CN104749132A - Method for measuring content of azodicarbonamide in flour - Google Patents

Abstract

The invention discloses a method for measuring the content of azodicarbonamide in flour. The method comprises the following steps: preparing standard flour samples with different contents of azodicarbonamide; collecting terahertz time-domain spectrums of the standard flour samples, and respectively converting the terahertz time-domain spectrums of the standard flour samples into corresponding optical parameters; establishing a test model of a corresponding relation of the content of azodicarbonamide in the flour and optical parameters of the flour according to the contents of azodicarbonamide in the standard flour samples and the optical parameters of the standard flour samples; and collecting a terahertz time-domain spectroscopy of the flour to be measured, converting each terahertz time-domain spectrum into a corresponding optical parameter of the flour to be measured, and inputting the optical parameters into the test model to obtain the content of azodicarbonamide in the flour to be measured. The method disclosed by the invention has the advantages of being simple, quick, free of destruction, and the like.

Description

A kind of method measuring the content of azodicarbonamide in flour

Technical field

The present invention relates to a kind of method measuring the content of azodicarbonamide in flour, belong to terahertz time-domain spectroscopy detection technique field.

Background technology

Azodicarbonamide (Azodiformamide, ADA) is a kind of flour improver, for yellow is to Chinese red crystalline powder.It instead of before flour improver potassium bromate, brighten muscle for flour and promote ripe.Regulation in China " food additives use hygienic standard " (GB 2760-2011): azodicarbonamide can use in wheat flour, and maximum use amount is 0.045g/kg, but not description standard detection method in regulation.

The existing method of testing for azodicarbonamide class adjuvant comprises high performance liquid chromatography, Ultra Performance Liquid Chromatography-tandem mass spectrometry, enzymatic isolation method.Contrast above detection method, can find liquid phase chromatography measuring tool have that capacity is little, mobile phase consumption is large and virose in the majority, need by shortcomings such as various filled columns, in addition, the shortcomings such as Measuring Time is longer; Enzymatic isolation method need to sample water-bath and enzymolysis time is longer, and detection limit is also larger.Therefore, a kind of detection method that can can't harm, detect azodicarbonamide content in flour is fast needed.

Summary of the invention

The object of the invention is to overcome above-mentioned the deficiencies in the prior art, a kind of method measuring the content of azodicarbonamide in flour is provided, with content that is harmless, that detect azodicarbonamide in flour rapidly.

For achieving the above object, the technical solution used in the present invention is as follows:

The method that the present invention measures the content of azodicarbonamide in flour comprises:

The standard flour sample that the content preparing azodicarbonamide does not wait; Gather the terahertz time-domain spectroscopy of each described standard flour sample, and the terahertz time-domain spectroscopy of each described standard flour sample is converted to corresponding optical parametric respectively; According to the content of the azodicarbonamide in each standard flour sample and the optical parametric of each described standard flour sample, set up the test model of the corresponding relation between the content of azodicarbonamide in flour and the optical parametric of flour; Gather the terahertz time-domain spectroscopy of flour to be measured, and be converted into the corresponding optical parametric of described flour to be measured, this optical parametric is input to the content obtaining azodicarbonamide in described flour to be measured in described test model.

Further, optical parametric of the present invention is refractive index or absorption coefficient.

Further, when the present invention gathers the terahertz time-domain spectroscopy of standard flour sample and/or flour to be measured, the sweep limit of spectrum is 0.10 ~ 3.00THz.

Preferably, when the present invention gathers the terahertz time-domain spectroscopy of standard flour sample and/or flour to be measured, the sweep limit of spectrum is 0.20 ~ 1.10THz.

Further, the terahertz time-domain spectroscopy of each described standard flour sample that the present invention collects is the arithmetic mean of the terahertz time-domain signal carrying out Multiple-Scan measurement to standard flour sample and obtain, and the terahertz time-domain spectroscopy corresponding to flour described to be measured collected is be arithmetic mean flour to be measured being carried out to the terahertz time-domain signal that Multiple-Scan measurement obtains.

Further, in flour of the present invention, the content of azodicarbonamide represents with mass percentage or molar content.

Further, terahertz time-domain spectroscopy of the present invention adopts transmission method collection.

Compared with prior art, the inventive method use terahertz time-domain spectroscopic technology can fast, harmless, simply, the content of azodicarbonamide in detection flour accurately.Specific as follows:

(1) fingerprint peaks: the frequency of Terahertz (THz) wave band is positioned at 0.1 ~ 10THz (1THz=10 ¹²hz), between the vibration of its photon energy and most of organic molecule and molecular group and rotational energy level, the energy of transition is roughly the same, therefore, the THz spectrum of material contains abundant physics and chemistry information, azodicarbonamide has obvious fingerprint peaks at terahertz wave band, flour does not then have, and therefore obviously can distinguish both in terahertz wave band.

