CN108490106B - Simple and convenient determination method for second-dimension retention index in full-two-dimension gas chromatography - Google Patents
Simple and convenient determination method for second-dimension retention index in full-two-dimension gas chromatography Download PDFInfo
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Abstract
The invention provides a simple and convenient determination method of a second-dimension retention index in a full-two-dimension gas chromatography, which comprises the following specific steps: (1) analyzing a mixed solution containing a plurality of (4 or more than 4) compounds with known retention indexes by using a full two-dimensional gas chromatography to obtain two-dimensional retention time and outflow temperature data of each known substance under the chromatographic condition; (2) substituting the data and the retention index data of the standard substance into the mathematical relational expression provided by the invention to obtain the exact relation of the second-dimensional retention time, the second-dimensional retention index and the outflow temperature under the used chromatographic condition; (3) analyzing the sample to be detected under the same chromatographic condition to obtain second-dimensional retention time and outflow temperature data of the compound to be analyzed; (4) retention index data for the substance to be analyzed can be calculated by a mathematical relationship. Compared with the method in the prior art, the method provided by the invention does not need repeated sample injection of normal alkane, and is simple and easy to implement.
Description
Technical Field
The invention belongs to the field of chemical analysis, and relates to a full two-dimensional gas chromatography.
Background
In the full two-dimensional gas chromatography, in order to improve the accuracy of qualitative analysis of an unknown substance, a second-dimensional chromatographic retention index of the unknown substance is often determined. The existing methods for establishing the retention index of the second-dimension chromatogram mainly comprise a method for repeatedly injecting normal paraffin into the second-dimension chromatographic column, a method for repeatedly injecting normal paraffin into the first-dimension chromatographic column by using a step column temperature, and a curve fitting method for repeatedly injecting normal paraffin under the isothermal chromatographic condition. Although the methods can establish a method for measuring the second-dimension chromatographic retention index in the full-two-dimension gas chromatography, the method needs complicated chromatographic conditions and repeated injection of normal alkane, is time-consuming and labor-consuming, and severely limits the application of the second-dimension chromatographic retention index in the full-two-dimension gas chromatography in the qualitative analysis of unknown substances. Therefore, it is urgently needed to establish a simple method for measuring the second-dimension retention index in the full-two-dimension gas chromatography. References (1) Bieri, s.; marriott, P.J.anal Chem 2006,78, 8089-8097; (2) bieri, s.; marriott, P.J.anal Chem 2008,80, 760-768; (3) jiang, m.; kulsing, c.; nolvachai, y.; marriott, P.J.anal Chem 2015,87, 5753-5761; (4) prodhan, m.a.i.; yin, x.; kim, s.; McClain, c.; zhang, X.J chromanogr A2018, 1539, 62-70.
Disclosure of Invention
The invention aims to provide a simple and convenient determination method for a second dimension retention index in a full two-dimensional gas chromatography, so as to overcome the defects that complicated chromatographic conditions are required and n-alkane is required to be injected repeatedly in the conventional determination method for establishing the second dimension retention index in the full two-dimensional gas chromatography.
The technical scheme for realizing the invention is as follows:
the invention provides a simple and convenient determination method of a second dimension retention index in a full two-dimensional gas chromatography, which comprises the following steps:
(1) measuring the outflow temperature and second-dimensional retention time data of 4 or more compounds with known retention index values under the analysis conditions used by the full two-dimensional gas chromatography; the compounds with known retention index values of 4 or more can be used, but are not limited to, the following or combinations thereof: 1) MegaMix A mixture (Restek Co.); 2) mixtures of grobmix (Restek corporation) with normal alcohols; 3) a mixture of normal alkanes and normal alcohols; 4) mixtures of grobmix (Restek corporation) with normal alkanes; 5) known substances in the sample to be analyzed.
(2) Substituting the effluent temperature, the second-dimensional retention time data and the second-dimensional retention index value of the known substance measured in the step (1) into the following formula 1, and fitting constants a, b, c and d to obtain an exact relational expression of the second-dimensional retention time, the second-dimensional retention index and the effluent temperature under the analysis conditions used for the full two-dimensional gas chromatography in the step (1); the fitting coefficient can use a solution plug-in of Excel;
log(log(2tR))＝[a(2I/100)+b]In(2T)+[c(2I/100)+d]
formula 1
In formula 1, a, b, c and d are constants,2tRfor the retention time of the second dimension,2i is the second dimension retention index of the compound;2t is a column temperature (hereinafter referred to as an outflow temperature) at which the compound flows out of the second-dimensional chromatography column.
