Determination of phosphine residues in whole grains and soybeans by ion chromatography via conversion to phosphate

An ion chromatographic (IC) method was developed for determining phosphine (PH3) in whole grains (barley, corn, oats, rice, rye, and wheat) and soybea ns. The method converts phosphine to phosphate (i.e., orthophosphate) and i solates the phosphate by IC with eluent-suppressed conductivity detection. Recoveries of unbound phosphine by the method were similar to those obtaine d by an established colorimetric method for 7 different products fortified at 3 levels. Mean recoveries were low (i.e., 30-60%) and varied with produc t type and level of fortification. Recoveries of PH3 from previously fumiga ted products fortified with aluminum phosphide ranged from 19.0% for barley fortified at 0.734 ppm to 88.3% for corn fortified at 1.691 ppm. Precision data from 3 products based on replicate analyses (n = 4 or 5) gave relativ e standard deviations of 1.78-4.66% for mean laboratory-fumigated PH3 level s of 0.679-1.309 ppm. Estimated limits of detection (LOD) and quantitation (LOQ) for PH3 were 0.010 mu g/g (10 ppb) and 0.0275 mu g/g (27.5 ppb) at si gnal-to-noise ratios (S/N) of 4:1 and 10:1, respectively. These values were also determined for a nonchemically suppressed IC system with LOD of 0.02 mu g/g (20 ppb) and LOQ of 0.055 mu g/g (55 ppb) at SIN of 4:1 and 10:1, re spectively Phosphate response was linear over the concentration range equiv alent to 0.30-10.0 mu g P/mL, with a mean correlation coefficient of 0.9988 based on replicate standard curves. The relationship of product compositio n to recovery from various products was also examined.