Rapid Screening Method for DDT in Milk with Gas Chromatography

A method is presented for the assay of DDT and DDE. Milk is hydrolyzed with alcoholic KOH and extracted once with hexane. A 50-/~1 portion of extract, equivalent to 50 mg milk, is injected into a chromatograph having an electron affinity detector (tritium). The column consists of two almninum segments, a 6-in. and a 6-ft length, ~ in. od, packed with CaC~ (20/30 mesh) and Fluoropak 80 coated with Silicon Dow 11 and Epon Resin 1001. For our work, the temperature of oven housing column and detector was 200 C and the flow rate of carrier gas, nitrogen, was 210 ml/min. Calibration curves were prepared by plotting peak heights against known concentrations of DDE and used for computing unknown concentrations in milk. An average recovery of 95 7.7% was obtained when either p,p'-DDT or DDE was added to milk at 0.04 to 0.12 ppm. The standard deviations in all recovery studies were homogeneous, with a value of 0.]07 cm peak height or +--0.003 ppm DDE. Comparison of the results obtained on split milk samples by this technique and by paper chromatography showed no signifcant differences. The method is simple and accurate. In one workday 20 to 25 samples can be analyzed by one technician with one instrument.