High Resolution Mass Spectrometry

Mass Spectrometry is the technology of ions, i.e. charged atoms and/or molecules. The method is direct and provides among the highest sensitivities for trace and ultratrace contaminats. Different Mass Spectrometry (MS) architectures can either filter specific mass ranges and scan sequentially the entire MS spectrum, or collect the entire spectrum at once. The former is possible in the case of a stable signal during the entire scanning process; the latter is necessary if the signal is a fast transient. Our research is devoted to steadly push the limits of state-of-the -art MS, by either improved instrumentation or data processing, and make new applications possible.

 

Transformation of short-chain chlorinated paraffins by the bacterial haloalkane dehalogenase LinB – Formation of mono- and di-hydroxylated metabolites
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Chemosphere, Volume 262, 2021, 128288, https://doi.org/10.1016/j.chemosphere.2020.128288

 

Short-chain chlorinated paraffins (SCCPs) are listed as persistent organic pollutants (POPs) under the Stockholm Convention. Such substances are toxic, bioaccumulating, transported over long distances and degrade slowly in the environment. Certain bacterial strains of the Sphingomonadacea family are able to degrade POPs, such as hexachlorocyclohexanes (HCHs) and hexabromocyclododecanes (HBCDs). The haloalkane dehalogenase LinB, expressed in certain Sphingomonadacea, is able to catalyze the transformation of haloalkanes to hydroxylated compounds. Therefore, LinB is a promising candidate for conversion of SCCPs. Hence, a mixture of chlorinated tridecanes was exposed in vitro to LinB, which was obtained through heterologous expression in Escherichia coli. Liquid chromatography mass spectrometry (LC-MS) was used to analyze chlorinated tridecanes and their transformation products. A chloride-enhanced soft ionization method, which favors the formation of chloride adducts [M+Cl]- without fragmentation, was applied. Mathematical deconvolution was used to distinguish interfering mass spectra of paraffinic, mono-olefinic and di-olefinic compounds. Several mono- and di-hydroxylated products including paraffinic, mono-olefinic and di-olefinic compounds were found after LinB exposure. Mono- (rt = 5.9–6.9 min) and di-hydroxylated (rt = 3.2–4.5 min) compounds were separated from starting material (rt = 7.7–8.5 min) by reversed phase LC. Chlorination degrees of chlorinated tridecanes increased during LinB-exposure from nCl = 8.80 to 9.07, indicating a preferential transformation of lower chlorinated (Cl<9) tridecanes. Thus, LinB indeed catalyzed a dehalohydroxylation of chlorinated tridecanes, tridecenes and tridecadienes. The observed hydroxylated compounds are relevant CP transformation products whose environmental and toxicological effects should be further investigated.

 

Trace-Level Persistent Organic Pollutant Analysis with Gas-Chromatography Orbitrap Mass Spectrometry—Enhanced Performance by Complementary Acquisition and Processing of Time-Domain Data
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J. Am. Soc. Mass Spectrom. 2020, 31, 2, 257–266, https://doi.org/10.1021/jasms.9b00032

 

The range of commercial techniques for high-resolution gas-chromatography–mass spectrometry (GC–MS) has been recently extended with the introduction of GC Orbitrap Fourier transform mass spectrometry (FTMS). We report on progress with quantitation performance in the analysis of persistent organic pollutants (POP), by averaging of time-domain signals (transients), from a number of GC–FTMS experiment replicates. Compared to a standard GC–FTMS measurement (a single GC–FTMS experiment replicate, mass spectra representation in reduced profile mode), for the 10 GC–FTMS technical replicates of ultratrace POP analysis, sensitivity improvement of up to 1 order of magnitude is demonstrated. The accumulation method was implemented with an external high-performance data acquisition system and dedicated data processing software to acquire the time-domain data for each GC–FTMS replicate and to average the acquired GC–FTMS data sets. Concomitantly, the increased flexibility in ion signal detection allowed the attainment of ultrahigh-mass resolution (UHR), approaching R = 700 000 at m/z = 200.