Analytical Sciences

Electrothermal Vaporization on a Tungsten Filament for the Determination of Arsenic in Chloride Solutions by Low-Pressure Helium ICP-MS

Hideo HAYASHI, Tomokazu TANAKA, and Masataka HIRAIDE

Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan

A combined method of electrothermal vaporization and low-pressure helium ICP-MS was developed for the determination of traces of arsenic in chloride solutions, because serious spectral interference occurred in conventional argon ICP-MS. On a tungsten filament was placed 5 ul of a sample and heated electrothermally to remove the solvent. The resulting residue on the filament was covered with a vaporization chamber, and after reducing the pressure to ca. 5 Torr, it was rapidly heated by discharging a high-capacity condenser (0.22 F). The vapor of arsenic was transferred to a helium plasma with a stream of carrier gas for the determination. The background was not observed at m/z of 75, which allowed the determination of arsenic at ng/ml levels in chloride solutions. Sodium chloride significantly enhanced the intensity of the arsenic signal, whereas other chlorides, including KCl, MgCl₂, CaCl₂ and NH₄Cl, suppressed the analytical signals. This enhancement due to sodium ions seems to be a peculiar phenomenon to the helium ICP. The proposed method can be applied to direct determinations of as low as 0.9 ng/ml of arsenic in seawater.

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