Calibration method and calibration application of fatty acid ester in gas phase-ion mobility spectrometry

Abstract

The invention relates to the field of chemical substance detection, and discloses a calibration method of fatty acid ester in gas phase-ion mobility spectrometry, which is characterized in that a retention index mean value of corresponding fatty acid ester in an NIST library is taken as a standard value, and a retention index of a target object is calculated by adopting a temperature programming retention index calculation formula. The method comprises the following specific steps: S1, mixing and injecting a plurality of fatty acid esters into a gas phase-ion mobility spectrometry system, recording the retention time of each fatty acid ester, and establishing a relationship between the retention time and a retention index mean value of the fatty acid esters in an NIST library; and S2, according to the ratio of the retention time of the target object to the retention time of the adjacent fatty acid ester, performing linear interpolation in the retention index range of the standard substance to obtain the retention index of the target object, and comparing the retention index of the target object with the retention index of the target object in the NIST library. The method can reduce the qualitative workload and improve the qualitative efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of chemical substance detection, and in particular to a calibration method and calibration application of fatty acid ester in gas phase-ion migration spectrometry. Background Art

[0002] Gas chromatography-ion mobility spectrometry is a technology that combines the advantages of gas chromatography (GC) and ion mobility spectrometry (IMS). It has shown extremely high sensitivity and accuracy in detecting trace volatile organic compounds in complex matrix samples. The characteristics of this technology are that it can achieve fast, efficient and low-energy detection without the need for complex sample pretreatment, and is particularly suitable for environmentally friendly application scenarios. GC-IMS can provide rich data analysis, for example, by constructing a two-dimensional data matrix, one dimension of which represents the retention time of the analyte, and the other dimension reflects the mobility or drift time of the ion, and the intensity of the ion signal is directly related to the concentration of the analyte in the sample.

[0003] Compared with traditional gas chromatography-mass spectrometry (GC-MS), although GC-IMS has significant advantages in response speed and energy consumption, it has certain limitations in qualitative analysis. Specifically, GC-MS can provide detailed ion fragmentation information, which helps to accurately identify compounds, while GC-IMS mainly relies on the comparison of retention index and mobility with known spectral libraries for qualitative analysis. This process can become complicated and time-consuming due to small differences in retention index. For example, when the retention index obtained by calibration with standard substances is 850 and a deviation of ±10 is allowed, it may be necessary to compare with up to 886 records in the NIST library. But if the deviation is reduced to ±5, the number of records to be compared will be reduced to 477, greatly reducing the difficulty of qualitative work. However, too small a deviation may lead to missing the correct match, so in actual operation, choosing an appropriate deviation range is the key.

[0004] It is worth noting that the retention indices in the NIST library are usually calculated based on normal alkanes, but these compounds may not respond in the ion mobility spectrum. Therefore, some GC-IMS systems recommend using 2-ketone compounds as standard substances to calculate the retention indices. Although this method is widely used in practice, it may also cause a large deviation between the calculated retention index and the standard value in the NIST library, thereby increasing the difficulty of qualitative analysis. Therefore, finding more suitable standard substances to ensure that the calculated retention index is as consistent as possible with the data in the NIST library is crucial to improving the efficiency and accuracy of GC-IMS qualitative analysis. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a calibration method and calibration application of fatty acid esters in gas phase-ion mobility spectrometry, which can reduce the workload of qualitative analysis and improve the efficiency of qualitative analysis.

[0006] The present invention solves the above technical problems by the following technical means:

[0007] Calibration method and application of fatty acid esters in gas phase-ion mobility spectrometry

[0008] In a first aspect, the present invention discloses a calibration method for fatty acid esters in gas phase-ion mobility spectrometry, taking the retention index mean value of the corresponding fatty acid esters in the NIST library as the standard value, and adopting a programmed temperature retention index calculation formula to calculate the retention index of the target.

[0009] The qualitative analysis of ion mobility spectrometry mainly relies on the comparison between the calculated retention index and the mean retention index in the NIST library. Therefore, the consistency of the two retention indices determines the workload of qualitative analysis. Fatty acid esters (such as fatty acid methyl esters and fatty acid ethyl esters) have increasing molecular weights, stable chemical properties, are easy to be separated by GC-IMS, and have clear retention indices in the NIST library, making them suitable as calibration series. A corresponding relationship is established between the retention time (RT) of fatty acid esters in the gas phase-ion mobility spectrometry system and the retention index of the corresponding fatty acid esters in the NIST standard library. The linear interpolation formula of the programmed temperature retention index is used to accurately calculate the retention index of the target within the retention time range of the known fatty acid ester standard substances. Within the retention index range of the fatty acid ester series compounds, linear interpolation is performed based on the proportional relationship between the retention time of the target and the adjacent fatty acid esters to obtain the retention index of the target.

