An efficient method for the determination of formaldehyde in frozen fish by SPME-gas chromatography-ion trap tandem mass spectrometry was developed and validated. Experimental design was used to investigate the effects of temperature of extraction, time of extraction and matrix stirring. The calculated regression model was used to find the experimental conditions providing the optimal SPME extraction yield. Validation was carried out in terms of limit of detection (LOD), limit of quantitation (LOQ), linearity, precision, trueness and selectivity. LOD and LOQ values in the low ng kg-1 were achieved, whereas linearity was established over one order of magnitude. Good precision was obtained both in terms of intra-day repeatability and between-day precision on two concentration levels (RSD% lower than 9%). Recovery values of 82.3±1.8% and of 95.3±1.2% (n=3) were calculated at 100 mg kg-1 and 3 mg kg-1 level. Method selectivity was demonstrated by adding 2,3,4,5,6-pentafluorobenzyl alcohol as interfering substance. The applicability of the method to the determination of formaldehyde in a number of frozen fish samples was finally demonstrated.
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