Abstract

Closed microwave-based digestion procedures have been tested on hair samples for determination of arsenic by hydride generation atomic absorption spectrometry (HGAAS). Six digestion procedures were compared and their performance evaluated according to the recovery of inorganic and organic arsenic compounds and to the certified hair reference sample analysis. The proposed procedure was performed by using small (2 mL) disposable polypropylene (PP) vials for some basic sequential operations: sample weighting, reagents addition, digestion and completion of volume. This procedure involves wet oxidation with sulfuric and nitric acids in combination with hydrochloric acid at a specific stage of microwave heating programme. Digests were treated with sulfamic acid before the dilution to volume and HGAAS determinations were made using L-cysteine as pre-reductant for As. The results provided quantitative recoveries, better than 98.6%, for As compounds (p-aminobenzenerasonic acid, dimethylarsinic acid and inorganic As) and an accuracy more than 98% was observed when compared to the results from certified hair reference analysis. The relative standard deviation was less than 6.4% for five replicates. Blank values were always low and no previous cleaning of commercial PP vials was needed. Background signals were low and absorbance signals were completely registered in 15 s. The proposed procedure allows the digestion of about 80 test samples in a period of one hour and a half.