Direct determination of the "organic extent" of tin species in environmental samples by X-ray absorption near-edge structure spectroscopy.

Abstract

A direct method for the speciation of Sn compounds in solid environmental samples by X-ray absorption near-edge structure spectroscopy (XANES) has been developed. It was found that the method can provide the "organic extent", the average number of organic ligands bound to Sn, for environmental samples. For Sn XANES at the L(III), L(I), and K edges, systematic variations were found in the spectra for butyl-, phenyl-, and methyl-substituted Sn compounds depending on the organic extent. A quantitative relationship between the organic extent and the characteristics in the XANES spectra was determined based on the peak position, peak area ratio, and peak width. The detection limit was better than 10 microg/g Sn when using the K edge, which is sensitive enough for some environmental samples, e.g., sediments, biological samples, and antifouling paints, and the sensitivity will be better if a more intense X-ray source such as an undulator or Wiggler beamline is used. The present XANES method is totally nondestructive, having the advantage that no complicated pretreatment procedures are needed, whereas such procedures are essential in conventional chromatographic analyses, which may cause experimental error by alteration of Sn species and poor recovery during analyses. Although the XANES method only provides the average number of organic ligands, the direct speciation using XANES will be helpful for estimating roughly the ratio of organic and inorganic Sn species, which can be used to study organotin transformations in sediment cores and inspection of organotin compounds in antifouling paints. In particular, micro-XANES analysis based on the present method is a promising tool in obtaining the distribution of organotin species in biological samples and specific phases in sediments.