Radiofrequency atomization and excitation with a hot graphite cup electrode for trace element determination by atomic emission spectrometry

Abstract

A discharge lamp was constructed as an excitation source for the determination of trace elements in small samples by atomic emission spectrometry. A graphite cup, in which an aliquot (10 mg) of sample solution or powder was loaded, was located in a stainless-steel cylinder. An r.f. discharge was formed between the graphite cup and the grounded cylinder under a reduced pressure of argon. Concurrently with the formation of the plasma, the graphite cup was heated to about 1900 °C owing to the r.f. power dissipation. As a result, the sample was thermally vaporized and/or atomized, and subsequently excited to emit radiation in the discharge plasma surrounding the graphite cup. Basic characteristics were studied in conjunction with the analytical performance. The matrix effect of sodium was tested and found to be negligible in the determination of copper in the presence of up to a 1000-fold excess of sodium. A linear dynamic range of the calibration graph was obtained over about four orders of magnitude of analyte mass. The discharge lamp was applied to the direct determination of copper, zinc and chlorine in National Institute of Standards and Technology Standard Reference Materials of biological samples.