High mass accuracy in-source collision-induced dissociation tandem mass spectrometry and multi-step mass spectrometry as complementary tools for fragmentation studies of quaternary ammonium herbicides

Fragmentation studies using both an ion-trap mass analyzer and a hybrid quadrupole time-of-flight (Q-TOF) mass spectrometer were performed in order to establish the fragmentation pathways of organic molecules. A general strategy combining MSn data (n = 1-4) in an ion-trap analyzer with tandem mass spectrometry and in-source collision-induced dissociation tandem mass spectrometry (CID MS/MS) in a Q-TOF instrument was applied. The MSn data were used to propose a tentative fragmentation pathway following genealogical relationships. When several assignments were possible, MS/MS and in-source CID MS/MS (Q-TOF) allowed the elemental compositions of the fragments to be confirmed. Quaternary ammonium herbicides (quats) were used as test compounds and their fragmentation pathways were established. The elemental composition of the fragments was confirmed using the TOF analyzer with relative errors <0.0023 Da. Some fragments previously reported in the literature were reassigned taking advantage of the high mass resolution and accuracy of the Q-TOF instrument, which made it possible to solve losses where nitrogen was involved.     

Determination of quaternary ammonium compounds in seawater samples by solid-phase extraction and liquid chromatography-mass spectrometry

A method for the simultaneous determination of two biocidal quaternary ammonium compounds; didecyldimethylammonium chloride (didecyldimethyl quat) and dodecylbenzyldimethylammonium chloride (benzyl quat), in seawater by solid phase extraction (SPE) followed by liquid chromatography-mass spectrometry (LC-MS) was developed. The optimised procedure utilised off-line extraction of the analytes from seawater using polymeric (Strata-X) SPE cartridges. Recoveries ranged from 80 to 105%, with detection limits at the low parts-per-trillion (ng/l) level for both analytes. To demonstrate sensitivity, environmental concentrations were measured at three different locations along the North East coast of England with measured values in the range 120-270ng/l.