(2) refractive index: terahertz time-domain spectroscopy detection technique can not only obtain the absorption coefficient of detected object, also can obtain the refractive index of detected object, for quantitative test provides more data and accuracy simultaneously.

(3) harmless: the photon energy of THz ripple is very little (only having milli electron-volt magnitude), can avoid causing harmful ionization to sample in test process, carry out Non-Destructive Testing to material.

(4) quick: terahertz time-domain spectroscopy detection technique is the one of spectral detection, has spectral detection advantage fast.

(5) multicomponent is measured simultaneously: flour and azodicarbonamide the absorption coefficient of terahertz wave band and refractive index difference obvious, refractive index or absorption coefficient can be utilized to measure the content of the azodicarbonamide in flour.

Accompanying drawing explanation

Fig. 1 is in embodiment 1 and embodiment 2, and standard flour sample pure azodicarbonamide used is in the terahertz wave band absorption spectra of 0.20 ~ 2.30THz and spectrum of refractive index;

Fig. 2 is in embodiment 1 and embodiment 2, and standard flour sample pure flour used is in the terahertz wave band absorption spectra of 0.20 ~ 1.50THz and spectrum of refractive index;

Fig. 3 is in embodiment 1, utilizes THz-TDS system transmittance to record the absorption spectra of the standard flour sample as calibration set;

Fig. 4 is in embodiment 1, the absorption spectra of the standard flour sample as checking collection utilizing THz-TDS system transmittance to record;

Fig. 5 is in embodiment 1, take absorption coefficient as the test value of mass percentage and the comparison diagram of actual value that the test model of optical parametric detects the azodicarbonamide in the standard flour sample obtained;

Fig. 6 is in embodiment 2, the spectrum of refractive index of the standard flour sample as calibration set utilizing THz-TDS system transmittance to record;

Fig. 7 is in embodiment 2, the spectrum of refractive index of the standard flour sample as checking collection utilizing THz-TDS system transmittance to record;

Fig. 8 is in embodiment 2, take refractive index as the test value of mass percentage and the comparison diagram of actual value that the test model of optical parametric detects the azodicarbonamide in the standard flour sample obtained.

Embodiment

Below in conjunction with accompanying drawing, method of the present invention is further described.

One, to measure the step of the method for the content of azodicarbonamide in flour as follows in the present invention:

(1) test model is set up

Mathematical method is adopted to set up the test model of the corresponding relation between the content of azodicarbonamide in flour and the optical parametric of flour.The mathematical method adopted can be partial least squares regression, linear regression, multiple linear regression, artificial neural network etc.

In the present invention, described test model is set up by the following method:

A. standard flour sample is prepared

The pure flour of known quality proportion relation and pure azodicarbonamide are mixed, the standard flour sample that the content making azodicarbonamide does not wait.In each standard flour sample, the mass percentage of azodicarbonamide is known, is also the actual value of the mass percentage of azodicarbonamide in standard flour sample.It should be noted that, the content of the azodicarbonamide in standard flour sample and flour to be measured, except can adopting the mass percentage of azodicarbonamide in flour, can also adopt the molar content etc. of azodicarbonamide in flour.

B. the terahertz time-domain spectroscopy of standard flour sample is gathered

Gather the terahertz time-domain spectroscopy of each standard flour sample, the sweep limit of spectrum can be 0.10 ~ 3.00THz.For improving the precision of test result, the sweep limit preferably 0.20 ~ 3.00THz of spectrum, more preferably 0.20 ~ 1.10THz.Test environment is generally dry nitrogen environment, and temperature is generally room temperature.When gathering the terahertz time-domain spectroscopy of standard flour sample, use the method for Multiple-Scan, and the terahertz time-domain signal all scanning obtained gets arithmetic mean.When gathering the terahertz time-domain spectroscopy of standard flour sample, transmission method can be adopted to measure.

C. the conversion of spectrum

The terahertz time-domain spectroscopy of gathered each standard flour sample is converted to corresponding optical parametric respectively.In the present invention, the optical parametric of flour can be refractive index or the absorption coefficient of flour.

D. test model is set up

According to the mass percentage of azodicarbonamide in each standard flour sample and the optical parametric of each standard flour sample, set up the test model of the corresponding relation between the mass percentage of azodicarbonamide in flour and the optical parametric of flour.Wherein, the optical parametric of flour is refractive index or the absorption coefficient of flour.

