The method for determining the molar ratios of the sensitivity of thermal conductivity detectors and flame ionization

 

(57) Abstract:

The invention relates to gas chromatography and can be used for qualitative and quantitative analysis not identified components of complex mixtures of substances belonging to different classes of organic compounds. According to the results of chromatographic analysis, using signals of two series-connected thermal conductivity detectors and flame ionization detector, calculate the relative sensitivity factor of the investigated components for the two detectors, the use of which in collaboration with index holding and experimental dependence of the indices of sensitivity for normal paraffin hydrocarbons to determine the molar ratios of sensitivity. The technical result of the present invention is expressed in increasing the accuracy of determining the molar ratios of sensitivity. table 2.

The invention relates to gas chromatography and can be used for qualitative and quantitative analysis of unidentified components of complex mixtures of substances belonging to different classes of organic compounds.

Known chromatographic the strain constraint equations on the results of chromatographic analyses of several mixtures of unidentified components with different content at constant volume of the sample [1].

The disadvantage of this method is the relatively low accuracy of determination of the correction coefficients, since the calculation is performed according to the results of several analyses (number mixtures must be greater than or equal to the number of identified coefficients for the components of these mixtures). The solution of the normalized system of equations is performed with relatively large errors.

There is also known a method of quantitative analysis of unidentified components of the mixture, close in molecular structure and physico-chemical properties to the standard substances comparison added in the analyzed sample, using the method of double internal standard according to the results of one cycle analysis [2].

However, the known method does not provide sufficient accuracy for the determination of the correction coefficients, as they are approximately taken equal to the geometric mean value of the sensitivity coefficients of the two standard substances, eluruumiks before and after the studied component.

Closest to the claimed invention to the technical essence is a gas chromatographic method for the determination of the concentration of compound which tion number, eluruumideta before and after the designated components and chromatographic signals measured simultaneously by two universal detectors of different types and determine the concentration of components interpolation using the dual internal standard, realizing the normalization correction factors the sensitivity of the individual detectors to the magnitude of the relative sensitivity of the two detectors [3].

The disadvantage of this method is the increase of the error to determine the molar ratios of sensitivity to separate the analyzed components, since the measurement results are influenced by many interrelated factors, including how well the selected substances comparison (standards N 1 and N 2), eluruumina before and after the analyte, the affinity of physico-chemical properties and structure of the component and standards, proximity to the unit values of the sensitivity of the analyte relative to the two standards, and the relationship of the retention indices of the index of sensitivity for the two detectors. Sensitivity index Ihwas proposed in [2] by analogy with the linear retention index I.

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where 1/KiTHAT 1/KzTHAT 1/Kz+1z+1> 1/Ki> 1/Kz.

The objective of the invention is to improve the accuracy of determining the molar ratios of the sensitivity of thermal conductivity detectors and flame ionization for a wider range of different substances and excluding the impact of the disadvantages of this method on the calculation results.

This problem is solved by a method for determining the molar ratios of the sensitivity of thermal conductivity detectors and flame ionization, in which the unidentified components of a complex mixture of chromatographic on a column with non-polar stationary phase, and chromatographic signals measured simultaneously by two series-connected with thermal conductivity detectors flame ionization detector and calculate the relative sensitivity factor of the investigated components for the two detectors, for each analyzed component by the method of selection is determined by two values of the index of sensitivity for each detector using the index holding and experimental dependence of the relative sensitivity of the two detectors from their indexes of sensitivity for normal paraffin is tion of the detector to the index holding, then the retention index minus one, two, three, etc. to obtain the corresponding index of the sensitivity of the detector thermal conductivity equal to or slightly smaller index holding, then reduce the selected index of the sensitivity of the flame ionization detector per unit and get the second value, and the molar ratios of the sensitivity of each detector is determined by the average value of the two corresponding indices of sensitivity.

