	Shenzhen Institute of measurement and quality inspection	F7100	HITACHI
8	Guangdong Academy of Metrology	Nanolog	HORIBA

The standard substance analysis equipment meets the verification qualification of JJG 537-.

1.3 preparation of a DPA ortho-xylene solution

1.3.1 preparation

Accurately weighing 20mg of 6- [4- (diphenylamino) phenyl ] coumarin-3-carboxylic acid ethyl ester (DPA), dissolving with chromatographic grade o-xylene, transferring into a 2000mL volumetric flask (qualified by the institute of metrology and science, Guangdong province, A grade), metering the o-xylene solution to a scale mark, and mixing uniformly.

1.3.2 subpackaging

The well-mixed DPA o-xylene solution is divided into 5mL brown ampoules, each containing 5mL of the standard substance candidate with respect to the fluorescence emission intensity, and the ampoules are divided into about 400.

1.3.3 storage and transportation

The standard substance should be stored in the dark at normal temperature (15-35 ℃), and severe collision is avoided during transportation.

2. Uniformity test

Respectively randomly extracting 15 samples from the DPA o-xylene solution which is divided and numbered according to serial numbers of head, tail and middle, carrying out fixed value measurement by using a Nanolog fluorescence spectrometer (the specific measurement step is detailed in the steps (1) - (3) of the following 4.1 combined fixed value process specific experiment step), setting the excitation wavelength to be 400nm, setting the widths of slits on the excitation side and the emission side to be 3nm, testing the fluorescence emission spectrum at intervals of 1nm for (440 + 780) nm, calculating the corrected relative emission intensity, totaling 341 data points, measuring 3 times at each wavelength, and taking the average value as the measurement result of uniformity evaluation.

This example only selects the examination process of correcting relative emission intensity of 1 emission wavelength as a representative process for describing the uniformity test, the representative emission wavelength is 600nm, the uniformity test process is as follows, and the uniformity test results at the other wavelengths are similar.

2.1 inspection of relative emission intensity uniformity with an emission wavelength of 600nm

The results of examining the uniformity of the relative emission intensity at an emission wavelength of 600nm are shown in Table 2 below:

TABLE 2 relative emission intensity uniformity test data (. lamda.)_em＝600nm)

The homogeneity of the samples was investigated using analysis of variance at 95% confidence probability and the results calculated are shown in table 3 below.

TABLE 3 analysis of variance (λ) of relative emission intensity uniformity_em＝600nm)

Source of difference

SS

df

MS

F

P-value

Fcrit

Between groups

3.45E-06

14

2.47E-07

0.470645

0.931439

2.03742

In group

1.57E-05

30

5.24E-07

From the data in table 3, one can see:

F_α(ν₁,ν₂)＝2.037,α＝0.05

F<F_αindicating that there was no significant difference between the samples.

As can be seen from the calculations: the statistic F of the result is smaller than the uniformity test critical value F_α(14,30): 2.037, demonstrating that the standard was homogeneous.

Good sample uniformity, but s_HAnd s₂Similarly, the total uncertainty must take uniformity considerations into account, and the standard deviation resulting from the non-uniformity needs to be incorporated into the constant final uncertainty.

The above results indicate that the relative emission intensities at 600nm are uniform. Similarly, the relative emission intensity of the DPA ortho-xylene solution at (440-780) nm was determined to be uniform. Table 4 lists the uniformity calculations for only a portion of the wavelengths.

TABLE 4 relative fluorescence emission intensity standard homogeneity test results for DPA o-xylene solution at part of wavelength

3. Stability survey

In the development of standard substances, it is necessary to determine the relative stability period by periodically examining them for a long period of time using analytical methods of high precision.

Randomly extracting a DPA (dinitrotoluene) o-xylene solution sample, carrying out fixed value measurement by using a Nanolog fluorescence spectrometer (the specific measurement steps are detailed in steps (1) - (3) of a specific experiment step of a 4.1 combined fixed value process below), setting the excitation wavelength to be 400nm, setting the widths of slits on the excitation side and the emission side to be 3nm, testing a fluorescence emission spectrum at intervals of 1nm for (440-780) nm, calculating the corrected relative emission intensity, counting 341 data points in total, measuring 3 times at each wavelength, and taking the average value of different times as the measurement result of stability evaluation.

In this example, only the corrected relative emission intensity of 1 emission wavelength is selected as a representative to introduce the stability test process, the taken representative emission wavelengths are respectively 600nm, the stability test process is as follows, and the stability test results at the other wavelengths are similar. In the invention, t is selected to be 12 months to examine the stability of the fluorescent standard substance.

3.1 relative emission intensity Long-term stability test with an emission wavelength of 600nm

The relative emission intensity stability results for an emission wavelength of 600nm are listed in table 5:

TABLE 5 relative emission intensity stability test data (. lamda.)_em＝600nm)

The stability analysis by variance results are shown in table 6:

TABLE 6 stability regression analysis of variance results (. lamda.)_em＝600nm)

	df	SS	MS	F	SignificanceF
						Regression analysis	1	1.28E-07	1.28E-07	0.158679	0.518
Residual error	4	3.23E-06	8.07E-07
						Total of	5	3.35E-06

Since no physical/chemical model can truly describe the degradation mechanism of the candidate standard sample, a straight line is used as an empirical model. The data in the table, x represents time, and y represents relative fluorescence emission intensity of the DPA dye, are fitted into a straight line to judge the stability of the sample. The slope of the line is:

the intercept is calculated by:

the uncertainty of the slope is:

the t distribution factor for the degree of freedom f-n-2-4 and p-0.95 (95% confidence level) is equal to 2.78.

t_0.95,n-2·s(b₁)＝2.78×9.0×10^-5＝2.4×10^-4

Due to | b₁|＜t_0.95,n-2·s(b₁) The slope is not significant. Thus, no instability was observed, indicating that within 12 months the regression was not significant, i.e. there was no significant trend change in the amount of DPA ortho-xylene solution relative to the fluorescence emission intensity standard, indicating that the storage conditions adopted in the present invention effectively guarantee the stability of the DPA ortho-xylene solution relative to the value of the fluorescence emission intensity standard.

