The Development of Iodine Based Impinger Solutions for the Efficient Capture of Hg⁰ Using Direct Injection Nebulization−Inductively Coupled Plasma Mass Spectrometry Analysis

Inductively coupled plasma mass spectrometry (ICP/MS) with direct injection nebulization (DIN) was used to evaluate novel impinger solution compositions capable of capturing elemental mercury (Hg⁰) in EPA Method 5 type sampling. An iodine based impinger solution proved to be very efficient for Hg⁰ capture and was amenable to direct analysis by DIN-ICP/MS. Hg⁰ capture efficiency using aqueous iodine (I₃^-) was comparable to Hg⁰ capture using acidified potassium permanganate impinger solutions which were analyzed by cold vapor atomic absorption spectrometry (CVAAS), with greater than 98% capture of Hg⁰ in the first oxidizing impinger. Using DIN-ICP/MS, it was demonstrated for the first time that iodine can be generated just prior to impinger sampling for efficiently oxidizing Hg⁰ and retaining it in solution as HgI₄^2-. Due to the increased interest in Hg speciation from combustion sources and the potential for using DIN-ICP/MS for multiple metals analyses, an impinger sampling train for gaseous Hg speciation and multiple metals analyses using DIN-ICP/MS analyses is presented. The unique feature of such a sampling train is that each impinger solution in the series is amenable to direct analysis by DIN-ICP/MS. A bituminous coal was combusted in a bench scale coal system, and gaseous Hg species (oxidized and elemental) were determined using the proposed impinger train. The DIN-ICP/MS instrumental detection limit was 0.003 ppb, and MDLs ranged from 0.007 to 0.116 μg/L (ppb) in a variety of impinger solutions used for Hg capture.