Problems and results of trace analysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin in 2,4,5-trichlorophenoxyacetic acid and its esters

Quantitative analysis of tetrachlorodibenzo-p-dioxins (TCDDs) has gained increasing importance in the public domain. The analytical problem is complex because of the large number of interfering isomers and the extremely low limit of determination enforced by legislation. DAPA elaborated a procedure based on the latest published methods and on the existing experience of the collaborators. This procedure involves preseparation of the original sample on a silica column and cleanup by liquid chromatography (LC) on alumina. Alkaline saponification of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) esters seems to create artificial dioxins in the organic extract. Final determination is performed by capillary gas chromatography (GC)-low resolution mass spectrometry (MS). Final international collaborative work was carried out on 4 samples. Results were reported by 13 of 20 laboratories. Mean values ranged from 3.5 to 8.7 micrograms/kg. The interlaboratory reproducibilities ranged from 3.4 to 8.2 micrograms/kg (about 100% of the mean value).