Slurry sampling graphite furnace atomic absorption spectrometry: determination of trace metals in mineral coal

A procedure for lead, cadmium and copper determination in coal samples base d on slurry sampling using an atomic absorption spectrometer equipped with a transversely heated graphite tube atomizer is proposed. The slurries were prepared by weighing the samples directly into autosampler cups (5-30 mg) and adding a 1.5 ml aliquot of a diluent mixture of 5% v/v HNO3, 0.05% Trit on X-100 and 10% ethanol. The slurry was homogenized by manual stirring bef ore measurement. Slurry homogenization using ultrasonic agitation was also investigated for comparison. The effect of particle size and the use of dif ferent diluent compositions on the slurry preparation were investigated. Th e temperature programmes were optimized on the basis of pyrolysis and atomi zation curves. Absorbance characteristics with and without the addition of a palladium-magnesium modifier were compared. The use of 0.05% m/v Pd and 0 .03% m/v Mg was found satisfactory for stabilizing Cd and Pb. The calibrati on was performed with aqueous standards. In addition, a conventional acid d igestion procedure was applied to verify the efficiency of the slurry sampl ing. Better recoveries of the analytes were obtained when the particle size was reduced to < 37 mu m. Several certified coal reference materials (BCR Nos. 40, 180, and 181) were analyzed, and good agreement was obtained betwe en the results from the proposed slurry sampling method and the certificate values. (C) 1999 Elsevier Science B.V. All rights reserved.