Evaluation of the spectral accuracy of mass spectrometers using compounds containing Cl or Br atoms.

Current procedures for the evaluation of spectral accuracy of mass spectrometers are limited by the lack of certified isotopic reference materials and the high uncertainty in the isotopic composition of natural abundance molecules. The calculated uncertainties in the ratio M + 1/M for natural abundance molecules containing any number of C, H, N and/or O atoms are close to 5% relative because of the natural variability of the isotopic composition of carbon. So, we have developed two alternative measurement procedures with much lower theoretical uncertainties for a better evaluation of spectral accuracy in both single and triple quadrupole analysers. The first method is based on the measurement of the M + 2/M, M + 4/M + 2, etc. ratios for halogenated organic compounds containing either Cl or Br. The theoretical uncertainties for these ratios because of natural variability are in the order of 0.3 to 1.0% making them suitable for the evaluation of spectral accuracy with the additional advantage that there is no need to take into account other limitations such as cluster purity or poor mass resolution. This procedure was applied to the evaluation of a single quadrupole GC-MS instruments using natural abundance PCB and PBDE standards with satisfactory results. The second method can be applied to tandem instruments and takes advantage of the loss of two halogen atoms when PCB and PBDE standards are fragmented by Collision Induced Dissociation. Theoretical SRM transition ratios can be calculated as a pure combinatorial probability with theoretical uncertainties lower than 0.1%. By combining PCBs and PBDEs with different number of halogen atoms, a mass range from 100 to 700 u and abundance ratios from 0.1 to 10 can be evaluated. The use of penta-chlorinated PCBs and/or penta-brominated PBDEs is finally recommended for the evaluation of spectral accuracy of mass spectrometers with the EI source. Copyright © 2016 John Wiley & Sons, Ltd.

Simultaneous determination of α-, ß- and γ-hexabromocyclododecane diastereoisomers in water samples by isotope dilution mass spectrometry using (81)Br-labeled analogs.

This work describes the synthesis, characterization and application of three (81)Br-labeled diastereosiomers of hexabromocyclododecane (HBCD) for the accurate and precise determination of α-, ß- and γ-HBCD in water samples by isotope dilution mass spectrometry. The synthesis of the labeled analogs was carried out by bromination of cis, trans, trans-1,5,9-cyclododecatriene with (81)Br-enriched bromine. After isolation and purification by semipreparative HPLC, each diastereoisomer was characterized in terms of concentration and isotopic enrichment. Then, they were added to the samples to simultaneously quantify the three HBCD diastereoisomers in a single LC-MS/MS injection without resorting to a methodological calibration graph. The results obtained here demonstrate that the use of (81)Br-labeled analogs provides accurate and precise determinations of α-, ß- and γ-HBCD in real water samples. The limits of quantification obtained in real samples for α-, ß- and γ-HBCD were 0.022, 0.073 and 0.015 ng L(-1), respectively, significantly lower than those required by the European Directive 2013/39/EC.

Determination of Polychlorinated Biphenyls in Solid Samples by Isotope Dilution Mass Spectrometry Using ³7Cl-Labeled Analogues.

This work describes the first application of (37)Cl-labeled compounds to isotope dilution mass spectrometry (IDMS). The synthesis of 12 (37)Cl-labeled polychlorinated biphenyls (PCBs) was carried out by the chlorination of biphenyl with isotopically enriched chlorine gas, generated by the direct oxidation of Na(37)Cl with potassium peroxymonosulfate. After an exhaustive purification due to the presence of other congeners, the concentration and the isotopic enrichment of all (37)Cl-labeled PCBs in the mixture was determined. The proposed procedure allows the simultaneous quantification of every isotope diluted PCB congener in a single gas chromatography-tandem mass spectrometry (GC-MS/MS) injection without resorting to a methodological calibration graph. The results obtained here demonstrate that the use of (37)Cl-labeled analogues provides results in agreement with the certified values of three different Certified Reference Materials (marine sediment SRM 1944, fish tissue 1947, and loamy soil CRM 962-50) and analytical figures of merit comparable to those obtained using regular IDMS procedures based on the use of commercially available (13)C-labeled analogues.