Development of a triple spike methodology for validation of butyltin compounds speciation analysis by isotope dilution mass spectrometry : Part I. Synthesis of the spike, characterisation and development of the mathematical equations

Abstract

A methodology for the determination of butyltin compounds by isotope dilution mass spectrometry based on a triple spike approach is presented. A spike solution containing monobutyltin, dibutyltin and tributyltin, each compound enriched with different tin isotopes, has been synthesised, characterised and applied to the simultaneous determination of the three butyltin compounds by isotope dilution GC-ICP-MS. Mathematical equations correcting for all possible degradation reactions which could occur during sample pre-treatment were developed, allowing the accurate calculation of the three butyltin concentrations sought plus the values of six possible interconversion yields, regardless of the extent of degradation. The triple tin spike solution has shown itself to be stable over more than 7 months, both in isotope composition and elemental concentration, provided that acetic acid is present in the solution. The proposed methodology has been finally evaluated by performing the determination of butyltin compounds in the certified reference material CRM-477 (Mussel Tissue), under different microwave assisted extraction conditions, with satisfactory results.