Improved microwave digestion procedure for inductively coupled plasma mass spectrometric determination of inorgnaic bromide residues in foodstuffs fumigated with methyl bromide

摘要

An improved microwave digestion procedure is described for the inductively coupled plasma mass spectrometric (ICP-MS) determination of inorganic bromide residues in foodstuffs fumigated with methyl bromide. It is based on the addition to the usual acid oxidizing mixture of small amounts of silver ions which cause bromides from the mineralized matrix to precipitate as sparingly soluble AgBr, thus, avoiding losses due to their conversion into volatile products. The silver bromide precipitate separated from the digested sample is dissolved with ammonia and the cationic complex [Ag(NH3)2]+ thus formed is removed on a cation-exchange column. The resulting solution is finally acidified and added with indium internal standard, to make it suitable for inductively coupled plasma mass spectrometric (ICP-MS) analysis. This modified procedure has been tested for the analysis of synthetic KBr samples by obtaining totally satisfactory results, in that bromide recoveries ranging from 98.6 to 100.2% were found, with an overall standard deviation of 5.17%. Its application to the bromide determination in some mushroom samples is reported and the results found are compared with those obtained on the same samples mineralized by conventional alkali fusion. The proposed procedure can be extended to the determination in biological samples of other anions which may be lost during a conventional acid oxidizing microwave mineralization, but are able to form insoluble silver salts.