Direct immersion solid-phase microextraction analysis of multi-class contaminants in edible seaweeds by gas chromatography-mass spectrometry.

The present work aimed at the development of a simple and accurate direct immersion-solidphase microextraction-gas-chromatography-mass spectrometry (DI-SPME-GC-MS) method for simultaneous determination of PAHs, PCBs, and pesticide residues in edible seaweeds. As the target contaminants possess a wide range of physical-chemical properties, multivariate experimental design was used for method optimization. In particular, two different methods were optimized and validated: one that allows for simultaneous determination of all targets, and an ad hoc method for determination of hydrophobic analytes, a class that often poses a challenge for extraction from food matrices. Optimum conditions suitable for simultaneous quantitation of all targeted compounds, namely buffer at pH = 7.0, 20% acetone (v/v), 10% NaCl (w/w), 0.02% NaN3, 60 min DI extraction at 55 °C, and 20 min desorption at 270 °C, afforded limits of quantitation (LOQs) in the range of 1-30 μg kg-1, a wide linear range of 5-2000 μg kg-1, the attainment of satisfactory determination coefficients (R2˃0.99) with no significant lack of fit (p > 0.05) at the 5% level, and satisfactory accuracy and precision values. By modifying the extraction conditions to favor extraction of the most hydrophobic analytes (e.g. higher amount of organic modifier and pH, and lower salt content) lower LOQs were obtained for these compounds ranging from 0.2 to 13.3 μg kg-1. The established methods were then used for screening of commercial, edible dry seaweeds, with PCBs (≤16.0 ng g-1) and PAHs (≤15.5 ng g-1) detected in some samples. This method overcomes most challenges commonly encountered in dry sample analysis applications, and represents the first report of a DI-SPME method employing the matrix-compatible fiber for simultaneous multiclass and multiresidue analysis of seaweeds.