Such as, the test model of the corresponding relation between the mass percentage of the azodicarbonamide in offset minimum binary (PLS) Return Law Criterion flour sample and the optical parametric of standard flour sample can be adopted.Pattern function is: Y=XB+E, and wherein, X is the optical parametric matrix of all standard flour samples, and it can be used as input matrix; Y be in all standard flour samples azodicarbonamide containing moment matrix, and it can be used as output matrix; B is regression coefficient matrix; E is residual matrix.

(2) content of the azodicarbonamide in flour to be measured is detected

Gather the terahertz time-domain spectroscopy of flour to be measured, and be converted into corresponding optical parametric, wherein, the optical parametric of flour is refractive index or the absorption coefficient of flour; Then this optical parametric is input in above set up test model, obtains the content of the azodicarbonamide in flour to be measured.

When gathering the terahertz time-domain spectroscopy of flour to be measured, use the method for Multiple-Scan, and the terahertz time-domain signal all scanning obtained is got arithmetic mean and obtains the terahertz time-domain spectroscopy of flour to be measured.

When gathering the terahertz time-domain spectroscopy of flour to be measured, transmission method can be adopted to measure.

Two, about the quality evaluation of test model

After test model is set up, can by the optical parametric Input matrix of standard flour sample in described test model, test model is utilized again to obtain the mass percentage (hereinafter referred to as " test value ") of the azodicarbonamide in standard flour sample, and the test value of the mass percentage of the azodicarbonamide in standard flour sample and its actual value are compared, carry out the quality of evaluation test model thus.

In order to the quality of evaluation test model, introduce following three parameters for comparing test value and the actual value of the content of azodicarbonamide in standard flour sample: i.e. coefficient R, the root-mean-square error RESE and absolute error E of test value and actual value _ab, the quality of evaluation test model is carried out according to the size of these three parameters.

The expression formula of these three parameters is respectively:

$R=\frac{\underset{i=1}{\overset{N}{\mathrm{\Σ}}}(y_r^i-{\stackrel{\‾}{y}}_r)(y_p^i-{\stackrel{\‾}{y}}_p)}{\sqrt{\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{(y_r^i-{\stackrel{\‾}{y}}_r)}^2\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{(y_p^i-{\stackrel{\‾}{y}}_p)}^2}}$

$\mathrm{RMSE}=\sqrt{(\frac{1}{N}\·\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{({y^i}_p-y_r^i)}^2)}$

$E_{\mathrm{ab}}=\max \left|(y_p^i-y_r^i)\right|,i=\mathrm{1,2},...N$

Wherein, with represent input value (actual value) and the test value of ADA content in i-th standard flour sample respectively, with represent the arithmetic mean of input value (actual value) and the arithmetic mean of test value of ADA content in each standard flour sample respectively, N is the number of standard flour sample.

The coefficient R of test value and actual value is larger, illustrates that the fitting effect of test model is better; Root-mean-square error RESE is less, illustrates that the precision of test model is higher; Absolute error E _abless, illustrate test value and actual value more close.

Below in conjunction with accompanying drawing, describe the present invention in detail by specific embodiment, but embodiments of the present invention are not limited to this.

Embodiment 1:

(1) set up test model and detect flour to be measured

Mathematical method is adopted to set up the test model of the corresponding relation between the content of the azodicarbonamide in flour and the optical parametric of flour.Concrete grammar is as follows:

A. standard flour sample is prepared

According to different mass percentage, weigh pure flour and pure azodicarbonamide, after mixing fully, take the potpourri of about 200mg, under the pressure condition of 4Mpa, be pressed into the standard flour sample that diameter is 13mm, thickness is about 1.50-2.00mm, even structure, the both ends of the surface of each standard flour sample are parallel.

11 standard flour samples are prepared by above method, wherein, the mass percentage (i.e. actual value) of the azodicarbonamide in standard flour sample, as the foundation of calibration set for test model, is that 4 standard flour samples of 74.83%, 35.08%, 9.91%, 1.99% are as the inspection of checking collection for test model by 7 the standard flour samples mass percentage (i.e. actual value) of the azodicarbonamide in standard flour sample being respectively 100%, 89.93%, 49.92%, 20.00%, 4.97%, 1.00% and 0%.

B. the terahertz time-domain spectroscopy of standard flour sample is gathered

Adopt terahertz time-domain spectroscopy (terahertz time-domain spectroscopy, THz-TDS) transmissive system to measure 11 standard flour samples, obtain their terahertz time-domain spectroscopies at 0.20 ~ 1.10THz wave band respectively.When the terahertz time-domain spectroscopy of measurement standard flour sample, whole Terahertz light path is filled with drying nitrogen, reduce the interference of moisture to test thus, the relative humidity of sample cavity is made to be 0%, each sample scans 3 times under equally accurate condition, the sweep limit of spectrum is at 0.20 ~ 1.10THz wave band, and temperature is room temperature; And the terahertz time-domain signal that 3 times scan is got arithmetic mean and obtains the terahertz time-domain spectroscopy of each standard flour sample.

