Compound peak searching method in chromatographic analysis

Abstract

The invention relates to a chromatographic technology, and particularly provides a compound peak searching method in chromatographic analysis, which comprises the following steps: A1, calibrating by using a standard gas sample to obtain the reference retention time t1i of each target factor and the reference retention time t01j of an internal standard factor, i = 1, 2... M, and j = 1, 2... N; a2, acquiring retention time t02j of the internal standard factor in the ambient air sample data; a3, obtaining a peak drift amount delta t0j which is equal to t02j-t01j and corresponds to each internal standard factor; a4, predicting the retention time t2i = t1i + delta t0k, k = 1, 2... N of the target factor in the ambient air sample according to the delta ts, so as to find the chromatographic peak of the target factor; delta t0k is the peak drift amount corresponding to the internal standard factor with the minimum reference retention time distance to the target factor. The method has the advantages of high detection precision and the like, and is applied to air detection.

Description

Technical Field

[0001] This invention relates to chromatographic techniques, and particularly to methods for finding peaks of compounds in chromatographic analysis. Background Technology

[0002] Volatile organic compounds (VOCs) are key air pollutants, and online monitoring technology at trace levels (ppb-ppt) is a core challenge in the field of environmental analysis.

[0003] While current mainstream gas chromatography-mass spectrometry (GC-MS) systems possess multi-component detection capabilities, they are limited by retention time drift. Traditional online gas chromatography analysis systems use a static reference system for retention time, which can lead to characteristic peak positioning deviations and high false recognition rates when the equipment operating environment fluctuates or the chromatographic column performance deteriorates. Another characteristic of online GCMS is that it generates data continuously, and the difference in ambient temperature between upper and lower groups is small, resulting in a certain correlation between peak drift between upper and lower groups. However, it is currently not possible to correlate and adjust the data between upper and lower groups.

[0004] Regarding the peak drift problem, although there are monitoring systems for excessive peak drift, the current mainstream solutions still rely on manual experience for correction, resulting in high manual analysis costs and reduced timeliness. Summary of the Invention

[0005] To address the shortcomings of the existing technical solutions, this invention provides a method for finding peaks of compounds in chromatographic analysis.

[0006] The objective of this invention is achieved through the following technical solution: A method for finding peaks of compounds in chromatographic analysis includes the following steps: A1. Using standard gas samples for calibration, obtain the baseline retention time t for each target factor. 1i and the baseline retention time t of the internal standard factor. 01j , i=1,2···M, j=1,2···N; A2. Obtain the retention time t of the internal standard factor from the ambient air sample data. 02j ; A3. Obtain the peak drift Δt corresponding to each internal standard factor. 0j = t 02j -t 01j ; A4. Predict the retention time t of the target factor in the ambient air sample based on Δts. 2i =t 1i +Δt 0k k=1,2···N, thus finding the chromatographic peak of the target factor; Δt 0k It is the peak drift corresponding to the internal standard factor that has the smallest distance from the baseline retention time of the target factor.

[0007] Compared with the prior art, the present application has the beneficial effects of: 1. The present application breaks through the systematic error generated by the traditional static calibration method in the environmental fluctuation, and realizes the error reduction from the internal standard calibration to the sensitive factor calibration by constructing a three-level factor classification model and a hierarchical progressive retention time calibration architecture. 2. The target factor with relatively low signal-to-noise ratio or high confidence is used to correct its reference retention time, and the reference retention time of the target factor is referenced to the actual retention time of the previous group, rather than rigidly referencing the standard sample, thereby improving the chromatographic peak positioning accuracy, improving the automatic peak searching and identification accuracy, and solving the peak drift problem in complex environment. 3. The automatic process reduces the dependence on experienced technical personnel, reduces the operation threshold and labor cost. BRIEF DESCRIPTION OF DRAWINGS

[0008] The disclosure of the present application will become more apparent with reference to the accompanying drawings. It is easily understood by those skilled in the art that these drawings are only used to illustrate the technical solutions of the present application, and are not intended to limit the protection scope of the present application. In the drawings: Figure 1 is a flowchart of the compound peak searching method in the chromatographic analysis according to the present application; Figure 2 is a schematic diagram of the reference retention time of the first-level factor bromochloromethane; Figure 3 is a schematic diagram of the actual retention time of the first-level factor bromochloromethane; Figure 4 is a schematic diagram of the reference retention time of the second-level factor toluene; Figure 5 is a schematic diagram of the actual retention time of the second-level factor toluene; Figure 6 is a schematic diagram of the reference retention time of the third-level factor 2-butenal; Figure 7 is a schematic diagram of the actual retention time of the third-level factor 2-butenal; Figure 8 is a schematic diagram of the reference retention time of the third-level factor 4-methyl-2-pentanone; Figure 9 is a schematic diagram of the actual retention time of the third-level factor 4-methyl-2-pentanone. DETAILED DESCRIPTION

[0009] Figures 1-9The following description illustrates optional embodiments of the invention to teach those skilled in the art how to implement and reproduce the invention. Some conventional aspects have been simplified or omitted to teach the technical solutions of the invention. Those skilled in the art should understand that variations or substitutions derived from these embodiments will be within the scope of the invention. Those skilled in the art should understand that the following features can be combined in various ways to form multiple variations of the invention. Therefore, the invention is not limited to the optional embodiments described below, but is defined only by the claims and their equivalents.

