Improved microwave digestion procedure for inductively coupled plasma massspectrometric determinations of inorganic bromide residues in foodstuffs fumigated with methyl bromide

An improved microwave digestion procedure is described for the inductively coupled plasma mass spectrometric (ICP-MS) determination of inorganic bromi de residues in foodstuffs fumigated with methyl bromide. It is based on the addition to the usual acid oxidizing mixture of small amounts of silver io ns which cause bromides from the mineralized matrix to precipitate as spari ngly soluble AgBr, thus, avoiding losses due to their conversion into Volat ile products. The silver bromide precipitate separated from the digested sa mple is dissolved with ammonia and the cationic complex [Ag(NH3)(2)](+) thu s formed is removed on a cation-exchange column. The resulting solution is finally acidified and added with indium internal standard, to make it suita ble for inductively coupled plasma mass spectrometric (ICP-MS) analysis. Th is modified procedure has been tested for the analysis of synthetic KBr sam ples 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 sam ples is reported and the results found are compared with those obtained on the same samples mineralized by conventional alkali fusion. The proposed pr ocedure can be extended to the determination in biological samples of other anions which may be lost during a conventional acid oxidizing microwave mi neralization, but are able to form insoluble silver salts. (C) 2001 Elsevie r Science B.V. All rights reserved.