Gas chromatography multiplexed with cyclic ion mobility mass spectrometry is a comprehensive two-dimensional separation technique that can resolve compounds that would otherwise coelute in a single-dimension separation. The cyclic geometry of the ion mobility cell enables ions to travel multiple passes, increasing their drift times to the detector and relative separation. However, the quality of the separation may be obfuscated when "wrap-around" occurs, during which speedier ions catch up with slower ion populations when allowed to travel through more than one pass. Consequently, cyclic ion mobility is incorrectly perceived as a targeted approach that requires preselection of ions prior to separation. The present study demonstrates that "wraparound" can be mitigated by comparing drift times measured during single-and multipass experiments and extrapolating the number of passes experienced by each ion. This straightforward calculation results in the "unwrapping" of cyclic ion mobility data so that the experiments can be interpreted in a nontargeted way while reaping the benefit of peak capacities that rival those achieved using other comprehensive two-dimensional separations.

Per-and polyfluoroalkyl substances (PFASs) have been widely used since the 1940s in industry and everyday household products. They also persist in the environment and bioaccumulate in humans and wildlife. Despite these concerns, the identities of most PFASs in environmental and biological samples are unknown. Herein, we describe a novel cyclic ion mobility mass spectrometer (cIMS), hyphenated with gas chromatography (GC) atmospheric pressure chemical ionization, that can reveal the presence of unknown PFASs on the basis of the ratio of their mass and collision cross section (CCS). Prediction of the CCS of ca. 20,000 chemicals used in industry and commerce indicates that most compounds characterized by CCS values that are less than the sum of 100 Å 2 and one-fifth of their mass are either PFASs or polybrominated flame retardants. When this filter is applied to GC-cIMS data collected from a set of 20 indoor dust samples, PFAS compounds are revealed without prior knowledge of their occurrence. Validation of this approach was performed using SRM 2585, a standard reference material of household dust, by comparing the PFASs detected with those (tentatively) identified in previous studies. Chlorofluoro phthalimides tentatively identified previously were confirmed with a synthesized standard. The method also reveals the presence of chlorofluoro n-alkanes as an emerging class of "forever chemicals" that contaminate the indoor environment.

Ortho-substituted isomers of tricresyl phosphates (TCPs) and their toxic metabolites (e.g., CBDP: cresyl saligenin phosphate) can cause neurotoxic effects in humans. When TCP is introduced to an atmospheric pressure chemical ionization source using gas chromatography, radical cations M •+ are formed by charge exchange. The mass spectrum of an ortho-substituted isomer displays two intense peaks that are absent in the spectra of non-ortho-substituted isomers, leading us to propose structure-diagnostic ion−molecule reactions between ions M •+ and oxygen species present in the source. However, the mechanisms of these reactions have not yet been established. In this study, we propose a mechanism and provide support through computational and experimental analyses using density functional theory and cyclic ion mobility-mass spectrometry. The mechanism consists of a multistep reaction starting with the rearrangement of the molecular ion into a distonic isomer followed by an oxidation step and then decomposition into [CBDP-H] + . This proposal is consistent with the results obtained from a series of isotopically labeled analogues. Cyclic ion mobility experiments with a tri-o-cresyl phosphate standard reveal the presence of at least two hydrogen shift isomers of the product ion [CBDP-H] + that are connected by a low-lying barrier. The selectivity of the ion−molecule reactions toward ortho-substituted cresyl TCP isomers provides us with an identification tool that can select potentially neurotoxic triaryl phosphate esters present in complex mixtures that are produced in large volume by industry.