[0010] Example 1

[0011] This embodiment describes a method for finding peaks of compounds in chromatographic analysis, such as... Figure 1 As shown, the steps include: A1. Calibrate using various standard gas samples to obtain the baseline retention time t for each target factor. 1i and the baseline retention time t of the internal standard factor. 01j , i=1,2···M, j=1,2···N.

[0012] A2. Obtain the retention time t of the internal standard factor from the ambient air sample data. 02j .

[0013] A3. Obtain the peak drift Δt corresponding to each internal standard factor. 0j = t 02j -t 01j .

[0014] A4. Predict the retention time t of the target factor in the ambient air sample based on Δts. 2i =t 1i +Δt 0k k=1,2···N, thus finding the chromatographic peak of the target factor; Δt 0k It is the peak drift corresponding to the internal standard factor that has the smallest distance from the baseline retention time of the target factor.

[0015] To obtain chromatographic peaks more accurately, the peak-finding method further includes the following steps: A5. Based on the obtained chromatographic peak parameters, such as signal-to-noise ratio or the ratio of the peak height of other peaks within the integration window to the peak height of this peak, a multi-level dynamic factor classification model is constructed. The quality of the parameters of the multi-level dynamic factors gradually deteriorates, and the first-level factor includes the internal standard factor.

[0016] For example, the classification criteria are: If the signal-to-noise ratio is greater than 10, or the ratio is less than 0.1, the factor belongs to the second level factor.

[0017] If the signal-to-noise ratio is not greater than 10, or the ratio is not less than 0.1, the factor belongs to the third level factor.

[0018] A6. Obtain the actual retention time t of the better target factor 2i .

[0019] A7. Obtain the peak drift amount Δt of the better target factor 1i = t 2i -t 1i .

[0020] A8. Obtain the internal standard factor with the smallest distance from the retention time of the worse target factor, or the better target factor, predict the retention time of the worse target factor using the peak drift amount of the internal standard factor or the better target factor, and re-search the peak.

[0021] A9. Obtain the parameters of all factors, such as signal-to-noise ratio, if the parameter exceeds the first threshold value, replace the retention time of the factor with the reference retention time of the factor in step A1.

[0022] Example 2

[0023] Application example of the compound peak searching method in the chromatographic analysis of the embodiment of the present application in air VOC monitoring.

[0024] In this application example, as shown in Figure 1 , the peak searching method includes the following steps: A1. Use various standard gas samples to calibrate, obtain the reference retention time t 1i of each target factor, and the reference retention time t 01j of the internal standard factor, i = 1, 2, ···, M, j = 1, 2, ···, 4.

[0025] Table 1 Reference retention time of standard gas sample calibration.

[0026]

[0027]

[0028]

[0029] Note: “*” is the internal standard A2. In the environmental air sample data, obtain the retention time t 02j of the internal standard factor.

[0030] Table 2 Comparison of internal standard retention time of environmental air sample and standard gas sample.

[0031]

[0032] A3. Obtain the peak drift amount Δt 0j = t 02j -t01j As shown in Table 2.

[0033] A4. According to the target factor in the ambient air sample, the retention time t of the target factor is predicted by Δt 2i = t 1i + Δt 0k , k = 1, 2, ··· N, so as to find the chromatographic peak of the target factor; Δt 0k is the peak drift amount corresponding to the internal standard factor with the smallest distance from the reference retention time of the target factor.

[0034] Table 3 Comparison of predicted retention time and actual retention time of ambient air sample.

[0035]

[0036]

[0037]

[0038]

[0039] A5. According to the parameters of the obtained chromatographic peak, such as the signal-to-noise ratio or the ratio of the peak height of other peaks in the integration window to the peak height of this peak, a multi-level dynamic factor classification model is constructed, and the quality of the parameters of the multi-level dynamic factors gradually deteriorates. The first level factor includes the internal standard factor.

[0040] The criteria for classification are: If the signal-to-noise ratio is greater than 10, or the ratio is less than 0.1, the factor belongs to the second level factor, and specifically: the second level factor is n-pentane, n-hexane, 1,1,1-trichloroethane, n-octane, n-nonane, n-decane, and undecane.

