Method gas chromatographic determination of the constants of distribution and device for its implementation

 

Usage: the invention relates to gas chromatography and can be used to determine the constants distribution and other physico-chemical variables, such as Henry's constants of volatile substances in the study of sorption equilibria in the system non-volatile liquid - gas. The inventive method consists in dividing the investigated substances in the evaporator chromatograph and the transfer of their vapors flow of carrier gas into the chromatographic column for separation and subsequent detection, the definition of the given retention time of the compounds under investigation and the total retention time nesorbiruyushchegosya substances from which exclude the time of passing through vneconomy volumes. The total retention time nesorbiruyushchegosya substance is measured from the moment of registration of the maximum peak of the sample, after passing the evaporator through the bypass line bypassing the chromatographic column. Additionally take into account the time from the start of registration detector front zone nesorbiruyushchegosya substances prior to registration of the maximum concentration. A device for implementing the method comprises a source of carrier gas, the evaporator, the chromatographic column and the bypass line and the detector, and the entrance is Elam and detector. Moreover, the bypass line is made in the form of a capillary tube of small cross section and includes at the input of the pneumatic resistance, and the tee at the outlet of the chromatographic column and the bypass line is connected to the detector by a capillary tube of small cross section, summed close to the sensitive element. The technical result of the invention is to improve the accuracy of determination of the distribution constants of KWith. 2 S. p. f-crystals, 2 tab., 1 Il.

The invention relates to gas chromatography and can be used to determine the constants distribution and other physico-chemical variables, for example, Henry's constants of volatile substances in the study of sorption equilibrium in the system non-volatile liquid - gas.

There are various ways chromatographic determination of constants of distribution under which the test substance is metered into the chromatographic column for separation and subsequent detection, and then determine the distribution constant on the basis of factor retention without the use value of flow rate of carrier gas, and various devices for their implementation, containing the source of the carrier gas chromatographic column, a detector and an input node of the PDF of the substances. M.: Nauka, 1970. C. 17].

However, the known methods and devices do not provide sufficient accuracy chromatographic determination of the constants of the distribution, as it does not take into account permanent and effective components uncolonized volume, making a significant systematic error in the measurements.

The closest to the invention by the combination of essential features is the way gas chromatographic determination of the constants of distribution, in which the analyte is metered into the evaporator chromatograph and translate them pair by the flow of carrier gas into the chromatographic column for separation and subsequent detection, and the distribution constant Kcis calculated, bypassing the stage of determining the flow rate of carrier gas using the values of the given retention time of the analyte to the total retention time nesorbiruyushchegosya component, from which subtract the time corresponding to the passage of the breakdown of the volume of the evaporator, the detector and the communication between them and the column [Pure Appl. Chem., 2001, Vol. 73, No. 6, pp.969-992].

The closest to the invention by the combination of essential features is a device for normalizing the pas, bypassing the separation column directly in the detector. When this occurs, a signal corresponding to the total number of shared components. The remainder of the sample is separated by passing through a chromatographic column, and the individual components of the mixture signal, for which the first signal corresponds to the relative amount of each component in the mixture [Clardy E. K., Ayers C. O. Chromatographic analysis normalizer. Pat. U.S. CL 73/23, 1 (01 No. 31/08), No. 4215563, Appl. 15.06.76 No. 705486, publ. 5.08.80].

The disadvantage of this method is the low accuracy of determination of the constants of the distribution due to disregarding effective components uneconomic volumes.

A disadvantage of the known device used to determine the distribution constants of KCis that the passage of a break of the bypass line takes time, resulting at the time of registration total peak sample can be in a column or in some area of the connecting tubing between the column and the bypass line, which increases the error in determining retention time.

The objective of the invention is to improve the accuracy of determining the distribution constants of KC.

This task of resew dosing of the investigated substances in the evaporator chromatograph and the transfer of their vapors flow of carrier gas into the chromatographic column for separation and subsequent detection, define lists the retention times of the substances under study and the total retention time nesorbiruyushchegosya substances from which exclude the time of passing through vneconomy volumes, and the total retention time nesorbiruyushchegosya substance is measured from the moment of registration the maximum detector peak part of the sample, after passing the evaporator through the bypass line bypassing the chromatographic column, and additionally take into account the time from the start of registration detector front zone nesorbiruyushchegosya substances prior to registration of the maximum concentration.

