Use of pressurized hot water extraction and high performance liquid chromatography–inductively coupled plasma–mass spectrometry for water soluble halides speciation in atmospheric particulate matter

The feasibility of pressurized hot water extraction (PHWE) has been novelty investigated to speed up water soluble halide species (bromide, Br−; bromate, BrO3−; iodide, I− and iodate, IO3−) leaching from atmospheric particulate matter (PM10 and PM2.5). Total bromine and iodine and total water soluble bromine and iodine have been assessed by inductively coupled plasma—mass spectrometry (ICP–MS). Water-soluble bromine and iodine species were also measured by ICP–MS after anion exchange high performance liquid chromatography (HPLC). Variables inherent to the pressurized hot water extraction process (temperature, modifier concentration, static time, pressure, number of cycles and dispersing agent mass) were fully studied. Results showed that the pressurized leaching procedure can be performed in 9 min (5 min for pre-heating, 2 min of static time, 1 min of purge time, and 1 min of end relief time). The use of diluted acetic acid as a modifier did not improve the target recoveries. Dispersing agent (diatomaceous earth) was not needed, which reduces the time for filling the cells. Water-soluble halides were reached under the following extraction conditions: extraction temperature of 100 °C, pressure of 1500 psi, static time of 2 min and 1 extraction cycle. Optimized HPLC conditions consisted of an isocratic elution with 175 mM ammonium nitrate plus 15% (v/v) methanol as mobile phase (optimum flow rate of at 1.5 mL min−1). Analytical performances, such as limits of detection and quantification, repeatability and analytical recoveries of the over-all procedure have been established. Results obtained show water soluble halides accounted for approximately 20.9±1.3 and 11.8±0.6% of the total bromine and total iodine, respectively. A 79 and 89% of bromine and iodine was non-water soluble, which may be organic non-water soluble species. Br− and IO3− were found to be the major species, and they accounted for 100% of the total water-soluble bromine and iodine.