[0041] If the signal-to-noise ratio is not greater than 10, or the ratio is not less than 0.1, the factor belongs to the third level factor, such as the other factors in Table 1 except the internal standard factor and the second level factor, including propylene, propane, and other compounds.

[0042] A6 Obtain the actual retention time t 2i of the second level factor.

[0043] A7. Obtain the peak drift amount Δt 1i of the better target factor. 2i = t 1i .

[0044] A8. Obtain the internal standard factor with the smallest distance from the retention time of the poor target factor or the better target factor, and predict the retention time of the poor target factor using the peak drift amount of the internal standard factor or the better target factor, and re-search the peak.

[0045] Table 4 Third order factors using "n-pentane" as reference.

[0046]

[0047]

[0048] Table 5 Third order factors using "n-hexane" as reference.

[0049]

[0050] Table 6 Third order factors using "1,1,1-trichloroethane" as reference.

[0051]

[0052] Table 7 Third order factors using "n-octane" as reference.

[0053]

[0054]

[0055] Table 8 Third order factors using "n-nonane" as reference.

[0056]

[0057] Table 9 Third order factors using "n-decane" as reference.

[0058]

[0059] Table 10 Third order factors using "undecane" as reference.

[0060]

[0061] Table 11 Data comparison.

[0062]

[0063]

[0064] A9. Obtain the parameters of all factors, such as signal-to-noise ratio, if the parameter exceeds the first threshold value, replace the retention time of the factor with the reference retention time of the factor in step Al.

[0065] Example 3

[0066] The application example of the compound peak searching method in the chromatographic analysis of the embodiment of the present application in the air VOC monitoring is different from example 2, and the difference is that: The first level factor (internal standard factor) is bromochloromethane, the second level factor is toluene, the third level factor is 2-butenal with reference to the first level factor bromochloromethane, and the third level factor is 4-methyl-2-pentanone with reference to the second level factor toluene. First level factor - bromochloromethane As shown in the following table, the standard sample retention time is 17.1822 min, and the actual retention time in the ambient air sample is 17.1468 min. Figures 2-3

[0067] The internal standard peak drift amount is calculated as 17.1468-17.1822=-0.0354 min Second level factor - toluene As shown in the following table, the standard sample retention time is 21.2904 min, and the actual retention time in the ambient air sample is 21.2632 min. Figures 4-5 The toluene reference time is calculated according to the first level factor peak drift amount

[0068] 21.2904+(-0.0354)=21.2550 min, and the deviation amount is 21.2632-21.2550=0.0084 min. The static calibration deviation amount is =|21.2632-21.2904|=0.0272 min.

[0069] Third level factor - 2-butenal.

[0070] As shown in the following table, the standard sample retention time is 18.7055 min, and the actual retention time in the ambient air sample is 18.6817 min.

[0071] Figures 6-7 The 2-butenal reference retention time is calculated according to the first level factor bromochloromethane.

[0072] 18.7055+(-0.0354)=18.6701 min, and the deviation amount is 18.6817-18.6701=0.0116 min.

[0073] The static calibration deviation amount is =|18.6817-18.7055|=0.0238 min.

[0074] Third level factor - 4-methyl-2-pentanone.

[0075] As shown in the following table, the standard sample retention time is 20.8710 min, and the actual retention time in the ambient air sample is 20.8509 min.

[0076] Figures 8-9

[0077] ​​​​The reference retention time for 4-methyl-2-pentanone is calculated with reference to the second order factor toluene.

[0078] 20.8710 + 0.7684 * (-0.0354) = 20.8438 min, the deviation (20.8509 - 20.8438) = 0.0071 min.

[0079] If only the reference retention time with reference to the first order factor bromochloromethane, 20.8710 + (-0.0354) = 20.8356 min, the deviation is 20.8509 - 20.8356 = 0.0153 min.

[0080] The static calibration deviation = |20.8509 - 20.8710| = 0.0201 min.

Claims

1. A method for finding a peak of a compound in chromatography, characterized by, The peak searching method comprises the following steps: A1. Using a standard gas sample calibration, obtain the reference retention time t of each target factor 1i and the reference retention time t of the internal standard factor 01j , i = 1, 2, ···, M, j = 1, 2, ···, N; A2. In the environmental air sample data, the retention time t of the internal standard factor is obtained 02j ; A3. Obtain the peak drift amount Δt corresponding to each internal standard factor 0j = t 02j -t 01j ; A4. According to Δt 0j Predicting the retention time t of a target factor in an ambient air sample 2i = t 1i + Δt 0k , k = 1,2, ···N, so as to find the chromatographic peak of the target factor; Δt 0k is the peak drift amount corresponding to the internal standard factor with the minimum "correlation coefficient R" of the target factor; R i = |t 01j - t 1i | + u, the first group of ambient air sample data is |t 2i - t 1i | without the target factor, u = 0 is selected, that is, only the nearest internal standard is considered, and u is obtained according to the following formula for the second group: If f < 1, then u = 1 / f; if f > 1, then u = f; where f = |t 2i - t 1i | Δt 0j .