The uncertainty contribution of the long-term stability of the validity period t of 12 months is:

u_(600nm)Its＝s_b·t＝9.0×10^-5×12＝0.0011

the above results show that the magnitude at 600nm does not undergo significant trend changes. Similarly, the relative emission intensities at (440-780) nm were determined to be stable, and Table 7 lists the long-term stability calculations at only a fraction of the wavelengths.

TABLE 7 long-term stability test results of DPA o-xylene solution relative to fluorescence emission intensity standard substance at part of wavelengths

3.2 short term stability test

Short term stability refers to the stability of a standard substance under transport conditions.

In order to investigate the influence of the transportation conditions on the stability of the standard substance and comprehensively consider the high-temperature weather in the south and the low-temperature weather in the north, the invention simulates the transportation conditions, namely (50 +/-2) DEG C.

The first consideration is the influence of the solvent, which is selected from chromatographic pure o-xylene, the melting point of which is-25 ℃ and the boiling point of which is 144.4 ℃, so that the phase change process such as solidification or boiling and the like hardly occurs in the temperature range simulating the transportation condition.

The short-term stability test is carried out by randomly taking 2 groups of samples, 6 parts of each group, respectively placing in an incubator, simulating transportation conditions, namely (50 +/-2) DEG C, selecting conventional storage conditions (25 +/-2) DEG C as reference, respectively storing for one week, respectively taking out from the simulated environment at about 15:00 pm on 1 st, 3 th, 5 th and 7 th days, and measuring relative emission intensity when the samples are recovered to the experimental temperature of 25 ℃. The stability of the DPA-o-xylene solution was evaluated by comparing the fluorescence emission intensity at 600nm, and it was found (see Table 8) that the DPA-o-xylene solution was not significantly changed from the standard value of fluorescence emission intensity under the transportation conditions.

TABLE 8 short term stability test data (. lamda.) for DPA o-xylene solution versus fluorescence emission intensity standard_em＝600nm)

Similarly, | b under simulated transport conditions can be calculated₁|＜t_0.95,n-2·s(b₁) Therefore quality of standard substanceThe values do not change significantly, so the slope is not significant. Thus, no instability was observed, indicating that the regression was not significant under 7-day shipping conditions, i.e., no significant trend change occurred in the amount of DPA ortho-xylene solution relative to the fluorescence emission intensity standard, indicating that shipping conditions did not affect the stability of the amount of DPA ortho-xylene solution relative to the fluorescence emission intensity standard at 600 nm. The uncertainty contribution of the short-term stability of the validity period t of 7 days is:

u_(600nm)Its＝s_b·t≈0.0008

similarly, the relative emission intensities at (440-780) nm are stable. Table 9 lists the results of the transportation stability calculations at only a portion of the wavelengths.

TABLE 9 transport stability test results of DPA o-xylene solution relative fluorescence emission intensity standard substance at part of wavelength

4. Constant value

4.1 specific Experimental procedures for Joint valuating Process

(1) Determination of SRM2943 standard substance: according to the requirements of NIST Standard Reference Material 2943 Certificate, the fluorescence spectrometer is placed at a laboratory temperature of (25 + -0.5) deg.C, the surfaces of the SRM2943 are cleaned with a clean piece of mirror paper, the test is performed in the measurement light path of the fluorescence spectrometer so that the excitation light beam is perpendicular to and concentrated on one light-transmitting surface of the SRM2943, and the emitted fluorescence is collected in the direction of the adjacent light-transmitting surface at an angle of 90 degrees to the excitation light beam. Setting the excitation wavelength to be 330.3nm, and setting the detection range of the emission wavelength as follows: (350-640) nm, the slits on the excitation side and the emission side are 3nm and 3nm (or 2.5nm and 2.5nm), the fluorescence intensity value is collected at intervals of 1nm, and the three times of parallel measurement are carried out. The spectral intensity at each wavelength is divided by the maximum spectral emission intensity to give the relative emission intensity at each wavelength. Dividing the relative emission intensity value given in the SRM2943 standard substance certificate by each relative emission intensity value to obtain a correction factor F value;

(2) determination of SRM2944 standard substance: according to the requirements of NIST Standard Reference Material 2944Certificate, the fluorescence spectrometer is at a laboratory temperature of (25 + -0.5) deg.C, the surfaces of the SRM2944 are cleaned with a clean piece of mirror paper, the test is performed in the measurement path of the fluorescence spectrometer so that the excitation light beam is perpendicular to and concentrated on one of the light transmitting surfaces of the SRM2944, and the emitted fluorescence is collected in the direction of the adjacent light transmitting surface at an angle of 90 degrees to the excitation light beam. Setting the excitation wavelength as 515nm, the emission wavelength detection range as follows: (530-830) nm, the slits on the excitation side and the emission side are 3nm and 3nm (or 2.5nm and 2.5nm), the fluorescence intensity value is collected at intervals of 1nm, and the fluorescence intensity value is measured in parallel three times. The spectral intensity at each wavelength is divided by the maximum spectral emission intensity to give the relative emission intensity at each wavelength. The relative emission intensity value given in the SRM2944 standard substance certificate is divided by the value of the correction factor F calculated for each relative emission intensity value.

