Method for determining content of vanillin in vanilla by utilizing gas chromatography

Abstract

The invention relates to the technical field of gas chromatography detection, in particular to a method for determining the content of vanillin in vanilla by using gas chromatography, and the method comprises the following steps: obtaining gas chromatograms of a sample solution to be analyzed, a standard solution and a contrast solution and environment temperatures at all moments in a loading process; acquiring a to-be-analyzed chromatographic peak of the to-be-analyzed gas chromatogram; calculating a first interference value of the gas chromatogram to be analyzed; calculating a temperature influence degree to obtain an interference difference degree, a second interference value and an interfered coefficient of the to-be-analyzed gas chromatogram, determining a heuristic threshold value of a wavelet denoising algorithm by combining a heuristic threshold value rule, and filtering the to-be-analyzed gas chromatogram through the wavelet denoising algorithm to obtain the to-be-analyzed gas chromatogram. And determining the content of vanillin in vanilla by using the peak area of a chromatographic peak to be analyzed in the filtered gas chromatogram to be analyzed. According to the method, noise interference in the to-be-analyzed gas chromatogram is effectively removed, and the accuracy of measuring the content of vanillin in vanilla is improved.

Description

Technical Field

[0001] The present application relates to the technical field of gas chromatography detection, and in particular to a method for determining the vanillin content in vanilla using gas chromatography. Background Art

[0002] Vanilla, also known as vanilla grass and vanilla, is a precious natural spice plant. An important criterion for measuring whether the fragrance of vanilla is strong is the vanillin content it contains. Vanillin can bring a unique milky flavor to food, but long-term intake of vanillin can cause adverse reactions such as dizziness and nausea, which is harmful to human health. Therefore, it is necessary to measure the vanillin content in vanilla to ensure that the quality of vanilla meets the requirements and effectively control the safe amount of additives in food.

[0003] Gas chromatography-mass spectrometry (GC-MS) is widely used for vanillin analysis due to its high separation power and qualitative and quantitative accuracy. In chromatographic analysis, parameters such as the retention time, width, and area of ​​the chromatographic peak are crucial for the identification and quantification of vanillin. Traditionally, the determination of vanillin in vanilla using gas chromatography is based on the peak area corresponding to the vanillin peak in the chromatogram. However, GC-MS instruments can be affected by a variety of interfering factors during chromatographic analysis, including instrument performance fluctuations, ambient temperature changes, and sample matrix residues. These interfering factors can cause chromatographic peak distortion, peak position shifts, or increased noise, thereby affecting the quantitative accuracy of vanillin content. Summary of the Invention

[0004] In order to solve the above technical problems, a method for determining the vanillin content in vanilla using gas chromatography is provided to solve the existing problems.

[0005] The solution to the technical problem of the present application is to provide a method for determining the vanillin content in vanilla using gas chromatography, comprising the following steps: Obtain chromatograms of the sample solution to be analyzed, the standard solution, and the reference solution, respectively, which are recorded as the gas chromatogram to be analyzed, the standard gas chromatogram, and the reference gas chromatogram, and obtain the ambient temperature of the three solutions at each moment during the process of being put on the machine; Based on the size of the peaks in the gas chromatogram to be analyzed, the peaks in the gas chromatogram to be analyzed are screened to obtain significant peaks; the differences in corresponding moments between different significant peaks in the gas chromatogram to be analyzed and the maximum peak in the standard gas chromatogram are analyzed to obtain the chromatographic peaks to be analyzed in the gas chromatogram to be analyzed; Analyze the difference in peak width between the chromatographic peak to be analyzed and the maximum peak in the standard gas chromatogram, as well as the offset at the corresponding time, and calculate the first interference value of the gas chromatogram to be analyzed; Based on the fluctuation of the response value at all times in the control gas chromatogram and the fluctuation of the ambient temperature during the process of the control solution being put on the machine, the temperature influence degree is calculated, and the interference difference degree of the gas chromatogram to be analyzed is obtained by combining the difference in the fluctuation of the ambient temperature during the process of the sample solution to be analyzed and the standard solution to be analyzed. In combination with the first interference value, a second interference value of the gas chromatogram to be analyzed is determined; The interference coefficient of the gas chromatogram to be analyzed is determined by the discreteness of the response values ​​​​except for the local range where the significant peak is located in the gas chromatogram to be analyzed and the second interference value. Combined with the heuristic threshold rule, the heuristic threshold of the wavelet denoising algorithm is determined. The gas chromatogram to be analyzed is filtered by the wavelet denoising algorithm. The vanillin content in vanilla is determined by using the peak area of ​​the chromatographic peak to be analyzed in the filtered gas chromatogram to be analyzed.

[0006] Preferably, the process of obtaining the significant peaks is: obtaining the peaks of the response values ​​at all moments in the gas chromatogram to be analyzed, obtaining the segmentation threshold of the peaks of all peaks in the gas chromatogram to be analyzed; and recording the peaks in the gas chromatogram to be analyzed whose peaks are greater than or equal to the segmentation threshold as significant peaks.

