RU2046336C1 - Chromatographic method for determining correction sensitivity coefficients to substances having similar properties - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: method involves analyzing two mixtures prepared from the initial mixture by adding different quantities of two or more standard substances from the same homologic series or additives. Each mixture is analyzed chromatographically twice using different arbitrary quantities of samples to be introduced. The difference of chromatographic signals is used to determine the values of analyzed components by means of internal double standard interpolation method. The determined differences of areas under peaks corresponding to the standard substances are used to calculate their reduced values by extrapolating the relation r_ст=⌀(ΔQ_ст) to the mean contents of analyzed components. The reduced differences of areas under peaks corresponding to these components is obtained by interpolating the calculated reduced differences of areas of peaks corresponding to two neighboring homologs of standard substances. The ratio of reduced differences of areas under peaks corresponding to one of the standard substances and analyzed components is used to determine the correction sensitivity coefficient for these components. EFFECT: enhanced accuracy of the method. 1 tbl

Description

 The invention relates to chromatography and can be used for qualitative and quantitative determination of the content of individual components of complex mixtures of arbitrary composition in various sectors of the economy: chemical, petroleum, gas, petrochemical, metallurgy, medicine, biology, ecology, etc.

 A known chromatographic method for determining correction sensitivity coefficients for individual known substances relative to a specially selected standard with a molecular structure close to this substance [1] Moreover, in order to obtain representative data, in addition to various mandatory requirements for the conditions and stability of the parameters of the chromatographic process, the amount of substance and the standard in the sample for analysis must be kept the same.

 The disadvantage of this method is the relatively low accuracy of the determination of correction factors due to unaccounted for systematic errors due to the presence of an initial coefficient in the equation of the calibration characteristics of the analyte and the standard, as well as the inability to determine correction sensitivity coefficients for individual unidentified components of complex mixtures.

There is also a method of determining correction coefficients using cumulative measurements with a normalized equation of coupling based on the results of several chromatographic analyzes of a mixture of unknown components of different contents with a constant sample volume [2]
However, the known method does not provide sufficient accuracy for determining the correction coefficients, since the content of the components in the analyzed mixtures is not the same and varies within certain limits, and the solution of the system of normalized equations is performed with relatively large errors due to the influence of the initial coefficient in the calibration equation.

The closest to the proposed invention by technical essence is the chromatographic method for determining the concentrations of the components of the mixture, in which the analyzed mixture is separated on a chromatographic column twice for different amounts of samples introduced into the column and the difference of the detector signals for each individual component of the mixture in each analysis with different samples determines concentration by known methods, and the correction values of sensitivity are determined by the values of the obtained concentrations [3]
The disadvantage of this method is that when it is used there is no possibility of determining correction sensitivity coefficients with the same content of the analyzed components and the standard, as a result of which the accuracy of determination of correction coefficients is reduced.

 The aim of the invention is to improve the accuracy of chromatographic determination of correction sensitivity coefficients for individual components of a complex mixture relative to a standard substance.

 The goal is achieved due to the fact that in the chromatographic method for determining correction coefficients of sensitivity to substances having similar properties, in which samples of the components of the test mixture together with two standard substances or additives of a fixed amount, eluting before and after the components to be studied, are separated on a chromatographic column and detecting detector signals, by which, using the interpolation method of the double internal standard, component concentrations are determined c and calculate correction factors for each standard substance or additive, characterized in that a different fixed amount of standard substances or additives is added to the test mixture before each analysis, each of the mixtures is separated and recorded twice for different sample volumes, and correction sensitivity factors are determined by the ratio reduced to the same content of the signal differences of one of the standard substances and the investigated components of the mixture.

 When solving this problem, a technical result is created that consists in reducing random and systematic errors in measuring the differences in the areas of chromatographic peaks of two neighboring standard homologs and the analyzed components according to the results of two analyzes of the mixture with different contents of the standards on two different volumes of the sample and bringing the difference in the areas of the standards to the value corresponding to the average content of the analyzed components according to the results of two analyzes of the mixture, as well as the determination of ivedennoy difference areas of analytes to calculate the correction factors obtained by interpolation of the differences given space standards peaks.