(3) Determination of DPA o-xylene solution relative to fluorescence emission intensity standard: the fluorescence spectroscopy laboratory temperature was maintained at (25 ± 0.5) ° c, no less than 3mL of the DPA solution was transferred to a 12.5mm x 45.0mm clean quartz cuvette, placed in the measurement light path of the fluorescence spectrometer for testing, such that the excitation light beam was perpendicular to and concentrated on one surface of the cuvette (below the liquid level), and the emitted fluorescence was collected in the direction of the adjacent surface at a 90 degree angle to the excitation light beam. Setting the excitation wavelength to be 400nm, and setting the emission wavelength detection range: (440-780) nm, the slits on the excitation side and the emission side are 3nm and 3nm (or 2.5nm and 2.5nm), the fluorescence intensity value is collected at intervals of 1nm, and each sample is parallelly measured three times for 9 times. The spectral intensity under each wavelength is multiplied by the corresponding correction factor F and then divided by the product of the maximum spectral emission intensity and the correction factor F value of the corresponding wavelength, and then the relative emission intensity under each wavelength can be obtained.

(4) A total of 8 laboratories participated in joint quantitation (as shown in table 1), and each laboratory instrument was certified by a legal metrology facility before use. The relative emission intensity of the DPA o-xylene solution at each wavelength was determined in each laboratory participating in the joint quantification by referring to the above steps (1) to (3).

(5) In order to judge the reasonability of the data of each laboratory, the following steps are respectively carried out: firstly, carrying out normal distribution analysis on measurement results in each fixed value laboratory group; analyzing suspicious values of measurement results in each fixed value laboratory group; 8, equal precision analysis among measurement result groups of the fixed value laboratory; fourthly, data consistency inspection among 8 constant value laboratory groups; 8, normal distribution analysis of fixed value measurement results. The calculation result shows that:

firstly, the measurement results in each fixed value laboratory group accord with normal distribution;

no suspicious value exists in the measurement result in each fixed value laboratory group;

the precision between the measurement result groups of 8 constant value laboratories is equal;

fourthly, the average values of the data among the 8 constant value laboratory groups are consistent;

combining 8 fixed value measurement results to accord with normal distribution;

and sixthly, merging the 8 fixed value measurement results to obtain no suspicious value.

The method comprises the following specific steps:

4.2 Normal distribution analysis of measurement results in each fixed value laboratory group

According to JJF1343-2012 'evaluation of standard substance definite value and uniformity and stability' data distribution condition examination: including visualization methods such as histogram, kernel density plot (kernel density plot), Q-Q plot, P-P plot, etc.; statistical tests deviating from a specific distribution, such as the skewing coefficient and kurtosis coefficient method (8. ltoreq. n.ltoreq.5000) for normal distribution test, Charcot-Williams' method (3. ltoreq. n.ltoreq.50), Dagordono (50. ltoreq. n.ltoreq.1000) method, the Elissi-pril method (n.ltoreq.8), and the like.

According to the invention, IBM SPSS20 software is used for carrying out normal analysis on 2728 groups of data (9 data in each group), firstly, the normal distribution analysis of the measurement results under all wavelengths in each set of rating laboratories is carried out, the analysis results of part of the wavelengths are shown in Table 10, the asymptotic significance (two sides) of the 8 sets of laboratory rating results obtained by the Kolmogorov-Smirnov method is shown in Table 10, and the calculated values of all the results are more than 0.05, so that the data obey normal distribution is shown.

TABLE 10 Normal distribution analysis of measurements in each set of fixed value laboratories

5.3 analysis of suspicious values in groups of Per-family fixed-value laboratories

According to JJF1343-2012 'standard substance definite value and uniformity, stability assessment' outlier test: including graphical tests, the Grubbs (Grubbs) method, the Dixon (Dixon) method, the mandel H and K statistics (for the outlier variance test).

There were 341 total data from 440nm to 780nm, 8 joint benchmarking laboratories, 2728 groups of data, and 9 measurements in each group. In this embodiment, the suspicious value analysis process in each set of fixed value laboratories is described by taking the relative emission intensity of fluorescence at 600nm as an example in one set of fixed value laboratories, and the data are arranged from small to large as follows:

0.7269<0.7272<0.7274<0.7280<0.7283＝0.7283<0.7287<0.7291<0.7292。

and (4) analyzing all data by adopting a dixon criterion and a Grabas criterion, wherein the specific analysis process is as follows, and no suspicious value is found.

4.3.1 Distinguishing by Dixon's criterion

The above data was analyzed using the Dixon (Dixon) criterion.

When n is 9, then

And (6) looking up a table to obtain: in this case, D (. alpha., n) is D (0.05,9) ═ 0.564, r'₁₁＜r₁₁And r is_ij< D (. alpha., n). Indicating that the group has no abnormal value.

4.3.2 discrimination Using the Grabbs criterion

Arithmetic mean of the above data:

calculating the standard deviation of the experiment: s-0.000812

Calculating each residual error separately

The residual error with the largest absolute value was 0.0012, which corresponds to a measurement value of 0.7269.

Search for the threshold of the gridbus criterion: g (0.05,9) ═ 2.215, so:

thus, no abnormal value was indicated.

4.3.3 outlier discrimination within all data sets

The Excel software can be used for carrying out abnormal value analysis on total (341 multiplied by 8)2728 groups of data (9 data in each group), the Dixon criterion and the Grasbus criterion are respectively adopted to judge whether suspicious values exist, and the calculation result shows that the data in all groups of each joint definite value laboratory do not have the suspicious values.

4.4 equal precision analysis between groups of measurement results of eight constant value laboratories

According to the precision test of JJF1343-2012 'fixed value and uniformity of standard substance, stability evaluation' intergroup data and the like: including the test by the Kokring (Cochran) method, the test by the F method, the test by the Bartlett method, the test by the Leven method and the like. The Excel software can be used for carrying out equal precision analysis on total (341 × 8)2728 groups of data (9 data in each group), and the Cochran criterion is adopted for discrimination, and the specific operation steps are as follows:

listing the relative emission intensity E data of 8 laboratories under the same wavelength in the same line of Excel (m is a laboratory number, n is a measurement time) in the following sequence:

545nm：E11，E12……E19……Em1，Em2，……Em9……E81，E82……E89

546nm：E11，E12……E19……Em1，Em2，……Em9……E81，E82……E89

…………

830nm：E11，E12……E19……Em1，Em2，……Em9……E81，E82……E89

for a total of 341 rows and 72 columns.

