JPS6329234A - Spectrophotometer - Google Patents

Abstract

PURPOSE:To expand a measurable concn. range by providing a calibration curve forming function by curvilinear approximation and calibration curve forming function by a method of least squares to a calibration curve forming function of a signal processing mechanism for a quantitative analysis by a standard addition method. CONSTITUTION:Light of the wavelength intrinsic to an element to be measured is projected from a hollow cathode lamp 1 to a sample tube 2. A spectroscope 3 selects the wavelength intrinsic to the element to be measured and sets the same. The sample placed in the sample tube 2 is thermally cracked by a heating program set by a microcomputer 7 to generate the atomic vapor of the element to be measured. The light signal attenuated by the change of the density distribution with time based on the generation and dissipation of the atomic vapor is detected in a photomultiplier 4 and is taken into the computer 7 by an A/D converter 6, by which the formation of the calibration curve for the purpose of the standard addition method and the arithmetic processing such as density calculation of the element to be measured in the sample are executed. The computer 7 is provided with the calibration curve forming function by the curvilinear approximation and the calibration curve forming function by the method of least squares so that the measurable concn. range can be increased.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a spectrophotometer, which is particularly useful for performing quantitative analysis using the standard addition method even when the calibration curve is curved in the direction of the concentration axis. The present invention relates to a suitable spectrophotometer such as an atomic absorption spectrophotometer or a spectrofluorometer.

[Conventional technology]

In spectrophotometers such as atomic absorption spectrophotometers and spectrofluorophotometers, highly accurate quantitative results (concentration) are obtained by correcting chemical or physical interference of coexisting substances that occur during quantitative analysis of the analyte. The standard addition method is an essential method for obtaining this. Therefore, in the case of many spectrophotometers, quantitative analysis using the standard addition method has become commonplace, and many spectrophotometers have signal processing functions and measurement functions using the standard addition method.

The standard addition method in conventional spectrophotometers is to add the sample solution to 3
~ Dispense equal amounts into 4 weighable containers, one of which
Add the standard solution of the analyte to the remaining containers except for one container in a fixed ratio. Then, each container is diluted to a constant volume with a solvent to prepare an aliquot for standard addition measurement. Weigh out the same amount of the blank solution as the sample solution and dilute it in the same way. Each measurement aliquot is measured with a spectrophotometer, and spectrophotometer readings such as absorbance values and fluorescence intensity values are determined, and the readings of the blank solution are corrected. Then, a calibration curve is created by plotting the indicated values against the concentration, with the concentration of the added standard solution of the analyte being plotted on the horizontal axis and the indicated values of the spectrophotometer, such as absorbance values and fluorescence intensity values, on the vertical axis. Assuming that this calibration curve is a straight line down to a sufficiently low concentration range, the spectrophotometer readings such as absorbance values and fluorescence intensity values are extrapolated to zero. (extend across the reading axis of the spectrophotometer until it intersects the concentration axis). The concentration of the analyte contained in the measurement aliquot to which no standard solution of the analyte has been added is obtained from the intersection of the linear extrapolation line and the concentration axis.

Therefore, it is applied only when the relationship curve between the added concentration of the standard solution of the analyte and the indicated value of the spectrophotometer such as the absorbance value or fluorescence intensity value, that is, the calibration curve, is a straight line. Therefore, the standard addition method technique in conventional spectrophotometers such as atomic absorption spectrophotometers and spectrofluorometers is standard addition linear extrapolation.

However, the calibration curve of a spectrophotometer such as an atomic absorption spectrophotometer or a spectrofluorometer does not necessarily show a straight line depending on the spectral characteristics and concentration range of the substance to be measured, and is often curved in the direction of the concentration axis. . In particular, the calibration curve of an atomic absorption spectrophotometer, in which quantitative analysis using the standard addition method is commonly used, generally shows a straight line in the low concentration region (absorbance of about 0.2 to 0.3), but in the concentration region When becomes high, it curves in the direction of the concentration axis. This is due to this. The concentration range in which a linear calibration curve can be obtained using the standard addition linear extrapolation method is at most 1.
It is very narrow and within the range of opposition. For this reason, when performing quantitative analysis of a sample in a high concentration region, several preliminary dilution operations and ΔIII It is necessary to repeat the same procedure before preparing aliquots for standard addition method measurements.
Equal quantitative analysis operations become complicated. In addition, if the dilution ratio is large, errors due to dilution and contamination are likely to occur, so
There was a risk of degrading quantitative analysis operations, and sufficient consideration was not given to the operability and versatility of quantitative analysis.