The essence of the proposed method lies in the fact that two mixtures are prepared for analysis, containing the initial mixture with a certain, but different amount of added two or more standard substances, each of which is chromatographed twice with different arbitrary amounts of the introduced sample and by the difference of chromatographic signals (peak areas) individual components of the mixture and standards for each analyzed mixture determine the content of these components in the initial mixture by known methods, for example, interpolation m using the double internal standard method [4] and with respect to the differences in peak areas of one of the standards and the individual components of the mixture reduced to the same content, the correction sensitivity coefficient for these components relative to the selected standard is determined. In this case, the values of the reduced differences in the peak areas of the standards corresponding to the same content of the mixture components and the standard are determined by extrapolation of the dependencies
r _st1 = f (Δ Q _st1 ); r _st2 = f (Δ Q _st2 ), (1) where r _st1 , r _{st2 are the} contents of the 1st and 2nd standard substances;
Δ Q _st1 , Δ Q _{st2 the} difference in the areas of chromatographic peaks of the 1st and 2nd standard substances.

(2) где r_i ⁽¹⁾, r_i ⁽²⁾ содержание i-го компонента из 1-го и 2го хроматографирования анализируемой смеси при различных фиксированных количествах двух стандартных веществ.To the average content of the i-th component from the 1st and 2nd chromatography of the mixture r _iav
r _{i avg} =

(2) where r _i ⁽¹⁾ , r _i ^{(2) is the} content of the ith component from the 1st and 2nd chromatography of the analyzed mixture with various fixed amounts of two standard substances.

(3) где Δ Q_i разность площадей хроматографических пиков i-го компонента, а приведенную разность площадей пиков, полученных по уравнениям (1-3) для двух соседних гомологов стандарта, определяют
ΔQ $\genfrac{}{}{0ex}{}{\text{п}}{\text{i}}$

(4) где Δ Q_i ^п, Δ Q_ст1 ^п, Δ Q_ст2 ^п приведенные к одинаковому содержанию значения разностей площадей хроматографических пиков i-го компонентов и 1-го и 2-го стандартных веществ.Moreover, r _i ⁽¹⁾ , r _i ⁽²⁾ is determined by the equation
r _i = ΔQ _i

(3) where Δ Q _{i is the} difference in the area of the chromatographic peaks of the i-th component, and the reduced difference in the areas of the peaks obtained by equations (1-3) for two neighboring homologs of the standard is determined
ΔQ $\genfrac{}{}{0ex}{}{\text{P}}{\text{i}}$

(4) where Δ Q _i ^p , Δ Q _{st 1} ^p , Δ Q _{st 2} ^p reduced to the same content values of the differences in the areas of chromatographic peaks of the i-th component and the 1st and 2nd standard substances.

 The method is characterized by a new set of essential features, ensuring the achievement of a technical result, which allows to increase the accuracy of determining correction sensitivity factors for individual components of a complex mixture relative to a specific standard.

 The method can be carried out as follows.

 PRI me R. The analyzes were carried out on a Color 570 chromatograph with a flame ionization detector.

 The chromatographic signals of the detector (peak areas) were measured by an electronic integrator of the chromatographic analysis automation system.

 The analyzed mixture was separated on a stainless steel chromatographic column (length 1 m, internal diameter 3 mm). As the stationary phase, tricresyl phosphate was used, deposited in an amount of 20% of the mass on a solid inert carrier.

Carrier gas helium, flow rate 30 cm ³ / min.

 Entering a sample for analysis with a microsyringe.

The temperature of the column thermostat is 100 ^° C.

 For the analysis, we used an artificial mixture containing hydrocarbons: hexane, octane, decane and 2-methylheptane. The detected component of the mixture is 2-methylheptane. Its content in the mixture is 14.95 vol. The content of the remaining components of the mixture was not normalized.

 As standard substances added to the initial mixture for joint analysis, heptane (standard N 1) and nonane (standard N 2) were used.

 Two mixtures were prepared from the starting mixture and standards for analysis on a chromatograph.

 The first mixture: the content of 2-methylheptane 14.95 vol. heptane content of 12.3 vol. nonane content 12.7 vol.

 The second mixture: the content of 2-methylheptane 14.95 vol. the heptane content of 16.8 vol. nonane content of 17.2 vol.

 The results of the experiment are summarized in table.

