Structural identification of hindered amine light stabilisers in coil coatings using electrospray ionisation tandem mass spectrometry.

Hindered amine light stabilisers (HALS) are the most effective antioxidants currently available for polymer systems in post-production, in-service applications, yet the mechanism of their action is still not fully understood. Structural characterisation of HALS in polymer matrices, particularly the identification of structural modifications brought about by oxidative conditions, is critical to aid mechanistic understanding of the prophylactic effects of these molecules. In this work, electrospray ionisation tandem mass spectrometry (ESI-MS/MS) was applied to the analysis of a suite of commercially available 2,2,6,6-tetramethylpiperidine-based HALS. Fragmentation mechanisms for the [M + H](+) ions are proposed, which provide a rationale for the product ions observed in the MS/MS and MS(3) mass spectra of N-H, N-CH(3), N-C(O)CH(3) and N-OR containing HALS (where R is an alkyl substituent). A common product ion at m/z 123 was identified for the group of antioxidants containing N-H, N-CH(3) or N-C(O)CH(3) functionality, and this product ion was employed in precursor ion scans on a triple quadrupole mass spectrometer to identify the HALS species present in a crude extract from of a polyester-based coil coating. Using MS/MS, two degradation products were unambiguously identified. This technique provides a simple and selective approach to monitoring HALS structures within complex matrices.

Using calibration approaches to compensate for remaining matrix effects in quantitative liquid chromatography/electrospray ionization multistage mass spectrometric analysis of phytoestrogens in aqueous environmental samples.

Signal suppression is a common problem in quantitative liquid chromatography/electrospray ionization multistage mass spectrometric (LC/ESI-MS(n)) analysis in environment samples, especially in highly loaded wastewater samples with highly complex matrix. Optimization of sample preparation and improvement of chromatographic separation are prerequisite to improve reproducibility and selectivity. Matrix components are reduced if not eliminated by optimization of sample preparation steps. However, extensive sample preparation may be time-consuming and risk the significant loss of some trace analytes. The best way to further compensate matrix effects is the use of an internal standard for each analyte. However, in a multi-component analysis, finding appropriate internal standards for every analyte is often difficult. In this present study, a more practical alternative option was sought. Matrix effects were assessed using the post-extraction addition method. By comparison of three different calibration approaches, it was found that matrix-matched calibration combined with one internal standard provides a satisfactory method for compensating for any residual matrix effects on all the analytes. Validating experiments on different sewage treatment plant (STP) influent samples analyzing for a range of phytoestrogens showed that this calibration method provided satisfactory results with concentration ratio 96.1-105.7% compared to those by standard addition.

A fragmentation study of isoflavones in negative electrospray ionization by MSn ion trap mass spectrometry and triple quadrupole mass spectrometry.

This study has elucidated the fragmentation pathway for deprotonated isoflavones in electrospray ionization using MS(n) ion trap mass spectrometry and triple quadrupole mass spectrometry. Genistein-d(4) and daidzein-d(3) were used as references for the clarification of fragment structures. To confirm the relationship between precursor and product ions, some fragments were traced from MS(2) to MS(5). The previous literature for the structurally related flavones and flavanones located the loss of ketene (C(2)H(2)O) to ring C, whereas the present fragmentation study for isoflavones has shown that the loss of ketene occurs at ring A. In the further fragmentation of the [M-H-CH(3)](-*) radical anion of methoxylated isoflavones, loss of a hydrogen atom was commonly found. [M-H-CH(3)-CO-B-ring](-) is a characteristic fragment ion of glycitein and can be used to differentiate glycitein from its isomers. Neutral losses of CO and CO(2) were prominent in the fragmentation of deprotonated anions in ion trap mass spectrometry, whereas recyclization cleavage accounted for a very small proportion. In comparison with triple quadrupole mass spectrometry, ion trap MS(n) mass spectrometry has the advantage of better elucidation of the relationship between precursor and product ions.

Simultaneous determination of isoflavones and lignans at trace levels in natural waters and wastewater samples using liquid chromatography/electrospray ionization ion trap mass spectrometry.

A high-performance liquid chromatography/electrospray ionization ion trap mass spectrometry (HPLC/ESI-MSn) method has been developed for the trace determination of phytoestrogens in aquatic environmental samples. The method includes solid-phase extraction (SPE) and analysis using liquid chromatography/electrospray ionization ion trap mass spectrometry. The aquatic environmental samples, influent of a wastewater treatment plant (WWTP) and creek water, were adjusted to pH approximately 5 before extraction. The analyzed phytoestrogens were identified by an MSn method and quantified against a deuterated internal standard (genistein-3',5',6,8-D4). In negative ion mode, 0.1% formic acid was employed in acetonitrile/water mobile phase. The method detection limits ranged from 0.5 to 10 ng/L in WWTP influent and from 0.1 to 5 ng/L in creek water. Average SPE recoveries for the analyzed phytoestrogens ranged from 85 to 95%, with a relative standard deviation (RSD) (%) ranging from 3.9 to 6.5. The concentrations of the six analyzed phytoestrogens varied from 0.2 to 600 ng/L with high levels of enterolignans (enterolactone and enterodiol) found in the collected wastewater. The method is shown to be suitable for the determination of phytoestrogens in aquatic environmental samples at nano- and sub-nanogram per liter levels.