ANALYTICAL METHODS FOR THE DETERMINATION OF ORGANOTINS IN THE MARINE-ENVIRONMENT

Analytical procedures for the determination of organotin compounds in sea water, sediments and mussels have been adopted in our laboratory, intercomparison/certification exercises with other European laboratories giving satisfactory results. The characteristics of the different methodologies are discussed, the balance between practical and analytical aspects leading to the selection of the following procedures. For water samples two alternative extraction techniques are used: liquid/liquid extraction (0.3% tropolone in methylene chloride) or liquid/solid extraction (C18- or Carbopack B-loaded extraction tubes). Solid-phase extraction ensures good results and is more suitable in the field, avoiding high volumes of organic solvents and transport of fragile glassware. Extraction tubes can be easily stored, and problems with the transfer of whole samples to the laboratory, and storage and conservation problems are prevented. For sediments and mussels, sonication (0.05% tropolone in methanol) can be used as the extraction procedure. Final detection is performed by GC (FPD or MS detection) after pentylation. GC-MS is generally necessary to confirm doubtful results in highly polluted sediments, particularly if high sulphur levels are present. AAS can be used as an alternative detection technique after selective elution from the solid-phase tubes without any derivatization. The detection limits are in the low-ppt range for water samples and in the low-ppb range for sediments and mussel samples, with a precision generally better than 10% for water samples and better than 15% for sediments and mussels.