Automated On-Line Analysis Using Thermal Desorption Modulators

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Abstract
A thermal desorption modulator is a short length of the analytical column (or a piece of tubing containing an adsorbent) placed at the head of the column in a GC. A carrier gas containing sample may be continuously introduced into a chromatographic column through a modulator. Analytes transfer from the carrier gas onto a stationary phase within the modulator and can be released from the modulator by rapid heating. A concentrated pulse of analytes generated in this fashion serves the same purpose as an injection. Thus, chromatography using modulators does not need any injection device because the equivalent of an injection is generated internally within the flow stream. In addition to serving as an alternative to an injection valve, a modulator also preconcentrates the sample. The purpose of this paper is to demonstrate the use of a thermal desorption modulator in automated on-line analysis. This had been done by continuously determining the concentration of H2S in the effluent stream from a reactor where a hydrodesulfurization reaction was carried out.