RU2044317C1 - Chromatographic method of determination of concentrations of components - Google Patents

Abstract

FIELD: chromatography. SUBSTANCE: analyzed mixture is chromatographed together with three or more standard matters or additives of fixed quantities twice with different quantities of injected sample. Rough values of concentrations of each component are determined by difference of chromatographic signals for each analyzed component including standards by interpolation method relative to each pair of adjacent standards. Proper pair of adjacent standards is chosen by magnitude of minimal deviation from unity of dependence of averaged values of computed correction coefficients of sensitivity for analyzed components relative to each standards from number of carbon atoms in molecular of standards. Sought for concentrations of individual components of mixture are determined by interpolation of rough values of concentration relative to chosen pair of adjacent standards to magnitude of averaged correction coefficient equal to one. EFFECT: enhanced precision of chromatographic method. 1 tbl

Description

 The invention relates to chromatography and can be used to quantify the individual components of multicomponent mixtures of unknown composition in various sectors of the economy: chemical, petroleum, gas, petrochemical, oil refining, metallurgy, medicine, biology, ecology, etc.

 A known method of chromatographic determination of the components of complex mixtures by introducing into the analyzed mixture a known amount of a standard substance that leaves the column, and it is recorded between two unknown substances. By calculating the ratio of the times of the release of the standard and the analyzed component, the retention index of the substance is determined and the analyzed component is identified by tabular data.

 The disadvantage of this method is the low accuracy of determination in the presence of a mixture of several substances with similar characteristics, retention in the selected separation conditions.

(1) где Q_i, Q_ст1, Q_ст2 площади хроматографических пиков i-го компонента и 1-го и 2-го внутренних стандартов;
K_i/K_ст1, K_i/K_ст2 поправочные (градуировочные) коэффициенты чувствительности i-го компонента относительно 1-го и 2-го внутренних стандартов;
r_ст1, r_ст2 отношение количества 1-го и 2-го внутренних стандартов к количеству анализируемой смеси без стандартов.A chromatographic method for determining the components of complex mixtures is also known, based on the introduction of three or more standard substances or additives into the analyzed mixture using a double internal standard to calculate the interpolation method, in which substances are eluted from the column and detector signals are recorded before and after the determined component. The content of the i-th component of the analyzed mixture C _i is determined by the formula
C _i = Q _i

(1) where Q _i , Q _st1 , Q _{st2 are the} areas of chromatographic peaks of the i-th component and the 1st and 2nd internal standards;
K _i / K _st1 , K _i / K _st2 correction (calibration) sensitivity coefficients of the i-th component relative to the 1st and 2nd internal standards;
r _st1 , r _{st2 the} ratio of the number of 1st and 2nd internal standards to the number of the analyzed mixture without standards.

 However, the known method has a limited scope in determining the concentrations of unknown components of the mixture, or in the absence of literature or experimental data on the values of correction sensitivity coefficients for the analyzed components of the mixture.

 The aim of the invention is to improve the accuracy of the chromatographic determination of the concentrations of individual, unidentified components of a complex mixture.

 The goal is achieved due to the fact that in the chromatographic method for determining the concentrations of the components, in which the components of the analyzed mixture are chromatographed together with three or more standard substances or additives of a fixed amount and the concentration of each component is determined by the interpolation method of the double internal standard with respect to the detected signals of a pair of neighboring standard substances or additives , according to the invention, the analyzed mixture is separated on a column twice at various amounts in of a single sample, the approximate concentrations of the components are determined by the difference of the detector signals relative to each pair of adjacent standard substances or additives and the corresponding pair of standard substances or additives is selected according to the minimum deviation from the unit of dependence of the average sensitivity coefficients for the analyzed components relative to each standard substance or additive on the number of carbon atoms in the molecules of standard substances or additives, and I determine the desired concentrations of the components by interpolating the approximate concentrations relative to the selected corresponding pair of neighboring standard substances or additives to the value of the average correction factor equal to one.

 The technical result consists in determining the corresponding pair of neighboring homologues of the standard having similar properties with the analyzed unidentified components, calculated from the analysis of the values of the correction sensitivity coefficients for these components relative to each standard substance. Given that the magnitude of the correction sensitivity coefficients for the homologous series linearly depends on the physicochemical properties and molecular structure of the analytes, for example, the number of carbon atoms in the molecules of the analytes for the flame ionization detector, and the criterion for choosing the appropriate pair of neighboring standard homologues for the interpolation method determination of the concentrations of the analyzed components relative to these standards is the minimum deviation from unity per the dependence of the geometric mean values of the correction sensitivity coefficients on the number of carbon atoms in standard molecules. Moreover, if the correction factor is equal to unity, the number of carbon atoms in the standard molecule is approximately equal to the number of carbon atoms in the molecule of the component being analyzed.