[0007] Preferably, the method of obtaining the chromatographic peak to be analyzed of the gas chromatogram to be analyzed includes: obtaining the peaks of the response values ​​at all times in the standard gas chromatogram, and recording the peak corresponding to the maximum peak as the chromatographic peak; calculating the interval time between the time corresponding to each significant peak in the gas chromatogram to be analyzed and the time corresponding to the chromatographic peak in the standard gas chromatogram; selecting the significant peak corresponding to the minimum interval time, and recording it as the chromatographic peak to be analyzed.

[0008] Preferably, the calculating of the first interference value of the gas chromatogram to be analyzed includes: Calculate the difference between the half-peak width corresponding to the chromatographic peak in the gas chromatogram to be analyzed and the half-peak width corresponding to the chromatographic peak in the standard gas chromatogram, and record it as the relative difference; The first interference value is a product of a result of performing positive mapping on the relative difference and a result of performing positive mapping on the minimum interval time.

[0009] Preferably, the calculation process of the temperature influence is: Calculate the discrete degree of the response at all moments in the control gas chromatogram, and record it as the first discrete degree; Calculate the dispersion of the ambient temperature at all times during the process of the control solution being placed on the machine, and record it as the second dispersion; The temperature influence degree is a ratio of the first dispersion degree to the second dispersion degree.

[0010] Preferably, obtaining the interference difference of the gas chromatogram to be analyzed includes: Calculate the product of the degree of dispersion of the ambient temperature at all times during the process of the sample solution to be analyzed and the standard solution being put on the machine and the temperature influence, and use them as the relative fluctuation of the gas chromatogram to be analyzed and the standard gas chromatogram respectively; The interference difference is the difference in relative fluctuation between the gas chromatogram to be analyzed and the standard gas chromatogram.

[0011] Preferably, the determining of the second interference value of the gas chromatogram to be analyzed includes: if the interference difference is 0, the second interference value of the gas chromatogram to be analyzed is the first interference value; otherwise, the second interference value of the gas chromatogram to be analyzed is the ratio of the first interference value to the interference difference.

[0012] Preferably, the determining of the interference coefficient of the gas chromatogram to be analyzed comprises: All moments in the neighborhood of the moments corresponding to the significant peaks in the gas chromatogram to be analyzed are recorded as local windows; the discreteness of the response values ​​of all moments in the gas chromatogram to be analyzed, except for the moments contained in the local windows corresponding to all the significant peaks, is taken as the baseline interference degree of the gas chromatogram to be analyzed; The interference coefficient is a normalized result of the product of the second interference value and the baseline interference degree.

[0013] Preferably, the determining of the heuristic threshold of the wavelet denoising algorithm comprises: Perform wavelet decomposition on the responsivity of all moments in the gas chromatogram to be analyzed, square the decomposed wavelet coefficients and arrange them in ascending order to form a wavelet coefficient vector; For each element in the wavelet coefficient vector, calculate the risk value corresponding to each element; Select the element corresponding to the minimum risk value in the wavelet coefficient vector, denoted as ; The sum of all elements in the wavelet coefficient vector is recorded as ;make , , then the heuristic threshold It can be expressed as: ,in, is the length of the wavelet coefficient vector, is the interference coefficient, is the number of all moments in the gas chromatogram to be analyzed, represents the logarithmic function with base 2, represents the logarithmic function with base 10, represents the minimum function, Represents square root.

[0014] Preferably, the first Risk value of each element The calculation formula is: ,in, is the first wavelet coefficient vector The element value corresponding to the element, is the first wavelet coefficient vector The sequence number of the elements, is the first wavelet coefficient vector The element value corresponding to the element.

[0015] This application has at least the following beneficial effects: The present application obtains significant peaks by screening the peaks in the gas chromatogram to be analyzed, which has the beneficial effect of eliminating the interference of low-intensity noise peaks and retaining the characteristic peaks related to the vanillin component; obtains the chromatographic peaks to be analyzed of the gas chromatogram to be analyzed, which has the beneficial effect of selecting the chromatographic peak corresponding to the vanillin component from the gas chromatogram to be analyzed by aligning the retention time between the significant peaks of the gas chromatogram to be analyzed and the chromatographic peaks in the standard gas chromatogram; calculates the first interference value of the gas chromatogram to be analyzed, which has the beneficial effect of aligning the retention time between the significant peaks of the gas chromatogram to be analyzed and the chromatographic peaks in the standard gas chromatogram; The differences in chromatographic peak width and time are used to evaluate the stability of the instrument performance and reflect the interference of the sample solution to be analyzed during chromatographic detection; the temperature influence is calculated, which has the beneficial effect of considering the influence of unit temperature change on the fluctuation of the response value in the control gas chromatogram, reflecting the sensitivity of the response value to the unit ambient temperature fluctuation; the interference difference of the gas chromatogram to be analyzed is obtained, which has the beneficial effect of considering the consistency of the interference of the sample solution to be analyzed and the standard solution during chromatographic detection by the ambient temperature; the second interference value of the gas chromatogram to be analyzed is determined, which has the beneficial effect of By compensating for the difference in interference caused by temperature change on the measurement results of the gas chromatogram to be analyzed and the standard gas chromatogram, the gas chromatogram to be analyzed and the standard gas chromatogram are made to be consistent in terms of the interference effect of the ambient temperature, thereby being able to truly reflect the characteristic difference of the chromatographic peak corresponding to vanillin between the gas chromatogram to be analyzed and the standard gas chromatogram, so as to accurately evaluate the influence of noise interference on the gas chromatogram to be analyzed; the interference coefficient of the gas chromatogram to be analyzed is determined, which has the beneficial effect of taking into account the influence of multiple interference sources on the gas chromatogram to be analyzed, and comprehensively evaluating the gas chromatogram to be analyzed when performing chromatographic detection on the sample solution to be analyzed. The gas chromatogram to be analyzed is affected by error interference; and combined with the heuristic threshold rule, the heuristic threshold of the wavelet denoising algorithm is determined, the gas chromatogram to be analyzed is filtered by the wavelet denoising algorithm, and the vanillin content in vanilla is determined by using the peak area of ​​the chromatographic peak to be analyzed in the filtered gas chromatogram to be analyzed. The beneficial effect is that the wavelet denoising threshold is dynamically adjusted according to the degree of noise interference on the gas chromatogram to be analyzed, thereby effectively removing the noise interference in the gas chromatogram to be analyzed, more accurately measuring the peak area of ​​the chromatographic peak to be analyzed, and improving the accuracy of the determination of the vanillin content in vanilla. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The method for determining the vanillin content in vanilla using gas chromatography of the present application is further described in detail below with reference to the accompanying drawings.

