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Development of the method for the analysis of organotin compounds (OTC) in seawater at sub-nanogram level per liter by solid-phase extraction (SPE) and GC-PFPD detection

The most toxic among all organotin compounds is tributyl tin (TBT), mainly used as biocide in antifouling paints. It is on the list of priority pollutants in the European Water Frame Directive since it was established that TBT can cause chronic and acute poisoning of aquatic organisms already at a level of 1-2 ng L-1. France was first to ban the use of TBT in antifouling paints in 1982, and since January 2008 its application is banned almost worldwide, including Croatia. According to Croatian regulation, the average TBT concentration in water must not be higher than 0.2 ng L-1, while maximum allowed single concentration is 1.5 ng L-1. Also, the OSPAR commission defined the Ecotoxicological Assessment Criteria (EAC) for TBT in seawater (based on possible adverse effects on mollusks populations) at 0.1 ng L-1 (lower value) and 1.5 ng L-1 (upper value). According to existing regulative in European countries and Croatia, pollution of marine environment by TBT should be monitored by measuring concentration of butyl tin compounds in seawater. Analytical method used for this purpose should have detection limit (DL) as low as 0.2 ng L-1. This very low DL can be reached, according to existing literature, only with sophisticated techniques such as GC-ICPMS, which is not readily available in routine laboratories. Therefore, it is essential to develop other methods for TBT determination in water with required DL, based on simpler and more economical techniques, such as GC-PFPD. The aim of this work was to develop and optimize an adequate analytical method for speciation of OTC (BuT and PhT) in seawater using solid-phase extraction (SPE) as a preconcentration method, followed by detection with GC-PFPD. Performances of cartridges with different polar and non-polar stationary phases were investigated. For this purpose Oasis HLB polymer and HyperSep C18 have been used as sorbents, while derivatization with sodium tetraethylborate was performed either before or after solid extraction. Preconcentration conditions of OTC on SPE were investigated by using different solvents as eluents (hexane, methanol, ethyl acetate and acetonitrile) and eluent volume was optimized to obtain quantitative elution of retained OTC. Furthermore, other details as breakthrough volume, addition of complexing agents, in-flow and elution rate were studied as well. As a certified reference material for determination of OTC in seawater does not exist, verification of the method was performed by the comparative analyses of selected samples with GC-ICPMS. Detection limits, recovery rates, and the precision of the whole procedure have been determined. The method was applied to determination of organotin compounds in natural seawater samples from the Adriatic Sea.

Organotin compounds ; tributyl tin ; solid phase extraction (SPE) ; GC-PFPD

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