When the task is created technical result, which is the use of retention indices of the investigated components on a column with non-polar stationary phase and experimental dependences of the relative coefficients of the two sensitive detectors from their indexes of sensitivity for normal paraffin hydrocarbons, which improves the accuracy of determining the molar ratios of the sensitivity of thermal conductivity detectors and flame ionization detector.

It is known [3, 4] that

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and 1/KiACCIDENT= a1+ b1ICACCIDENTthat ... (3) and 1/KiPID= a2+ b2ICPID, ... (4) where 1/KiACCIDENTand 1/KiPeloponese (RTA) and flame ionization (PID); KOTNACCIDENT/PIDthe relative sensitivity factor of the i-th component of the two detectors accident and PID; QiACCIDENT, QbACCIDENTand QiPID, QbPID- areas of the chromatographic peaks of the i-th component and standard substances comparison of benzene detectors accident and PID; ICACCIDENTand ICPIDthe indices of sensitivity of the i-th component for the accident and the PID defined by the equation (1); a1b1and a2b2- empirical coefficients of correlation equations for detectors accident and PID, determined by the method of least squares according to the results of the chromatography was carried out on binary mixtures of a fixed number of normal paraffin hydrocarbons with benzene.

Substituting in equation (2) the value of the relative molar sensitivity of (3) and (4) obtain a linear relationship between the indices of sensitivity investigated the i-th component detectors accident and PID.

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where KACCIDENTRel/PiID- determine the results of the chromatography was carried out of the i-th component with benzene according to equation (2).

To determine the indices of sensitivity according to equation (5) is used with non-polar stationary phase, as well as following having place and known in the literature patterns:

1. The retention index of the investigated component on a column with non-polar stationary phase is greater than or equal to its index of sensitivity to thermal conductivity detectors and flame ionization when used as a carrier gas of nitrogen, i.e., Ii-ICACCIDENTand Ii-ICPIDchange of zero or more.

2. The index of the sensitivity of the PID proportional to the effective carbon number AUC or the number of carbon atoms in molecules of the analyzed substances Z, responsible for the formation of the signal detector. For hydrocarbons AUC = Z, and for non-hydrocarbon AUC < Z;

3. The retention index Iiand the sensitivity indices ICACCIDENTand ICPIDcharacterize the structure and properties of the i-th substance, comparing them to the properties of a hypothetical n-paraffins, therefore, for two extreme values of the index within the "preferred pair of adjacent homologues standards, i.e., within I=1 (number of carbon atoms in the molecule homologues Z and Z+1) can be identified and the index according to their average value.

The sequence of operations when selecting indexes Ci- 2, Ii- 3, etc. to obtain the corresponding equation (5) IC(1)ACCIDENTequal to or slightly smaller Ii. Received IC(1)ACCIDENTand IC(1)PIDcelebrate one of the extreme values within a "preferred pair of adjacent homologues standards. The second extreme value of the index will meet the reduction obtained IC(1)PIDper unit. You get a IC(2)PIDand IC(2)ACCIDENT.

Next, compute the sensitivity indices of the i-th component for each detector according to the average values of two derived indices:

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and

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Then determine the molar ratios of the sensitivity of the i-th component for thermal conductivity detectors KiACCIDENTand flame ionization KiPIDsubstituting (6) and (7) in equations (3) and (4) respectively.

The invention is characterized by a new set of essential features that ensure the achievement of the technical result, which improves the accuracy of determining the molar ratios of the sensitivity of unidentified components of complex mixtures for detectors accident and PID.

Examples of specific performance of propranodol (RTA) and flame ionization (PID), connected in series, i.e. the output of the separation column is connected to a working chamber of an accident, from which the eluate is sent to the PID. As chromatographic columns used stainless steel tube (length 1.0 m, internal diameter 3.0 mm). Stationary liquid phase - polydimethylsiloxane PMS-1000, deposited on a solid carrier chromaton N-AW, the grain size of 0.16 - 0.20 mm in the amount of 15% of the mass. Hard copy pre-modified with polyethylene glycol PEG-20M in the amount of 1.5% by weight of the carrier. The temperature of thermostat columns 120oC, the temperature of the evaporator 170oC, the temperature of thermostat detectors 120oC. carrier Gas: nitrogen, flow rate 25 cm3/min. Volume of the input samples is not more than 1.0 μl.