[0010] Preferably, the specific steps of the calibration method are:

[0011] S1. Inject a variety of fatty acid esters into a gas phase-ion mobility spectrometry system, record the retention time of various fatty acid esters, and establish a relationship between the retention time and the mean retention index of the fatty acid esters in the NIST library;

[0012] S2. According to the ratio of the retention time of the target substance to the retention time of the adjacent fatty acid ester, linear interpolation is performed within the retention index range of the standard substance, and the retention index of the target substance is obtained according to the calculation formula, and then compared with the retention index of the target substance in the NIST library.

[0013] Preferably, the calculation formula of step S2 is: RIx=RIS+(RIl-RIs)×(RTx-RTs) / (RTl-RTs),

[0014] In the formula, RIx represents the retention index of the target compound,

[0015] RIS represents the retention index library mean of a standard substance immediately before and immediately after the target elution.

[0016] RI1 represents the retention index library mean of a standard substance immediately after the target substance flows out.

[0017] RTx represents the retention time of the target compound.

[0018] RTs represents the retention time of a standard substance immediately before the target elution.

[0019] RT1 represents the retention time of a standard substance immediately before and after the target stream.

[0020] Preferably, the fatty acid esters include fatty acid methyl esters and fatty acid ethyl esters.

[0021] Preferably, the fatty acid methyl esters include methyl propionate, methyl butyrate, methyl valerate, methyl hexanoate, and methyl heptanoate.

[0022] Preferably, the fatty acid ethyl esters include ethyl propionate, ethyl butyrate, ethyl valerate, ethyl hexanoate, ethyl heptanoate, and ethyl octanoate.

[0023] Preferably, the concentration of the fatty acid ester in step S1 is 10 ppm.

[0024] In a second aspect, the present invention discloses the calibration application of fatty acid esters in gas phase-ion mobility spectrometry, using fatty acid esters as calibrants in gas phase-ion mobility spectrometry.

[0025] Beneficial effects of the present invention:

[0026] (1) The present invention uses a programmed temperature retention index calculation method combined with a linear interpolation strategy to significantly improve the accuracy of target retention index calculation, reduce the error caused by retention time fluctuations, and thus improve the qualitative reliability of the target.

[0027] (2) Fatty acid esters are stable and easy to obtain as calibrants. There is no need to use complex or expensive standards. The calibration process is simple and efficient, which can significantly improve the consistency between the calculated retention index and the library mean and reduce the workload of qualitative analysis. DETAILED DESCRIPTION

[0028] The following will be combined with the specific embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention:

[0029] Specific steps of the calibration method of fatty acid esters in gas phase-ion mobility spectrometry

[0030] S1. Inject a variety of fatty acid esters into a gas phase-ion mobility spectrometry system, record the retention time of various fatty acid esters, and establish a relationship between the retention time and the mean retention index of the fatty acid esters in the NIST library;

[0031] S2. According to the ratio of the retention time of the target substance to the retention time of the adjacent fatty acid ester, linear interpolation is performed within the retention index range of the standard substance, and the retention index of the target substance is obtained according to the calculation formula, and then compared with the retention index of the target substance in the NIST library.

[0032] The calculation formula is RIx=RIS+(RIl-RIs)×(RTx-RTs) / (RTl-RTs),

[0033] In the formula, RIx represents the retention index of the target compound,

[0034] RIS represents the retention index library mean of a standard substance immediately before and immediately after the target elution.

[0035] RI1 represents the retention index library mean of a standard substance immediately after the target substance flows out.

[0036] RTx represents the retention time of the target compound.

[0037] RTs represents the retention time of a standard substance immediately before the target elution.

[0038] RT1 represents the retention time of a standard substance immediately before and after the target stream.

[0039] Example 1

[0040] A weak polar chromatographic column (HP-5MS (30 m×0.25 mm×0.25 µm)) was used to analyze 29 substances using five programmed temperature methods. The heating rate and carrier gas flow rate range in the method parameters covered the range of commonly used analytical methods, that is, they included the main factors affecting the retention index. The main method parameters are shown in Table 1. The 29 substances were methyl butyrate, methyl valerate, methyl hexanoate, methyl heptanoate, ethyl propionate, ethyl butyrate, ethyl valerate, ethyl hexanoate, 2-hexanone, 2-heptanone, 2-octanone, 2-nonanone, guaiacol, amyl alcohol, leaf alcohol, hexanol, benzyl alcohol, octanol, pyridine, amyl alcohol, butyl acetate, furfuryl alcohol, isoamyl acetate, amyl acetate, 2,3-dimethylpyrazine, methyl heptenone, hexyl acetate, benzyl alcohol, and acetophenone.