② calculate the standard deviation s of every 9 data (i.e. every laboratory)₁，s₂……s₉；

Calculating the sum of variances

Fourthly, screening the maximum standard deviation of each laboratory, and calculating the statistic C according to the Kocurin formula

The precision of the data among all groups is judged by adopting the Kokern criterion, and the like, wherein the precision of the data among all groups is judged by analyzing the precision of the measurement results among 8 constant value laboratories under all wavelengths, the analysis results of partial wavelengths are shown in a table 11, and the result of dividing the statistic C value under all wavelengths by C (0.05,8,9) into 0.2926 is calculated to be less than 1.

TABLE 11 partial results of equal precision analysis between groups of eight constant value laboratory measurement results

4.5 data consistency test among eight-family fixed-value laboratory groups

According to JJF1343-2012 'evaluation of standard substance constant value and uniformity and stability' group data consistency test: the method comprises the steps of average value consistency t test and compatibility test. And selecting the group with the maximum average value and the group with the minimum average value of the 8 constant value laboratory constant value results to carry out average value consistency t-test. The specific operation steps are as follows:

the relative emission intensity E data of 2 laboratories with the largest and smallest average values at the same wavelength are listed in the same line of Excel (m is the laboratory number, n is the number of measurements) in the following order:

545nm, E11, E12 … … E19; e21, E22 … … E29, average value

Standard deviation s₁，s₂；

546nm, E11, E12 … … E19; e21, E22 … … E29, average value

Standard deviation s₁，s₂；

…………

830nm, E11, E12 … … E19; e21, E22 … … E29, average value

Standard deviation s₁，s₂。

For a total of 341 rows and 18 columns.

Then per-row statistics:

in the formula n₁＝n₂＝9。

It can be proved that t obeys a degree of freedom of n₁+n₂-2 distribution of t according to degree of freedom n₁+n₂-2 and given a significance level α, the critical t can be found from the t-test threshold table_αThe value t (0.05,16) is 2.12. If the value of t is less than t_αThen it is considered as

Are consistent.

The present invention utilizes IBM SPSS20 software to analyze all wavelengths, and the results of the analysis of some wavelengths are shown in Table 12. All statistics t divided by t (0.05,16) are calculated to be 2.12, the obtained results are all less than 1, and the significance factor p is greater than 0.05, which indicates that the data among all groups are judged to be equal in accuracy by using the t-test.

4.6 merging of 8 constant value measurements Normal distribution analysis

The present invention performed normal analysis on all wavelengths using the IBM SPSS20 software on a total of (341X 8)2728 sets of data (9 data per set), with some of the wavelengths analyzed as shown in Table 12. Column 4 in table 12 shows the asymptotic significance (two-sided) of the 8 laboratory-rated merged results calculated using the Kolmogorov-Smirnov method, and if the calculated values of all the results are greater than 0.05, the data obey normal distribution.

TABLE 128 data consistency test between the quantitative laboratory groups and partial results of the merged Normal distribution analysis

4.7 Merge 8 constant value data outlier test

Excel software was used to analyze outliers of 2728 total data (9 data per group) in the same manner as in section 4.3 (r 'was not calculated again when calculating)'₁₁And r₁₁But is calculated r'₂₂And r₂₂) And the result shows that no suspicious value exists in the combined joint definite value laboratory group under each wavelength.

Therefore, according to JJF1006-1994 "first-class Standard substance Specification", all data can be regarded as a new set of measured data, and the total mean and standard deviation of all raw data can be calculated.

According to the statistical result, averaging the 8 laboratory constant value results

The final quantitative value of the relative fluorescence emission intensity standard substance of the DPA o-xylene solution is obtained.

5. Uncertainty analysis

5.1 sources of uncertainty

The total uncertainty for a well-defined standard value consists of three parts, as specified by JJJG 1006 plus 1994 Primary Standard substance Specification. The first part being a constant standard uncertainty component u_{Constant value}The second part being a non-uniformly generated uncertainty component u_{Uniformity of}And a third part of the instability-generated uncertainty component u_{Stability of}。

When the concentration of the fluorescent dye is extremely large (higher than 1mol/L), the self-absorption and self-quenching effects can influence the fluorescence intensity ratio. Therefore, the influence of uncertainty introduced by concentration is not considered in the development process of the standard substance.

The method adopts a mode of jointly valuing 8 quality laboratories. The method adopted by each laboratory was a quantitative value by comparing the relative emission intensity of the fluorescent standard substance with that of the SRM2943 or SRM2944 fluorescent standard substance of NIST at the same emission wavelength by using a fluorescence spectrometer. Thus, sources of fixed value uncertainty include the uncertainty u of NIST standards_{1 constant value}Uncertainty u of fixed value repeatability combined with 8 laboratories_{2 constant value}And uncertainty u introduced by temperature change_{Constant value of T}。

Stability-induced uncertainty includes long-term stability-induced uncertainty u_{1 stability of}Uncertainty u introduced by transport stability_{2 stability of}And uncertainty u introduced by illumination stability_{3 stability of}. When the light stability of the DPA o-xylene solution is inspected by irradiating the DPA o-xylene solution for 48 hours by a 450W xenon lamp, the relative fluorescence emission intensity of the DPA o-xylene solution shows a linear descending trend along with time in the 48 hours of illumination, and the maximum descending slope is 0.00076%/min. Since the DPA o-xylene solution is in liquid form relative to the fluorescence emission intensity standard substance, it is disposable and generally does not exceed 1 per time when used for calibration or testingAnd 0min, wherein the change of the fluorescence emission intensity value under the condition is about 0.0076 percent and can be ignored. Therefore, this influencing factor of illumination is not taken into account in the final uncertainty evaluation.

