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The aqueous-phase reaction of dimethylarsinc acid (DMAs(V)) with NaBH4 (THB) was studied under non-analytical conditions (1000 μg/mL As, 0.1 M HCl, 1% NaBH4) 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 Me2As–AsMe–AsMe2 and the arsonium species [Me3As–AsMe2]+ and [Me2As–AsMe2–AsMe2]+. 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 (Me2AsH, Me2AsOH, Me3As, Me3AsO, Me2AsAsMeH, Me2AsAsMe2, and Me2As–O–AsMe2)‚ 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. [ABSTRACT FROM AUTHOR]

[Display omitted] • Simple extraction of Met and SeMet from food samples using methanesulfonic acid in a static oven without reflux. • Single-step aqueous derivatization of Met and SeMet by triethyloxonium ions. • Reactions conditions optimized by central composite design. • Quantitation by high-precision isotope dilution GC–MS. A novel analytical method for the simultaneous gas chromatography–mass spectrometry (GC–MS) determination of methionine and selenomethionine in food samples is described. Samples were digested with methanesulfonic acid in a closed vessel without the need for reflux. A single step derivatization using triethyloxonium tetrafluoroborate was optimized for the conversion of the analytes into their ethyl derivatives, followed by their extraction with hexane and GC–MS analysis.. This derivatization approach was simpler and/or safer with respect to current methods based on alkyl chloroformate or silylating reagents and it yielded very clean chromatography. A design of experiment approach, based on an open source chemometric software, was used to optimize the experimental conditions. When analysis of a 1 mL volume of aqueous standard was performed, detection limits of 1 ng/g methionine and 10 ng/g for selenomethionine were obtained. The method was validated by analysis of a selenized yeast Certified Reference Material NRC SELM-1. [ABSTRACT FROM AUTHOR]

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-BuNH2·BH3 and Me2NH·BH3 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., R3N·BH3 + H3O+ → R3NH+ + H2OBH3). At higher acidity, N-tert-butyl, cyclotriborazane, and bis(dimethylamino)boronium were identified, for the first time, during the hydrolysis of t-BuNH2·BH3 and Me2NH·BH3, respectively. Formation of these intermediates was ascribed to a hydrolysis pathway starting with the ionization of the amine-borane, (i.e., R3N·BH3 + H3O+ → [(H2O)R3NBH2] + + H2). 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 [ABSTRACT FROM AUTHOR]

Direct analysis in real time (DART) has been applied in conjunction with high-resolution Orbitrap mass spectrometry to characterize the aqueous reduction of monomethylarsenate by tetrahydroborate (B/As molar ratio ≈ 4 mol/mol). Under these conditions, the reaction gives rise to a complex mixture of arsenic compounds which result in the formation of a reddish precipitate. The use of the DART revealed the presence of a number of polymeric arsanes – up to eight arsenic atoms – associated with the liquid/solid phase of this reaction system. From a reactivity point-of-view, these polymers exhibit an uncommon ionization pathway. In fact, similar to the alkanes, the action of the DART results in the generation of [M − H] + ions. Furthermore, for each oligomer MeHAs–(AsMe) n –AsHMe ( n = 0–8), a series of oxidation products [(M + n O) − H] + were also identified and their formation has been discussed. [ABSTRACT FROM AUTHOR]

When working with humid gaseous samples, the amount of water vapour collected in a needle trap along with volatile analytes may vary from sample to sample and decrease during the storage. This has a major impact on desorption efficiency and recovery. We propose the addition of a labelled internal standards to nullify the effect of variable humidity on the analytical performance of needle trap micro-extraction combined with gas chromatography mass spectrometry. Triple-bed (Divinylbenzene/Carbopack X/Carboxen 1000) and single-bed (Tenax GR) needles were tested with standard gaseous mixtures prepared at different relative humidity levels (85%, 50% and 10%). The standard mixtures contained twenty-five analytes representative of breath and ambient air constituents, including hydrocarbons, ketones, aldehydes, aromatics, and sulphurs, in the concentration range 0.1–700 ppbv. The two needles showed different behaviours, as recovery was independent of humidity for single-beds, whereas a low recovery (10–20%) was observed when triple-beds trapped very volatile compounds at low humidity (e.g. pentane and ethanol, 10% relative humidity. Triple-beds showed an almost quantitative recovery (>90%) of all the analytes at 50% and 85% relative humidity. This big difference was probably due to the reduced action of water vapour pressure during the desorption step. The addition of 6D-acetone and 8D-toluene to the sorbent material before gas sampling and the normalization of raw data nullified this effect, thereby lowering the variations of analyte recovery at different humidity levels down to 20%. Internal standards were also exploited to limit within 10–20% alterations in peak areas of very volatile compounds during needle storage at room temperature. This variation may results from a loss of water vapour either retained from the sorbent material and/or condensed on triple-bed needle walls. After normalization, the inter- and intra-day precision were halved to 5% and 10% in the case of single-beds, respectively, and to 15% and 20% with three-beds. The addition of an internal standard to the sorbent helps to keep the overall analytical procedure under control and improves the reliability of needle trap micro-extraction for the analysis of volatile organic compounds at ultra-trace levels. fx1 • Analysis of volatile organic compounds by needle trap micro-extraction and GC-MS. • Reliable addition of known amounts of labelled internal standards into a needle trap. • Amount of water vapour in the needle strongly affects reproducibility of desorption. • Labelled internal standards improve the quality of analytical data. [ABSTRACT FROM AUTHOR]

The mechanisms controlling the generation of PbH 4 by reaction of inorganic Pb(II) with aqueous NaBH 4 were investigated both in the presence and in the absence of the additive K 3 Fe(CN) 6. For the first time PbH 4 has been identified in analytical chemical vapor generation (CVG) by using gas chromatographic mass spectrometry (GC-MS), which allows the use of deuterium labelled experiments. In the absence of the additive, under reaction conditions typically employed for trace lead determination by CVG, Pb(II) is converted to solid species and no volatile lead species can be detected by either atomic or mass spectrometry for Pb(II) concentration up to 100 mg L−1. In alkaline conditions Pb(II) substrates are unreactive towards NaBH 4. In the presence of K 3 Fe(CN) 6 , deuterium labelled experiments clearly indicated that the generated PbH 4 is formed by the direct transfer of hydride from borane to lead atoms. Kinetic experiments were carried out to evaluate the rate of reduction of K 3 Fe(CN) 6 by NaBH 4 , the rate of hydrolysis of NaBH 4 both in the presence and in the absence of K 3 Fe(CN) 6 , and the rate of dihydrogen evolution following NaBH 4 hydrolysis. The effect of delayed addition of Pb(II) to NaBH 4 –HCl– K 3 Fe(CN) 6 , and K 3 Fe(CN) 6 to NaBH 4 –HCl–Pb(II) reaction mixtures on the efficiency of plumbane generation was investigated by continuous flow CVG coupled with atomic fluorescence spectrometry. The collected evidences, complemented with thermodynamic considerations and literature data, have made it possible to clarify long-standing controversial aspects related to the mechanism of plumbane generation and the role of K 3 Fe(CN) 6 additive. [Display omitted] • The mechanism of plumbane generated by NaBH 4 derivatization have been clarified. • Plumbane generated in analytical conditions has been identified by modified GC-MS. • D-labelled experiments and GC-MS identified the mechanism of hydrogen transfer. • The additive K 3 Fe(CN) 6 reacts with Pb species formed in the early stage of reaction. • Hydrolysis products of NaBH 4 are active species in plumbane generation. [ABSTRACT FROM AUTHOR]