Investigation of automated determination of germanium by hydride generation using in situ trapping on stable coatings in electrothermal atomic absorption spectrometry

Abstract

Sequestering and in situ concentration of Ge hydride in the graphite furnace can be automated by using a highly stable trapping reagent to replace the Pd modifier. In a systematic study, two groups of trapping reagents which require only a single application, i.e., carbide-forming elements (Zr, Nb, Ta or W) and noble metals (Ir, Pd–Ir), were investigated and trapping temperature curves were measured. It was shown that effective trapping of germane is possible on Zr-coated tubes and platforms at trapping temperatures of 550–750 and 600–800 °C, respectively. Trapping temperatures should not exceed 650 °C (the ‘critical temperature’) because at temperatures higher than 650 °C errors in absorbance values could occur owing to an adsorptive ‘carry-over effect’. Good signal stability was observed over more than 400 complete trapping and atomization cycles, and a precision of better 3% was obtained. Comparatively small signals were observed for the Nb-, Ta- and W-coatings. Ir-coated graphite tubes allowed trapping of germane at lower temperatures (400–500 °C) but the signals were small and of low stability, compared with those for the Zr coating. Characteristic masses of about 54 pg of Ge on Zr-coated graphite tubes (peak height) and 108 pg of Ge on Zr-coated platforms (integrated absorbance) were observed, and the calibration graphs were linear up to 4 ng of Ge on both tubes and platforms. The detection limit was 18 pg of Ge for a 1 ml sample volume using flow injection hydride generation. The method was tested by applying it to the determination of Ge in sediment, geological and low-alloy steel certified reference materials.