SU1122965A1 - Method of chromatographic analysis of substance mixtures and device for application thereof - Google Patents

Abstract

1. A method of chromatographic analysis of mixtures of substances using an L / W-FM capillary column, in which a sample is periodically introduced into the loop of the mobile phase, and the separated components of the mixture are detected at the outlet of the column, characterized in that , in order to reduce the cost of carrying out chromatographic analysis, as well as expanding the range of analyzed multicomponent mixtures by providing the ability to adjust the selectivity and separation capacity of the column during the chromatographic th analysis, as the chromatographic column using the empty capillary tube, in which S is carried out continuously feeding the liquid vapor nokY output vapor therefrom, and the tube wall temperature is maintained at a temperature close to the condensation of liquid vapors. }

Description

, 2, The method of Claim 1, distinguished by the fact that liquid vapors introduced into a capillary tube, or a mixture of them with an inert carrier gas, are used as the mobile phase.,

3. Method pp. 1 and 2, characterized in that the composition of the liquid, the vapors of which are supplied to the capillary tube, is changed during the separation of the components of the analyzed mixture.

4. A method according to claims 1 to 3, characterized in that a sample of the analyzed mixture is introduced into the liquid stream before it is evaporated and vapor is introduced into the column.

5. A device for chromatographic analysis of mixtures of substances containing a source of carrier gas, a device for introducing a sample of the analyzed mixture, an evaporator, a capillary chromatographic column in the form of an empty capillary tube (the INPUT of which is connected to an evaporator; a thermostat in which

a chromatographic column, and a detector connected to the output of the chromatographic column, characterized in that, in order to expand the range of analyzed multicomponent mixtures by providing the ability to control the selectivity and separation capacity of the column during chromatographic analysis, a capacitance filled with liquid and connected are introduced into it with an evaporator a channel for supplying liquid, and a device for regulating the supply of liquid from said container to the evaporator.

6. The device according to claim 1, which is designed so that the device for introducing the sample of the analyzed mixture is installed in the channel for supplying the liquid to the evaporator.

/. The device according to PP.5 and 6.0 t of l is that the evaporator is equipped with an ejector installed inside the evaporator housing and connected to a source of carrier gas and a container with a liquid phase.

one

The invention relates to analytical instrumentation, in particular to capillary gas chromatography, and is intended for the analysis of multicomponent mixtures of substances.

A known method for chromatographic analysis of mixtures of substances using a nozzle-type chromatographic column in which the analyzed mixture is injected with a stream of a mobile phase into a chromatographic column filled with sorbent particles, and the mixture components separated in the column are detected at its output. As a mobile phase, which serves to transfer substances to the sorbent layer, use pairs of some lx substances, in particular water.

A device for carrying out the described method includes a steam generator, a device for introducing samples of the analyzed mixture into the steam stream fed to the chromatographic column. The chromatographic column thermostat and detector are installed at the column outlet. The use of vapor vapors as a mobile phase instead of the commonly used carrier gases (Hj ,, N / HeiH et al.) In many cases leads to an increase in the efficiency of chromatographic separation. This is due to a decrease in the values of diffusion coefficients.

analytes in the mobile phase l.,

However, to change the selectivity of the X1X mathematics separation in the known method and device for replacing it with the analysis of a new mixture of substances, replacement of the sorbent used in the column is usually required. it

0. Be sure to disconnect the device, remove the thermostat cover, disconnect the column from the evaporator and detector, and refill the column or. replacing it with a new one. Operations

since replacing the column, great care is required, especially when working with glass and columns, and it is associated with the significant time required for co-dosing a new column, putting the chromatograph to the mode and p. In addition, the columns have a limited separation capacity, since an increase in their length, which is necessary to improve the separation capacity, leads to an increase in the pressure drop across the column.

