SU832468A1 - Device for introducing samples into liquid chromatograph - Google Patents

Description

The invention relates to chromatography, namely to devices for introducing samples of analytes, a capillary column of a liquid chromatograph, and can be used in the operation of standard liquid chromatographic instruments with capillary columns. To increase the efficiency of operation, it is desirable to introduce a sample without stopping the flow of solvent, since in the event of a stop, a certain time is required to restore the steady state in the column, therefore it can be difficult to determine the retention time, and it is possible to change the volume of the sample, which varies in analytical chromatography liquid within 5–20 µm, and in the case of capillary columns, within 1–5 µl} the device should have high reproducibility; the volume of connecting tubes between the device and the column, as well as the volumes of the connecting channels in the device should be minimal. A device is known for introducing: samples into a column containing a microsyringe or a metering valve. The microsyringe is used at pressures not higher than 20 atm. using polymer partitions when introducing self-driving givagacies. 1. At higher pressures, microsyringes Use, generally, cdc to stop the flow, which is highly undesirable, moreover, when working with a microsyringe under such conditions, it is difficult to achieve reproducibility of the input volumes. Significantly more convenient in this are the slatting and surface dosing cranes. The sample fills a hole in the valve stem, the volume of which is precisely known, after which the rod is remade (in sliding type valves) or rotated (in turning type valves) to a position from which the sample is displaced by the standard into the column. Sample injection using metering cranes is performed with sufficient reproducibility without stopping the flow and can be easily automated. However, in the manufacture of dosing cranes, extremely careful grinding of sliding surfaces is necessary, which leads to the high cost of such installations. When working with samples that are prone to the formation of precipitation, the taps quickly collapse as a result of solid particles between the rubbing surfaces. Sliding surfaces are also very sensitive to corrosion. In addition, with the help of crane dozers, only samples with a fixed volume can be introduced. It is also known a device for introducing samples into a liquid chromatograph of samples consisting of a housing, metering channels in it and a flow switching system. The valves of the system can be in two positions: the introduction of the sample into the dosing unit and the introduction of the sample into the chromatographic column. In the first position, the two valves close the metering channels and the solvent is injected into the column through a bypass. At this moment, a dosed sample volume is injected into the channel with a microsyringe. The solvent filled channel is forced out through a specially provided slot and an open third tap to the outside. In the second position, the first two cranes are opened and the third is closed. The solvent, the passage through the metering channel and the helix, captures the sample in the channel and transfers it to the column. A special stopper 2 is screwed in instead of a syringe. In a known system, injection of samples is performed without stopping the flow, the volume of the sample can be adjusted. .However, when working with capillary columns, before entering the chromotographic column, the sample is analyzed using a microspot. is introduced into the channel, having a substantially larger volume than the volume of the sample being analyzed, which leads to a decrease in the concentration of the analyte, an increase in the volume of the sample introduced into the column, and, consequently, to an expansion of the peaks of the analyzed samples on the chromatogram. as a result, the sensitivity inevitably decreases and the separation efficiency deteriorates. When the syringe is removed from the system and the tube is screwed in its place, there is a danger of getting into the column and further into the air bubble detector, which impairs the detector's operation and reduces the reproducibility of the injection. In addition, the need to work with the syringe eliminates the possibility of automation of the input. The valves used in the system are sensitive to precipitation and corrosion and are not reliable enough at high pressures. The slightest leakage of valves leads to sample loss and deterioration of the reproducibility of chromatograms. The purpose of the invention is to increase the reliability and reproducibility of dosing. This goal is achieved by the fact that in the proposed device for introducing samples into a liquid chromatograph comprising a housing, metering channels made in the housing and a flow switching system in which, according to the invention, the flow switching system is made in the form of a polymeric membrane covering the inlets and outlets of the channels recesses of the housing and provided with movable rods installed in the openings of the housing opposite the recesses, and the metering channel is equipped with a device for changing its working volume; filled in the form of a calibrated metal wire with a micrometer screw for moving it in the channel. FIG. 1 shows the proposed device in section; in fig. 2 view of the device in the plan. The device has a metal body 1, on the surface of which five spherical recesses 2-6 are made. A through channel 7 is drilled in the housing, intersecting the recesses 2 and 3, the through channel 8, intersecting the recesses 4 and 5, the channel 9 connecting the channels 7. and 8 and crossing the recess b, and the channel 10 connecting the channels 7 and 8 and derived on the end of the case. The through channel 7 forms holes 11 and 12 on the side panels of the case, which are then used to attach the column and remove the analyte, respectively. The through channel B forms at the lateral ends of the casing holes 13 and 14, which are then used to enter the mobile phase and the analyte, respectively. In channel 10 there is a calibrated wire 15, which can be moved through the channel with a micrometer screw. An elastic membrane 16 made of a polymeric material, for example polyethylene, is superimposed on the surface of the housing 1 by means of bolts with a metal plate 17 with holes above depressions 2-6, into which metal rods 18 are inserted. The device operates as follows. The rods 18 of the system can be in two positions: the sample is introduced into the metering device (A) and the sample is introduced into the column in position A and the rods are lowered over holes 2 and 5; . The mobile phase enters the device through the opening 11, passes through the channel 9 used as a bypass line (the rod above the opening 6 is raised), and through the opening 13 enters the chromatographic column. At this moment, the analyte is pumped through the opening 12 into the metering channel 10 an excess amount of the analyte leaves through the channel 8 through the opening 14 (the stem above the openings 3 and 4 is raised). Volume, doses of the correct channel, and, respectively. In this case, the volume of the injected sample is determined by the position of the calibrated wire in the metering channel and when the wire is completely removed from the channel, it is maximum, and when fully inserted, it is minimal.

In position B, the stems above the holes 3, 4 and b are lowered, above the holes 2 and 5 they raise. The mobile phase moves along the metering channel 10, expelling the analyte from it through the opening 13 into the chromatographic column. After that, the rods above the holes 2 and 5 are lowered, the rod above the hole 6 is lifted and during the entire analysis the mobile phase enters the column through the bypass channel 9.

The proposed device provides high reliability and convenience in operation with good reproducibility and minimal losses with separation efficiency and sensitivity.

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Claims (2)

1. US patent number 4022065, class. 73-422, 1977. 2.Lugovik B.A. High pressure liquid chromatography. Tomsk. 1976, p. 83-85 (prototype); IS 18 n