Collect. Czech. Chem. Commun. 1998, 63, 347-355

Determination of Arsenic in High-Saline Mineral Waters by Inductively Coupled Plasma Mass Spectrometry

Oto Mestek

Department of Analytical Chemistry, Prague Institute of Chemical Technology, 166 28 Prague, Czech Republic


Determination of As by ICP-MS is aggravated by the presence of Cl- ions, forming in the plasma the 40Ar35Cl+ ion from which the 75As+ ion cannot be discriminated. The presence of 1 000 mg l-1 Cl- gives rise to a signal corresponding approximately to 3 μg l-1 As. Interferences can be reduced by about 70% by the addition of 4 vol.% methanol, the remaining fraction has to be corrected mathematically. A treatment based on the measured intensities of the 40Ar37Cl+ or 35Cl16O+ ions can result in overcorrection; the signal of the 35Cl+ ion was found more suitable for the purpose. The 35Cl+/40Ar35Cl+ signal ratio is constant in the concentration range of 400-1 000 mg l-1 Cl- at least. The detection limit (3σ) found by measuring solutions which contained various amounts of Cl- ions was 0.03 μg l-1 As. This two-step correction for interferences was applied to the analysis of a mineral water with a chloride concentration of 1 400 mg l-1. The results obtained by the calibration graph method and by the standard addition method were in a good agreement (1.50 μg l-1 vs 1.44 μg l-1 As, respectively), whereas a high overestimation (4.2 μg l-1 As) resulted if the correction was omitted. Relative standard deviation of the determination was 3.2%.

Keywords: Arsenic; Mineral water; Inductively-coupled plasma mass spectrometry.