 The method can be carried out as follows.

PRI me R. As the analyzed mixture we used a specially prepared artificial mixture containing the following components: heptanol-1, (C _i ), the concentration of which must be determined by the proposed and known methods, its content in the artificial mixture is 7.35 vol. pentane (C _st1 ), content 7.13 vol. hexane (C _st2 ), the content of 7.65 vol. heptane (C _st3 ), content 7.96 vol. octane (C _st4 ), the content of 8.12 about. nonane (C _st5 ), the content of 8.44 about. dean (C _st6 ), content 9.14 vol.

C _st1 C _{st6 is a} grid of standard substances of the same homologous series.

 The analysis was performed on a Color-560 chromatograph.

The chromatographic column from a stainless tube (length 1 m, inner diameter 3 mm) is filled with 20 wt. SE-30 on inertok. The temperature of the column thermostat is 100 ^° C. The flame-ionization detector, PID. The chromatographic signals of the detector (peak areas) were measured by an electronic integrator of the chromatographic analysis automation system. Carrier gas helium, flow rate 30 cm ³ / min. Entering a sample for analysis with a microsyringe.

 Comparative data of the experimental verification of the known and proposed methods are shown in the table.

 The determination of heptanol-1 concentrations in the mixture was carried out in the following sequence.

The first chromatographic analysis of the mixture was carried out with an approximate sample volume of 0.2 μl. The measured areas of chromatographic peaks of the analyzed components Q ₁ are given in paragraph 2 of the table. The analyzed components are shown in the table in the order of their elution isochromatographic columns.

A second analysis of the mixture was carried out with an approximate sample volume of 0.15 μl. The measured peak areas of Q ₂ are given in paragraph 3 of the table.

According to the results of the first and second analyzes, the difference of the areas of chromatographic peaks ΔQ Q ₁ Q _{2 was} determined (paragraph 4 of the table).

(3)
Ориентировочные значения концентраций гептанола-1 приведены в п.5 таблицы.The differences in peak areas were used to determine the estimated values of the calculated concentrations of the analyzed component (heptanol-1) relative to each pair of neighboring standard homologues by the interpolation method
C _i = ΔQ _i

(3)
Estimated heptanol-1 concentrations are given in paragraph 5 of the table.

(4)
Значения поправочных коэффициентов приведены в п.6 таблицы, а их усредненные значения К_ст ^ср в п.6.1 таблицы. В соответствии с зависимостью усредненных, например среднегеометрических, значений K_i/K_стот числа углеродных атомов в молекулах стандартов минимальное отклонение от единицы имеет усредненный поправочный коэффициент, вычисленный относительно гептана при предварительных значениях концентраций гептанола-1 6,4 об. и 7,42 об.Using the values of C _i according to (3), heptanol-1 correction sensitivity coefficients were calculated relative to each standard

(4)
Values of correction factors are given in clause 6 of the table, and their average values of K _st ^Wed in clause 6.1 of the table. In accordance with the dependence of averaged, for example, geometric mean, K _i / K _st on the number of carbon atoms in the standard molecules, the minimum deviation from unity has an average correction factor calculated with respect to heptane at preliminary heptanol-1 concentrations of 6.4 vol. and 7.42 vol.

 The choice of the appropriate pair of neighboring homologues of the standard was to determine the significance of one of the two heptanol-1 concentrations: 6.4 vol. a pair of neighboring standards heptane octane or 7.42 vol. a pair of adjacent heptane hexane standards.

