Determination of As, Mn, Pb and Se in coal by slurry electrothermal vaporization inductively coupled plasma mass spectrometry

Abstract

A method for the determination of trace elements in coal by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS), introducing the sample as a slurry, is proposed. The slurry was prepared by mixing the powdered coal (<45 µm) with aqueous 5% v/v nitric acid solution in an ultrasonic bath. An ultrasonic probe was used to homogenize the slurry in the autosampler cup just before its introduction into the graphite tube. The best compromise conditions for the furnace temperature program, the amount of palladium used as modifier, the carrier gas flow rate, etc., were determined. By introducing 10 µL of a 4.0 mg mL−1 coal slurry, using 3 µg of Pd as a modifier, and a pyrolysis temperature of 600°C, most of the obtained values for four coal reference materials were well within the certified range, using external calibration with aqueous solutions. No carrier had to be added in addition to the palladium modifier. Using a lower slurry concentration of 1.3 mg mL−1 and 2 µg of Pd as the modifier, the values obtained for lead were significantly lower than the certified ones. This problem could be solved in part by adding NaCl as a physical carrier, in addition to the palladium, showing that this carrier reduces the differences in the analyte transport from the sample and from the calibration solutions. However, results for most elements, except for arsenic, tended to be a little low even under these conditions, hence, preference was given to the higher slurry concentration.