[0017] Figure 1 A flow chart of the steps of the method for determining the vanillin content in vanilla using gas chromatography provided in an embodiment of the present application; Figure 2A flowchart of the steps of the method for obtaining the heuristic threshold provided in an embodiment of the present application. DETAILED DESCRIPTION

[0018] To further clarify the objectives, technical solutions, and advantages of this application, the method for determining the vanillin content in vanilla using gas chromatography, as proposed in this application, is described in further detail below with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are intended only to illustrate this application and are not intended to limit this application.

[0019] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0020] See also Figure 1 , which shows a flow chart of the steps of a method for determining the vanillin content in vanilla using gas chromatography provided in one embodiment of the present application, the method comprising the following steps: Step 1: Obtain chromatograms of the sample solution to be analyzed, the standard solution, and the reference solution, respectively, which are recorded as the gas chromatogram to be analyzed, the standard gas chromatogram, and the reference gas chromatogram, and obtain the ambient temperature of the three solutions at each moment during the process of being put on the machine.

[0021] Gas chromatography is a chromatographic technique that uses gas as the mobile phase to separate and analyze volatile or gaseous substances. The specific process is as follows: When a sample is injected into a chromatographic column, it is first heated in a vaporizer and converted into vapor. This vapor is then carried into the column by a carrier gas (such as nitrogen, hydrogen, or helium). Within the column, sample components pass through the column at different speeds due to their different distribution coefficients between the stationary and mobile phases, ultimately generating an electrical signal in the detector, forming a chromatogram.

[0022] Therefore, the vanilla was cut into 0.5 cm segments, and 1 g of vanilla was weighed, and then 20 mL of 75% ethanol was added to a conical flask. Ultrasonic extraction was performed at 40 degrees and 40 kHz for 20 min each time. After the extract was filtered, the residue was washed with 75% ethanol. The filtrate was combined, cooled to room temperature, and the volume was made up to 50 mL with 75% ethanol. The solution was shaken evenly and filtered with a 0.22 μm microporous filter membrane to obtain the sample solution to be analyzed. Next, take 500 mg of vanillin standard sample dried to constant weight from a desiccator, dissolve it in 75% ethanol and dilute to 50 mL, shake well to prepare a 10 mg / mL standard solution. Furthermore, 50 mL of 75% ethanol solution was used as the control solution; The sample solution to be analyzed, the standard solution, and the control solution were analyzed in sequence using a gas chromatography-mass spectrometry (GC-MS) instrument to obtain a gas chromatogram to be analyzed, a standard gas chromatogram, and a control gas chromatogram, respectively. A wavelet transform algorithm was used to perform baseline correction on the gas chromatogram to be analyzed, the standard gas chromatogram, and the control gas chromatogram, respectively. The wavelet transform algorithm is a well-known technique and will not be described in detail herein. It should be noted that since the control solution does not contain any solvent solution containing vanillin components, its control gas chromatogram should show a smooth baseline without obvious peaks or fluctuations when it is not interfered with. If the chromatographic detection process is interfered with by changes in ambient temperature, internal factors of the instrument, or other external factors, certain fluctuations will appear in the control gas chromatogram.