This problem can be solved also due to the fact that the device for gas chromatographic determination of the constants of the distribution contains the source for the carrier gas, the evaporator, the chromatographic column and the bypass line and the detector, and the entrance and exit of the chromatographic column and the bypass line with tees are connected respectively with the evaporator and the detector, and the bypass line is made in the form of a capillary tube of small cross section and includes at the input of the pneumatic resistance, and the tee at the outlet of the chromatographic column and the bypass line is connected to the detector by a capillary tube of small cross section, summed close to the sensitive element.

the bookmark constant distribution taking into account the effective components uncolonized volume, including the amount of carrier gas emerging from the column during the time from the start of registration zone nesorbiruyushchegosya substances prior to registration of the maximum concentration, and the internal volume of the evaporator when it is eliminated through the bypass line.

This allows us to conclude that the claimed invention are connected by a single inventive concept.

A specific example of the method and the device for its implementation.

The figure schematically shows a device for gas chromatographic determination of the constants of the distribution. The device comprises: a source of carrier gas 1, which feeds the carrier gas (nitrogen) for chromatographic separation; an evaporator 2 for evaporating liquid samples; a connecting line 3 between the evaporator and the tee 4; a connecting line 5 between the tee 4 and chromatographic column 6; a connecting line 7 between the chromatographic column 6 and tee 8; flame ionization detector 9; a bypass line 10, is made in the form of a capillary tube of small cross section and containing on input the pneumatic resistance 11, and the output of the tee 8, which on the one hand connected to the detector 9 a capillary tube of small cross section 12 connected closely to Chu the effect of carrier gas inlet of the chromatographic column 6.

The device operates as follows.

The sample is introduced into the evaporator 2 chromatograph, is converted into steam and the flow of carrier gas is transferred through the connecting line 3, the tee 4 and the connector 5 in the chromatographic column 6. Separated in the column of components in a mixture with a carrier gas recorded a flame ionization detector 9 in the form of chromatographic peaks. Part of the entered sample after the connecting line 3 is transferred by the flow of carrier gas through the tee 4 and the bypass line 10 to the nozzle of the flame ionization detector 9 and is recorded in the form of a total maximum of all the sample components on the chromatogram before the peaks of the sample components separated by the column. The retention times of the components of the mixture when it is measured from the moment of occurrence of the maximum total peak.

The length of the bypass line 10 together with the capillary tube of small cross section 12 selects no more than 25 cm in internal diameter of 0.025 see Time passing breakdown of the volume of the bypass line and the capillary 12 is determined by the equation

where- the volume of the bypass line and the capillary 12; l and d are length and diameter of the capillary;- the speed of the carrier gas in bide src="https://img.russianpatents.com/chr/931.gif">- speed carrier gas at a pressure Piinlet tee 4.

Table 1 shows the results of the determination of the confidence interval measure time passing breakdown bypass line 10 and the capillary 12, ttotal.

As can be seen from the data in table 1, the time breakdown of the volume of the bypass line 10 and the capillary 12B. to.less confidence limitsttotal. Given that the velocity of the carrier gas into the capillary 12 more speed F1in the bypass line 10 by adding the basic flow of carrier gas from the column 6 through t-joint 8, the real time tB. to.will be much less than 0,08 C.

Install pnevmoobrushenija 11 input bypass line 10 enables the reduction of gas pressure in the bypass line and, consequently, increasing its flow rate, which also contributes to reduction of size tB. to..

So we can assume that in the beginning of the time holding the main part of the sample is branching line 3 to the bypass line 10 and the connector 5. Thus, from measurements excluded the internal volume of the evaporator, depending on temperative value.

The internal volume of the camera detector is excluded from the measurement by placing the capillary 12, going from the tee 8 in the cavity of the detector close to the nozzle.

To improve the accuracy of determining the constants of the distribution is measured additionally check detector front of the chromatographic strip nesorbiruyushchegosya substances corresponding to the volume of carrier gas emerging from the column during the time from the start of registration zone nesorbiruyushchegosya substances prior to registration of the maximum concentration t1/2.