C. the conversion of terahertz time-domain spectroscopy

Reference Signal (namely scanning the terahertz time-domain spectroscopy of air gained) and sample signal (namely scanning the terahertz time-domain spectroscopy of each standard flour sample gained) convert frequency domain spectra to, then process according to following fresnel formula, obtain refractive index and the absorption coefficient of 11 standard flour samples respectively:

$n\left(\mathrm{\ω}\right)=\frac{\mathrm{\φ}\left(\mathrm{\ω}\right)}{\mathrm{\ωd}}+1$

$\mathrm{\α}\left(\mathrm{\ω}\right)=\frac{2k\left(\mathrm{\ω}\right)\mathrm{\ω}}{c}=\frac{2}{d}\ln \frac{4n\left(\mathrm{\ω}\right)}{A\left(\mathrm{\ω}\right){(n\left(\mathrm{\ω}\right)+1)}^2}$

Wherein, the ratio that A (ω) is sample signal and the reference signal amplitude in frequency domain spectra, the phase differential that φ (ω) is sample signal and the reference signal amplitude in frequency domain spectra; D is the thickness that flour is pressed into that diameter is the disk of 13mm, the refractive index that n (ω) is sample, the absorption coefficient that α (ω) is sample; K (ω) is extinction coefficient, and ω is the frequency of frequency domain spectra, and c is the light velocity in vacuum.

Fig. 1 is standard flour sample pure azodicarbonamide used in the absorption spectra of 0.20 ~ 2.30THz and spectrum of refractive index, and Fig. 2 is standard flour sample pure flour used in the absorption spectra of 0.20 ~ 1.50THz and spectrum of refractive index.As seen from Figure 2, the pure flour in standard flour sample does not have characteristic absorption peak at terahertz wave band.As seen from Figure 1, near 1.93THz, there is obvious characteristic absorption peak in the pure azodicarbonamide in standard flour sample.Fig. 3 is the absorption spectras of 7 standard flour samples at 0.20 ~ 1.10THz wave band.As can be seen from Figure 3,7 absorption coefficients as the standard flour sample of calibration set rise successively gradually along with the minimizing of azodicarbonamide content in standard flour sample.

D. test model is set up

According to 7 as the mass percentage of the azodicarbonamide in the standard flour sample of calibration set and the absorption coefficient of these 7 standard flour samples, set up the test model of the corresponding relation between the mass percentage of the azodicarbonamide in flour and the absorption coefficient of flour.Concrete grammar is as follows:

Adopt partial least square method founding mathematical models: Y=XB+E.Wherein, X is input matrix, and Y is output matrix, and B is regression coefficient matrix, and E is residual matrix.Specifically, with 7 standard flour samples at the absorption coefficient matrix of 0.20 ~ 1.10THz wave band for input matrix, to set up for output matrix with the mass percentage matrix of the azodicarbonamide of 7 standard flour samples and obtain test model.

E. the mass percentage of azodicarbonamide in flour to be measured is detected

Gather the terahertz time-domain spectroscopy of flour to be measured, and be converted into corresponding absorption coefficient, then this absorption coefficient is input in test model the content of the azodicarbonamide obtained in flour to be measured.Concrete grammar is as follows:

Adopt terahertz time-domain spectroscopy transmissive system to test flour to be measured, obtain the terahertz time-domain spectroscopy of flour to be measured at 0.20 ~ 1.10THz wave band.When measuring terahertz time-domain spectroscopy, whole Terahertz light path is filled with drying nitrogen, reduce the interference of moisture to test thus, the relative humidity of sample cavity is made to be 0%, temperature is room temperature, flour to be measured is scanned under equally accurate condition the terahertz time-domain signal obtaining flour to be measured for 3 times, the sweep limit of spectrum is at 0.20 ~ 1.10THz wave band, and temperature is room temperature; Then the terahertz time-domain signal that 3 times scan got arithmetic mean and obtain the terahertz time-domain spectroscopy of flour to be measured.