[0023] The ambient temperature of the sample solution to be analyzed, the standard solution, and the control solution at each moment when the sample solution to be analyzed, the standard solution, and the control solution are tested on the machine is obtained by the temperature sensor. Thus, the ambient temperature of the sample solution to be analyzed, the standard solution, and the control solution at each moment when the sample solution to be analyzed, the standard solution, and the control solution are tested on the machine are obtained respectively. In the present embodiment, the chromatographic column is a DB-5MS elastic quartz capillary column, the column temperature is an initial temperature of 60 ° C, maintained for 1 min, then heated to 260 degrees at 10 ° C / min and held for 6 min, then heated to 290 degrees at 6 ° C / min and held for 8 min; the carrier gas is helium, the flow rate is 1.0 mL / min, the injection volume is 1 uL, and the sample is not split; mass spectrometry conditions: ionization mode is EI, ion source temperature is 200 degrees, interface temperature is 220 degrees, electron bombardment voltage is 70 eV, detector voltage is 1.0 kV, mass-to-nuclear ratio scanning range is 40-500 amu, automatic tuning, solvent delay is 3 minutes; the chromatographic data of the sample solution to be analyzed, the standard solution and the control solution within 43 min are recorded respectively by gas chromatography-mass spectrometry, therefore, the acquisition time interval of the temperature sensor is 1 s, and the acquisition time is 43 min. As other implementation methods, the implementer can set it according to actual conditions; wherein, the wavelet transform algorithm is a well-known technology and will not be described here.

[0024] At this point, the gas chromatogram to be analyzed, the standard gas chromatogram and the reference gas chromatogram are obtained, as well as the ambient temperature at each moment during the loading process of the sample solution to be analyzed, the standard solution and the reference solution.

[0025] Step 2: Based on the size of the peaks in the gas chromatogram to be analyzed, the peaks in the gas chromatogram to be analyzed are screened to obtain significant peaks; the differences between the corresponding moments between different significant peaks in the gas chromatogram to be analyzed and the maximum peak in the standard gas chromatogram are analyzed to obtain the chromatographic peaks to be analyzed of the gas chromatogram to be analyzed; the differences in peak widths between the chromatographic peaks to be analyzed in the gas chromatogram to be analyzed and the maximum peak in the standard gas chromatogram, as well as the offsets at the corresponding moments, are analyzed to calculate the first interference value of the gas chromatogram to be analyzed.

[0026] When using a gas chromatography-mass spectrometer for on-machine analysis, the performance of the instrument may change due to various factors, such as sample matrix residue in the inlet, aging of the chromatographic column, and state drift of the mass spectrometer detector. These changes can cause the measurement results to deviate from the true value, thereby introducing systematic bias and generating interference noise, which in turn affects the accuracy of subsequent vanillin content detection.

[0027] Secondly, if the gas chromatogram to be analyzed and the standard gas chromatogram are subject to less interference, the retention time of vanillin in the sample solution to be analyzed in the gas chromatogram to be analyzed and its retention time in the standard gas chromatogram should be relatively consistent, and the duration of the chromatographic peak corresponding to vanillin is relatively consistent.

[0028] Based on the above analysis, the chromatographic peak to be analyzed in the gas chromatogram to be analyzed is obtained by analyzing the interval between the peak in the gas chromatogram to be analyzed and the peak in the standard gas chromatogram, specifically: Obtain the peaks of the response values ​​at all times in the standard gas chromatogram, and record the peak corresponding to the maximum peak as the chromatographic peak; In this embodiment, an AMPD (Automatic Multiscale-based Peak Detection) peak detection algorithm is used to obtain the peak value. The AMPD peak detection algorithm is a well-known technology and will not be described in detail here.

[0029] It should be noted that, since the standard gas chromatogram is obtained by detecting a standard solution prepared with vanillin, in addition to the peak caused by noise interference, the peak corresponding to the maximum peak in the standard gas chromatogram is the chromatographic peak corresponding to vanillin.

[0030] Obtaining the peaks of the response values ​​at all moments in the gas chromatogram to be analyzed, and obtaining the segmentation thresholds of the peaks of all the peaks in the gas chromatogram to be analyzed; In this embodiment, the AMPD (Automatic Multiscale-based Peak Detection) peak detection algorithm is used to obtain the peak, wherein the AMPD peak detection algorithm is a well-known technology and will not be described in detail here; secondly, the Otsu threshold segmentation algorithm is used to obtain the segmentation threshold, wherein the Otsu threshold segmentation algorithm is a well-known technology and will not be described in detail here. As other implementation methods, the implementer can adopt other methods of the existing technology, such as the cross-validation method, etc., and this embodiment does not impose any special restrictions on this.

[0031] The peaks in the gas chromatogram to be analyzed that are greater than or equal to the segmentation threshold are recorded as significant peaks; It should be noted that since vanilla contains many components, there will be many peaks in the gas chromatogram to be analyzed. By screening out significant peaks, peak interference caused by noise can be avoided, and the influence of minor fluctuations caused by instrument fluctuations or sample matrix residues can be eliminated.

[0032] Calculate the time interval between the time corresponding to each significant peak in the gas chromatogram to be analyzed and the time corresponding to the chromatographic peak in the standard gas chromatogram; Select the significant peak corresponding to the minimum interval time and record it as the chromatographic peak to be analyzed; It should be noted that the smaller the interval time is, the closer the retention time of this significant peak is to the retention time of the chromatographic peak corresponding to vanillin in the standard gas chromatogram, and the more likely this significant peak is the chromatographic peak to be analyzed corresponding to vanillin in the sample solution to be analyzed.

[0033] Calculate the difference between the half-peak width corresponding to the chromatographic peak in the gas chromatogram to be analyzed and the half-peak width corresponding to the chromatographic peak in the standard gas chromatogram, and record it as the relative difference; In this embodiment, the absolute value of the difference between the half-peak width corresponding to the chromatographic peak to be analyzed in the gas chromatogram to be analyzed and the half-peak width corresponding to the chromatographic peak in the standard gas chromatogram is calculated and recorded as the relative difference.