Subtract this time from the total retention time nesorbiruyushchegosya matter, as well as the consideration of the effective value of the internal volume of the evaporator eliminates the systematic error present in the experiment and not accounted for in the known methods and devices for gas chromatographic determination of the constants of the distribution.

Experimental evaluation of the proposed and known methods gas chromatographic determination of the constants of the distribution was carried out on the example of a combined analysis of four substances: nesorbiruyushchegosya substance propane and solutes n-heptane, benzene and butanol-1 at column temperature Twith=354,2 To filled with 20 wt.% three

For the studied substances was calculated distribution constant knownand offerways, and to compare the distribution constant of the solutesusing specific volume retention by the following equations:

where VTg- held specific volume of sorbate;- the retention time of the sorbate;- the volumetric rate of the carrier gas with an average column pressure P and the column temperature TC; WL- the mass of the stationary liquid phase in the column;Lthe stationary density of the liquid phase at a temperature of column TC; tgMthe total retention time nesorbiruyushchegosya substances; text- time of the breakdown of the volume of the evaporator, the detector and the communication between them and the column; VM- gas volume of the column; VL- fixed volume of the liquid phase in the column at the temperature TC; tg*M- retention time nesorbiruyushchegosya substances semerenkoukrainka strip nesorbiruyushchegosya substances; V*- total gas volume of the column and uneconomic communications, excluding the volume of the evaporator.

The derivation of the equation for calculating KIIICincludes the following conversions.

The expression for time of flight rezorbiruetsa substance of the gas volume of the column can be written as follows:

The time rezorbiruetsa substance of the gas volume of the column and the connection lines 5 and 7 with respect to time the front Desk of the chromatographic strip nesorbiruyushchegosya substance is defined by the equation

Expressing equation (**) the value ofand substituting it into equation (*), we obtain

The total gas volume of the column and uneconomic communications is calculated by the formula

where V1- the volume of the connecting line 5; V2- the volume of the connecting line 7; pa- atmospheric pressure (the pressure at the outlet of the column); pi- the pressure at the inlet to the column;- coefficient James - Martin (factor correction for the compressibility of the gas phase).

About the speriment are summarized in table 2 Comparative data experimental verification of known and proposed methods".

As can be seen from the table, the proposed method provides a significant improvement of the accuracy of gas chromatographic determination of the constants of the distribution compared with the known method. Systematic measurement error is reduced from 13.9 to 3.0%.

the relative deviation constant distribution determined in a known manner, from constants, calculated from the specific volume retention, %;

the relative deviation of the distribution constants of, certain of the proposed method, constants, calculated from the specific volume retention, %.

Using the proposed method and device to improve accuracy, gas chromatographic determination of constants distribution without measuring the flow rate of carrier gas, by excluding from the measurement of the effective internal volume of the evaporator, the internal volume of the detector, taking into account the time registered by the detector front of the chromatographic strip nesorbiruyushchegosya substances and other components uneconomic volumes.

Claims

1. The way ha is Ariel chromatograph and translate them pair by the flow of carrier gas into the chromatographic column for separation and subsequent detection, define lists the retention times of the substances under study and the total retention time nesorbiruyushchegosya substances from which exclude the time of passing through vneconomy volumes, characterized in that the total retention time nesorbiruyushchegosya substance is measured from the moment of registration of the maximum peak of the sample, after passing the evaporator through the bypass line bypassing the chromatographic column, and additionally take into account the time from the start of registration detector front zone nesorbiruyushchegosya substances prior to registration of the maximum concentration.

2. Device for gas chromatographic determination of the constants of the distribution contains the source for the carrier gas, the evaporator, the chromatographic column and the bypass line and the detector, and the input and output of the chromatographic column and the bypass line with tees are connected respectively with the evaporator and the detector, characterized in that the bypass line is made in the form of a capillary tube of small cross section and includes at the input of the pneumatic resistance, and the tee at the outlet of the chromatographic column and the bypass line is connected to the detector by a capillary tube of small cross section, summed close to the sensitive element.

 

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