Quick estimation of dieldrin in fresh cotton-leaf samples

Hexane was the most convenient extraction solvent. Consistent recoveries of 80% dieldrin were obtained after cold grinding with 10 mi hexane/g of leaf for 5 min. After filtering, solutions did not require a “clean‐up” before g.l.c. analysis, provided they were not concentrated further. Radioactive dieldrin in such extracts could be directly counted with a simple scintillation apparatus if pre‐treated with acidified potassium permanganate solution to eliminate the colour‐quenching effect and stored in the dark for 24 h to allow phosphorescence from some leaf materials to decay. Extractions using other solvents would need a “clean‐up” procedure before g.l.c. analysis, but radioactive dieldrin in hexane‐isopropanol extracts could be quickly estimated by simple scintillation counting after decolorisation with sodium hypochlorite and storage in the dark for 24 h.