A comparative study of chemical modifiers in the determination of total arsenic in marine food by tungsten coil electrothermal atomic absorption spectrometry

Three platinum group elements (Pd, Ir and Rh) both in solution and in pre-reduced form, and also combined with Mg(NO₃)₂ or ascorbic acid, were assessed as possible chemical modifiers on the atomization of As in digest solutions of seafood matrices (clam and fish tissue) by tungsten coil electrothermal atomic absorption spectrometry (TCA-AAS) and compared without a modifier. Of 28 modifier alternatives in study including single form and binary mixtures, and based on maximum pyrolysis temperature without significant As loss and best As absorbance sensitivity during atomization, three modifiers: Rh (0.5 μg), Ir (1.0 μg) and Rh (0.5 μg) + ascorbic acid (0.5 μg), at optimum amounts were pre-selected and compared. The definitive modifier (rhodium (0.5 μg)) was selected by variance analysis. The mean within-day repeatability was 3% in consecutive measurements (25-300 μg l⁻¹) (three cycles, each of n = 6) and showed good short-term stability of the absorbance measurements. The mean reproducibility was 4% (n = 18 in a 3-day period) and the detection limit (3σ_blank/slope) was 42 pg (n = 16). Quantitation was by standard additions to compensate for matrix effects not corrected by the modifier. Three sample digestion procedures were compared in fish and clam tissue samples: microwave acid digestion alone (A) or combined with the addition of 2% (m/v) K₂S₂O₈ solution followed either by UV photo-oxidation (B) or re-digestion in a thermal block (C). The accuracy was established by determination of As in certified reference material of dogfish muscle (DORM-2). Procedures B and C showed good recoveries (102% (n = 4) and 103% (n = 7), respectively), whereas procedure A was not quantitative (85%). The methodology is simple, fast, reliable, of low cost and was applied to the determination of total As in lyophilized samples of clam and fish collected in the Chilean coast.