5.2 uncertainty analysis

The fluorescence emission spectra were measured at 1nm intervals at (440-780) nm, and a total of 341 data points were analyzed indefinitely. In this embodiment, the calculation process of a part of wavelengths is taken as a representative example, and the uncertainty of the relative emission intensity value is analyzed, the uncertainty analysis processes at other wavelengths are similar, and table 15 lists the specific uncertainty analysis results at a part of wavelengths.

5.2.1 fixed value-induced uncertainty

And according to a fixed value result, finally reserving 2-3 bits behind the decimal point for the uncertainty, reserving 4-bit effective digits in the following calculation process for the sake of accuracy, and finally, carrying out reduction when calculating the extended uncertainty U.

(1) Uncertainty u of NIST standard substance_{1 constant value}

And the relative emission intensity of the SRM2943 is adopted as a calibration basis for (440-560) nm, and the relative emission intensity of the SRM2944 is adopted as a calibration basis for (561-780) nm.

Taking the relative emission intensity of fluorescence at 600nm as an example, SRM2944 gives a relative emission intensity value at 600nm as E_r0.1427, extend uncertainty U_95,SRM0.0070. Thus, the relative expansion uncertainty U at 600nm is 0.0070/0.1427 4.8798%. According to the "4, fixed" section, the relative fluorescence emission intensity at 600nm of a DPA ortho-xylene solution relative fluorescence emission intensity standard is 0.72812, and therefore its standard uncertainty is:

u_{(600nm)1, constant value}＝E·U/k＝(0.72812×0.048798)/2＝0.0178

The process of uncertainty analysis at other wavelengths is similar. The results of the analysis at some wavelengths are shown in Table 15.

(2) Uncertainty u introduced by fixed value repeatability in 8 laboratories_{2 constant value}

The uncertainty of the multi-laboratory collaboration rating may be estimated using analysis of variance according to ISO guidelines 35. Taking the relative emission intensity at a wavelength represented by 600nm as an example, the measurement results are shown in table 13:

TABLE 13 summary of 600nm values in eight laboratories

According to JJF1006-1994 first-class Standard substance Specification, all data can be treated as a new set of measured data, and the total mean and standard deviation of all raw data can be calculated.

The process of uncertainty analysis at other wavelengths is similar. . The results of the analysis at some wavelengths are shown in Table 15.

(3) Uncertainty u introduced by temperature change_{Constant value of T}

According to the invention, the change of the relative intensity in the temperature range of 10-40 ℃ is calculated, and the approximate linear change of the relative emission intensity under each wavelength along with the temperature is found, so that the uncertainty caused by the temperature change can be calculated.

Take the relative fluorescence emission intensity change at 600nm as an example: the average fluorescence relative emission intensity at 10.0, 20.0, 25.0, 30.0, 40.0 degrees celsius for the 6 vials, respectively, was determined as shown in table 14:

TABLE 14 uncertainty introduced by temperature change

The relative emission intensity of fluorescence at 600nm shows linear change with temperature within the temperature range of 10-40 ℃, and the correlation coefficientUp to 0.998. The slope of the linear change relationship obtained by fitting is-0.00084 DEG C^-1. Thus, taking into account the temperature variation + -3 deg.C, an uncertainty is introduced of

u_{(600nm) T, constant value}＝0.00084×3＝0.0025

In the same way, the linear change of the relative fluorescence emission intensity of other wavelengths in the temperature range of 10-40 ℃ along with the temperature can be respectively obtained. The relative fluorescence emission intensity uncertainty contributions introduced at temperature changes of + -3 deg.C for some wavelengths are shown in Table 15.

5.2.2 Standard uncertainty due to uniformity

From the calculation results of the "2, homogeneity test" section, the standard deviation resulting from the inhomogeneities needs to be incorporated into the constant final uncertainty.

When the inter-group mean square is larger than the intra-group mean square, calculation is performed according to the formula (2-5).

When the inter-group mean square is less than the intra-group mean square, the calculation is performed according to equation (2-6).

The uncertainty introduced by uniformity at different wavelengths can be calculated using the above formula, and the specific analysis results at some wavelengths are listed in table 15.

5.2.3 stability-induced uncertainty

The stability impact was examined in two parts, the first being the uncertainty contribution of the validity period at 12 months and the second being the short term stability uncertainty contribution under 7-day transport conditions.

(1) Long term stability under storage conditions

Within the 12-month validity period, the regression analysis of variance table for stability assessment was used to estimate the standard uncertainty. By adopting a method of '3, stability investigation', the method is effectiveThe uncertainty contribution to long-term stability for a period t of 12 months is: u. of_{1 stability of}＝s_βT. The long term stability induced uncertainty at different wavelengths is calculated in the same way and the long term stability induced uncertainty at some wavelengths is listed in table 15.

(2) Short term stability under transport conditions

The standard uncertainty was estimated using a regression analysis of variance table to assess stability under 7 day transport conditions. By adopting a method of '3, stability investigation', the uncertainty contribution of the short-term stability with the validity period t being 7 days is as follows: u. of_{2 stability of}＝s_βT. The transport stability induced uncertainty at different wavelengths was calculated in the same way and is listed in table 15 for some wavelengths.

5.2.4 synthetic uncertainty

The process of analysis of uncertainty introduced by synthetic constants at other wavelengths is similar. The results of the analysis at some wavelengths are shown in Table 15.

TABLE 15 results of uncertainty analysis of DPA ortho-xylene solutions at partial wavelengths against fluorescence emission intensity standards

5.2.5 extended uncertainty

If k is 2, the expansion uncertainty is U_(600nm)＝0.0357×2＝0.072。

The detailed uncertainty of the relative emission intensity at all wavelengths is shown in table 16. Table 16 shows the amount of the emission intensity of the DPA ortho-xylene solution relative to the fluorescence emission intensity standard under excitation at 400nm, wherein the coverage of the emission wavelength is (440) -780) nm, and the wavelength interval is 1 nm.

