Analysis of Volatile Substances in Samples containing Non-volatile Substances by Process Gas Chromatography

Abstract

RECENTLY, we experienced difficulties with the automatic analysis by gas chromatography of a process stream consisting of a liquid mixture of organic chemicals. These arose because traces of non-volatile tars and polymers in the sample eventually accumulated in the entrance of the first column of the chromatograph. (This chromatograph normally uses two columns to perform the analysis and has a thermal conductivity detector. The first column is used to separate and backflush volatile heavy ends out of the analyser; the second column completes the separation of the substances to be analysed.) Eventually, after a series of analyses, the accumulation of non-volatile materials in the first column was sufficient to block it completely, thus putting the analyser out of commission. The analyser was, in fact, injecting 10-µl. samples every 15 min into a 0.125-in. bore column. The concentration of non-volatiles was about 0.5–1.0 per cent by weight. Blockage occurred after 7–10 days of continuous operation.