A preliminary study on the speciation of inorganic and organic tin compounds using XAFS

Abstract

It is well known that organotin compounds such as tributyltin (TBT) and triphenyltin (TPT) leached from ship's antifouling paints cause disrupting endocrine called “imposex” in some species of marine snails. In this paper, XANES and EXAFS spectra for some Sn species including TBT and TPT were measured. Tin LI-edge (4.464 keV) and LIII-edge (3.928 keV) XAFS were recorded in fluorescence mode using a Lytle detector at BL-9A, KEK-PF, Japan. In the beam line, all paths including I0 ion chamber and a sample cell were purged with He, which enabled us to measure XAFS at soft x-ray region even for liquid samples like TBT. The XANES and EXAFS spectra of Sn metal, SnCl2, SnO2, TBT, and TPT showed that we can distinguish these species by this technique. This shows that XAFS can be a powerful tool for the speciation of Sn. Since XAFS is a non-destructive method, it can exclude the alteration of Sn compounds during pretreatment of conventional chromatographic analyses. It was also suggested that the difference in the features of XANES is more distinct at the LI-edge than at the LIII-edge, whereas the detection limit is lower for the LIII-edge. The XANES spectrum at the LIII-edge was obtained even for the sample containing only 50 ppm of Sn as TBT in ethanol. Although the sensitivity may be insufficient for the Sn in seawater, the method can be applied to the speciation of Sn enriched in some biological samples or used in antifouling paints.