The closest to the invention is a method for chromatographic analysis of mixtures of substances using a capillary column, in which a sample of the analyzed mixture is periodically introduced into the column in the flow of the mobile phase and the mixture components separated in the column are detected at the outlet of the column. Moreover, on the inner surface of the capillary column a LAYER of the liquid phase is applied. A device for carrying out a known method comprises a source of carrier gas, a device for injecting a sample of the analyzed mixture, an evaporator, a capillary chromatographic column, the inlet of which is connected to an evaporator, a thermostat in which the chromatographic column is installed, and a detector connected to the output of the chromatographic column 2. A disadvantage of the known method and device for its implementation is that the change in the selectivity of the chromatographic separation is required when switching to the analysis of a mixture of substances of a new class, coupled with the replacement of the column. In practice, this means that in order to be able to analyze a wide range of substances, the chromatograph must be equipped with several capillary chromatographic columns filled with different phases. Buying ready-made speakers abroad is extremely expensive. The self-fabrication of columns requires the use of special expensive equipment and the high qualification of the employee engaged in the manufacture of such columns. The purpose of the invention is to reduce the cost of carrying out chromatographic analysis, as well as expanding the range of analyzed multicomponent measurements by making it possible to control the selectivity and separation capacity of a column during the chromatographic analysis. This goal is achieved by the fact that according to the method of chromatographic analysis of mixtures of substances using capillaries column, in which the column is periodically injected into the flow of the mobile phase sample of the analyzed mixture, and the separated components of the mixture are The flow from the column is measured, and as a chromatographic column using an empty capillary tube into which the liquid vapor is continuously supplied and the vapor is removed from it and the temperature of the tube walls is maintained close to or equal to the condensation temperature of the liquid vapor so that some of the vapor condenses in the tube forming a liquid phase film that moves from the inlet to the outlet of the column. liquid vapors introduced into the capillary tube or a mixture of them with an inertia carrier gas are used as the mobile phase. The composition of the liquid, the vapor of which is fed into the capillary tube, is changed during the separation of the components of the analyzed mixture. A sample of the analyzed mixture is introduced into the liquid stream before it evaporates and injects vapor into the column. Into a device for chromatographic analysis of mixtures of substances containing a source of carrier gas, a device for injecting a sample of the analyzed mixture, an evaporator, a capillary chromatographic column in the form of an empty capillary tube, the inlet of which is connected to an evaporator, a thermostat in which the chromatographic column is installed, and a detector connected to the outlet of the chromatographic column, a container filled with liquid and connected to the evaporator by a liquid feed channel and a device for adjustable feeding of liquid are introduced bones from said capacitance in the Spanish. the ritor. A device for introducing samples of the analyzed mixture is installed in the channel for feeding the liquid phase to the evaporator. An ejector is installed in the evaporator housing for spraying the liquid phase, which is connected to a source of carrier gas and a tank with a liquid phase. This ensures the expansion of the range of analyzed multicomponent mixtures. As the working fluid in the proposed method is used. highly volatile liquids, such as voda, hexane, ormamid, etc., with one substance (working fluid) being used to form two phases — a liquid phase on the walls of the capillary and a vapor or vapor-gas in the center of the capillary. This not only simplifies the process of chromatography, but also allows for the injection of the analyzed mixture into milder temperature conditions, preventing the thermal decomposition of the sample substances. Due to the noted features of the method, streams of two phase-vapor or vapor-gas phases moving in the center of the column at a linear velocity of 10-20 cm / s and condensed from a vapor of a liquid phase moving in the form of a liquid film along the capillary walls are formed in the empty capillary tube. rnuy tube. The linear velocity of the film of the liquid phase is significantly less (ОO-100 times) the linear velocity of the vapor or vapor-gas phase. Separation of the mixture components is achieved as in any chromatographic separation method due to the difference in the distribution coefficients of the substances in the phases indicated. At the same time, the selectivity and separation capacity of such a column can be varied during chromatographic separation over a wide range by changing the composition of the vapor and, consequently, the liquid phases, changing the thickness of the liquid phase film by, for example, changing the temperature of the tube walls, adjusting the flow of the carrier gas, etc. FIG. shows a schematic diagram of the device for carrying out the proposed method; in fig. the same with dividing the flow of gas-carrying bodies in front of the evaporator; Fig. A vaporizer with an ejector for spraying a liquid phase in a carrier gas stream; Figures 4 and 5 show chromatograms of separation of a mixture of hydrocarbons A device for carrying out the inventive method contains an evaporator 1, the output of which is connected to a capillary chromatographic column 2, which is an empty capillary tube, such as stainless steel, fused glass, quartz, etc., installed in a thermostat 3, the output of which is connected to the detector 4, for example, flame ionization. The evaporator 1 has two entrances, one of which is connected to the channel 5 for supplying the liquid phase from the tank. 6, the latter is partially filled with a liquid phase, for example water, and provided with a channel 7 for supplying a carrier gas. The regulation of the flow rate of the liquid phase from the tank 6 to the evaporator i is accomplished by controlling the pressure of the carrier gas at the inlet to the tank 6. In channel 5 for supplying the liquid phase to the corrector 1, a device 8 is installed to introduce the sample of the analyzed mixture into the liquid phase stream. As such a device, a rotary-type metering valve or a flow cell with a sealing gasket, a syringe needle and others can be used. The second input of the evaporator is connected to the channel 9 for supplying the carrier gas, in which the pressure regulator 10 is installed. The outlet of the evaporator i is also connected to the channel 11 for discharge of the excess vapor-gas mixture, in which an adjustable choke is