Rapid Method for Determination of Phosphine Residues in Wheat
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Rapid Method for Determination of Phosphine Residues in Wheat Francesco Longobardi & Michelangelo Pascale & Marco Silvestri & Angelo Visconti
Received: 5 December 2007 / Accepted: 25 January 2008 / Published online: 21 March 2008 # Springer Science + Business Media, LLC 2008
Abstract A rapid method for spectrophotometric determination of phosphine residues in wheat has been developed. Phosphine-fumigated wheat kernels were added with 10% sulfuric acid in a gas-tight flask, and phosphine was released into the headspace by microwave irradiation. Phosphine was spectrophotometrically determined after reaction with silver nitrate. A good linearity of the calibration curve was obtained with wheat spiked at levels ranging from 0.035 to 0.230 μg/g with correlation coefficient (r) of 0.9965 and a detection limit of 0.026 μg/g. The total time of analysis was 10 min. Headspace analysis was also performed by micro-gas chromatography (GC) with a thermal conductivity detector (microGC-TCD). Results obtained with the spectrophotometric and micro-GC-TCD methods showed good correlations with those obtained with the most widely used GC with nitrogen– phosphorus detector with r values of 0.9940 and 0.9946, respectively. Keywords Phosphine Residues . Spectrophotometric Method . Micro-gas Chromatography . Rapid Method
F. Longobardi (*) : M. Pascale : A. Visconti Institute of Sciences of Food Production (ISPA), National Research Council (CNR), Via G. Amendola 122/O, 70126 Bari, Italy e-mail: [email protected] M. Silvestri Barilla G. & R. Fratelli S.p.A., via Mantova 166, 43100 Parma, Italy
Introduction Phosphine (PH3) is a fumigant used worldwide to disinfest stored products and processed foods. PH3 has been approved for use in many food storage situations and is typically applied to cereals, nuts, dried fruits, pulses, oilseeds, and dried animal products. Although PH3 is extremely volatile and diffuses rapidly, residues could persist in food commodities following fumigation using the recommended application rates (Working Party on Pesticide Residues 1998). Several PH3-based pest control procedures generate PH3 by decomposition of metal phosphides. The most widely used phosphides, aluminum phosphide and/or magnesium phosphide, do not entirely decompose leaving some residues in the food commodities that can be converted by acid hydrolysis to PH3 (Nowicki 1978; Banks 1986; Bruce et al. 1962; Calzolai 1990). The maximum residue limit (MRL) recommended by the Codex Alimentarius Commission of the World Health Organization (WHO) and Food Agriculture Organization (FAO) for phosphine in raw cereals, i.e., 0.1 μg/g, is based on the measurement of PH3 as the sum of intact physically bound PH3 and PH3 derived from any residual phosphides present (FAO/WHO 1983). Rapid, sensitive, and repeatable methods for the determination of total PH3 residues in cereals are therefore needed for screening a large number of samples. Several methods, originally developed for the analysis of metal phosphides by PH3 generation, were later applied to
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