Reference Signal (namely scanning the terahertz time-domain spectroscopy of air gained) and sample signal (namely scanning the terahertz time-domain spectroscopy of flour gained to be measured) convert frequency domain spectra to, then process according to following fresnel formula, obtain refractive index and the absorption coefficient of flour to be measured:

$n\left(\mathrm{\ω}\right)=\frac{\mathrm{\φ}\left(\mathrm{\ω}\right)}{\mathrm{\ωd}}+1$

$\mathrm{\α}\left(\mathrm{\ω}\right)=\frac{2k\left(\mathrm{\ω}\right)\mathrm{\ω}}{c}=\frac{2}{d}\ln \frac{4n\left(\mathrm{\ω}\right)}{A\left(\mathrm{\ω}\right){(n\left(\mathrm{\ω}\right)+1)}^2}$

Wherein, the ratio that A (ω) is sample signal and the reference signal amplitude in frequency domain spectra, the phase differential that φ (ω) is sample signal and the reference signal amplitude in frequency domain spectra; D is the thickness that tested surface pruinescence is pressed into that diameter is the disk of 13mm, the refractive index that n (ω) is sample, the absorption coefficient that α (ω) is sample; K (ω) is extinction coefficient, and ω is the frequency of frequency domain spectra, and c is the light velocity in vacuum.

Finally, the absorption coefficient of flour to be measured is input in test model the content of the azodicarbonamide obtained in flour to be measured.

(2) quality of evaluation test model

A) quality using 7 as the standard flour sample validation test model of calibration set

The absorption coefficient of above 7 standard flour samples as calibration set is input in test model respectively as input value, obtains the test value of the mass percentage of the azodicarbonamide in these 7 standard flour samples.The test value of mass percentage and the coefficient R of actual value of the azodicarbonamide in these 7 standard flour samples are 1.0000, and root-mean-square error is 0.0018%.Fig. 5 is shown in the test value of mass percentage and the contrast of actual value of the azodicarbonamide in these 7 standard flour samples.The test value of the mass percentage of the azodicarbonamide in these 7 standard flour samples and the concrete numerical value of actual value are in table 1.As shown in Table 1, these 7 mass percentage as the azodicarbonamide in the standard flour sample of calibration set that this test model tests out are compared with its actual value, value maximum in absolute error is 0.0153%, the maximal value of absolute error and root-mean-square error are all less than the minimum value 1.00% of the actual value of the mass percentage of the azodicarbonamide in these 7 standard flour samples, and the above results illustrates that the quality of the test model set up is good.

B) quality using 4 as the further validation test model of standard flour sample of checking collection

Gather the terahertz time-domain spectroscopy of 4 parts of standard flour samples (namely verifying collection) with reference to above method respectively, extract corresponding absorption coefficient, result as shown in Figure 4.By in above for the input of the absorption coefficient of 4 the standard flour samples test model set up, the test value of mass percentage and the coefficient R of actual value that obtain the azodicarbonamide in these 4 standard flour samples are 1.0000, and root-mean-square error is 0.0769%.Fig. 5 is shown in the test value of mass percentage and the contrast of actual value of the azodicarbonamide in these 4 standard flour samples, and the test value of the mass percentage of the azodicarbonamide in these 4 standard flour samples and the concrete numerical value of actual value are in table 2.As shown in Table 2, the test value of the mass percentage of the azodicarbonamide in these 4 standard flour samples and the absolute error of actual value maximum be 0.3636%; The test value of mass percentage of azodicarbonamide in these 4 standard flour samples and the maximal value of the root-mean-square error of actual value and absolute error are all less than the minimum 1.99% in the actual value of the mass percentage of the azodicarbonamide in these 4 standard flour samples.This result confirms further, the mass percentage of the test model utilizing the present embodiment to set up to the azodicarbonamide in these 4 standard flour samples measures obtained test value and actual value is very close, general effect is good, can be used in the content of the azodicarbonamide detected in flour to be measured.

Table 1 is as the test value of mass percentage of azodicarbonamide in the standard flour sample of calibration set and comparing of actual value

Table 2 is as the test value of mass percentage of azodicarbonamide and comparing of actual value in the standard flour sample of checking collection

In addition, the measurement result of the present embodiment has following characteristics:

(1) difference of the Terahertz absorption coefficient of azodicarbonamide and flour is large

As shown in Figure 1 and Figure 2, pure flour does not have characteristic absorption peak at terahertz wave band, and pure azodicarbonamide exists obvious characteristic absorption peak near 1.93THz, and the absorption coefficient of pure flour is greater than the absorption coefficient of pure azodicarbonamide and both do not occur simultaneously.

(2) the result precision of quantitative test is high

Absorption coefficient is the build-in attribute of detected object, affect little by extraneous factor, when therefore utilizing absorption coefficient to test the content of azodicarbonamide in the content as azodicarbonamide in the standard flour sample of calibration set and the standard flour sample as checking collection, their root-mean-square error is respectively 0.0018% and 0.0769%, illustrate that the quality of the test model that the present invention sets up is good, accuracy of quantitative analysis is better than 1.00%.