[0041] Table 1 Parameters of programmed temperature method

[0042]

[0043] After collecting data for 29 substances using the above five methods, different series of substances were used as standard substances, and the retention index of the target substances was calculated using the corresponding retention index values. The calculated retention index was compared with the corresponding library mean to obtain the absolute value of the deviation of each substance from the library mean under each method. Then, all absolute values ​​were added up and divided by the number of substances and methods to obtain the average deviation of the calculated retention index from the library mean (Table 2).

[0044] Table 2 Average deviations of retention indices calculated using different series of reference materials from the library mean

[0045]

[0046] As can be seen from Table 2, the average deviation of the retention index calculated using different series of reference materials as standards and the library mean is comparable for fatty acid methyl esters and fatty acid ethyl esters, and is less than 2-ketones; the average deviation of the retention index calculated using the default value of 2-ketones in the ion mobility spectrometry software as the standard and the library mean is the largest; this indicates that the retention index calculated using fatty acid methyl esters and fatty acid ethyl esters as standards is more consistent with the library mean, which can reduce the workload of qualitative analysis.

[0047] Example 2

[0048] The calibration method of the present invention was used to detect four substances, namely pyridine, isoamyl acetate, benzyl alcohol and acetophenone. Different series of substances were used as standard substances, and the retention index of the target substance was calculated using the corresponding retention index value. The calculated retention index was compared with the corresponding library mean to obtain the absolute value of the deviation of each substance from the library mean under this method. Finally, all absolute values ​​were added to obtain the deviation sum of the calculated retention index and the library mean (Table 3).

[0049] Table 3 The deviations of the retention indices calculated using different series of reference materials from the library mean and the deviations and

[0050]

[0051] As can be seen from Table 3, the deviations and the sum of the deviations of the retention indices calculated using different series of references as standards from the library mean are smaller for fatty acid methyl esters and fatty acid ethyl esters than for 2-ketones; the deviations and the sum of the deviations of the retention indices calculated using the default values ​​of 2-ketones in the ion mobility spectrometry software as standards from the library mean are the largest; this indicates that the retention indices calculated using fatty acid methyl esters and fatty acid ethyl esters as standards are more consistent with the library mean, which can reduce the workload of qualitative analysis.

[0052] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should be included in the scope of the claims of the present invention. The techniques, shapes, and structural parts not described in detail in the present invention are all known technologies.

Claims

1. A method for calibrating fatty acid esters in gas phase-ion mobility spectrometry, characterized in that: The retention index of the target compound was calculated using the programmed temperature retention index calculation formula, with the mean retention index of the corresponding fatty acid esters in the NIST library as the standard value.

2. The calibration method of fatty acid ester in gas phase-ion migration spectrometry according to claim 1, characterized in that, The specific steps of the calibration method are: S1. Inject a variety of fatty acid esters into a gas phase-ion mobility spectrometry system, record the retention time of various fatty acid esters, and establish a relationship between the retention time and the mean retention index of the fatty acid esters in the NIST library; S2. According to the ratio of the retention time of the target substance to the retention time of the adjacent fatty acid ester, linear interpolation is performed within the retention index range of the standard substance, and the retention index of the target substance is obtained according to the calculation formula, and then compared with the retention index of the target substance in the NIST library.

3. The calibration method of fatty acid ester in gas phase-ion migration spectrometry according to claim 2, characterized in that, The calculation formula of step S2 is: RIx=RIS+(RIl-RIs)×(RTx-RTs) / (RTl-RTs), In the formula, RIx represents the retention index of the target compound, RIS represents the retention index library mean of a standard substance fatty acid ester immediately before and adjacent to the target elution. RI1 represents the retention index library mean of a standard substance fatty acid ester immediately after the target outflow, RTx represents the retention time of the target compound. RTs represents the retention time of a standard fatty acid ester immediately before the target elution. RT1 represents the retention time of a standard fatty acid ester immediately before and after the target stream.

4. The calibration method of fatty acid ester in gas phase-ion migration spectrometry according to claim 2, characterized in that, The fatty acid esters include fatty acid methyl esters and fatty acid ethyl esters.

5. The calibration method of fatty acid ester in gas phase-ion migration spectrometry according to claim 4, characterized in that, The fatty acid methyl esters include methyl propionate, methyl butyrate, methyl valerate, methyl hexanoate and methyl heptanoate.

6. The calibration method of fatty acid ester in gas phase-ion migration spectrometry according to claim 4, characterized in that, The fatty acid ethyl esters include ethyl propionate, ethyl butyrate, ethyl valerate, ethyl hexanoate, ethyl heptanoate, and ethyl octanoate.

7. The calibration method of fatty acid ester in gas phase-ion migration spectrometry according to claim 2, characterized in that, The concentration of the fatty acid ester in step S1 is 1-50 ppm.

8. The application of the fatty acid ester according to any one of claims 1 to 7 in the calibration of gas phase-ion mobility spectrometry, characterized in that: Fatty acid esters were used as calibrants in gas phase ion mobility spectrometry.

Images