=

1,00016
Для концентрации гептанола-1 7,42 об. соответственно
K $\genfrac{}{}{0ex}{}{\text{3-}}{\text{cp}}$ ²

=

1,000018
Учитывая, что величина усредненного поправочного коэффициента К_ср ^3-2 значительно меньше отклоняется от единицы, чем К_ср ^3-4, то пара соседних стандартов соответствует стандартам N 2 и 3, т.е. гексану и гептану. В этом случае значение искомой концентрации гептанола-1, которое должно быть больше 6,4 об. и меньше 7,42 об. более приближается к величине ориентировочной концентрации 7,42 об. так как К_ср ^3-2 значительно меньше отличается от единицы, чем К_ср ^3-4.The geometric mean of the correction factors for a concentration of 6.4 vol. determined from the values of 0.934 and 1.071 (paragraph 6 of the table)
K $\genfrac{}{}{0ex}{}{\text{3-}}{\text{cp}}$ ⁴

=

1.00016
For a concentration of heptanol-1, 7.42 vol. respectively
K $\genfrac{}{}{0ex}{}{\text{3-}}{\text{cp}}$ ²

=

1,000018
Given that the value of the average correction factor K _cf ^{3-2 is} much less deviating from unity than K _cf ^3-4 , then a pair of neighboring standards meets the standards N 2 and 3, i.e. hexane and heptane. In this case, the value of the desired concentration of heptanol-1, which should be more than 6.4 vol. and less than 7.42 vol. more close to the value of the estimated concentration of 7.42 vol. since K _cf ^{3-2 is} much less different from unity than K _cf ^3-4 .

7,42+(1-1,0011) ×
×

7,42-0,1067 7,31об% или по формуле
C_i= C $\genfrac{}{}{0ex}{}{\text{3}}{\text{i}}$ ^-2+(1-K $\genfrac{}{}{0ex}{}{\text{3-}}{\text{cp}}$ ²)

Значение искомой концентрации гептанола-1, определенное предлагаемым способом, приведено в п.7 таблицы.The desired concentration of heptanol-1 by the proposed method was determined by interpolation of the obtained approximate concentrations of 7.43 vol. and 6.46 vol. relative to the selected pair of neighboring standards N 2 and 3 to the value of the average correction sensitivity coefficient equal to unity, according to the formula
C _i = C $\genfrac{}{}{0ex}{}{\text{3}}{\text{i}}$ ^-2 + (1-K _i / K $\genfrac{}{}{0ex}{}{\text{(cp}}{\text{st3}}$ ⁾ ))

7.42+ (1-1.0011) ×
×

7.42-0.1067 7.31% or by the formula
C _i = C $\genfrac{}{}{0ex}{}{\text{3}}{\text{i}}$ ^-2 + (1-K $\genfrac{}{}{0ex}{}{\text{3-}}{\text{cp}}$ ² )

The value of the desired concentration of heptanol-1, determined by the proposed method, is given in paragraph 7 of the table.

The concentration of heptanol-1 in a known manner was determined by expression (3) by interpolation relative to standards N 5 and 6 (nonane and decan), which are eluted before and after heptanol-1 on this column, C _i = 5.02 vol. Section 8 of the table.

 The error in determining the concentration of heptanol-1 by the proposed and known methods is given in clauses 7.1 and 8.1, respectively.

∮(Z) (5) где Z число углеродных атомов в молекуле стандарта.An additional criterion for the correct choice of the corresponding pair of standards adjacent to the homologue can be the minimum function of the difference in the correction coefficients of the neighboring standards from the number of carbon atoms in the standard molecules

∮ (Z) (5) where Z is the number of carbon atoms in the standard molecule.

минимум функции (5) лежит между гептаном и гексаном.For example, according to paragraph 6 of the table, you can get

the minimum of function (5) lies between heptane and hexane.

минимум функций (5) лежит между гептаном и октаном.

the minimum of functions (5) lies between heptane and octane.

 As can be seen from the data in the table, the method provides for determining the concentration of heptanol-1 in the mixture more than 50 times more accurately than the known.

Claims (1)

 CHROMATOGRAPHIC METHOD FOR DETERMINING THE CONCENTRATIONS OF COMPONENTS, in which the components of the analyzed mixture are chromatographed together with three or more standard substances or additives of a fixed amount and the concentrations of the components are determined by the interpolation method of the double internal standard with respect to the detection signals of a pair of neighboring standard substances or additives, characterized in that the analyzed mixture is divided into chromatographic column twice for various quantities of the injected sample, determined determine the approximate concentrations of the components according to the difference of the chromatographic signals of the detector relative to each pair of adjacent standard substances or additives and select the corresponding pair of standard substances or additives according to the minimum deviation from the unit of dependence of the average sensitivity coefficients for the analyzed components relative to each standard substance or additive on the number of carbon atoms in the molecules standard substances or additives, and the desired concentrations of the components determine interpolation of the estimated concentration values relative to the selected corresponding pair of neighboring standard substances or additives to the value of the average correction factor equal to one.

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