Determination of ultratrace arsenic and selenium by electrothermal vaporization in a torch followed by ICP-MS

A detachable sample-injector with a coiled tungsten filament (0.2 mm in dia m. x 45 mm) was constructed for the effective introduction of tiny amounts of sample into ICP-MS. A 5 mul volume of the sample was placed on a filamen t and an injector was inserted into a plasma torch. After desolvating the s ample for 30 s with an electric current of 2.6 A, the filament was rapidly heated to ca. 2500 degreesC by discharging a high-capacity condenser (0.54 F). The resulting vapor was transferred to the plasma with a stream of argo n for the determination of As and Se. The intensities of the analytical sig nals increased by almost 100 times as compared with the values in a previou s study, where a looped tungsten filament was electrically heated outside t he plasma torch. The absolute detection limits were 0.5 pg for As and 1.1 p g for Se with relative standard deviations of 10 similar to 14%. The filame nt was used at least 100 times without any distortion of the signal profile s. The proposed method was applied to the determination of As and Se in cer tified reference human hair. The analytical results were 0.29 +/- 0.03 mug g(-1) for As and 1.8 +/- 0.2 mug g(-1) for Se, which are in good agreement with the certified values.