Furthermore, the calibration curve of a spectrophotometer is often curved in the direction of the concentration axis and does not show a straight line, regardless of the concentration range.

It is difficult to quantitatively analyze a substance to be measured that shows such a calibration curve using the standard addition method. It often happens that it is necessary to use interference cancellation measures such as targets.

[Problem that the invention seeks to solve]

This method has been generalized as a method for correcting chemical or physical interference of coexisting substances during quantitative analysis of a substance to be measured using conventional spectrophotometers such as the above-mentioned atomic absorption spectrophotometers and spectrofluorophotometers. The standard addition method involves adding two to three standard solutions of the analyte with known concentrations to a sample solution, measuring spectrophotometer readings such as absorbance and fluorescence intensity, and detecting interference. Assuming that the received calibration curve is a straight line down to a sufficiently low concentration range, extrapolate the spectrophotometer readings such as absorbance values and fluorescence intensity values to zero, and from the intersection of the straight extrapolated line and the concentration axis. This was a standard addition linear extrapolation method to obtain the concentration of the analyte contained in the sample solution.

Therefore, quantitative analysis using the standard addition method is applicable only when a prepared standard solution of the analyte is added.

However, all calibration curves in spectrophotometers do not always show a straight line, and are often curved in the direction of the concentration axis depending on the spectral characteristics and concentration range of the substance to be measured. For example, the calibration curve of an atomic absorption spectrophotometer, in which quantitative analysis using the standard addition method is relatively often performed, is generally in the low concentration region (absorbance Q,
2 to 0.3), it shows a straight line, but as the density region increases, it curves in the direction of the density axis. The concentration range showing a linear calibration curve to which quantitative analysis using the standard addition method can be applied is very narrow, within about one stroke at most. Furthermore, in the case of other spectrophotometers, the calibration curve often curves in the concentration axis direction regardless of the concentration region and does not show a straight line due to the spectral characteristics of the substance to be measured.

For this reason, the standard addition method technology used in conventional spectrophotometers does not take into account quantitative analysis using calibration curves that curve in the direction of the concentration axis, which is relatively common in atomic absorption spectrophotometers, spectrofluorometers, etc. Quantitative analysis is performed by repeating several preliminary dilution operations and measurement operations so that the concentration of the analyte in the sample solution is within the concentration range that allows a linear calibration curve to be obtained. The standard addition method is complicated, the accuracy of quantitative analysis is reduced due to dilution errors and contamination that occur during dilution, and the calibration curve curves in the concentration axis direction regardless of the concentration range and has no linear range. There were problems such as low versatility due to incompatibility and complication of quantitative analysis operations due to the adoption of interference removal methods using coexisting substances other than standard addition methods such as sample pretreatment.

The purpose of the present invention is to provide a signal processing mechanism for standard addition methods in spectrophotometers such as atomic absorption spectrophotometers and spectrofluorophotometers so that the indicated values of the spectrophotometer, such as absorbance values and fluorescence intensity values, are equivalent to concentration values. By providing a calibration curve creation function using curve approximation, in which the relationship or concentration value is a function of spectrophotometer readings such as absorbance values and fluorescence intensity values, and a calibration curve creation function using the least squares method, concentration values and Relationship curves with spectrophotometer readings such as absorbance values and fluorescence intensity values, that is, calibration analysis results can be obtained, and the measurable concentration range using the standard addition method, quantitative analysis operability, and the standard addition method The object of the present invention is to provide a spectrophotometer that can greatly expand its versatility.

