Green fat removal in the analysis of polychlorinated biphenyls in biotic samples

A green analytical method based on the use of a deep eutectic solvent (DES) has been proposed for fat removal in the analysis of polychlorinated biphenyl (PCBs) in biotic samples. Using priority PCB congeners as model compounds, a novel sample preparation approach fully avoiding the use of mineral acids has been developed. Once optimized, the procedure allowed fat removal to be accomplished by 30min treatment with [chlorine chloride]:[oxalic acid dihydrated] 1:1 molar ratio at 60°C, with 3s vortexing every 5min to facilitate the homogenization of the slurry. Then, the target PCBs were recovered from the slurry by 20min extraction with 4mL of n-hexane. This DES-based method was combined with gas chromatography-quadrupole mass spectrometry (GC-qMS) for final PCB determination. The complete analytical method provided satisfactory recoveries of the target compounds (above 87% for all analytes), using as a small amount of sample as 0.150g. The repeatability of the complete procedure, expressed as relative standard deviation, was less than 5%, and the intermediate precision better than 14%. Final validation of the proposed methodology included the satisfactory comparison of the concentrations calculated for the endogenous PCBs in selected fatty foodstuffs with lipid contents under 18% (w/w fresh weight, fw) with those found when the same samples were analyzed by a more conventional and accepted reference procedure. The limits of detection were in all cases lower than 30 pg/g fw (as calculated for real samples), demonstrating the feasibility of the proposed procedure for accurate determination of the target compounds in biotic samples.