Determination of lead in coal using direct solid sampling and high-resolution continuum source graphite furnace atomic absorption spectrometry

A method has been developed for the determination of Pb in coal using direct solid sampling (SS) and high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS). The certified coal reference materials used in this study were ground in an agate mortar to particle size <= 50 mu m. Mass aliquots between 0.1 and 1 mg were weighed onto pyrolytic graphite platforms, and inserted directly into the graphite tube. For pyrolysis temperatures lower than 600 degrees C, a continuous background due to radiation scattering at solid particles preceded the atomic signal, as the coal matrix could not be sufficiently eliminated under these conditions. An optimized pyrolysis temperature of 700 degrees C was adopted for Pb without the use of a modifier. The optimum atomization temperature was found to be 1700 degrees C. Under these conditions, interference-free determination could be performed with calibration against aqueous standards in 0.5% v/v HNO3. A total of six certified reference coal samples were analyzed, and the results obtained were all in good agreement with certified and informed values, respectively, according to a Student t-test at a 95% confidence level. A detection limit of 0.008 mu g g(-1) for Pb was obtained at the 217.000 nm resonance line, a value comparable to those obtained by other sensitive, but much more sophisticated techniques, showing that the absence of dilution in the SS-HR-CS GF AAS method allows at least equivalent detection performance.