AQUEOUS ETHYLATION OF ORGANOTIN COMPOUNDS IN SIMPLE SOLUTION FOR SPECIATION ANALYSIS BY CRYOFOCUSING AND DETECTION BY ATOMIC-ABSORPTION SPECTROMETRY - COMPARISON WITH HYDRIDE GENERATION

A 2(3) factorial experimental design has been used to determine the op timum reaction conditions for organotin ethylation in simple aqueous s olutions for speciation by Cryogenic Trapping/ Gas Chromatography/Atom ic Absorption Spectrometry (CT/GC/AAS). The factors chosen and their l evels of variation (- and +) were the pH of the solution (levels 3 and 5), the amount of NaBEt(4) added (levels 1 and 9 mg) to the organotin s and the time of ethylation reaction (levels 10 and 20 min). Optimum conditions were investigated for monomethyltin (MMT), diethyltin (DET) and dibutyltin (DBT) in mixed solution at a concentration of 10 ng of each Sn compound in 50 ml of solution (200 ng . l(-1)). The influence of the different factors on the yield of the ethylation reaction in t he ranges investigated depends on the degree of substitution and the n ature of the alkyl groups of the organotins. The ethylation reaction f or DET and DBT is more efficient at high pH levels, MMT gives higher y ields at lower pH. Both MMT and DET require a high amount of reagent, while reagent concentration has no real influence on the DBT signal. C omparison of hydride generation and ethylation as derivatisation proce dures for organotin speciation has been performed in simple solutions. Under these analytical conditions, hydride generation is shown to be slightly more sensitive than ethylation by a factor of 1.4 for MMT and DET and 2 for DBT. However derivatisation using ethylation provides m ore reproducible results and is not affected by inorganic interferents .