Embodiment 2:

The present embodiment measures the method for the content of azodicarbonamide in flour, as follows with the difference of embodiment 1:

(I) survey flour optical parametric be refractive index.

(II) refractive index formula:

In above formula, φ (ω) by the signal (i.e. the terahertz time-domain spectroscopy of scanning institute survey flour gained) of survey flour and reference signal (i.e. the terahertz time-domain spectroscopy of the scanning air gained) phase differential in frequency domain spectra; D by survey flour be pressed into the thickness that diameter is the disk of 13mm, ω is the frequency of frequency domain spectra, n (ω) by the refractive index of survey flour.

The method that the present embodiment measures the content of azodicarbonamide in flour is specific as follows:

(1) set up test model and detect flour to be measured

A. standard flour sample is prepared

According to the method preparation standard flour sample of embodiment 1.Wherein, the mass percentage (i.e. actual value) of the azodicarbonamide in standard flour sample be 7 samples of 100%, 74.83%, 35.08%, 20.00%, 9.91%, 1.99%, 0% as the foundation of calibration set for test model, the mass percentage (i.e. actual value) of the azodicarbonamide in standard flour sample is that 4 samples of 89.93%, 49.92%, 4.97%, 1.00% are as the inspection of checking collection for test model.The spectrum of refractive index of the standard flour sample of calibration set and checking collection is shown in Fig. 6 and Fig. 7 respectively.

B. the terahertz time-domain spectroscopy of standard flour sample is gathered

Adopt terahertz time-domain spectroscopy (terahertz time-domain spectroscopy, THz-TDS) transmissive system to measure 11 standard flour samples, obtain their terahertz time-domain spectroscopies at 0.20 ~ 1.10THz wave band respectively.When the terahertz time-domain spectroscopy of measurement standard flour sample, whole Terahertz light path is filled with drying nitrogen, reduce the interference of moisture to test thus, the relative humidity of sample cavity is made to be 0%, each sample scans 3 times under equally accurate condition, the sweep limit of spectrum is at 0.20 ~ 1.10THz wave band, and temperature is room temperature; And the terahertz time-domain signal that 3 times scan is got arithmetic mean and obtains the terahertz time-domain spectroscopy of each standard flour sample.

C. the conversion of terahertz time-domain spectroscopy

Reference Signal (namely scanning the terahertz time-domain spectroscopy of air gained) and sample signal (namely scanning the terahertz time-domain spectroscopy of each standard flour sample gained) convert frequency domain spectra to, then process according to following fresnel formula, obtain refractive index and the absorption coefficient of 11 standard flour samples respectively:

$n\left(\mathrm{\ω}\right)=\frac{\mathrm{\φ}\left(\mathrm{\ω}\right)}{\mathrm{\ωd}}+1$

$\mathrm{\α}\left(\mathrm{\ω}\right)=\frac{2k\left(\mathrm{\ω}\right)\mathrm{\ω}}{c}=\frac{2}{d}\ln \frac{4n\left(\mathrm{\ω}\right)}{A\left(\mathrm{\ω}\right){(n\left(\mathrm{\ω}\right)+1)}^2}$

Wherein, the ratio that A (ω) is sample signal and the reference signal amplitude in frequency domain spectra, the phase differential that φ (ω) is sample signal and the reference signal amplitude in frequency domain spectra; D is the thickness that flour is pressed into that diameter is the disk of 13mm, the refractive index that n (ω) is sample, the absorption coefficient that α (ω) is sample; K (ω) is extinction coefficient, and ω is the frequency of frequency domain spectra, and c is the light velocity in vacuum.

Fig. 1 is standard flour sample pure azodicarbonamide used in the absorption spectra of 0.20 ~ 2.30THz and spectrum of refractive index, and Fig. 2 is standard flour sample pure flour used in the absorption spectra of 0.20 ~ 1.50THz and spectrum of refractive index.As shown in Figure 1, the mean refractive index of the pure azodicarbonamide that standard flour sample is used is 1.870 ~ 1.876; As shown in Figure 2, the mean refractive index of the pure flour that standard flour sample is used is 1.806 ~ 1.786.There is not overlap in the refractive index of pure flour and pure azodicarbonamide.

Can be found by Fig. 6 and Fig. 7, along with the minimizing of the content of the azodicarbonamide in standard flour sample, the refractive index of standard flour sample presents downtrending gradually.It is because the refractive index of pure flour is lower than pure azodicarbonamide that above-mentioned phenomenon occurs, and along with the ratio of pure azodicarbonamide in standard flour sample reduces, the refractive index characteristic of standard flour sample also can move closer to the refractive index of pure flour.

