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The aqueous-phase reaction of dimethylarsinc acid (DMAs(V)) with NaBH 4 (THB) was studied under non-analytical conditions (1000 μg/mL As, 0.1 M HCl, 1% NaBH 4 ) with the aim of identifying intermediates and reaction products. The use of direct analysis in real time (DART) with high-resolution mass spectrometry (HRMS), in combination with two different chemical vapor generation systems, allowed the identification of some species not detected by GC-MS such as Me 2 As-AsMe-AsMe 2 and the arsonium species [Me 3 As-AsMe 2 ] + and [Me 2 As-AsMe 2 -AsMe 2 ] + . Many other methylated species of arsenic containing up to four arsenic atoms have been observed. Unfortunately, the oxidation mechanism that took place in the DART source interfered with the identification of some of those species formed in solution following THB reduction. The species identified by DART-HRMS, together with those previously identified by GC-MS (Me 2 AsH, Me 2 AsOH, Me 3 As, Me 3 AsO, Me 2 AsAsMeH, Me 2 AsAsMe 2 , and Me 2 As-O-AsMe 2 )' enabled the formulation of hypotheses on the possible reaction pathways and revealed an aqueous-phase reactivity of DMAs(V) which could not be explained on the basis of current knowledge. Graphical Abstract.

In this work, a straightforward analytical approach based on headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry was developed for the analysis of salivary volatile organic compounds without any prior derivatization step. With a sample volume of 500 μL, optimal conditions were achieved by allowing the sample to equilibrate for 10 min at 50 °C and then extracting the samples for 10 min at the same temperature, using a carboxen/polydimethylsiloxane fibre. The method allowed the simultaneous identification and quantification of 20 compounds in sample headspace, including short-chain fatty acids and their derivatives which are commonly analysed after analyte derivatization. The proof of applicability of the methodology was performed with a case study regarding the analysis of the dynamics of volatile metabolites in saliva of a single subject undergoing 5-day treatment with rifaximin antibiotic. Non-stimulated saliva samples were collected over 3 weeks from a nominally healthy volunteer before, during, and after antibiotic treatment. The variations of some metabolites, known to be produced by the microbiota and by bacteria that are susceptible to antibiotics, suggest that the study of the dynamics of salivary metabolites can be an excellent indirect method for analysing the gut microbiota. This approach is novel from an analytical standpoint, and it encourages further studies combining saliva metabolite profiles and gut microbiota dynamics. Graphical abstract.

Anthropogenic impact over the Pasvik River (Arctic Norway) is mainly caused by emissions from runoff from smelter and mine wastes, as well as by domestic sewage from the Russian, Norwegian, and Finnish settlements situated on its catchment area. In this study, sediment samples from sites within the Pasvik River area with different histories of metal input were analyzed for metal contamination and occurrence of metal-resistant bacteria in late spring and summer of 2014. The major differences in microbial and chemical parameters were mostly dependent on local inputs than seasonality. Higher concentrations of metals were generally detected in July rather than May, with inner stations that became particularly enriched in Cr, Ni, Cu, and Zn, but without significant differences. Bacterial resistance to metals, which resulted from viable counts on amended agar plates, was in the order Ni 2+ >Pb 2+ >Co 2+ >Zn 2+ >Cu 2+ >Cd 2+ >Hg 2+ , with higher values that were generally determined at inner stations. Among a total of 286 bacterial isolates (mainly achieved from Ni- and Pb-amended plates), the 7.2% showed multiresistance at increasing metal concentration (up to 10,000 ppm). Selected multiresistant isolates belonged to the genera Stenotrophomonas, Arthrobacter, and Serratia. Results highlighted that bacteria, rapidly responding to changing conditions, could be considered as true indicators of the harmful effect caused by contaminants on human health and environment and suggested their potential application in bioremediation processes of metal-polluted cold sites.

A high-precision exact-matching quadruple isotope dilution method (ID 4 MS) was employed for the quantitation of nitrate in an air-dried spinach powder Certified Reference Material (CRM). The analyte was extracted in hot water following addition of 15 NO[Formula: see text] internal standard. The blend was then treated with sulfamic acid to remove nitrite and with triethyloxonium tetrafluoroborate to promote aqueous conversion of nitrate into volatile EtONO 2 . The derivative was analyzed by headspace GC-MS with 3-min elution time. The method performance was validated with a series of tests which demonstrated adequate selectivity and ruggedness. This method supported the development of novel SPIN-1 CRM giving a modest contribution to its uncertainty (u char = 0.85%). With respect to previous attempts, the SPIN-1 was proven stable, homogeneous (u hom = 0.44%), and suitable for spinach monitoring under EU regulations. On dried basis, the nitrate content of SPIN-1 was found to be 22.53 ± 0.43 mg/g (U c = 1.9%, k = 2). The material was also used in an inter-laboratory study where four laboratories employed a total of ten measurement methods. Graphical Abstract SPIN-1 Certified Reference Material for nitrate in spinach powder.

In order to elucidate controversial results emerging in chemical vapor generation (CVG) for trace element determination, we conducted a series of experiments devoted to the identification of intermediates formed by acid hydrolysis of amine-boranes. For the first time, direct analysis in real time coupled with high-resolution mass spectrometry (DART-Orbitrap) was applied for detection of this class of compounds. Mass spectra of both solid amine-boranes and their aqueous solutions (pH ~ 8, no hydrolysis) were acquired for understanding their ionization pathway. Mass spectra of aqueous solutions of t-BuNH 2 ·BH 3 and Me 2 NH·BH 3 were acquired under conditions that are employed in CVG (0.017-4.0 mol L -1 HCl, 0.167-0.2 mol L -1 borane reagent). The results disclose a reactivity driven by pH of amine-boranes undergoing hydrolysis. At low acidity, the hydrolysis proceeds according to the currently accepted displacement mechanisms (i.e., R 3 N·BH 3 + H 3 O + → R 3 NH + + H 2 OBH 3 ). At higher acidity, N-tert-butyl, cyclotriborazane, and bis(dimethylamino)boronium were identified, for the first time, during the hydrolysis of t-BuNH 2 ·BH 3 and Me 2 NH·BH 3 , respectively. Formation of these intermediates was ascribed to a hydrolysis pathway starting with the ionization of the amine-borane, (i.e., R 3 N·BH 3 + H 3 O + → [(H 2 O)R 3 NBH 2 ] + + H 2 ). The new evidence explains the anomalous behavior observed in CVG by amine-borane derivatization, and updates the currently accepted mechanisms for the acid hydrolysis of amine-boranes. Graphical Abstract.