Method development for the determination of thallium in coal using solid sampling graphite furnace atomic absorption spectrometry with continuum source, high-resolution monochromator and CCD array detector

The determination of thallium by graphite furnace atomic absorption spectrometry (GFAAS) is plagued by several difficult-to-control interferences. High-resolution continuum-source GFAAS, a technique not yet commercially available, was used to investigate and eliminate spectral interferences, and to develop a reliable method for the determination of thallium in coal using direct solid sampling. The resolution of 2.1 pm per pixel, and the display of the spectral environment +/-0.2 nm on both sides of the analytical line were ideally suited for that purpose. The thallium signal was preceded by excessive non-specific absorption due to the coal matrix when pyrolysis temperatures less than or equal to600 degreesC were used, and a characteristic molecular absorption with pronounced fine structure was following the atomic absorption. With a pyrolysis temperature of 700 degreesC the non-specific absorption at the beginning of the atomization stage could be eliminated, and using an atomization temperature of 1700 degreesC, and no modifier, the atomic absorption could be separated in wavelength and in time from the molecular structures, making possible an interference-free determination of thallium, using Pixel 260 at 276.8085 mn for background correction. The results obtained for 11 coal samples and one coal fly ash were in agreement at a 95% confidence level without a modifier, with palladium added in solution, and with ruthenium as permanent modifier, respectively, using aqueous standards for calibration. A characteristic mass of m(0) = 12 pg and 5.5 pg was obtained with the center pixel only, and the center pixel +/-1, respectively. The precision, expressed as relative standard deviation was typically better than 5%, and the limit of detection, based on three times the standard deviation of the coal with the lowest analyte content, was 0.01 mug g(-1). (C) 2004 Elsevier B.V. All rights reserved.