Direct and fast determination of polychlorinated biphenyls in contaminated soils and sediments by thermal desorption-gas chromatography-tandem mass spectrometry.

A direct procedure based on thermal desorption-gas chromatography-tandem mass spectrometry (TD-GC-MS-MS) was developed for the fast extraction of seven polychlorinated biphenyls (PCBs) from sediments and soils. PCBs were directly extracted, from 20 to 75 mg of sample, without any chemical pre-treatment or use of organic solvents, after the addition of 10 µL internal standard (PCB 195) in acetone. Sample treatment was totally automated. PCBs were extracted at 250 °C for 20 min, using a helium flow and the PCBs were trapped in a cryogenic Tenax trap at -10 °C. After that, analytes were directly desorbed at 270 °C and introduced to the GC-MS-MS system. Recoveries were established using spiked soil and sediment from 2.5 to 50 ng g-1, obtaining values from 74 to 127%. The limits of quantification were from 1.0 to 1.7 ng g-1 for soil and from 0.3 to 0.4 ng g-1 for sediments, respectively. Precision, assessed as the relative standard deviation (RSD), was lower than 8 and 11% for sediment and soil analysis, respectively, except for PCB-28 in soil samples which provided a RSD of 18%. Certified reference material and field samples were analysed by the proposed TD-GC-MS-MS method. Results were compared by a paired samples Student's t-test with those obtained by a reference extraction procedure based on pressurized solvent extraction, followed by stir bar sorptive extraction, being statistically comparable (α = 0.05). A comprehensive greenmetric evaluation of the proposed method was carried out, having the TD extraction a negligible environmental impact as compared to conventional extraction procedures.