Water-Soluble and Total Sulfur in Particulate Matter Determined by Inductively Coupled Plasma Dynamic Reaction Cell Mass Spectrometry (ICP-DRC-MS)

Environmental Context. Sulfate in particulate matter is usually collected by a high-volume air sampler and analysed as a soluble extract by ion chromatography. The use of an inductively coupled plasma mass spectrometer fitted with a dynamic reaction cell enables not only the water-soluble, but also the total sulfate to be determined at the same time as the analyses of metal ions. Results from Hong Kong show that sulfate is strongly correlated with crustal species in particulate matter.

Abstract. An instrumental method has been developed for the determination of sulfur in particulate matter using inductively coupled plasma dynamic reaction cell mass spectrometry. The reaction gas O₂ was employed to convert S⁺ into the diatomic species SO⁺, and analysed at two different mass-to-charge ratios. The limit of detection for the ³²S¹⁶O⁺ determination is ~1 ng S m^–3. The method has the advantages that not only soluble sulfur (as commonly analysed by ion chromatography) but also total sulfur can be determined on the same instrument as many metal species. The mean values (± standard deviations) for a spring sampling program of particulate matter of diameter less than 10 μm (PM₁₀) in Hong Kong (n = 13) for soluble and total S were 5.2 ± 1.2 μg m^–3 and 5.5 ± 1.3 μg m^–3 respectively. These values are quite low owing to a predominantly easterly airstream. Sulfur in PM₁₀ is strongly correlated with the crustal species Ca, Al and Mn.