Levels of selected ortho and non-ortho polychlorinated biphenyls in UK retail milk

Nineteen pooled samples of retail cow's milk were analysed for ortho (PCBs 28, 52, 101, 118, 138, 153 and 180) and non-ortho (PCBs 77, 126 and 169) polychlorinated biphenyls. Concentrations of individual congeners in whole milk were in the ranges 2 to 95 ng/kg for ortho substituted PCBs (51 to 2440 ng/kg fat) and 0.05 to 0.6 ng/kg for non-ortho substituted PCBs (1.3 to 15.4 ng/kg fat). These values provide a preliminary estimate of background contamination levels for polychlorinated biphenyls in UK milk. Results expressed in TEQs, using the recently proposed WHO/IPCS TEFs, averaged 0.06 ng TEQ/kg whole milk.

Selective chemical ionization of nitrogen and sulfur heterocycles in petroleum fractions by ion trap mass spectrometry

A procedure is reported for the selective ammonia chemical ionization of some nitrogen and sulfur heterocycles in petroleum fractions using ion trap mass spectrometry (ITMS). The ion trap scan routine is designed to optimize the population of ammonium reagent ions and eject from the trap (by radio frequency/direct current isolation) electron ionization products formed during reagent ion formation prior to ionization of the sample. The ITMS procedure is compared with standard ion trap detector and conventional quadrupole ammonia chemical ionization for the determination of nitrogen and sulfur heterocycles in gas oil and kerosine samples. Greatly enhanced selectivity is shown for the ITMS procedure by suppression of competing charge-exchange processes.