D. according to the method for embodiment 1, partial least square method is adopted to set up test model.

Specifically, according to 7 as the mass percentage of the azodicarbonamide in the standard flour sample of calibration set and the refractive index of these 7 standard flour samples, set up the test model of the corresponding relation between the mass percentage of the azodicarbonamide in flour and the refractive index of flour.Concrete grammar is as follows:

Adopt partial least square method founding mathematical models: Y=XB+E.Wherein, X is input matrix, and Y is output matrix, and B is regression coefficient matrix, and E is residual matrix.Specifically, with 7 standard flour samples at the refractive index matrix of 0.20 ~ 1.10THz wave band for input matrix, to set up for output matrix with the mass percentage matrix of the azodicarbonamide of 7 standard flour samples and obtain test model.

E. the mass percentage of azodicarbonamide in flour to be measured is detected

Gather the terahertz time-domain spectroscopy of flour to be measured, and be converted into refractive index, then this refractive index is input in test model the content of the azodicarbonamide obtained in flour to be measured.Concrete grammar is as follows:

Adopt terahertz time-domain spectroscopy transmissive system to test flour to be measured, obtain the terahertz time-domain spectroscopy of flour to be measured at 0.20 ~ 1.10THz wave band.When measuring terahertz time-domain spectroscopy, whole Terahertz light path is filled with drying nitrogen, and reduce the interference of moisture to test thus, make the relative humidity of sample cavity be 0%, temperature is room temperature.Flour to be measured is scanned under equally accurate condition the terahertz time-domain signal obtaining flour to be measured for 3 times, the sweep limit of spectrum is at 0.20 ~ 1.10THz wave band, and temperature is room temperature; Then the terahertz time-domain signal that 3 times scan got arithmetic mean and obtain the terahertz time-domain spectroscopy of flour to be measured.

Reference Signal (namely scanning the terahertz time-domain spectroscopy of air gained) and sample signal (namely scanning the terahertz time-domain spectroscopy of flour gained to be measured) convert frequency domain spectra to, then process according to following fresnel formula, obtain refractive index and the absorption coefficient of flour to be measured:

$n\left(\mathrm{\ω}\right)=\frac{\mathrm{\φ}\left(\mathrm{\ω}\right)}{\mathrm{\ωd}}+1$

$\mathrm{\α}\left(\mathrm{\ω}\right)=\frac{2k\left(\mathrm{\ω}\right)\mathrm{\ω}}{c}=\frac{2}{d}\ln \frac{4n\left(\mathrm{\ω}\right)}{A\left(\mathrm{\ω}\right){(n\left(\mathrm{\ω}\right)+1)}^2}$

Wherein, the ratio that A (ω) is sample signal and the reference signal amplitude in frequency domain spectra, the phase differential that φ (ω) is sample signal and the reference signal amplitude in frequency domain spectra; D is the thickness that tested surface pruinescence is pressed into that diameter is the disk of 13mm, the refractive index that n (ω) is sample, the absorption coefficient that α (ω) is sample; K (ω) is extinction coefficient, and ω is the frequency of frequency domain spectra, and c is the light velocity in vacuum.

Finally, the refractive index of flour to be measured is input in test model the content of the azodicarbonamide obtained in flour to be measured.

(2) quality of evaluation test model

Verifying being input to test model respectively as the refractive index of 7 of calibration set standard flour samples as input value in the present embodiment 2, obtaining the test value of the mass percentage of the azodicarbonamide in these 7 standard flour samples.The test value of the mass percentage of the azodicarbonamide in 7 standard flour samples and the related coefficient of actual value are 1.0000, and root-mean-square error is 0.0052%; Fig. 8 is shown in the test value of the mass percentage of the azodicarbonamide in standard flour sample and the contrast of actual value, and the test value of the mass percentage of the azodicarbonamide in standard flour sample and the concrete numerical value of actual value are in table 3.As shown in Table 3, in the absolute error of the mass percentage of the azodicarbonamide in 7 standard flour samples that this test model draws, maximum value is 0.0505%, the maximal value of absolute error and root-mean-square error are all less than the minimum value 1.99% in the actual value of the mass percentage of the azodicarbonamide in these 7 standard flour samples, and the above results illustrates that the quality of the test model set up is good.