TABLE 16 DPA ortho-xylene solution relative fluorescence emission intensity standard mass value table

Note: lambda [ alpha ]_em: a fluorescence emission wavelength (nm); e: relative fluorescence emission intensity; u shape₉₅: and expanding uncertainty (k is 2).

Using a concentration of 10^-7-1mol/L DPA o-xylene solution, or a solution prepared from other solvents (such as water, acetonitrile, ethanol, acetone, chloroform, etc.) with moderate polarity and concentration of 10^-7DPA solution of-1 mol/L can be used for preparing relative fluorescence emission intensity standard substances. When DPA solutions of different concentrations prepared from different solvents were used to prepare relative fluorescence emission intensity standard substances, the excitation wavelength ranges and emission wavelength coverage ranges (i.e., emission wavelength ranges) of the prepared relative fluorescence emission intensity standard substances are shown in table 17.

TABLE 17 excitation wavelength and emission wavelength range of DPA solutions versus fluorescence emission intensity standard

Solvent(s)	Excitation wavelength range/nm	Emission wavelength range/nm
			Benzene and its derivatives	380～420	400～800
Toluene	380～420	400～800
			Ortho-xylene	380～420	400～800
Meta-xylene	400～450	430～830
			Para-xylene	400～450	430～830

Different DPA solutions were used to prepare relative fluorescence emission intensity standards by re-valuing and confirming the uncertainty in the same manner as in example 1.

Example 2 results of the use of DPA ortho-xylene solution versus fluorescence emission intensity standard for different instrument parts

Referring to the standard substance development process of SRM2944 of NIST, when the fluorescent standard substance is used, the uncertainty caused by the change of absorption and inner filtering effects due to the change of the position of incident excitation light on a sample is also considered; uncertainty introduced by the slit of the incident grating and the emergent grating; uncertainty introduced by instrument components such as a light source, a reflector and a detector; and fourthly, uncertainty is introduced due to the anisotropy of light and the polarization of the standard substance.

1.1 positional Change of incident light and Anisotropic Effect of light

When considering the factors of the first two, because the DPA o-xylene solution is uniform relative to the fluorescence emission intensity standard substance solution system, the slight change of the incident beam irradiation on the sample position does not cause the change of the absorption or the inner filtering effect, and the change of the anisotropy and the polarization degree is not considered here.

Thirdly, the uncertainty introduced by the factors is generated among different detection instruments, and in the calibration process using the SRM2943 and the SRM2944, the uncertainty range listed in the certificate already contains the influence of the three factors, so that the two factors are not the influence of the standard substance on the magnitude but depend on the measurement instruments. Aiming at common fluorescence spectrometers in the market, the invention carries out preliminary experiments in consideration of the common conditions of different instrument components such as a possible grating slit and the like.

1.2 Grating slit differential Effect

In the common fluorescence spectrometers in the market, two types of continuously adjustable and discontinuously adjustable grating slits mainly exist, wherein the grating slits on the two sides of excitation and emission can be set to be 3nm and 3nm required by DPA (deep fluorescence emission) o-xylene solution relative fluorescence emission intensity standard substances. The fluorescence spectrometer with the discontinuously adjustable grating slits is an old instrument, and only the grating slits on the excitation side and the emission side can be set to be 2.5nm and 2.5 nm. In order to research the influence factor, 10 grating slits are continuously adjustable, the slits on two sides are set to be 3nm, the fluorescence emission spectrum of the DPA o-xylene solution relative to a fluorescence emission intensity standard substance after the fluorescence emission spectrum is calibrated by an SRM2944 standard substance is measured, and the average result of the emission spectrum is given. Meanwhile, in 10 grating slits of the discontinuous adjustable fluorescence spectrometer, the slits on two sides are both 2.5nm, the fluorescence emission spectrum of the DPA o-xylene solution relative to a fluorescence emission intensity standard substance after the fluorescence emission spectrum is calibrated by an SRM2944 standard substance is measured, and the average result of the emission spectrum is given. The results are shown in FIG. 5.

As can be seen from FIG. 5, the DPA o-xylene solution exhibits very similar fluorescence emission spectra to the fluorescence emission intensity standard substance, no matter under the condition that the slits on both sides of 10 grating slits continuously adjustable fluorescence spectrometers are 3nm, or under the condition that the slits on both sides of 10 grating slits discontinuously adjustable fluorescence spectrometers are 2.5 nm. Since the spectrogram contains all fixed value data, and the deviation between the spectrums does not exceed 0.1%. The DPA o-xylene solution provided by the invention is suitable for calibrating a fluorescence spectrometer with a continuously adjustable grating slit and a discontinuously adjustable grating slit relative to a fluorescence emission intensity standard substance.

1.3 Effect of different light sources

In the common fluorescence spectrometers on the market, most Xe lamp continuous light sources or LED single-wavelength light sources are used, and a small part of the Xe lamp continuous light sources or LED single-wavelength light sources are provided with pulse light sources. There are also three cases for the wavelength of the excitation light required by the DPA o-xylene solution relative to the fluorescence emission intensity standard to be 515nm, namely that the Xe lamp is generated by using a light splitting system to split light at 515nm, or a 515nm LED light source is directly used, or a 515nm pulse light source is used. FIG. 6 shows fluorescence emission spectra of DPA ortho-xylene solution versus fluorescence emission intensity standard for three different light sources, wherein the pulsed light source was selected with the same pulse period of 80 μ s as that used in the development of SRM2944 standard.

Wherein the DPA o-xylene solution using Xe lamp continuous light source or LED single wavelength light source presents very similar fluorescence emission spectrum compared with fluorescence emission intensity standard substance. Since the spectrogram contains all fixed value data, and the deviation between the spectrums does not exceed 0.1%. The developed DPA o-xylene solution is simultaneously suitable for the calibration of fluorescence spectrometers equipped with Xe lamp continuous light sources or LED single-wavelength light sources relative to fluorescence emission intensity standards.