(3) The second dimension retention of the compound to be analyzed is calculated by the following method A or method B:
the method A comprises the following steps: analyzing the sample to be tested under the same analysis conditions used by the full-two-dimensional gas chromatography in the step (1), obtaining second-dimensional retention time and outflow temperature data of the compound to be analyzed, substituting the second-dimensional retention time and outflow temperature data into the formula 1 after the constants a, b, c and d are determined in the step (2), and calculating to obtain a second-dimensional retention index of the compound to be analyzed;
the method B comprises the following steps: substituting the standard retention index value of the normal alkane into the formula 1 after the constants a, b, c and d are determined in the step (2), calculating the second-dimension retention time of the normal alkane at different outflow temperatures, thereby obtaining a retention index map (i.e. an equal volatilization curve) under the same analysis conditions for the full-two-dimensional gas chromatography as in the step (1), filling the retention index map with the second-dimension retention time and outflow temperature data of the substance to be analyzed, and calculating the second-dimension retention index of the substance to be analyzed according to a kovat (Kov a-ts) retention index calculation formula shown in the following formula 2,
formula 2: kovat (Kov-ts) retention index calculation formula
RI in formula 2 is retention index;2tRn and n +1 are the numbers of carbon atoms contained in the normal paraffin before and after the outflow of the target compound (i), respectively;2tR(n)<2tR(i)<2tR(n+1)。
the simple determination method for the second-dimension retention index in the full-two-dimension gas chromatography provided by the invention is a simple determination method for the second-dimension retention index in the full-two-dimension gas chromatography, which is established according to the correlation between the second-dimension retention time and the outflow temperature of the normal alkane in a retention index map (i.e. isovolatility curves). (1) The complex chromatographic condition and the repeated and repeated injection of the normal paraffin are not needed, only a plurality of compound mixed liquids with known retention indexes are injected once, or a plurality of known compounds in a sample to be analyzed can be directly used to establish a determination method of a second dimension retention index in the full two-dimension gas chromatography, (2) the method has high accuracy: if a suitable known compound is selected to establish the method, the absolute error of the retention index calculation can be controlled to be within 20.
Drawings
FIG. 1 is a process flow diagram of a simple method for determining the second-dimension retention index in a full-two-dimensional gas chromatography according to the present invention;
FIG. 2 is a graph showing comparison between the isovolatility curve obtained by the conventional method and the simple method for measuring the second-dimension retention index in the full-two-dimensional gas chromatography of the present invention, wherein the solid line is established in the present invention; the dashed line is established by the reference method;
FIG. 3 is a comparison graph of the second dimension retention index of the compounds in the boswellia volatile oil measured by the simple method for measuring the second dimension retention index in the full two-dimensional gas chromatography of the invention and the traditional method.
Detailed Description
Example 1
The comprehensive two-dimensional gas chromatography conditions used in the simple determination method of the second-dimensional retention index in the comprehensive two-dimensional gas chromatography are as follows: agilent 7890A gas chromatograph, Agilent 7200QTOFMS as detector, and LMCS (Chromatography Concepts Ltd, Doncaster, Australia) as whole two-dimensional gas Chromatography modulator. Helium was used as a carrier gas at a flow rate of 1.2 mL/min. The initial column temperature of the gas chromatograph was 40 degrees celsius and held for 2 minutes, and then the temperature was raised to 240 degrees celsius at 5 degrees celsius/minute and held for 20 minutes. SUPELCOWAX 10 capillary chromatography column (specification: 30m × 0.25mm I.D.. times.0.25 μm; Supelco, Bellefonte, Pa.) was used as the first dimension chromatography column, Rxi-5Sil MS capillary chromatography column (specification: 1.0m × 0.1mm I.D.. times.0.1 μm; Restek Corp., Bellefonte, Pa.) was used as the second dimension chromatography column, and the two column components were connected by a connector (Press-light connector). A mixture (concentration: 5ppm) of Grobmix (Restek Co.) and a normal alcohol compound (C8, C11-C18 normal alcohol) was used as a known standard substance used in the present invention. The temperature of a gas chromatography sample inlet is 250 ℃, and 1 microliter of sample is injected in a non-split-flow mode. The modulator temperature was set to 0 degrees celsius and the modulation period was 6 seconds. The ion source temperature, emission current, voltage and sampling frequency of the mass spectrometer were 230 ℃,35 μ A,70eV and 50Hz, respectively. The second dimension retention time and the efflux temperature of Grobmix (Restek) and normal alcohols were analyzed under the chromatographic conditions (see Table 1).