[Means for solving problems]

The above purpose is to use the calibration curve creation function of the signal processing mechanism for quantitative analysis using the standard addition method that spectrophotometers such as atomic absorption spectrophotometers and spectrofluorophotometers have. It combines a calibration curve creation function using curve approximation, in which the meter reading is a function of the concentration value, or a concentration value is a function of the spectrophotometer reading, such as absorbance value or fluorescence intensity value, and a calibration curve creation function using the least squares method. In addition, the relationship curve between concentration values and spectrophotometer readings such as absorbance values and fluorescence intensity values, that is, highly accurate quantitative analysis results using the standard addition method even when the calibration curve curves in the direction of the concentration axis. In addition to this, we achieved this with a configuration that greatly expanded the measurable concentration range using the standard addition method.

[Effect]

The effect of the present invention is shown in the relationship curve between the absorbance value and the concentration value measured by an atomic absorption spectrophotometer using a flameless atomization device as illustrated in FIG. 6, FIG. 7, and FIG. 8, that is, a calibration curve. explain.

FIG. 6 is an example of a calibration curve in a relatively large concentration range of Cr, Cu, and Pb. The calibration curve of an atomic absorption spectrophotometer does not necessarily show a linear relationship due to spectral characteristics such as the self-absorption of the hollow-quad drag that is the light source and the density gradient of the atomic vapor of the element to be measured generated in the atomization device. No 3. -Generally low concentration region (absorbance 0.2-0.
up to about 3).

shows a linear relationship, but as the concentration region becomes higher than that, it shows a tendency to curve in the concentration axis direction.

The degree and shape of the curvature of the calibration curve depend on the element to be measured. Further, the concentration range in which the calibration curve shows a linear relationship is very narrow, within about one stroke at most. For this reason, the concentration range of the analyte element contained in the sample solution is a very narrow concentration range that shows a linear calibration curve. It is necessary to prepare an aliquot for standard additive oil measurement after repeating several preliminary dilution operations and measurement operations to ensure that the standard additive oil is within

Figure 7 shows the high concentration region of Mn (0,02~0,2
This is an example of a calibration curve in ppm). The calibration curve for Mn is a linear calibration curve because the absorbance value is proportional to the concentration value in a low concentration region where an absorbance of about 0.3 or less is generally obtained. Therefore, quantitative analysis using the standard addition linear extrapolation method, which is a conventional technique, becomes possible. However, in the high concentration region (0.02 to 0.2 ppm) where an absorbance of about 0.5 or more can be obtained,
), the absorbance value and concentration value are not proportional. For this reason, if you create a calibration curve using a straight line (y = ax + b, where y: spectrophotometer readings such as absorbance value and fluorescence intensity value, x: concentration value, and a, b: constant) using the least squares method, , Figure 7(a)
As shown in the calibration curve shown in Figure 2, the calibration curve created using a straight line does not match the absorbance value of each concentration. In such a case, quantitative analysis using the conventional standard addition linear extrapolation method is completely impossible, and it becomes difficult to obtain highly accurate analysis results (concentration). In such a case (the calibration curve curves in the direction of the concentration axis)
If you use the calibration curve creation function by curve approximation using a high-order functional formula, you can create a highly accurate calibration curve. The calibration curve shown in Figure 7(b) is based on the curve approximation of the quadratic function equation (
y=axz+bx+o, where C is a constant), and was created by the least squares method (1]). In this case, since the created calibration curve and the absorbance values at each concentration match, it can be seen that the calibration curve is highly accurate. As a result, quantitative analysis can be performed even in the concentration range where the calibration curve curves in the concentration axis direction by using the standard addition curve extrapolation method, which has a calibration curve creation function using curve approximation ↓ and a calibration curve creation function using the least squares method. It turns out that it is possible. Therefore, highly accurate analysis results can be obtained, and the concentration range that can be measured using the standard addition method and the operability of quantitative analysis (in the case of high concentration samples, the concentration is adjusted to within the concentration range where the calibration curve shows a straight line) (preliminary dilution and measurement operations) can greatly expand the versatility of the LT4m quasi-addition method.

