Sampling and determination of antimony isotopes in airborne particles: an assessment of membrane filter materials

Abstract

Isotopic compositions of antimony (Sb) in airborne particles could reveal the sources and geochemical processes of Sb. Today, the precise analysis of the Sb isotopic ratio in airborne particles is still challenging due to technical difficulties in the sampling and pretreatment processes. In this study, traditional methods of sampling and pretreatment of Sb in airborne particles were optimized to meet the isotope measurement requirements. Suitable digestion methods were suggested for various membrane filters (MF) of different materials and brands, and the Sb blank values in these membrane filters were compared. The results showed that the Whatman brand quartz microfiber MF had the lowest Sb blank value (1.13 ng cm⁻²), and could meet the needs of continuous large flow sampling, making it the most ideal MF for sampling Sb in airborne particles for the subsequent measurement of Sb isotope ratios. Synthetic samples of the MF spiked with certified reference materials (CRMs) were digested and tested. Nearly identical ε¹²³Sb values were observed among CRMs, (MF + CRMs), and (MF + CRMs) subtracting the content proportion of MF, which indicated that the isotope fractionation occurred during the pretreatment was negligible, and that the Sb isotopic composition of airborne particulate matter was basically not affected by the Whatman brand quartz microfiber MF. This method has been successfully applied to total suspended particles and fine particulate matter (PM_2.5) collected in Guiyang in southwest China.