The chromatograph for the implementation of the proposed method was previously graduated in homologous series of normal paraffin hydrocarbons. Why were analyzed by binary mixtures of pentane to tridecane fixed amount with benzene. According to the averaged results of the chromatography was carried out for each homologue on two separate detectors was calculated molar ratios, which are systematized by the method of least squares with respect to the number of carbon atoms in molekularbiologie for different classes of compounds. For the accident: 1/KiACCIDENT= 0,295 ICACCIDENT- 0,82 (8) and for PID: 1/KiPID= 0,164 ICPID+ 0,06 (9).

Comparison of known (prototype) and the proposed method was carried out according to the results of the analysis of two model mixtures of different substances. First a mixture of Butanone, benzene, toluene, orthoxylene, heptanol-1, adamantane. The second mixture: Diethyl ether 2,3-Dimethylbutane, cyclohexane, pentanol, pentalateral, Dean.

The results of measurements and calculations for the components of the first and second mixtures are summarized respectively in table. 1 and 2 Comparative data experimental verification of known and proposed methods".

The sequence of operations and calculations the following:

1. From the obtained two chromatograms, recorded as a separate detectors accident and PID, defined square khromatograficheskikh peaks Qiusing system automation analysis CAA-06 (p. 1 table. 1 and 2), as well as the retention time of each component mixtures of N 1 and N 2 and was calculated by linear retention indices of the Iiparagraph 2 of the table. 1 and 2.

2. The molar ratios of the sensitivity of the two components of mixtures for each detector KiACCIDENTand KiPIDpre-determined by habirova on N-paraffins, p. 3 of table. 1 and 2.

3. The obtained values of KiACCIDENTand KiPIDused to assess the accuracy of determination of the molar ratios of the sensitivity of the proposed and conventional methods.

3.1. The known method (prototype)

3.1.1. Was determined by two values of the relative sensitivity of the two detectors for each of the analyzed components, using as standard substances comparison, components of the same mixtures, eluruumina before and after the analyzed component by the following equations:

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and

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where i-1, i, i+1 is the number of output components on the chromatogram. i = 2 - 5, as for the first and sixth components of mixtures can be calculated by (10) only one value of KOTNACCIDENT/PID.

3.1.2. Values of KOTN/i-1ACCIDENT/PIDand KOTN/i+1ACCIDENT/PIDdefined by equation (10) shown in paragraph 4.1. table. 1 and 2.

3.1.3. Method of valuation was determined average values of the molar ratios of the accident and the PID of the investigated components relative to benzene according to the following scheme:

Assume that

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then using (10) respectively, received

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Then calculate the average of testing the Ki+1(p. 3 of table. 1 and 2) and received average molar sensitivity coefficients of the i-th component relative to benzene KiACCIDENTand KiPID.

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and

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3.1.4. Calculated according to the equations (11) molar values of the sensitivity coefficients of the two components of the mixtures for the accident and PID in a known manner and the accuracy of their determination against known values (p. 3 of table. 1 and 2) are shown respectively in paragraph 4.2. and 4.3. table. 1 and 2.

3.2. The proposed method.

3.2.1. Determined the relative sensitivity of the two detectors for the mixture components N 1 relative to benzene in equation (2), and for the components of the mixture N 2 equation

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where Q6ACCIDENT, K6ACCIDENT, Q6PID, K6PIDrespectively the peak areas of the Dean and the molar ratios of the sensitivity of the Dean relative to benzene for the accident and PID (item 1 and 3 of table. 2).

Calculated according to the equations (2) and (12) values are given in paragraph 5.1. table. 1 and 2.