Figure 8 also shows a high Mn concentration region (0.05 to 0.25
This is an example of a calibration curve in ppm). The difference from the case in Figure 7 is that the concentration range is from 0.02 to 0.20 ppm to 0.
．． 05-0.25pp+n, which is slightly higher. Concentration range in Figure 7 (0.02~0.20p
pm), it was found that a highly accurate calibration curve could be created by curve approximation of the quadratic function equation (y = axz + bx + c) and the least squares method. Even if the value becomes slightly higher, the degree of curvature of the calibration curve in the direction of the concentration axis increases. Therefore, in the method of creating a calibration curve by approximating a curve using a quadratic function equation, a highly accurate calibration curve can only be created using the National Electrical System. The calibration curve in Figure 8 is
Cubic function formula (y=ax"+bx"+cx+d, where,
d: constant) curve approximation and the method of least squares. Since the created calibration curve and the absorbance values at each concentration match, it can be seen that the calibration curve is highly accurate.

Atomic absorption spectroscopy) The relationship curve between the concentration value on a spectrophotometer such as a spectrophotometer or spectrofluorometer and the indicated value of the spectrophotometer such as absorbance value or fluorescence intensity value, that is, the curvature of the calibration curve in the direction of the concentration axis. The degree and shape of the difference vary depending on the substance being measured and the concentration region. However, for the signal processing and measurement functions of the standard addition method, it is necessary to use a standard addition curve extrapolation method that is equipped with curve approximation using a higher-order function equation than the quadratic function equation and a calibration curve creation method using the least squares method. (]3) makes it possible to perform quantitative analysis using the standard addition method even in the case of calibration curves of various shapes.

〔Example〕

The embodiment of the present invention shown in FIG. 1 and FIGS. 2 to 5 are as follows.
This will be explained in detail using figures.

FIG. 1 is a block diagram showing an embodiment of the spectrophotometer of the present invention, and shows the case of an atomic absorption spectrophotometer using a frameless atomization device equipped with a standard addition curve extrapolation function. A sample tube 2 made of carbon or the like as a resistance heating element is irradiated with light having a wavelength specific to the element to be measured from a hollow cathode lamp 1 as a light source. The spectrometer 3 selects and sets a wavelength specific to the element to be measured, and the sample placed in the sample tube 2 is set using a microcomputer 7 that has the function of controlling the current flowing to the sample tube 2. It is thermally decomposed by a heating program to generate atomic vapor of the element to be measured. Atomic absorption, in which the light with a wavelength specific to the element to be measured emitted from the hollow cathode lamp 1 is absorbed and reduced by the time change in the density distribution based on the generation and dissipation of atomic vapor, and then returns to the original light intensity. phenomenon occurs. The absorbed and attenuated optical signal is converted into an electrical signal by a photomultiplier tube 4 and amplified by a preamplifier 5. The data then enters the microcomputer 7 via the analog/digital converter 6, where arithmetic processing such as creating a calibration curve for the standard addition method and calculating the concentration of the element to be measured in the sample is performed. Information in atomic absorption spectrometry, such as the state of the atomic absorption spectrum, the shape of the calibration curve, the analysis results of sample concentration, and the measurement conditions required for quantitative analysis, is displayed on the CRT 8 and recorded on the printer/plotter 9. .

The microcomputer 7 is equipped with the function of quantitative analysis technology using the standard addition curve extrapolation method.

Figures 2, 3, and 4 illustrate the quantitative analysis technology using the seed type addition curve extrapolation method of this example in comparison with the conventional quantitative analysis technology using the standard addition linear extrapolation method. .

This is an example of quantitative analysis of Cu contained in wastewater using an atomic absorption spectrophotometer using a flameless atomization device.

Figure 2 shows the low concentration region (absorbance 0.2) where the calibration curve is a straight line.
standard addition method (standard addition linear extrapolation method)
Quantitative analysis was carried out to determine the amount of Cus contained in the sample (wastewater).
This is an example of checking the degree.

Add 1. , Om
O.

Separate each portion. A standard solution of Cu with a concentration of 10 ppm was added to 0.
0. ．． Add 10,0.20 and 0,30 mQ. Then, each volumetric flask is quantified (10 mα) with distilled water to prepare an aliquot for standard addition method measurement. The sample was diluted 10 times, and the concentrations of the added Cu standard solution were 0, 0.10, 0.20 and Q, 30pp.
+m. Maximum peak height of atomic absorption spectrum 3
The absorbance at 24.8 nm) was determined, a calibration curve was created using the signal processing function of the standard addition method, and the concentration of O contained in the sample was obtained.

