Residual DDT was also determined by gas chromatography
(GC). The extract in ethyl acetate was
evaporated to dryness after passage through florisil
column. Moisture was removed by adding solid
Na2SO4 and evaporated to dryness. The residue was
re-dissolved in known volume of acetone. A Known
quantity of this was injected into GC (Fisons 8000) with
Ni63 electron capture detector. The conditions used
were: SS column (200 cm/2 mm) packed with 1.5%
OV-17 plus QF-1 on 80/100 mesh chromosorb W. The
column and injector were maintained at 230 8C and the
detector was maintained at 320 8C. Flow rate of the
carrier nitrogen gas was 50 ml/min. Under these
conditions, the retention time of DDT was 7.4 min.