[0034] It should be noted that the calculation of half-peak width is a well-known technique and will not be described in detail here.

[0035] The product of the result of positive mapping of the relative difference and the result of positive mapping of the minimum interval time is used as the first interference value of the gas chromatogram to be analyzed; In this embodiment, the specific process of positive mapping is: positive mapping is performed through an exponential function, assuming that the relative difference is recorded as , the minimum interval time is recorded as ,but The result is the result of positive mapping of the relative difference, The result is the result of the positive mapping as the minimum interval time, where It is an exponential function with a natural constant as the base; through the positive mapping process, it avoids the relative difference or the minimum interval time being 0, resulting in the first interference value being 0.

[0036] It should be noted that, the greater the relative difference, the greater the difference in half-peak width between the chromatographic peak corresponding to vanillin in the gas chromatogram to be analyzed and the standard gas chromatogram, reflecting that the consistency of the duration of vanillin in the gas chromatogram to be analyzed and the standard gas chromatogram is poor, and the gas chromatogram to be analyzed is more significantly affected by noise interference; the larger the minimum interval time, the greater the difference in retention time of the chromatographic peak corresponding to vanillin between the gas chromatogram to be analyzed and the standard gas chromatogram, reflecting that the gas chromatogram to be analyzed is more affected by noise interference, and the larger the obtained first interference value, indicating that the gas chromatogram to be analyzed is highly affected by the interference of the instrument itself, reflecting that the error interference generated by the gas chromatography-mass spectrometry when performing chromatographic detection of the sample solution to be analyzed is greater, and it is necessary to filter and denoise the data in the gas chromatogram to be analyzed to improve the accuracy of subsequent vanillin content determination.

[0037] At this point, the first interference value of the gas chromatogram to be analyzed is obtained.

[0038] Step 3: Calculate the temperature influence based on the fluctuation of the response value at all times in the control gas chromatogram and the fluctuation of the ambient temperature during the control solution operation. Combined with the difference in ambient temperature fluctuations of the sample solution to be analyzed and the standard solution during the operation, obtain the interference difference of the gas chromatogram to be analyzed. Combined with the first interference value, determine the second interference value of the gas chromatogram to be analyzed.

[0039] Furthermore, because vanillin is significantly affected by temperature and is sensitive to the measurement environment, the column and injection temperatures of the gas chromatography-mass spectrometer are typically fixed to specific values ​​when detecting vanillin. However, changes in ambient temperature can also affect the stability of the instrument temperature, potentially leading to additional errors.

[0040] Therefore, the temperature influence is calculated based on the fluctuations in the control gas chromatogram of the control solution and the changes in the ambient temperature during the control solution loading process. Specifically, Calculate the discrete degree of the response at all moments in the control gas chromatogram, and record it as the first discrete degree; Calculate the dispersion of the ambient temperature at all times during the process of the control solution being placed on the machine, and record it as the second dispersion; In this embodiment, the degree of discreteness is measured by calculating the variance of the response at all times in the control gas chromatogram and the variance of the ambient temperature at all times during the control solution application process. As other implementation methods, the implementer may adopt other methods of the prior art, such as standard deviation, coefficient of variation, etc., and this embodiment does not impose any special restrictions on this.

[0041] Calculating a ratio of the first dispersion to the second dispersion as a temperature influence; It should be noted that the first discreteness reflects the fluctuation of the response value on the baseline of the control gas chromatogram during chromatographic detection of the control solution, and the second discreteness reflects the fluctuation of the ambient temperature during chromatographic detection of the control solution. The larger the first discreteness, the greater the fluctuation of the response value in the control gas chromatogram and the worse the baseline stability. The larger the second discreteness, the greater the fluctuation of the ambient temperature and the worse the temperature stability. The greater the temperature influence, the greater the impact of the change in ambient temperature on the instrument during detection and analysis, and the greater the sensitivity of the response value in the control gas chromatogram to the unit ambient temperature fluctuation.

[0042] Secondly, the influence of ambient temperature fluctuations on the sample solution and standard solution during the process of loading the sample solution and standard solution on the machine was used to evaluate the interference differences between the gas chromatogram to be analyzed and the standard gas chromatogram, and the interference difference was calculated, specifically: Calculate the product of the degree of dispersion of the ambient temperature at all times during the process of the standard solution being put on the machine and the temperature influence as the relative fluctuation of the standard gas chromatogram; Calculate the product of the degree of dispersion of the ambient temperature at all times during the process of the sample solution to be analyzed being loaded onto the machine and the temperature influence, as the relative fluctuation of the gas chromatogram to be analyzed; In this embodiment, the degree of dispersion is measured by calculating the variance of the ambient temperature at all times during the process of the standard solution being put on the machine, and calculating the variance of the ambient temperature at all times during the process of the sample solution to be analyzed being put on the machine. As other implementation methods, the implementer may adopt other methods of the prior art, such as standard deviation, coefficient of variation, etc., and this embodiment does not impose any special restrictions on this.