The calibration curve 10 is a straight line (a linear function equation of y2ax10s) created by the least squares method. Since the created calibration curve and the absorbance values at each concentration match, it can be seen that the calibration curve is highly accurate. In other words, if an aliquot for standard addition method measurement is prepared by increasing the dilution ratio of the sample (10 times) and considering the concentration range to be within the concentration range that shows a linear calibration curve, Quantitative analysis using the standard addition linear extrapolation method is now possible. From this quantitative analysis result, the concentration of Cu contained in the sample was 1.6p.
pm (0.16 ppm×10).

Figure 3 shows the same sample (waste water) as in Figure 2 at a distance of 10 m.
A standard solution of Cu with a concentration of 1.0 ppma was added to 4 Om Q volumetric flasks at 0°1.
After addition of 0, 2.0 and 3, OmQ, each volumetric flask was diluted to a constant volume (10 mu) with distilled water.
0 and 3,0 ppm. Determine the maximum peak height (absorbance) of the atomic absorption spectrum, create a calibration curve using the signal processing function of the standard addition method, and calculate the carbon content in the sample.
The concentration of u was obtained. The calibration curve 11 is obtained by standard addition linear extrapolation method (straight line creation method using the least squares method) using the conventional standard addition method.
It was created by The absorbance obtained was 0.3
~0.8, which is considerably larger than the 10-fold dilution shown in FIG. 2, and is a high concentration within the measurement concentration range of a frameless atomic absorption spectrophotometer. Therefore, the calibration curve in this concentration range is curved in the concentration axis direction. For this reason, the standard addition linear extrapolation method (y=a
The calibration curve 11 created in x+b) and the absorbance values of each concentration do not match. In such cases, quantitative analysis is impossible and it is difficult to obtain highly accurate analysis results (concentration). This means that the Cu concentration value of 3 ppm (1.5 ppm x 2) determined from the quantitative analysis results is in the low concentration region (absorbance 0.2 to
1.6 ppm of quantitative analysis results (up to about 0.3 ppm)
This can be confirmed by the large difference between the two. In other words, the standard addition linear extrapolation method, which is a technique used in the conventional standard addition method, is applied to quantitative analysis in the low concentration region (absorbance of about 0.2 to 0.3) where the calibration curve is a straight line; Quantitative analysis in a high concentration region (absorbance of about 0.3 or more) that curves in the axial direction is completely impossible, and it can be seen that there is no versatility.

FIG. 4 shows the results of quantitative analysis using the standard addition method measurement aliquot prepared in the measurement shown in FIG. 3 using the standard addition curve extrapolation method, which is the standard addition method technique according to the present invention.

The calibration curve 12 is a cubic function equation (y=ax”
+bx"+cx+d). Since the created calibration curve 12 and the absorbance values at each concentration agree well, it can be seen that a highly accurate calibration curve for standard addition measurement was created. This means that the obtained 1
, 6ppm (0,8ppIIX2) analysis results are
The low concentration region (
This can also be confirmed from the fact that it is consistent with the quantitative analysis result of 1.6 ppm (0.16 ppm x 10') at absorbance of about 0.2 to 0.3). That is, by having the standard addition curve extrapolation method, which is the standard addition method technology according to the present invention, quantitative analysis by the standard addition method is possible even when the calibration curve is curved in the concentration axis direction.

Figure 5 shows Ce contained in wastewater measured using a spectrofluorophotometer.
This is an example of quantitative analysis using the standard addition method. Relative fluorescence intensity obtained during quantitative analysis of Ce by fluorescence method (
Sensitivity) depends on the concentration of coexisting acids such as 11CQ (interference). Therefore, the standard addition method, which is a measurement method for correcting interference, is essential. The higher the concentration of acid such as HcQ contained in the sample, the more significantly the obtained relative fluorescence intensity decreases. Therefore, it is advantageous in terms of sensitivity to measure the concentration of IIcQ and the like contained in the sample at a low level. However, when the concentration of coexisting acids is low, the calibration curve is independent of the concentration range (even in the low concentration range), unlike in the case of an atomic absorption spectrophotometer.
Curved in the concentration axis direction. This (drainage) 0.25 to 2mff
, 50.75 and 1100 pp concentrations of Ce standard solutions (INIIcQ solution) were added in an amount of 2 μQ each to prepare aliquots for standard addition method measurements. Fluorescence wavelength 3
The relative fluorescence intensity was determined at an excitation wavelength of 260 nm.

