Abstract
The microwave plasma detector is highly specific and much more sensitive than most current detectors for arsenic. But when this detector is used for the determination of arsine, the presence of large amounts of hydrogen makes the discharge unstable. Therefore, the arsine evolved from the sample was separated from hydrogen by gas chromatography. An air-dried soil sample (0.1 g) was decomposed with 3 ml of nitric acid and 4 ml of sulfuric acid (1+1), and the solution was evaporated to (0.51) ml at 200°C. After cooling, the residue was centrifuged, the supernatant liquid transferred to a 10-ml volumetric flask, and 1 ml of 20% potassium iodide, 2 ml of 20% tin (II) chloride and water (to the mark) were added. A 1 ml aliquot was taken with a syringe and introduced into a 15 ml reaction vessel containing 0.5 g of zinc {(0.51)mm diam.} through a silicone rubber stopper. The reaction was allowed by agitating the mixture with a magnetic stirrer until the gauge pressure reached 0.5 atm, and the evolved gas was swept by an argon flow (45 ml/min) into a column (0.3 φ×250 cm) containing PEG 6000/C-22 {(80100) mesh}. The As 228.8 nm line intensity was monitored and the peak height measured for the determination. The lower limit of detection was 0.2 ppm of arsenic in soil and the relative standard deviation was 3% for 10 ppm. The time required for a determination was 1 hr.
