Method development for the determination of bromine in coal using high-resolution continuum source graphite furnace molecular absorption spectrometry and direct solid sample analysis

Abstract

This work reports a simple approach for Br determination in coal using direct solid sample analysis in a graphite tube furnace and high-resolution continuum source molecular absorption spectrometry. The molecular absorbance of the calcium mono-bromide (CaBr) molecule has been measured using the rotational line at 625.315nm. Different chemical modifiers (zirconium, ruthenium, palladium and a mixture of palladium and magnesium nitrates) have been evaluated in order to increase the sensitivity of the CaBr absorption, and Zr showed the best overall performance. The pyrolysis and vaporization temperatures were 800°C and 2200°C, respectively. Accuracy and precision of the method have been evaluated using certified coal reference materials (BCR 181, BCR 182, NIST 1630a, and NIST 1632b) with good agreement (between 98 and 103%) with the informed values for Br. The detection limit was around 4ng Br, which corresponds to about 1.5μgg−1 Br in coal, based on a sample mass of 3mg. In addition, the results were in agreement with those obtained using electrothermal vaporization inductively coupled plasma mass spectrometry, based on a Student t-test at a 95% confidence level. A mechanism for the formation of the CaBr molecule is proposed, which might be considered for other diatomic molecules as well.