Quality using 4 as the further validation test model of standard flour sample of checking collection

Gather 4 terahertz time-domain spectroscopies as the standard flour sample of calibration set in the present embodiment 2, and extract corresponding refractive index, result as shown in Figure 7.By the refractive index input test model of 4 standard flour samples, the related coefficient of the test value and actual value that obtain the mass percentage of the azodicarbonamide of 4 standard flour samples is 1.0000, and root-mean-square error is 0.0381%.Fig. 8 is shown in the test value of mass percentage and the contrast of actual value of the azodicarbonamide in 4 standard flour samples, and the test value of the mass percentage of the azodicarbonamide in 4 standard flour samples and the concrete numerical value of actual value are in table 4.

As shown in Table 4, the maximal value in the test value of mass percentage of the azodicarbonamide in these 4 standard flour samples and the absolute error of actual value is 0.1172%; Maximal value in the test value of mass percentage of the azodicarbonamide in these 4 standard flour samples and the root-mean-square error of actual value and absolute error is all less than the minimum value 1.00% of the mass percentage of the azodicarbonamide in these 4 standard flour samples, this result confirms further, test value and the actual value of the mass percentage of the azodicarbonamide in these 4 standard flour samples that the test model that the present embodiment is set up obtains are very close, general effect is good, can be used in the content of the idol band formamide tested in flour.

Table 3 is as the test value of mass percentage of azodicarbonamide in the standard flour sample of calibration set and comparing of actual value

Table 4 is as the test value of mass percentage of azodicarbonamide and comparing of actual value in the standard flour sample of checking collection

In addition, the method for testing of the present embodiment and measurement result have following characteristics:

(1) in the extraction of optical parametric, refractive index is that tera-hertz spectra is different from specific to other spectrum, for quantitative test provides more data point.Refractive index is the inherent characteristic of detected object, is not subject to ectocine.

(2) precision of quantitative test is high

The root-mean-square error of the test value that the test model that utilization is set up for optical parametric with refractive index detects the content as the azodicarbonamide in the standard flour sample of calibration set and obtains and actual value is 0.0052%, and the test value detect the content of the azodicarbonamide in the standard flour sample as checking collection and the root-mean-square error of actual value are 0.0381%; The test value of content of azodicarbonamide in the standard flour sample of checking collection and the maximal value of the absolute error of actual value are 0.1172%, and illustrate that the quality of the test model that the present invention sets up is good, accuracy of quantitative analysis is better than 1.00%.

More than describing is only description to the specific embodiment of the present invention, not departing from any modification or partial replacement in the scope of the invention, all should belong to the protection domain of claim of the present invention.

Claims (9)

1. measure a method for the content of azodicarbonamide in flour, it is characterized in that, comprising:

The standard flour sample that the content preparing azodicarbonamide does not wait; Gather the terahertz time-domain spectroscopy of each described standard flour sample, and the terahertz time-domain spectroscopy of each described standard flour sample is converted to corresponding optical parametric respectively; According to the content of the azodicarbonamide in each standard flour sample and the optical parametric of each described standard flour sample, set up the test model of the corresponding relation between the content of azodicarbonamide in flour and the optical parametric of flour;

Gather the terahertz time-domain spectroscopy of flour to be measured, and be converted into the corresponding optical parametric of described flour to be measured, this optical parametric is input to the content obtaining azodicarbonamide in described flour to be measured in described test model.

2. method according to claim 1, is characterized in that: described optical parametric is refractive index or absorption coefficient.

3. method according to claim 2, is characterized in that: when gathering the terahertz time-domain spectroscopy of standard flour sample and/or flour to be measured, the sweep limit of spectrum is 0.10 ~ 3.00 THz.

4. method according to claim 3, is characterized in that: when gathering the terahertz time-domain spectroscopy of standard flour sample and/or flour to be measured, the sweep limit of spectrum is 0.20 ~ 1.10THz.

5. method according to any one of claim 1 to 4, it is characterized in that: the terahertz time-domain spectroscopy of each described standard flour sample collected is the arithmetic mean of the terahertz time-domain signal carrying out Multiple-Scan measurement to standard flour sample and obtain, and the terahertz time-domain spectroscopy corresponding to flour described to be measured collected is be arithmetic mean flour to be measured being carried out to the terahertz time-domain signal that Multiple-Scan measurement obtains.

6. method according to any one of claim 1 to 5, is characterized in that: in described flour, the content of azodicarbonamide represents with mass percentage or molar content.

7. method according to any one of claim 1 to 4, is characterized in that: described terahertz time-domain spectroscopy adopts transmission method collection.

8. method according to claim 5, is characterized in that: described terahertz time-domain spectroscopy adopts transmission method collection.

9. method according to claim 6, is characterized in that: described terahertz time-domain spectroscopy adopts transmission method collection.