installed. The device (the described embodiment) works as follows. The liquid phase, for example distilled water, used to form a film of the liquid phase on the inner surface of the capillary column 2, is poured into a container 6 connected by a channel 7 with a source of compressed gas (not shown) .. Before performing the chromatographic analysis, the channel 9 is fed to the evaporator 1 a controlled flow of carrier gas, which after the evaporator 1 is divided into two parts. One part of the carrier gas (smaller) enters the capillary column 2 and from its exit into the detector 4. Most of the flow through the channel 11 through the adjustable choke 12 is discharged into the atmosphere. Using the thermostat 3, the temperature of the wall of the capillary column 2 is maintained at or slightly below (on) the condensation temperature of the vapor phase liquid filling the tank 6. After the specified flow rate of the carrier gas through the column 2 and the set temperature in the thermostat 3 has been established, indicates a stable zero line of the detector 4, in the evaporator 1 begin to carry out a controlled flow of the liquid phase. For this purpose, an inert gas is fed to the inlet of the vessel b through the channel 7, under a permanently controlled branch, as which the gas carrier can be used from the same source as the carrier gas supplied to the evaporator 1. The container 6 is equipped with a graduated scale that allows controlling the flow of the liquid phase. Pac-.i; the course of the liquid phase in the proposed method is 10 - 10 µl / min. In the evaporator 1, continuous evaporation of the liquid phase takes place, and the Vapor mixture is mixed with the carrier gas into two parts. One part of the vapor-gas mixture flow (0.5-2 ml / min) enters the capillary column 2, and the other is discharged through the channel 11 through an adjustable choke to the atmosphere. Before discharge of the vapor – gas stream into the atmosphere, vapors of the liquid phase can be condensed in a condenser (not shown). The passage inside the capillary column 1 of the liquid phase vapor is partially condensed on the walls of the column, forming a thin (1-5 micron) film of the liquid phase. After some time from the moment the capillary column 1 is purged with vapor of the liquid phase in column 1, an equilibrium is established, characterized by the fact that how much liquid vapor is injected with the flow of carrier gas into column 1, so much is removed from it. After reaching such a dynamic equilibrium, as can be judged by the signal constancy of the detector 4, a metered amount of liquid analyte mixture is directly injected into the liquid phase stream before the evaporator 1 using the sample injecting device 8. The sample along with the liquid phase flow into the evaporator 1, the sample of the analyzed mixture evaporates and, together with the liquid phase flow, picked up by the carrier gas flow, enters the inlet of the capillary column 2. In this case, the sample is divided into two parts in proportion to the flow KctM in column 2 and discharged through channel 11, and a smaller part of the sample (initial quantity) enters column 1 in the gas-vapor mixture stream. In column 2, a conventional chromatographic separation process occurs associated with the redistribution of the substances to be separated between the liquid. (relatively stationary) and mobile vapor-gas phases and due to differences in the distribution coefficients of the mixture components. The separated components at the outlet of the column 2 are detected with the aid of the detector 4. When using a flame ionization detector as a substance, the liquid phase is necessary. apply substances to which the detector does not exhibit sensitivity. Water, formamide, carbon disulfide, etc. can serve as such vets. The device embodiment (Fig. 2) differs from that described in that the discharge of most of the carrier gas flow through channel 11 takes place before evaporator 1, and not after it. In this case, the whole substance, having been introduced into the flow of the liquid phase, enters the column. This option is also characterized by a note that a part of the carrier gas stream discharged into the atmosphere is used as charge gas in the detector 4 and an additional adjustable throttle 13 is inserted into the circuit. Fig. 3 shows one of the structures of the evaporator 1, which can be used in the proposed device. It is made on the basis of standard evaporation for gas chromatography. The evaporator 1 contains a cylindrical case 14 provided with an external heating device 15. Inside the case 14 along its axis a liquid capillary leakage cap 16 is installed, connected by a channel 5 for supplying the liquid phase. The capillary leak collector 16 is sealed to a disk 17, which is placed on an annular sealing gasket 18 lying on the end of the body 4. A nut 19 is screwed on the head body 14, which presses the disk 17 and the ring. The sealing gasket 18 to the end of the body 14, sealing the evaporator chamber 1. Inside the body 14 A tubular insert 20 encompasses a capillary leak of 1b and is {fixed in the body 14 on its opposite end, using a sealing element 21 and a cap nut 22. The tubular insert 20 has holes 23 located at the end of the accumulator 16 through which the insertion channel 20 receives a flow of carrier gas supplied to the body 14 of the evaporator 1 via channel 9. At the opposite end of the supply gas carrier and liquid phase of the end of the tubular insert 20, the end of the capillary column 2 and channel 11 are introduced to reset most of rogazovogo stream. The point of entry of these channels into the tubular insert 20 is sealed with a sealing element 24 and a flare nut 25. The dimensions of the tubular insert 20, the drip 16 and the arrangement of the holes 23 are chosen in such a way that, at flow rates of carrier gas of 100-150 ml / min, they work as an ejector, in which the liquid phase is sprayed with its instantaneous evaporation. The resulting liquid phase vapors, under haechene flow of carrier gas, are removed from the tubular insert 20 through two channels, the channel of the capillary column 2 and channel 11. Example p 1. To confirm the basic feasibility of the proposed method n devices, chromatograms of separation of a complex mixture of hydrocarbons were obtained C24 on an empty capillary column, shown in Figures 4 and 5. The separation of components was carried out on a column, which was a capillary of fused quartz with an external heat-resistant polymeric coating, having y m and an inner diameter of 23 mm. A crystal chromatograph 5002 was used to analyze the mixture. It was equipped with a sample inlet system in a capillary column, including an evaporator 1 and a flow divider mounted at its outlet, connected to a flexible capillary quartz column 2 and a carrier gas discharge channel 11. Flame-ionization was used as detector 4, and nitrogen was used as carrier gas. At the initial moment, before introducing the sample into the evaporator, the following conditions were established: the flow rate of the carrier gas through the column was 0.2 ml / min, the division ratio