3.2.2 Substituting the values of the empirical coefficients of correlation equations (8) and (9) in equation (5), received the dependence of ICPIDfrom the ICACCIDENTwith regard to experimentally determine which of the retention indices of the investigated components (see p. 2 table. 1 and 2), were determined by the indices of sensitivity of the method of selection in the following sequence:

1) set the IC(1)PID= Iithen Ii- 1; Ii- 2; Ii- 3, etc. to obtain the IC(1)ACCIDENT(13) equal to or slightly smaller Ii. Received IC(1)ACCIDENTand IC(1)PIDmeet one of the extreme values within a "preferred pair of adjacent homologues standards;

2) Reduce the received IC(1)PIDper unit. You get a IC(2)PIDand the corresponding (13) the value of IC(2)ACCIDENTthat meet the second extreme value index;

3) to Calculate the sensitivity indices of the i-th component for each detector according to the average values of two derived indices in equations (6) and (7) are described in paragraph 5.2. table. 1 and 2.

3.2.4. Determined molar ratios of the sensitivity of the i-th component for each detector KiACCIDENTand KiPIDusing computational values of ICACCIDENTand ICPIDand the corresponding correlation according to (8) and (9). The obtained molar sensitivity coefficients of the two components of the mixtures for the accident and the PID of the PDP. 5.3. and 5.4. table. 1 and 2.

4. The influence of nature and physico-chemical properties of the standards and the time of their holding, in relation to the analyzed component, the error in the determination of the molar ratios of sensitivity known method, for example, toluene, shows that when used as standard substances benzene and orthoxylene error is 4.5% (p. 4.3. table. N 1). If used as standards butanone and heptanol, it is possible to show that for toluene using equation (10)

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and

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Using equation (11) is calculated:

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and

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Thus the measurement error increases significantly and reaches 41.7 per cent

Comparative data experimental verification of known and proposed methods.

As can be seen from the data tables, the proposed method of determining the molar ratios of the sensitivity of thermal conductivity detectors and flame ionization compared with the known has greater accuracy.

The use of the invention allows to:

1. To improve the accuracy of the chromatographic determination of the molar ratios of the sensitivity of unidentified substances, DVD/P> 2. To provide a quantitative interpretation of the chromatograms in the analysis of complex mixtures of unidentified components.

3. To obtain additional information for group and individual identification of the analyzed components in the index of sensitivity for the accident and PID, as well as the relative ratio of sensitivity.

Sources of information

1. Farzaneh N. G., The Ilyasov L. C. Automatic gas detectors. M: Energy. 1972. S. 168

2. Arutyunov Y. I., Vigdergauz M. S. Journal of analytical chemistry. 1994. so 49. N 8. C. 796-803

3. Vigdergauz M. S., Y. Arutyunov I. RF Patent N 2046335. Bull. Fig. N 29 from 29.10.95.

4. Vigdergauz M. S., Y. Arutyunov, I., E. Kolosov, A. Kurbatov, S. C. Journal of analytical chemistry. 1995. so 50 N 8. C. 827-833

The method for determining the molar ratios of the sensitivity of thermal conductivity detectors and flame ionization, in which the unidentified components of a complex mixture of chromatographic on a column with non-polar stationary phase, and chromatographic signals measured simultaneously by two series-connected detectors thermal conductivity and flame ionization detector and calculate the relative sensitivity factor of the investigated component is Aut two index values of sensitivity for each detector using the index holding and experimental dependence of the relative sensitivity of the two detectors from their indexes of sensitivity for normal paraffin hydrocarbons, the first value chosen by equating the index of the sensitivity of the flame ionization detector to the retention index, then the index is holding minus one, two, three, etc. to obtain the corresponding index of the sensitivity of the detector thermal conductivity equal to or less than the index holding, then reduce the selected index of the sensitivity of the flame ionization detector per unit and get the second value, and the molar ratios of the sensitivity of each detector is determined by the average value of the two corresponding indices of sensitivity.

 

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