[0043] It should be noted that the relative fluctuation reflects the degree of interference of the standard gas chromatogram and the gas chromatogram to be analyzed by the ambient temperature. The greater the relative fluctuation, the greater the interference of the ambient temperature on the instrument, and the lower the measurement accuracy of the chromatographic detection of the sample solution to be analyzed and the standard solution.

[0044] Calculate the difference in relative fluctuation between the gas chromatogram to be analyzed and the standard gas chromatogram as the interference difference of the gas chromatogram to be analyzed; In this embodiment, the absolute value of the difference in relative fluctuation between the gas chromatogram to be analyzed and the standard gas chromatogram is calculated as the interference difference of the gas chromatogram to be analyzed.

[0045] It should be noted that, the greater the interference difference, the greater the difference in relative fluctuation between the gas chromatogram to be analyzed and the standard gas chromatogram, and the sample solution to be analyzed and the standard solution are differently affected by the fluctuation of ambient temperature during chromatographic detection; the smaller the interference difference, the smaller the difference in relative fluctuation between the gas chromatogram to be analyzed and the standard gas chromatogram, reflecting that the sample solution to be analyzed and the standard solution are relatively consistently interfered with by the fluctuation of ambient temperature during chromatographic detection.

[0046] Furthermore, based on the interference difference and the first interference value, a second interference value is determined, specifically: If the interference difference is 0, the second interference value of the gas chromatogram to be analyzed is the first interference value; otherwise, the second interference value of the gas chromatogram to be analyzed is the ratio of the first interference value to the interference difference; It should be noted that if the interference difference is 0, it means that the gas chromatogram to be analyzed and the standard gas chromatogram are affected by the interference of the ambient temperature in the same way. If the interference difference is not 0, it means that there is a large difference in the interference of the ambient temperature between the gas chromatogram to be analyzed and the standard gas chromatogram. Through the second interference value, the interference difference of the measurement results of the gas chromatogram to be analyzed and the standard gas chromatogram caused by temperature changes can be compensated, so that the gas chromatogram to be analyzed and the standard gas chromatogram are affected by the interference of the ambient temperature and tend to be consistent, thereby being able to truly reflect the characteristic differences of the chromatographic peaks corresponding to vanillin between the gas chromatogram to be analyzed and the standard gas chromatogram. Therefore, the larger the obtained second interference value, the greater the influence of noise interference on the gas chromatogram to be analyzed, and the more it is necessary to filter and denoise the data in the gas chromatogram to be analyzed.

[0047] At this point, the second interference value of the gas chromatogram to be analyzed is obtained.

[0048] Step 4: Determine the interference coefficient of the gas chromatogram to be analyzed by the discreteness of the response values ​​​​except for the local range where the significant peak is located in the gas chromatogram to be analyzed and the second interference value, and determine the heuristic threshold of the wavelet denoising algorithm in combination with the heuristic threshold rule. Filter the gas chromatogram to be analyzed by the wavelet denoising algorithm, and use the peak area of ​​the chromatographic peak to be analyzed in the filtered gas chromatogram to be analyzed to determine the vanillin content in vanilla.

[0049] Furthermore, in the gas chromatogram to be analyzed, except for the key components contained in vanilla, which have a significant response at the corresponding retention time, that is, a significant peak will appear, the fluctuation of the response value at other times is mainly due to the influence of baseline noise, instrument drift, or the fluctuation of weak signals of non-critical elements. Therefore, by analyzing the fluctuation of the response value at other times except the area contained in the significant peak, the baseline interference is calculated, specifically: All the moments in the neighborhood of the moments corresponding to the significant peaks in the gas chromatogram to be analyzed are recorded as local windows; In this embodiment, the length of the local window is twice the half-width of each significant peak. As other implementation methods, the implementer can set it according to actual conditions.

[0050] The discrete degree of the response values ​​at all moments except the moments within the local windows corresponding to all significant peaks in the gas chromatogram to be analyzed is taken as the baseline interference degree of the gas chromatogram to be analyzed; In this embodiment, the degree of discreteness is measured by calculating the variance of the response values ​​at all moments except the moments contained in the local windows corresponding to all significant peaks in the gas chromatogram to be analyzed. As other implementation methods, the implementer may adopt other methods of the prior art, such as standard deviation, etc., and this embodiment does not impose any special restrictions on this.

[0051] It should be noted that, the greater the baseline interference, the greater the degree of noise interference on the gas chromatogram to be analyzed.

[0052] Furthermore, based on the second interference value and the baseline interference degree, an interference coefficient is determined, specifically: taking a normalized result of the product of the second interference value and the baseline interference degree as the interference coefficient of the gas chromatogram to be analyzed; In this embodiment, the sigmoid function is used for normalization processing, wherein the sigmoid function is a well-known technology and will not be described in detail here. As other implementation methods, the implementer may adopt other methods of the existing technology, such as the tanh function, the softmax function, etc., and there is no special limitation on this in this embodiment.

[0053] It should be noted that the larger the interference coefficient is, the greater the error interference is when the sample solution to be analyzed is subjected to chromatographic detection. In order to improve the accuracy of vanillin content determination, it is necessary to filter and denoise the data in the gas chromatogram to be analyzed.