in the column 1/500, the temperature of the evaporator and, detector, and the temperature at the column temperature T (; s: 30 ° C. After entering the sample into the evaporator (1 m of the C 24 mixture was introduced using a gas syringe Gasogrom 101), the initial temperature of the column was kept 2 minutes, then the temperature of the column was sharply raised at a speed of 45s, minutes to, at which isothermal aging was again made for 2 minutes.

The resulting xpOMaTorpaNwe (FIG. 4) shows a clear separation of all light components from C to C and blurred peaks of heavy components. This means that a capillary column is empty, which does not have a liquid phase layer on the inner walls, works in a purely adsorption version and is capable of separating the Multicomponent mixture of the indicated composition in one step.

 To ensure the separation of all the components of the mixture in one step on the same capillary column, the initial mixture was diluted with respect to

1k 100 by decane, which was introduced into the mixture in an excess amount to form a liquid phase layer on the walls of the column. The separation of the mixture was carried out under the following conditions: temperature of the evaporator and detector,; carrier gas flow rate: at the initial time of 0.2 ml / min through the capillary column, dividing coefficient of the flow at the evaporator outlet 1/500. After entering the sample, diluted with dean, the column temperature was kept for

2min, then increased with speed

V, 45 ° C / min to T (temperament; N-decane boiling point 174 C), which was kept for 1 min again, raised the column temperature at a rate of V 15 ° C / MIN to 200 ° C and made isothermal exposure for 4 min

The obtained chromatogram (Fig. 5) clearly shows the peaks of all components of the analyzed mixture from Cg to C24. In this case, the light components Сfe-C, о are separated due to the difference in absorption coefficient on the inner surface of the quartz capillary. The heavy components Cn - € 14 are separated in the mode of distribution chromatography using the film partially condensed on the walls of the capillary as the liquid phase.

Thus, in the proposed method and device for its implementation by introducing vapor into the capillary in a vein phase and maintaining the temperature of the capillary at the value

close to or equal to the condensation temperature of the vapors of the liquid phase, the formation of a layer of the liquid phase on the inner surface of the capillary capstan is ensured directly during the chromatographic analysis of this particular mixture. After the completion of the analysis process, the flow of the liquid phase to the column to the layer of the liquid phase is blown out of the column by a carrier gas stream. When analyzing a new mixture, a new, volatile liquid phase corresponding in polarity is selected, which is deposited onto the walls of the capillary described. method, carried out the separation of the new mixture.