The calibration curve 13 is calculated using a quadratic function equation (y=a
It was created by curve approximation of The quantitative analysis result (concentration) Q, 28 ppm is highly accurate.In particular, the standard addition curve extrapolation method, which is the standard addition technique according to the present invention, is similar to the example of quantitative analysis of Ce using a spectrofluorometer in Figure 5. In addition, it is effective when performing quantitative analysis using the standard addition method even when the calibration curve curves in the concentration axis direction and does not show a straight line, completely unrelated to the concentration range.

According to this embodiment, in a spectrophotometer such as an atomic absorption spectrophotometer or a spectrofluorophotometer, the concentration value, absorbance value, fluorescence intensity value, etc. Highly accurate quantitative analysis results using the standard addition method, which is an analysis method that corrects for interference caused by coexisting substances even when the calibration curve curves in the direction of the concentration axis. It is effective in obtaining (concentration).

〔Effect of the invention〕

As explained above, according to the present invention, when performing quantitative analysis of a substance to be measured using a spectrophotometer such as an atomic absorption spectrophotometer or a spectrofluorophotometer, chemical or physical interference caused by coexisting substances can be detected. In the standard addition method, which is a generalized analytical method to correct quantitative analysis results (concentration) and obtain highly accurate quantitative analysis results (concentration), the indicated value of the spectrophotometer, such as absorbance value or fluorescence intensity value, is the known concentration added. Standard spectrophotometer functions include a function to create a calibration curve by curve approximation, in which the added known concentration value is a function of the indicated value of the spectrophotometer, such as absorbance value or fluorescence intensity value, and a function to create a calibration curve by the least squares method. Since it has the standard addition curve extrapolation function that is included with the addition method signal processor ellipse, quantitative analysis is completely impossible with the standard addition linear extrapolation method, which is the conventional standard addition method technology, and , it is now possible to perform quantitative analysis using the standard addition method even when the calibration curve is curved in the direction of the concentration axis, which was difficult to obtain highly accurate analysis results (concentration). This has the effect of significantly improving the measurable concentration range by the standard addition method, the versatility of the standard addition method, and the operability of quantitative analysis of the analyte.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the spectrophotometer of the present invention, and FIGS. 2, 3, 4, and 5 show the standard addition method according to the embodiment of the present invention and the conventional standard addition method. FIG. 6 is a diagram illustrating a comparison between the two methods. FIGS. 7 and 8 are relationship curve diagrams between concentration and absorbance in an atomic absorption spectrophotometer. 1... Hollow cathode lamp, 2... Carbon sample tube, 3... Spectrometer, 4... Photomultiplier tube, 5...
・Preamplifier, 6...Analog/digital converter,
7...Microphone equipped with signal processing function of standard addition curve extrapolation method (5 figures, 6 figures, groove 7 degrees (PP claw))

Claims (1)

[Claims] 1. The calibration curve creation function of the signal processing mechanism for quantitative analysis using the standard addition method of spectrophotometers such as atomic absorption spectrophotometers and spectrofluorophotometers has the ability to generate absorbance values, fluorescence intensity values, etc. It is equipped with a function to create a calibration curve by curve approximation, where the indicated value is a function of the concentration value, or a concentration value is a function of the indicated value of the spectrophotometer, such as absorbance value or fluorescence intensity value, and a function to create a calibration curve by the least squares method. Even when the relationship curve between the concentration value and the spectrophotometric indicator value such as absorbance value or fluorescence intensity value, that is, the calibration curve curves in the direction of the concentration axis, the standard addition method can be used to obtain highly accurate quantitative analysis results. , a spectrophotometer characterized by having a configuration that greatly expands the measurable concentration range using the standard addition method.