2. The peak finding method of claim 1, wherein, The peak searching method further comprises the following steps: A5. According to the parameters of the obtained chromatographic peaks, a multi-level dynamic factor classification model is constructed, the parameters of the multi-level dynamic factors gradually deteriorate in quality, and the first level factor comprises an internal standard factor; A6 actual retention time t for which a good target factor is obtained 2i ; A7. Peak drift amount Δt for better target factor 1i = t 2i -t 1i ; A8. Obtain the correlation coefficient R of the poor target factor and the internal standard factor or the better target factor, select the smaller R value as the reference target, and use the peak drift amount of the internal standard factor or the better target factor to predict the retention time of the poor target factor, and re-search the peak.

3. The peak finding method of claim 2, wherein, The parameter of the chromatographic peak is the signal-to-noise ratio and the ratio of the peak height of other peaks in the integral window to the peak height of the peak.

4. The peak finding method of claim 3, wherein, If the signal-to-noise ratio is greater than 10 and the ratio is greater than 0.1, the factor belongs to the second level factor; If the signal-to-noise ratio is not greater than 10 and the ratio is less than 0.1, the factor belongs to the third level factor.

5. The peak finding method of claim 2, wherein, The peak searching method further comprises the following steps: A9. Obtain the parameters of all factors, and if the parameter exceeds the first threshold value, replace the retention time of the factor with the reference retention time of the factor in step A1.

6. The peak finding method of claim 5, wherein, The parameter of the factor is the signal-to-noise ratio.

7. The peak finding method of claim 1 or 2, wherein, The internal standard factor is bromochloromethane, 1,4-difluorobenzene, deuterated chlorobenzene and 4-bromofluorobenzene.

8. The peak finding method of claim 2, wherein, The second level factor is n-pentane, n-hexane, 1,1,1-trichloroethane, n-octane, n-nonane, n-decane and undecane.

9. The peak finding method of claim 2 or 8, wherein, In step A8, the third level factor with n-pentane as the reference includes propylene, propane, difluorodichloromethane, 1,2-dichlorotetrafluoroethane, isobutane, monochloromethane, n-butene, n-butane, chloroethylene, 1,3-butadiene, trans-2-butene, acetaldehyde, cis-2-butene, bromomethane, chloroethane, isopentane, trichlorofluoromethane, 1-pentene, cis-2-pentene, 2-methyl-1,3-butadiene, trans-2-pentene, propenal, propionaldehyde, 1,1,2-trifluorotrichloroethane, 1,1-dichloroethylene, 2,2-dimethylbutane, acetone, isopropyl alcohol and carbon disulfide; The third level factor with n-hexane as the reference includes dichloromethane, 2,3-dimethylbutane, 2-methylpentane, cyclopentane, methyl tert-butyl ether, cis-1,2-dichloroethylene, 3-methylpentane, 1-hexene, methylpropenal, 1,1-dichloroethane and vinyl acetate; The third level factor with 1,1,1-trichloroethane as the reference includes tetrahydrofuran, 2-methylhexane, cyclohexane, 2,3-dimethylpentane, 3-methylhexane, carbon tetrachloride and benzene.

10. The peak finding method of claim 2 or 8, wherein, In step A8, the third level factor with n-octane as the reference includes monobromodichloromethane, 2,3,4-trimethylpentane, 2-methylheptane, 3-methylheptane, trans-1,3-dichloropropene, 4-methyl-2-pentanone, toluene, cis-1,3-dichloropropene, 1,1,2-trichloroethane, 2-hexanone and tetrachloroethylene; The third level factor with n-nonane as the reference includes ethylbenzene, m,p-xylene, o-xylene and styrene; The third level factor with n-decane as the reference includes n-propylbenzene, m-ethyltoluene, p-ethyltoluene, 1,3,5-trimethylbenzene, o-ethyltoluene and 1,2,4-trimethylbenzene; The tertiary factors with undecane as the reference included benzaldehyde, m-dichlorobenzene, p-dichlorobenzene, 1,2,3-trimethylbenzene, chlorotoluene, m-diethylbenzene, p-diethylbenzene, o-dichlorobenzene, m-methylbenzaldehyde, dodecane, 1,2,4-trichlorobenzene, hexachloro-1,3-butadiene, and naphthalene.

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