This makes the capillary gas chromatograph versatile, i.e. the same empty capillary column of sufficient length can be used to separate different classes of chemical compounds. Accordingly, this leads to a reduction in the preparation time of the chromatograph for analyzing a particular mixture by eliminating the need for preparing a new capillary column, reducing the cost of the gas chromatograph, since there is no need to have the chromatograph complete with several capillary columns filled with different phases.

In addition, the use of a volatile liquid phase should theoretically contribute to the effectiveness of a capillary chromatographic column. A height equivalent to a theoretical plate (WETT) of a capillary chromatographic column can be expressed with the sp: the equation

four

2Da k K

TG (IR) 2

H is the value of WATT;

and is the linear velocity of the mobile phase; K - coefficient of relative

the distribution of the substance between the liquid and gas phases;

 the diffusion coefficient of the substance in the gas phase; D is the diffusion coefficient of the substance in the liquid phase; DJ. - Capillary diameter (internal);

d is the thickness of the liquid phase layer on the inner walls of the capillary.

In this case, the main contribution to VETT is the third term of equation (1). use of volatile liquids a, N, hexane, etc., as a liquid phase;

The diffusion coefficient of a substance in the liquid phase (D) increases noticeably and by choosing the temperature of the capillary walls, the thickness of the liquid layer (d) can be significantly reduced, which leads to a decrease in the HETP value and, consequently, to an increase in the separation efficiency.

In the proposed method, it is possible to program the composition of the liquid phase in the analysis process using those techniques that are currently used in liquid chromatography, which provides an increase in the selectivity of the chromatographic separation.

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The use of a volatile liquid introduced as a vapor into the column as a liquid phase eliminates the thermal decomposition of the analyzed substances in the chromatograph evaporator and increases the reliability of the chromatographic analysis.

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In addition, the proposed method provides higher reliability of operation of a capillary chromatograph, since defects such as column failure due to entrainment of the liquid phase, contamination of the detector with low-volatile substances of the detector, breakage of the column during its dismantling, etc. are eliminated.

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Claims (6)

1. The method of chromatographic analysis of mixtures of substances using a capillary column, in which my mixture is periodically introduced into the column in a flow of the mobile phase, and the separated components of the mixture are detected at the outlet of the column, characterized in that, in order to reduce costs by carrying out chromatographic analysis, as well as expanding the range of analyzed multicomponent mixtures by providing the ability to control the selectivity and separation ability of the column in the process of chromatographic analysis, as an chromatographic column, an empty capillary tube is used, into which a continuous supply of liquid vapor and j vapor withdrawal from it are carried out, and the temperature of the tube walls is maintained close to the liquid vapor condensation temperature. figure 1. 2. The method according to claim 1, distinguish join and th with the fact that as a mobile phase, liquid vapors introduced into the capillary tube, or a mixture of them with an inert carrier gas, are used. , 3. The method of paragraphs. 1 and 2, which is due to the fact that the composition of the liquid, the vapor of which is supplied to the capillary tube, is changed during the separation of the components of the analyzed mixture. 4. The method according to claims 1 to 3, characterized in that the sample of the analyzed mixture is introduced into the liquid stream before it evaporates and vapor is introduced into the column. 5. A device for chromatographic analysis of mixtures of substances, containing a source of carrier gas, a device for introducing samples of the analyzed mixture, an evaporator, a capillary chromatographic column in the form of an empty capillary tube (the inlet of which is connected to the evaporator, a thermostat in which the chromatographic column is installed, and detectors ^: 'torus connected to the chromium output of a toga-, raffic column, characterized in that, in order to expand the range of analyzed multicomponent mixtures by providing the ability to control select In the course of chromatographic analysis, the column is filled with liquid and connected to the evaporator with a channel for supplying liquid, and a device for regulating the supply of liquid from the specified container to the evaporator. 6. The device according to claim 1, with the fact that the device for introducing samples of the analyzed mixture is installed in the channel for supplying liquid to the evaporator. 1 · The device according to claims 5 and b, characterized in that the evaporator is equipped with an ejector installed inside the body of the evaporator and connected to a source of carrier gas and a container with a liquid phase.