Microwave emission spectrometric determination of arsenic at the ppb level in aluminum

Abstract

This method is based on the conversion of arsenic into arsine followed by microwave excitation in a quartz discharge tube. An aluminum sample {(0.51.0) g} was placed in a reaction vessel, 50 ml of 6 M hydrochloric acid and 0.2 ml of 10% tin(II) chloride solution were added, and the vessel was quickly connected to a liquid nitrogen trap (50 × 0.8 cm o.d., U-shaped glass tubing) via a CaCl2 tube. Arsine generated was swept by a nitrogen flow of 30 ml/min into the trap. When the sample had been completely dissolved, 2.0 g of granular zinc was added to the vessel and the nitrogen was passed for another 60 min. The trap was then disconnected from the vessel and connected to a discharge tube. Argon was introduced into the trap at a rate of 30 ml/min, and to optimize the discharge conditions, an additional argon flow of 470 ml/min was fed to the discharge through a bypass. When nitrogen had been completely expelled, the discharge was ignited with a Tesla coil. The trap was removed from liquid nitrogen; after 30 s, the arsenic 228.8 nm line appeared, and its peak intensity was measured for the determination. The recovery of arsenic measured with As-76 was about 90%, due to sorption loss on CaCl2. The lower limit of determination was ca. 0.05 ppm of arsenic in aluminum and the coefficient of variation was 9% at the 0.5 μg level. The time required for a determination was ca. 2 hrs.