Volatile germanium tetrachloride for sample introduction and germanium determination by inductively coupled plasma atomic emission spectroscopy

Abstract

The chemical vaporization of germanium(IV) with chloride ions is described as a means of introducing gaseous germanium into an inductively coupled plasma atomic emission spectrometer for the determination of Ge. The vapour is produced in a discontinuous mode by injection of 200 µl of aqueous solution of GeIV and 380 µl of 10% m/v sodium chloride solution into 385 µl of concentrated sulfuric acid. The gaseous analyte is introduced into the plasma torch by a flow (1.2 l min−1) of Ar carrier gas. The analytical method was studied by experimental design. The main effects and interactive effects of five experimental variables on the germanium atomic emission signal were evaluated by a two-level fractional factorial design. After the experimental study the three most influential factors (sulfuric acid volume, sodium chloride concentration and sample volume) were optimized by the modified simplex method. Under the optimized conditions, germanium could be determined by measuring its atomic emission at 209.426 nm produced in an inductively coupled plasma. The analytical method shows an absolute detection limit (3σ) of 0.6 ng for the injection of 200 µl of sample solution. The precision was 3.2%, expressed as the relative standard deviation, when seven replicates of 100 ng (200 µl of a 0.5 µg ml−1) solution were measured. The interference effects of alkali, alkaline earth, metallic and metalloid elements were studied; anions were also considered. A high selectivity of the reaction was observed and only Pb and alkaline earth elements interfered when present in amounts 50-fold greater than the GeIV concentration. The method was applied to determine germanium in coal and lignite samples and the results obtained were validated by a standard method.