[0054] Secondly, based on the interference coefficient and combined with the heuristic threshold rule, the heuristic threshold of the wavelet denoising algorithm is determined. The specific process is: Perform wavelet decomposition on the responsivity of all moments in the gas chromatogram to be analyzed, square the decomposed wavelet coefficients and arrange them in ascending order to form a wavelet coefficient vector; It should be noted that wavelet decomposition is a well-known technology and will not be described in detail here.

[0055] For each element in the wavelet coefficient vector, the risk value corresponding to each element is calculated. The calculation formula is: in, is the first wavelet coefficient vector The risk value of each element, is the length of the wavelet coefficient vector, is the first wavelet coefficient vector The element value corresponding to the element, is the first wavelet coefficient vector The sequence number of the elements, is the first wavelet coefficient vector The element value corresponding to the element, where Before The sum of the squares of the elements.

[0056] Select the element corresponding to the minimum risk value in the wavelet coefficient vector, denoted as ; The sum of all elements in the wavelet coefficient vector is denoted as S; let , , then the heuristic threshold can be expressed as: in, is the heuristic threshold, is the interference coefficient, is the number of all moments in the gas chromatogram to be analyzed, represents the logarithmic function with base 2, represents the logarithmic function with base 10, represents the minimum function, Represents square root.

[0057] It should be noted that the heuristic threshold rule is a well-known technology and will not be described in detail here.

[0058] The flowchart of the method for obtaining the heuristic threshold provided in the embodiment of the present application is as follows: Figure 2 shown.

[0059] Based on the heuristic threshold, the wavelet denoising algorithm was used to filter the response values ​​in the gas chromatogram to be analyzed, and the vanillin content in vanilla was determined by the peak area corresponding to the chromatographic peak in the filtered gas chromatogram. It should be noted that the wavelet denoising algorithm and the calculation of the peak area are well-known technologies and will not be described in detail here.

[0060] The determination process of the vanillin content in vanilla is as follows: By taking 0.04mL, 0.05mL, 0.10mL, 0.60mL, and 1.10mL of the standard solution, respectively, placing them in 10.0mL volumetric flasks, adding 75% ethanol to dilute to the scale, shaking well, and respectively preparing 0.04mg / mL, 0.05mg / mL, 0.10mg / mL, 0.60mg / mL, and 1.10mg / mL standard solutions, that is, standard solutions of different concentrations are obtained; The standard solution of each concentration was analyzed by gas chromatography-mass spectrometry, with an injection volume of 1 uL, to obtain the standard gas chromatogram corresponding to each concentration; Based on the peak area of ​​the chromatographic peak in the standard gas chromatogram, the peak area corresponding to each concentration and its standard gas chromatogram is formed into a two-dimensional array, and a linear fitting is performed on all the two-dimensional arrays to obtain the fitting equation; It should be noted that the least square method is used for linear fitting, wherein the least square method is a well-known technology and will not be described in detail here; In this embodiment, the fitting equation is: ,in, represents the concentration of vanillin, is the peak area; The peak area corresponding to the chromatographic peak to be analyzed in the filtered gas chromatogram to be analyzed is substituted into the fitting equation to obtain the concentration of vanillin in the sample solution to be analyzed, and the content of vanillin in vanilla is determined based on the dilution multiple and injection volume of the sample solution to be analyzed.

[0061] It should be understood that although Figure 1 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. In addition, Figure 1 At least part of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the sub-steps or stages of other steps.

[0062] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0063] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the present application. It should be noted that a person skilled in the art can make various modifications and improvements without departing from the spirit of the present application. Therefore, any simple modifications, equivalent variations, and modifications to the above embodiments made in accordance with the technical essence of the present application without departing from the content of the present application's technical solution fall within the scope of protection of the present application's technical solution.

Claims

1. A method for determining the content of vanillin in vanilla using gas chromatography, characterized in that: The method comprises the following steps: Obtain chromatograms of the sample solution to be analyzed, the standard solution, and the reference solution, respectively, which are recorded as the gas chromatogram to be analyzed, the standard gas chromatogram, and the reference gas chromatogram, and obtain the ambient temperature of the three solutions at each moment during the process of being put on the machine; Based on the size of the peaks in the gas chromatogram to be analyzed, the peaks in the gas chromatogram to be analyzed are screened to obtain significant peaks; the differences in corresponding moments between different significant peaks in the gas chromatogram to be analyzed and the maximum peak in the standard gas chromatogram are analyzed to obtain the chromatographic peaks to be analyzed in the gas chromatogram to be analyzed; Analyze the difference in peak width between the chromatographic peak to be analyzed and the maximum peak in the standard gas chromatogram, as well as the offset at the corresponding time, and calculate the first interference value of the gas chromatogram to be analyzed; Based on the fluctuation of the response value at all times in the control gas chromatogram and the fluctuation of the ambient temperature during the process of the control solution being put on the machine, the temperature influence degree is calculated, and the interference difference degree of the gas chromatogram to be analyzed is obtained by combining the difference in the fluctuation of the ambient temperature during the process of the sample solution to be analyzed and the standard solution to be analyzed. In combination with the first interference value, a second interference value of the gas chromatogram to be analyzed is determined; The interference coefficient of the gas chromatogram to be analyzed is determined by the discreteness of the response values ​​​​except for the local range where the significant peak is located in the gas chromatogram to be analyzed and the second interference value. Combined with the heuristic threshold rule, the heuristic threshold of the wavelet denoising algorithm is determined. The gas chromatogram to be analyzed is filtered by the wavelet denoising algorithm. The vanillin content in vanilla is determined by using the peak area of ​​the chromatographic peak to be analyzed in the filtered gas chromatogram to be analyzed.

