Simultaneous determination of halogens (F, Cl, Br, and I) in coal using pyrohydrolysis combined with ion chromatography
Monitoring the halogen levels in coal is important because oftheir effects on human health and the environment. Few methodscan be adopted to determine halogens in coal simultaneously. Fcan only be determined through ion chromatography (IC) and ionselectiveelectrode (ISE), whereas instrumental neutron activationanalysis (INAA) and inductively coupled plasma-mass spectrometry(ICP-MS) can only analyze Cl, Br, and I [1–4]. Sample decomposition is a critical step in halogen analysis. Halogens are volatile and readily lost when the sample is treated; furthermore, the reagents used for sample digestion may interfere with the determination process itself. To eliminate these drawbacks, pyrohydrolysis and microwave-induced combustion (MIC) have been proven effective and reliable digestion methods for determining halogens in coal and oil [2–9]. MIC combined with IC, a routine and classic analytical method for determining halogens in water , has been successfully used to determine halogens simultaneously in coal . However, about 15% of Chinese coal has less than 2.5 lg g_1 Br and 75% have less than 3.0 lg g_1 I. Therefore, the limits of detections (LODs) for Br and I (2.5 and 3.0 lg g_1, respectively) obtained using IC coupled with MIC is relatively high .
To lower the LODs of Br and I further, the present study establishes a quantitative method for determining F, Cl, Br, and I in coal using the IC system after pyrohydrolysis. The pyrohydrolysis conditions, as well the types and concentrations of the absorption solutions are optimized. The method is validated using certified reference coals (for F) or spikes (for Cl, Br, and I).