Mixing the above grobmix (Restek corporation) is substituted into the relationship with the outflow temperature of the normal alcohol compound and the corresponding second-dimensional retention time data: log (log: (2tR))＝[a(2I/100)+b]In(2T)+[c(2I/100)+d]The exact relationship of the second dimension retention time, second dimension retention index and exit temperature under the chromatographic conditions used is found by solving the constant coefficients a, b, c and d in the equation using a hypothetical analysis tool (e.g., solvar in excel): log (log: (2tR))＝[-0.0767(2I/100)+0.044109]In(2T)+[0.479553(2I/100)+-1.79066]. The retention index map (i.e., isovolatility curves) under the chromatographic conditions was obtained by substituting the retention index standard value of n-alkane into the relational expression to obtain the second dimension outflow time of n-alkane at different temperatures, as shown by the solid line in fig. 2.
For comparison with the method established in this example, the isovolatility curve of n-alkane under the chromatographic conditions used in this example was also determined by the literature-reported method of repeatedly feeding n-alkane at the first dimension column using a stepped column temperature, as shown by the dashed line in FIG. 2. Comparing the isovolatilization curves of the example and the literature report method in FIG. 2, the results obtained by the two methods are almost completely consistent, thus proving that the method is accurate and reliable.
To further prove the reliability of the method, the volatile oil of the frankincense, a traditional Chinese medicine, is subjected to sample injection analysis under the chromatographic condition used in the embodiment, and the second-dimensional retention time and outflow temperature data of each substance in the volatile oil are obtained. The data obtained were filled in the equal volatilization curves obtained in this example and the conventional method described above, and the second-dimensional retention index of the substance to be analyzed was calculated according to the Kovat (Kov a ts) retention index calculation formula. The retention index pair obtained by the two methods is shown in FIG. 3, and it can be seen from the graph that the correlation of the retention index data calculated by the two methods is very good, and the difference of the retention index data obtained by the two methods is less than 20, thus further confirming the accuracy of the invention.
TABLE 1 second dimension retention time, retention index and outflow temperature of selected grobmix and normal alcohols in this example
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (2)
1. A method for determining a second dimension retention index in a full two-dimensional gas chromatography comprises the following steps:
(1) measuring the outflow temperature and second-dimensional retention time data of more than 4 compounds with known retention index values under the analysis conditions used by the full two-dimensional gas chromatography;
(2) substituting the effluent temperature, the second-dimensional retention time data and the second-dimensional retention index value of the known substance measured in the step (1) into the following formula 1, fitting constants a, b, c and d to obtain an exact relational expression of the second-dimensional retention time, the second-dimensional retention index and the effluent temperature under the analysis conditions used for the full two-dimensional gas chromatography in the step (1),
log(log(2tR))＝[a(2I/100)+b]In(2T)+[c(2I/100)+d]
formula 1
In formula 1, a, b, c and d are constants,2tRfor the retention time of the second dimension,2i is the second dimension retention index of the compound;2t is the column temperature when the compound flows out of the second dimension chromatographic column, namely the outflow temperature;
(3) the two-dimensional retention number of the compound to be analyzed was calculated by the following method A or method B:
the method A comprises the following steps: analyzing the sample to be tested under the same analysis conditions used by the full-two-dimensional gas chromatography in the step (1), obtaining second-dimensional retention time and outflow temperature data of the compound to be analyzed, substituting the second-dimensional retention time and outflow temperature data into the formula 1 after the constants a, b, c and d are determined in the step (2), and calculating to obtain a second-dimensional retention index of the compound to be analyzed;
the method B comprises the following steps: substituting the standard retention index value of the normal alkane into the formula 1 after the constants a, b, c and d are determined in the step (2), calculating the second-dimensional retention time of the normal alkane at different outflow temperatures, thus obtaining a retention index map under the same analysis conditions of the full-two-dimensional gas chromatography as the step (1), namely an equal volatilization curve, filling the second-dimensional retention time and outflow temperature data of the substance to be analyzed into the retention index map, and calculating the second-dimensional retention index of the substance to be analyzed according to a Kovat (Kov a ts) retention index calculation formula.
2. The method of claim 1, wherein the fitting tool in step (2) is a solution plug-in for Excel.
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