SU1444659A1 - Photoionization detector for capillar gas chromatography - Google Patents

Abstract

The invention relates to the field of analytical instrumentation. The purpose of the invention is to simplify the design and increase the maximum operating temperatures of the detector. The photoionization detector has a gap between the ionization chamber and the window of the ultraviolet lamp. The carrier gas and the sample from the column are fed directly into the gas inlet and out through the gap between the ionization chamber and the lamp. An additional difference of the detector is that the size of the gap between the outer surface of the capillary column and the gas inlet is smaller than the cross-sectional area between the ionization chamber and the lamp window, as well as the presence of an annular abutment inside the ionization chamber, 3 s. f-ly, 1 ill. with s

Description

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The invention relates to analytical instrumentation, in particular to chromatographic instrumentation.

The purpose of the invention is to simplify the design and increase the maximum operating temperatures of the detector.

The drawing shows the proposed detector (with an ionization chamber with a longitudinal section),

The detector contains an electric discharge lamp 1 with a window 2 made of materials that are transparent in the wavelength region emitted by the lamp. The ionization chamber 3 includes a housing 4, which is separated from the window by a gap 5. 2, the ionization chamber also contains electrodes 6 and 7 connected to the electrometer and power supply unit of the detector, respectively. An outlet part of the capillary column 9 is introduced into the inlet 8. In the ionization chamber building there is an annular abutment 10 securing the output part of the capillary column. The ionization chamber is enclosed in a thermostat 11. The lamp is fixed to the ionization chamber by means of a holder 12,

The detector works as follows.

Carrier gas comes from exit-f. Noah portion of a 9c capillary column. the working volume of the ionization chamber 3 and through the gap 5 is led out of the chamber. Ultraviolet radiation emitted by lamp 1 through window 2 enters the working volume of the chamber, but does not produce ionization, since the ionization energy of carrier gases (Ar, Ne, He, N) is greater than the energy of photons emitted by the lamp. Therefore, between the electrodes 6 and 7, the background current flows due to the bulk and surface conductivity of the insulating elements of the chamber, as well as the photoelectric effect.

When an analyte is fed into the ionization chamber from capillary chromatographic column 9, it is ionized (if the lowest ionization energy is less than the energy of the acting photons), new electrons and ions appear, the movement of which forms

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useful signal - an increase in current. The characteristics of the current signal determine the nature of the substance and the change in its concentration in the working volume of the chamber.

Since the gaps are chosen in such a way as to ensure an advantageous gas outlet through the gap between the window of the lamp and the housing of the ionization chamber, there are practically no turbulent flows in the chamber.

The feasibility of using a photoionization detector in chromatographs is provided by combining the simplicity of the detector design with the high allowable temperature of its operation (up to 450 ° C).

Since it is possible to use ionization chambers with a volume of 30 µl or less, it is particularly promising to use the proposed detector for working with capillary columns. Based on the use of the proposed detector, small-sized portable chromatographs and gas analyzers can be created to analyze the environment, locate leaks at chemical plants, etc.

Claims (4)

1. A photoionization detector for capillary gas chromatography containing a source of ultraviolet radiation — an electric discharge lamp with a window of a material that transmits vacuum ultraviolet emitted by the lamp and an ionization chamber containing a channel for introducing gas from a capillary chromatographic column, installed in the chamber polarizing and collecting electrodes, characterized in that, in order to simplify the design and increase the maximum operating temperatures of the detector, between the ionization chamber and the lamp window you there is a gap forming the channel for the gas outlet, 2. A detector according to claim 1, characterized in that, in order to simplify the procedure for changing the column, a capillary column is introduced directly into the gas inlet channel with a gap with the channel walls. 3. The detector according to claims 1 and 2, characterized in that, in order to eliminate turbulence of flows in the detector, the size of the area of the gap between the outer surface of the capillary tube S59 column and the gas inlet channel is smaller than the cross-sectional area of the gap between the ionization chamber and the lamp window. 4. The detector according to claims 1–3, which is designed so that, in order to fix the column, an annular abutment is made in the channel inside the housing of the ionization chamber.