For a pulse light source, the measurement has larger noise, although the maximum signal fluctuation caused by calculation does not exceed 2.5 percent and does not exceed the fixed value uncertainty range of partial quantity values, the measurement has larger influence on the continuity of the quantity value change in the measurement spectrum. It is therefore not recommended to use DPA ortho-xylene solution versus fluorescence emission intensity standard for the calibration of fluorescence spectrometers equipped with pulsed light sources only.

Example 3 comparison and verification of quality values of similar standards

Respectively adopting the following steps:

comparing and analyzing the SRM2941 standard substance of NIST (the emission wavelength range is basically consistent with that of the DPA o-xylene solution relative fluorescence emission intensity standard substance, and the size is the same during measurement) with the DPA o-xylene solution relative fluorescence emission intensity standard substance prepared in example 1.

(E) GBW 130100 quinine sulfate fluorescence standard substance (the selection reason is that the emission wavelength range is coincident with the three relative fluorescence emission intensity standard substances and is in a liquid form) is compared with the DPA o-xylene solution relative fluorescence emission intensity standard substance prepared in the example 1 for analysis.

2 fluorescence spectrophotometers (which pass JJJG 537-2006) are calibrated by using a DPA o-xylene solution relative fluorescence emission intensity standard substance, then fluorescence emission spectra of the SRM2941 at (450-650) nm and GBW (E)130100 quinine sulfate fluorescence standard substance at (450-675) nm, which are overlapped with the DPA o-xylene solution relative fluorescence emission intensity standard substance calibration wavelength range, are measured, relative emission intensities at 500nm and 600nm are respectively compared with the certificate quantity value of the SRM2941, relative emission intensities at 450nm and 550nm are compared with the certificate quantity value of the GBW (E)130100, and the results are shown in Table 18, and the measurement results of different instruments by using the DPA o-xylene solution relative fluorescence emission intensity standard substance are all in the uncertain range of the SRM2941 and GBW (E)130100 standard substance quality values.

TABLE 18 comparison of DPA o-xylene solution standards with other standards (25 ℃ C.)

Example 4 method of using a DPA o-xylene solution as a fluorescence standard with respect to fluorescence emission intensity

The DPA o-xylene solution is suitable for calibrating a fluorescence spectrometer or similar fluorescence instruments with a continuously adjustable light source or an LED light source relative to a fluorescence emission intensity standard substance.

Taking a DPA o-xylene solution with a concentration of 0.010mg/mL as an example of a relative fluorescence emission intensity standard, a laboratory temperature is maintained at (25 +/-3) ° C when in use, no less than 3mL of the standard solution is transferred to a 12.5mm x 45.0mm clean quartz cuvette and placed in a measurement light path of a fluorescence spectrometer or the like, so that an excitation light beam is perpendicular and concentrated on one surface of the cuvette (below the liquid level), and emission fluorescence is collected in the direction of an adjacent surface at an angle of 90 degrees to the excitation light beam. Setting Excitation wavelength (Excitation wavelength) to be 400nm, setting detection range of Emission wavelength (Emission wavelength) to be 440-780nm, setting slits (Slit) on an Excitation side and an Emission side to be 3nm and 3nm (grating Slit continuous adjustable instrument) or 2.5nm and 2.5nm (grating Slit discontinuous adjustable instrument), and setting data acquisition Step length (Step) to be 1 nm.

Collecting fluorescence Emission spectrum (Emission spectrum) of DPA o-xylene solution relative to fluorescence Emission intensity standard substance, and reading fluorescence Emission intensity value E at each wavelength_em. And if the conditions allow, simultaneously acquiring the excitation spectrum intensity corresponding to each data point, and dividing the fluorescence emission intensity by the fluorescence excitation intensity to be used as a calibration fluorescence emission intensity value. The fluorescence emission intensity values (or calibration fluorescence emission intensity values) at all wavelengths were divided by the maximum fluorescence emission intensity value at 553nm to obtain a normalized fluorescence emission intensity value E at each wavelength_em,norm. Dividing the relative fluorescence emission intensity characteristic value E of the standard substance at the corresponding wavelength by the normalized measured value E at the corresponding wavelength_em,normTo obtain an energy correction factor F at each emission wavelength. The daily emission spectrum measured value is multiplied by an energy correction factor F under the corresponding wavelength or is directly led into an energy calibration system file of the instrument, and then the energy/intensity calibration at the emission side can be realized.

What has been described above are merely some embodiments of the present invention. It will be apparent to those skilled in the art that various changes and modifications can be made without departing from the inventive concept thereof, and these changes and modifications can be made without departing from the spirit and scope of the invention.

Claims

A method for preparing a DPA solution relative fluorescence emission intensity standard substance, which is characterized by comprising the following steps:

preparing DPA into a DPA solution; wherein the emission spectrum of the DPA solution does not contain impurity fluorescence peaks;

carrying out uniformity inspection, stability inspection, value determination and uncertainty analysis on the relative fluorescence emission intensity values of the prepared DPA solution at intervals of 1nm within the corresponding emission wavelength coverage range, and obtaining a DPA solution relative fluorescence emission intensity standard substance if the DPA solution can meet the requirements of the standard substance at intervals of 1nm within the corresponding emission wavelength coverage range;

wherein the step of measuring the relative fluorescence emission intensity value of the DPA solution at intervals of 1nm within the corresponding emission wavelength coverage range comprises the following steps:

