A gas-chromatographic method for the determination of trace amounts of a toxic impurity, 2,3,7,8-tetrachlorodibenzo-p-dioxin, is described. A purified extract of the sample was subjected to gas chromatography on a column containing either 2 per cent. of OV-17 on Diatomite CQ or 1 per cent. of Hi-Eff 8 BP on Gas-Chrom Z with electron-capture detection. 2,4,5-Trichlorophenoxyacetic acid and 2,4,5-trichlorophenol were purified by chromatography of an ether extract of the sample on a column of alumina, followed by shaking with sulphuric acid. For 2,4,5-trichlorophenoxyacetic acid esters and formulations, saponification and chromatography on a Celite-sulphuric acid column, followed by chromatography on a column of alumina, were necessary.Recoveries of 2,3,7,8-tetrachlorodibenzo-p-dioxin ranged from 89 to 98 per cent., and the standard deviation of the method at a level of 0·3 p.p.m. was 0·03 p.p.m. The limit of detection was about 0·05 p.p.m.
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D. A. Elvidge (1971) studied this question.