Measuring and testing – Gas analysis – Gas chromatography
Patent
1983-05-20
1985-09-17
Kreitman, Stephen A.
Measuring and testing
Gas analysis
Gas chromatography
73 19, 55158, G01N 1300
Patent
active
045412685
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a method and apparatus for the sampling of trace elements in gases, liquids, on solids or in surface layers for the purpose of subsequent detection, identification or quantification.
STATE OF THE ART
It is known to detect the smallest traces of organic substances in gases, for example air, in liquids, for example water, as well as in and on solids by enriching the trace components by solvent extraction, adsorption by means of a gradient and sorption tube (filled, for example, with Tenax-GC, XAD-2, active carbon etc. as sorbents), or by freezing out. With heterogeneous systems, for example suspended matter in air or water, it is possible to use filters for the sampling, which on loading are subjected to a solvent extraction.
Traces enriched on gradient or sorption tubes from a gas by means of adsorption may be desorbed, if need be, with the help of a relatively simple pneumatic system by directly heating the traces in a carrier gas, and then admitted into the gas detector.
However, a labor-intensive and complicated preparation of the samples often connected with a loss of sample material due to volatilization or decomposition is required in most cases before the samples are loaded in the analyzer. This preparatory work requires a high degree of careful work and experience. If the analysis apparatus is a gas-chromatograph or a combination of GC/MS, the sample must be applied to the inlet of the separating column, for example with the help of an injection needle and through a septum in order to evaporate the solvent and trace components contained in said solvent.
The disadvantages of the procedures specified above are also known in particular with routine analyses with high amounts of sample throughput. Therefore, efforts have been made to load the analysis apparatus discontinuously or continuously with selectively enriched, volatile trace components in gases, liquids, aqueous slurries or solid granulates with the help of diaphragms and membrane separators. In such a procedure, a relative enrichment is achieved by way of the diaphragm/membrane without increasing the partial pressure of the component to be measured after it has passed through the diaphragm/membrane. In the most favorable case, its partial pressure is equal the partial pressure before the membrane/diaphragm. Said techniques aim for the discontinuous detection of highly volatile substances such as lower alcohols, or of permanent gases such as oxygen and carbon monoxide, which are present in each case in relatively high concentrations (FR, A, No. 1573147/1969), or they require an extremely sensitive detector if carried out continuously, for example a mass spectrometer with a multi-stage, differentially evacuated membrane separator system (DE, A, No. 1673239/1970; DE, A, No. 2022958/1970; and DE, A, No. 2310264/1973). More recent applications specify an inlet head that can be used advantageously in a discontinuous operation as a GC inlet system, making the injection through a septum superfluous (DE, P, No. 3009069.8/1980, and PCT/DE No. 81/00043/1981). In this case, the sample is loaded, for example, by successively applying the solution to be tested to a contact membrane, which is flushed with carrier gas and adjusted to a relatively low temperature T.sub.1, whereby the solvent evaporates and the trace components of the solution to be analylized, which components are concentrated in the contact membrane almost without any losses, pass into the carrier gas only after the temperature has been increased to T.sub.2. If the temperatures T.sub.1 and T.sub.2 are adjusted or adapted to the gas-chromatographic mobility behavior of the trace component and the carrier gas throughflow volume and the dead volume between the membrane and detector is low, high partial pressures can be produced for short periods behind the contact membrane particularly by rapidly heating to the desorption temperature T.sub.2 even with very low absolute amounts sorbated in the small volume of the membrane. Said partial pressures exceed
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Bruker-Franzen Analytik GmbH
Kreitman Stephen A.
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