Headspace solid-phase microextraction-capillary gas chromatography-ICP mass spectrometry for the determination of the organotin pesticide fentin in environmental samples

Abstract

The extraction and preconcentration capabilities of headspace solid-phase microextraction (headspace SPME) were combined with the separation power of capillary gas chromatography (CGC) and the low limits of detection (LODs) of inductively coupled plasma mass spectrometry (ICP-MS) for the determination of the organotin compound triphenyltin (TPhT or fentin) in aqueous standard solutions and in potatoes and mussels after digestion with tetramethylammonium hydroxide (TMAH) or KOH–EtOH. Throughout, tricyclohexyltin (cyhexatin, TCT) was used as internal standard. Derivatization to transform TPhT and TCT into sufficiently volatile compounds was carried out with sodium tetraethylborate (NaBEt₄), at pH 8 (0.2 mol L⁻¹ ammonium buffer). Headspace extraction was performed for 10–20 min at 75 or 85 °C (depending on the type of sample) with a 100 µm polydimethylsiloxane (PDMS) fiber. Absorption curves showed that even at high temperature (75 °C) no equilibrium conditions were obtained for either compound. Direct aqueous SPME was also studied, but the sensitivity was 11 times lower at 25°C than that observed when using headspace SPME at 75 °C. After 2 min desorption of the SPME fiber at 270 °C in the GC inlet, the organotin compounds were separated on a capillary column with a polydimethylsiloxane coating and transported into the ICP by means of a home-made heated (270 °C) transfer line. Monitoring of the ¹²⁰Sn⁺ signal by ICP-MS during the run of the GC provided extremely low LODs for fentin in water: 2 pg L⁻¹ (instrumental) and 125 pg L⁻¹ (procedure) as well as a good repeatability of 8% RSD (n = 10). For mussels and potatoes, concentrations in the range 3–10 and 0.9–3 ng g⁻¹ (dry weight, as Sn), respectively, were found.