Monitoring Gas Chromatography for H3- and C14-Labeled Compounds by Liquid Scintillation Counting
Isotopic assay of the isolated products from gas chromatography has frequently posed a difficult problem because of the small amounts of individual components isolated. When starting materials or reaction products are of relatively high specific activity (e.g., 0.1 mc/mg and higher), ion-chamber procedures of monitoring in gas chromatography are readily and effectively carried out , even at high temperatures . This high-temperature technique, used for studying reaction products from the tritium-exposure procedures [3–7] and for C14-labeled compounds of high specific activity, has been reported . Proportional counting has been used directly on effluents from gas chromatographic columns  and after combustion of all eluted material to carbon dioxide over heated copper oxide . Differential-type curves are obtained by ratemeter-recorder systems. Unfortunately, much biological and organic research is conveniently or necessarily carried out at low levels of specific activity. For example, if 4 mc of C14-labeled linoleic acid is administered in human experimentation, many orders of dilution will be experienced if complete equilibration of the C14-labeled linoleic acid occurs in body linoleic acid; indeed, the amount of radioactivity subsequently isolated from gas chromatography becomes very small. A system of mixing a scintillation solution with the exit gas stream from a chromatographic column and circulating the solution over the face of a photomultiplier tube has been described by Popják et al. . In this way they obtained an integral curve for radioactivity concurrently with a differential “analytical” curve from their gas density balance.
KeywordsLiquid Scintillation Methyl Oleate Methyl Linolenate High Specific Activity Linolenate Content
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