Determination of phosphine by adsorption sampling with modified silica gel and colorimetry of phosphate.

Abstract

A method for determining phosphine was developed using adsorption sampling followed by colorimetric measurement. Two types of adsorbent used in this study were prepared from silica gel by impregnation with potassium permanganate (1% w/w) or (mercury(II) chloride and sodium chloride) (0.2 + 0.2% w/w). Each adsorbent (150 mg) packed in a glass tube had the capacity to adsorb 0.3 ppm of phosphine in 3 l of test gas passing through at a rate of 300 ml/min without breakthrough. The adsorbed phosphine was desorbed into solutions as phosphate and the recovered phosphate was determined by ICP-AES or by one of two kinds of colorimetric methods for phosphate based on the molybdenum blue method, i.e., the colorimetric method following JIS K 0102 and that following the NIOSH Manual of analytical method, No. S 332. When 0.01 ppm of phosphine in 3 l of test gas was adsorbed on the potassium permanganate adsorbent and determined by the JIS method, 93.8% of the phosphine was recovered as phosphate with a CV of 12.9% (n = 3). This method was applicable to field surveys of phosphine in workplaces. The other method with the mercury(II) chloride adsorbent followed by the NIOSH method resulted in lower recovery of phosphate in low phosphine concentration range. ICP-AES was less sensitive than the colorimetries. The effect of coexistent arsenite or silicate on the colorimetry of phosphate was assessed.