Determination of barium by electrothermal atomic absorption spectrometry

Abstract

Barium atomization in electrographite, pyrolytic graphitecoated (pyrocoated) and tungsten-coated graphite tubes, using argon or nitrogen as sheath gas, was studied. Sensitivity, appearance time, pyrolysis and atomization temperature curves, tube lifetime and scanning electron micrographs were obtained for the different surfaces. The best characteristic mass and longest lifetime were obtained in a pyrocoated tube without a platform, using argon as sheath gas. Nitrogen increases the appearance time and decreases the sensitivity owing to the formation of gaseous barium monocyanide. High-purity argon or a lower pyrolysis temperature does not increase the tube lifetime. The appearance temperature, around 2200 °C, suggests that barium is atomized through the reduction of barium by the carbon. Complete atomization was not obtained with any of the conditions, as a plateau was not verified on the atomization temperature curve up to 2650 °C. Nitrogen also decreases the maximum pyrolysis temperature in a pyrocoated tube. The micrographs of the tungsten pretreated tube explained its bad performance. The tungsten coverage is discontinuous and melting of the tungsten phase decreases the coverage and leads to the destruction of the pyrocoating. Non-spectral interferences were observed, specially at high salt concentrations. The analysis of real samples is possible if the standard additions method is used. The concentration of barium found in Citrus Leaves agreed with the certified value.