Simple spectrophotometric method for determination of phosphine residues in wheat.

A method was developed for detn. of phosphine residues in wheat, based on the reaction of phosphine with silver nitrate in aqueous solution to form an egg-yellow chromophore with an absorption max. at 400 nm. At this wavelength, there is a linear relationship between absorbance and concn. of phosphine in the range 10-100 ng/ml. Phosphine-fumigated wheat is soaked in a known volume of AgNO3 solution, and the absorbance of the filtrate is read against a blank at 400 nm. The method is sensitive, with lower detection and estimation limits of 0.008 and 0.01 mug PH3, resp. Recovery of added phosphine from a closed system was 85-100%. Accuracy for this method was compared with that for the gas chromatographic method.