(1) under the experimental temperature condition of (25.0 +/-0.5) DEG C, setting the excitation wavelength to be 330.3nm, the emission wavelength detection range to be 350-640nm, the excitation side slit and the emission side slit to be 3nm simultaneously or 2.5nm simultaneously by using a qualified fluorescence spectrometer under the irradiation of excitation light required by the SRM2943 standard substance certificate, and acquiring the spectral emission intensity value at the interval of 1 nm; then dividing the spectral emission intensity under each wavelength by the maximum spectral emission intensity of the SRM2943 standard substance to obtain the relative emission intensity under each wavelength; taking 3 SRM2943 standard substance samples, carrying out parallel measurement on each sample for 3 times, and calculating the average relative emission intensity value under each wavelength; finally, the relative emission intensity value under each wavelength given in the SRM2943 standard substance certificate is divided by the average relative emission intensity value of the corresponding wavelength to calculate the correction factor of the SRM2943 standard substance under each wavelength within the wavelength range of 350-640nmFA value;

(2) at an experimental temperature of (25.0 +/-0.5) DEG CUnder the condition of certain degree, a qualified fluorescence spectrometer is used, under the irradiation of excitation light required by the specification of an SRM2944 standard substance certificate, the excitation wavelength is set to be 515nm, the detection range of the emission wavelength is 530-; then dividing the spectral emission intensity under each wavelength by the maximum spectral emission intensity of the SRM2944 standard substance to obtain the relative emission intensity under each wavelength; taking 3 SRM2944 standard substance samples, carrying out parallel measurement on each sample for 3 times, and calculating the average relative emission intensity value under each wavelength; finally, the relative emission intensity value under each wavelength given in the SRM2944 standard substance certificate is divided by the average relative emission intensity value of the corresponding wavelength to calculate the correction factor of the SRM2944 standard substance under each wavelength within the wavelength range of 530-830nmFA value;

(3) under the experimental temperature condition of (25.0 +/-0.5) DEG C, placing the DPA solution in a sample chamber by using a qualified fluorescence spectrometer, setting corresponding excitation wavelength and emission wavelength detection ranges, setting an excitation side slit and an emission side slit to be 3nm or 2.5nm at the same time, and collecting a spectrum emission intensity value at intervals of 1 nm; the spectral emission intensity at each wavelength is then multiplied by a correction factor for the corresponding wavelengthFDividing the value by the correction factor of the maximum spectral emission intensity and the corresponding wavelength of the DPA solutionFThe relative emission intensity under each wavelength is obtained by multiplying the values, wherein, for each wavelength in the wavelength range of 400-529nm, the correction factor of the corresponding wavelength of the SRM2943 standard substance is selectedFCalculating the relative emission intensity of DPA solution, and optionally selecting the correction factor of the corresponding wavelength of the SRM2943 standard substance for each wavelength in the wavelength range of 530-640nmFCorrection factor for the value or wavelength corresponding to the SRM2944 standardFCalculating the relative emission intensity of DPA solution, and selecting the correction factor of corresponding wavelength of SRM2944 standard substance for each wavelength in the range of 641-830nmFCalculating the relative emission intensity of the DPA solution; optionally selecting 3 DPA solution samples, parallelly measuring each sample for 3 times, and taking the calculated average relative emission intensity value at each wavelength as the relative fluorescence emission at the corresponding wavelength of the DPA solutionMeasurement of intensity values.
2. The method of claim 1, wherein the determination of the relative fluorescence emission intensity values of the DPA solution at 1nm intervals within the corresponding emission wavelength coverage comprises the steps of:

s1, utilizing n laboratories to respectively refer to the measurement steps (1) - (3) of the relative fluorescence emission intensity values of the DPA solution at every 1nm in the corresponding emission wavelength coverage range to determine the relative fluorescence emission intensity values of the DPA solution at every 1nm in the corresponding emission wavelength coverage range; wherein n is more than or equal to 3;

s2, performing normal distribution analysis and suspicious value analysis in groups on the fixed value result of each laboratory respectively; then, performing equal precision analysis between groups and consistency test of data between groups on the fixed value results of all laboratories; finally, combining the fixed value results of all laboratories to perform normal distribution analysis and data abnormal value test; if the following conditions are met simultaneously: the method comprises the steps that the default setting result of each fixed value laboratory accords with normal distribution, no suspicious value exists in the default setting result of each fixed value laboratory, the precision among the constant setting result groups of all fixed value laboratories is equal, the average value of data among all fixed value laboratory groups is consistent, the fixed value results of all fixed value laboratories are combined to accord with normal distribution, no suspicious value exists in the fixed value results of all fixed value laboratories, and then the average value of the fixed value results of all laboratories under the corresponding wavelength is used as the final fixed value of the DPA solution.
3. The method according to claim 1 or 2, wherein the solvent of the DPA solution is at least one selected from the group consisting of o-xylene, m-xylene, p-xylene, toluene, and benzene.
4. The method of claim 3, wherein the DPA solution has a concentration of 10^-7-1 mol/L。
5. The method as claimed in claim 4, wherein when the solvent is benzene, the DPA solution has an emission wavelength coverage of 400-800nm under the excitation of 380-420nm relative fluorescence emission intensity standard substance;

when the solvent is toluene, the DPA solution relative fluorescence emission intensity standard substance is excited at the wavelength of 380-420nm, and the emission wavelength coverage range is 400-800 nm;

when the solvent is o-xylene, the DPA solution has an emission wavelength coverage range of 400-800nm under the excitation of a 380-420nm wavelength relative fluorescence emission intensity standard substance;

when the solvent is m-xylene, the emission wavelength coverage range of the DPA solution relative to the fluorescence emission intensity standard substance is 430-830nm under the excitation of the wavelength of 400-450 nm;

when the solvent is paraxylene, the emission wavelength coverage range of the DPA solution relative to the fluorescence emission intensity standard substance is 430-830nm under the excitation of the wavelength of 400-450 nm.
6. The method as claimed in claim 5, wherein the DPA solution is a DPA o-xylene solution with a concentration of 0.010mg/mL, and the emission wavelength coverage is 440-780nm under 400nm excitation.