2. The method for determining the vanillin content in vanilla using gas chromatography according to claim 1, wherein: The process of obtaining the significant peaks is as follows: obtaining the peaks of the response values ​​at all moments in the gas chromatogram to be analyzed, obtaining the segmentation threshold of the peaks of all peaks in the gas chromatogram to be analyzed; and recording the peaks in the gas chromatogram to be analyzed whose peaks are greater than or equal to the segmentation threshold as significant peaks.

3. The method for determining the vanillin content in vanilla using gas chromatography according to claim 1, wherein: The method of obtaining the chromatographic peak to be analyzed of the gas chromatogram to be analyzed includes: obtaining the peaks of the response values ​​at all times in the standard gas chromatogram, and recording the peak corresponding to the maximum peak as the chromatographic peak; calculating the interval time between the time corresponding to each significant peak in the gas chromatogram to be analyzed and the time corresponding to the chromatographic peak in the standard gas chromatogram; and selecting the significant peak corresponding to the minimum interval time and recording it as the chromatographic peak to be analyzed.

4. The method for determining the vanillin content in vanilla using gas chromatography according to claim 3, wherein: The calculating of the first interference value of the gas chromatogram to be analyzed includes: Calculate the difference between the half-peak width corresponding to the chromatographic peak in the gas chromatogram to be analyzed and the half-peak width corresponding to the chromatographic peak in the standard gas chromatogram, and record it as the relative difference; The first interference value is a product of a result of performing positive mapping on the relative difference and a result of performing positive mapping on the minimum interval time.

5. The method for determining the vanillin content in vanilla using gas chromatography according to claim 1, wherein: The calculation process of the temperature influence is: Calculate the discrete degree of the response at all moments in the control gas chromatogram, and record it as the first discrete degree; Calculate the dispersion of the ambient temperature at all times during the process of the control solution being placed on the machine, and record it as the second dispersion; The temperature influence degree is a ratio of the first dispersion degree to the second dispersion degree.

6. The method for determining the vanillin content in vanilla using gas chromatography according to claim 1, wherein: The obtaining of the interference difference of the gas chromatogram to be analyzed includes: Calculate the product of the degree of dispersion of the ambient temperature at all times during the process of the sample solution to be analyzed and the standard solution being put on the machine and the temperature influence, and use them as the relative fluctuation of the gas chromatogram to be analyzed and the standard gas chromatogram respectively; The interference difference is the difference in relative fluctuation between the gas chromatogram to be analyzed and the standard gas chromatogram.

7. The method for determining the vanillin content in vanilla using gas chromatography according to claim 1, wherein: The determining of the second interference value of the gas chromatogram to be analyzed includes: if the interference difference is 0, the second interference value of the gas chromatogram to be analyzed is the first interference value; otherwise, the second interference value of the gas chromatogram to be analyzed is the ratio of the first interference value to the interference difference.

8. The method for determining the vanillin content in vanilla using gas chromatography according to claim 1, wherein: Determining the interference coefficient of the gas chromatogram to be analyzed includes: All moments in the neighborhood of the moments corresponding to the significant peaks in the gas chromatogram to be analyzed are recorded as local windows; the discreteness of the response values ​​of all moments in the gas chromatogram to be analyzed, except for the moments contained in the local windows corresponding to all the significant peaks, is taken as the baseline interference degree of the gas chromatogram to be analyzed; The interference coefficient is a normalized result of multiplying the second interference value by the baseline interference degree.

9. The method for determining the vanillin content in vanilla using gas chromatography according to claim 1, wherein: The heuristic threshold of the wavelet denoising algorithm is determined, comprising: Perform wavelet decomposition on the responsivity of all moments in the gas chromatogram to be analyzed, square the decomposed wavelet coefficients and arrange them in ascending order to form a wavelet coefficient vector; For each element in the wavelet coefficient vector, calculate the risk value corresponding to each element; Select the element corresponding to the minimum risk value in the wavelet coefficient vector, denoted as ; The sum of all elements in the wavelet coefficient vector is recorded as ;make , , then the heuristic threshold It can be expressed as: ,in, is the length of the wavelet coefficient vector, is the interference coefficient, is the number of all moments in the gas chromatogram to be analyzed, represents the logarithmic function with base 10, represents the logarithmic function with base 2, represents the minimum function, Represents square root.

10. The method for determining the vanillin content in vanilla using gas chromatography according to claim 9, wherein: The wavelet coefficient vector Risk value of each element The calculation formula is: ,in, is the first wavelet coefficient vector The element value corresponding to the element, is the first wavelet coefficient vector The sequence number of the elements, is the first wavelet coefficient vector The element value corresponding to the element.

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