Improvements and application of a modified gas chromatography atomic fluorescence spectroscopy method for routine determination of methylmercury in biota samples

Improvements to the application of a combined solid-phase microextraction followed by gas chromatography coupled to pyrolysis and atomic fluorescence spectrometry method (SPME-GC-AFS) for methylmercury (MeHg) determination in biota samples are presented. Our new method includes improvements in the methodology of determination and the quantification technique. A shaker instead of a stirrer was used, in order to reduce the possibility of sample contamination and to simplify cleaning procedures. Then, optimal rotation frequency and shaking time were settled at 800 rpm and 10 min, respectively. Moreover, the GC-AFS system was equipped with a valve and an argon heater to eliminate the effect of the decrease in analytical signal caused by the moisture released from SPME fiber. For its determination, MeHg was first extracted from biota samples with a 25% KOH solution (3h) and then it was quantified by two methods, a conventional double standard addition method (AC) and a modified matrix-matched calibration (MQ) which is two times faster than the AC method. Both procedures were successfully tested with certified reference materials, and applied for the first time to the determination of MeHg in muscle samples of goosander (Mergus merganser) and liver samples of white-tailed eagle (Haliaeetus albicilla) with values ranging from 1.19 to 3.84 mg/kg dry weight (dw), and from 0.69 to 6.23 mg kg−1 dw, respectively.