A SPECTROPHOTOMETRIC METHOD FOR PHOSPHINE RESIDUE DETERMINATION IN LEGUMES

A simple spectrophotometric method for the determination of phosphine residue in legumes has been developed. It is based on the reaction of phosphine with silver nitrate in iso-propanol to form a pale yellow ch romophore, with an absorption maximum at 436 nm. It gave a linear rela tionship between the absorbance at 436 nm and the amount of phosphine in the range of 0.02 to 0.48 mu g/3 ml reagent. The crop extractives f rom the legumes showed a low absorbance of 0.008 at 436 nm, and did no t interfere in the chromophore reaction. The method is sensitive with determination limit of 0.015 mu g phosphine arid can be applied for de termination of 0.02 mu g residue in 10g legume samples. Phosphine resi due on legumes, when extracted with a known volume of 2% aqueous isopr opanolic silver nitrate, formed egg yellow chromophore with absorption maximum at the same range. Recovery of fortified phosphine from a clo sed system ranged from 97 to 98%.