Abstract
A modification of the White-Bushey method of phosphine analysis is described, designed for study of the release characteristics of phosphine-generating fumigant formulations and their residues. Phosphine was estimated indirectly from the acid produced when the gas, entrained in nitrogen, was absorbed in mercuric chloride solution. The acid production was measured, continuously and cumulatively, by titration using a pH-stat to maintain pH 3.0. The low pH minimised the pH-dependent reactions that can lead to erroneous phosphine estimations and enabled the analysis to be carried out at room temperature. The method was found to be accurate within 1%, when checked against known quantities of phosphine, and with a standard deviation of ± 1.4% as found by comparison with indirect analysis of phosphine by oxidation of the phosphine-mercuric chloride reaction product with bromine and subsequent colorimetric estimation of the phosphate produced. The presence of ethanol, normally used for preference in the aqueous absorbing solution, was found to interfere with the colorimetric estimation. Examples are given of the use of the titrimetric system to study release of phosphine from a fumigant formulation and a formulation residue.
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