Chromatographic determination of correction sensitivity coefficients for the determined component of the initial 2-methylheptane mixture relative to heptane or nonane standards was carried out in the following sequence:
1. The first mixture was chromatographed twice at approximate sample volumes of 200 and 150 μl.

 The values of the areas of chromatographic peaks of heptane, 2-methylheptane and nonane and their difference are given in p.p. 1.1, 1.2 and 1.3 tables.

 2. The second mixture was chromatographed twice at approximate sample volumes of 200 and 150 μl as well. The areas of chromatographic peaks of the components and their difference are given in p.p. 2.1, 2.2 and 2.3 tables.

 3. Using the values of the difference in peak areas of heptane, 2-methylheptane and nonane in paragraphs 1.3 and 2.3 of the table, we determined two values of the concentration of 2-methylheptane by the interpolation method of the double internal standard according to equation (3), the values of which are given in paragraphs 1.4 and 2.4 tables.

 4. Using two values of the content of 2-methylheptane according to the analysis of mixtures of N 1 and N 2, according to (2), the average value of the content of 2-methylheptane was determined in Section 3 of the table.

 5. According to dependence (1), two values of the reduced peak area difference were determined by extrapolation to the average value of the content of 2-methylheptane p.p. 4.1 and 4.2 tables.

 6. According to the given differences in the peak areas of heptane and nonane p.p. 4.1 and 4.2 tab. the reduced peak area difference for 2-methylheptane was determined from the expression (4) of clause 4.3. tables.

и K_i/K_ст2=

, где

и

поправочные коэффициенты чувствительности i-го компонентов относительно 1-го и 2-го стандартов; определяли поправочные коэффициенты 2-метилгептана относительно гептана и нонана предлагаемым способом п. 6.1 таблицы.7. According to the equations K _i / K _st1 =

and K _i / K _st2 =

where

and

sensitivity correction coefficients of the i-th component relative to the 1st and 2nd standards; determined correction factors of 2-methylheptane relative to heptane and nonane by the proposed method, paragraph 6.1 of the table.

и K_i/K_{ст 2}=

, где C_i, C_ст1 и С_ст2 концентрации соответствующих компонентов; определяли поправочные коэффициенты 2-метилгептана относительно гептана и нонана известным способом по результатам анализа смеси N 1 и N 2 п.п. 5.1 и 5.2 таблицы.8. According to the equations K _i / K _st1 =

and K _i / K _{st 2} =

Where C _i, C _{CT1 CT2} and C concentrations of the respective components; determined correction factors of 2-methylheptane relative to heptane and nonane in a known manner according to the results of the analysis of a mixture of N 1 and N 2 p.p. 5.1 and 5.2 tables.

 9. Errors in the determination of correction coefficients of 2-methylheptane by known and proposed methods with respect to correction coefficients from published data are given in paragraphs. 5.1.1, 5.2.1 and 6.2 tables.

 As can be seen from the data in the table, the accuracy of determination of the correction sensitivity coefficients of 2-methylheptane relative to heptane and nonane, the proposed method is much higher than the known.

 Using the present invention allows to increase the accuracy of the chromatographic determination of correction sensitivity coefficients of the individual components of a complex mixture; to obtain additional information for group and individual identification of the analyzed components according to the dependences of their correction sensitivity coefficients on the molecular structure and physico-chemical properties, for example, the number of carbon atoms, molecular weight, boiling point, etc. to carry out a quantitative interpretation of chromatograms when analyzing complex mixtures of identified and unidentified components.

Claims (1)

 CHROMATOGRAPHIC METHOD FOR DETERMINING CORRECTIVE SENSITIVITY COEFFICIENTS TO SUBSTANCES HAVING CLOSE PROPERTIES, in which samples of the components of the analyzed mixture together with two standard substances or additives of a fixed amount, eluting before and after the components under study, are separated by the chromatographic column, which is recorded using a chromatographic column double internal standard method determine the concentration of components and calculate the correction coefficients Inventions for each standard substance or additive, characterized in that a different fixed amount of standard substances or additives is added to the test mixture before each analysis, each of the mixtures is separated and recorded twice for different sample volumes, and correction sensitivity coefficients are determined by the ratio of reduced to the same content differences of signals of one of the standard substances and the investigated components of the mixture.

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