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The aqueous-phase reaction of dimethylarsinc acid (DMAs(V)) with NaBH

The degree of knowledge of the mechanisms operating in chemical vapor generation (CVG) by aqueous boranes (MBH4, R3N·BH3, M = Na, K and R = H, alkyl) for trace element determination by atomic or mass spectrometry, have been reviewed in the light of the most recent evidence. The attention has been mainly focused on the role played by sample composition – acidity, type of acid or buffer and chemical additives – in the control of the mechanism of CVG of volatile hydrides (Ge, Sn, Pb, As, Sb, Bi, Se, Te, Hg and Cd) under analytical conditions (analyte < 10−6 mol L−1, borane ≥ 10−2 mol L−1) in the absence of interfering species. The available evidence is reported in order to discuss the role played in CVG by some key chemical species, among them the hydrolysis products of borane reagents. Particular emphasis was given to those mechanistic aspects of the chemistry of aqueous boranes that have been clarified thanks to the contribution of CVG coupled with atomic or mass spectrometry, to those that are still controversial and that could stimulate further studies to understand the reactivity of aqueous boranes also for their applications other than CVG.

[object Object]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

The high toxicity of cyanide, along with its widespread industrial use, has fuelled interest in the development of analytical methods for its determination in complex matrices. In this study, we propose a novel approach for the measurement of total cyanide in soil samples based on single-step derivatization with pentafluorobenzyl bromide (F₅Bn−Br) followed by quantitation with gas chromatography mass spectrometry in negative chemical ionization mode. The reaction between CN⁻ and F₅Bn−Br resulted in the identification of several derivatives such as F₅Bn−CN, (F₅Bn)(F₅Ph)CH−CN, and (F₅Bn)₂(F₅Ph)C−CN. The relative proportion between such compounds was dependent on experimental conditions. When a 100 μL aliquot of an alkaline-aqueous extract was reacted with 700 μL of 1.3% F₅Bn−Br in acetone, the tri-alkylated derivative was the most abundant. In such conditions a detection limit of 0.5 ng/g of CN⁻ was attained. Soil samples were initially spiked with an alkaline solution of K¹³C¹⁵N internal standard and suspended in 7.5% aqueous NaOH. Determination of total cyanide was achieved by digestion of the alkaline extract with H₃PO₄ to produce HCN which was then trapped in 0.1% NaOH in a sealed double vial system, followed by reaction with F₅Bn−Br. Isotope dilution calibration was chosen for quantitation, and the validity of the novel method was demonstrated by analysis of soil Certified Reference Materials (CRMs) and by spike recovery tests., yes

The behavior of NaBH4 (THB) and the amine boranes, NH3BH3 (AB), tertbutylNH2BH3 (TBAB), Me2NHBH3 (DMAB) was investigated in continuous flow chemical vapor generation of H2Se from aqueous SeIV coupled with atomic absorption spectrometry. Unexpected higher efficiency of H2Se generation was obtained with amine boranes compared to THB (TBAB > AB > THB) using millimolar concentration of reductant (0.001–0.1 mol L−1) under strongly acidic conditions (HCl, HClO4, H2SO4, HNO3, 0.5–5 mol L−1 H+). Analytical applicability of the CVG system was tested by the determination of SeIV in natural water samples certified reference materials, using 0.01 mol L−1 TBAB in 0.5 M H2SO4. In order to explain this unexpected higher efficiency of amine boranes with respect of THB, the kinetic of hydrolysis of AB, TBAB and DMAB was investigated in acid media typically employed in chemical vapor generation for trace element determination. The kinetic was investigated by monitoring the rate the hydrogen gas evolved during hydrolysis, using a laboratory made thermostated reaction cell. Kinetics were measured for AB, TBAB and DMAB in 0.1, 0.5, 5 mol L−1 HCl or HClO4 reaction media and in 0.1 mol L−1 cysteine +0.1 mol L−1 HCl or HClO4 buffer, for reaction times from 0 to 30 min. Under strongly acidic conditions, the rates of hydrogen evolution produced by amine boranes hydrolysis appear to be much slower than those predicted by a pseudo-first order reaction and using the rate constants reported in the literature. This suggests that, at elevated acidities (5 mol L−1 HCl or HClO4), the hydrolysis of amine boranes takes place in two steps, generating a first amount of H2 (0.67–1.15 mol) much faster than the remaining about 2 mol. This evidence indicates a different mechanism of hydrolysis to the one accepted in the literature for amine boranes. The relatively high efficiencies of H2Se observed with amine borane reduction of inorganic SeIV at elevated acidities can be addressed to the action of borane intermediates, most probably amine borane cations, formed during amine borane hydrolysis in the same reaction conditions.

Photochemical vapor generation (photo-CVG) with flow injection - atomic fluorescence spectrometry was investigated for the determination of selenium, using formic and acetic acids as photochemical reagents. Using a germicidal low power ultraviolet mercury-based lamp, emitting both the 185 and 254 nm Hg lines, mild reaction conditions can be achieved in formic acid medium, where optimal sensitivity was obtained at 0.3–0.5% w/w acid concentrations, whereas the optimal sensitivity could be attained with acetic acid in the range from 12 to 35% w/w. The only volatile Se product identified by gas chromatography–mass spectrometry from formic acid-based photo-CVG was selenium carbonyl. A series of dedicated experiments were performed using photo-CVG and pure dimethylselenide in order to identify reaction pathways contributing to the formation of non-volatile selenium species or to the degradation of volatile selenium species. Under the optimized conditions in formic acid, using 250 μL sample volume, the limits of detection and quantification were 0.10 and 0.35 μg L− 1, respectively. The effect of several interfering species was investigated and the method was tested in the analysis of certified reference materials.

A reaction model describing the reactivity of metal and semimetal species with aqueous tetrahydridoborate (THB) has been drawn taking into account the mechanism of cheniical vapor generation (CVG) of hydrides, recent evidences on the mechanism of interference and formation of byproducts in arsane generation, and other evidences in the field of the synthesis of nanoparticles and catalytic hydrolysis of THB by metal nanoparticles. The new "non-analytical" reaction model is of more general validity than the previously described "analytical" reaction model for CVG. The non-analytical model is valid for reaction of a single analyte with THB and for conditions approaching those typically encountered in the synthesis of nanoparticles and macroprecipitates. It reduces to the previously proposed analytical model under conditions typically employed in CVG for trace analysis (analyte below the mu M level, borane/analyte >> 10(3) mol/mol, no interference). The non-analytical reaction model is not able to explain all the interference effects observed in CVG, which can be achieved only by assuming the interaction among the species of reaction pathways of different analytical substrates. The reunification of CVG, the synthesis of nanoparticles by aqueous THB and the catalytic hydrolysis of THB inside a common frame contribute to rationalization of the complex reactivity of aqueous THB with metal and semimetal species. (C) 2016 Elsevier B.V. All rights reserved.

Deatailed Conference Report : CSI XL June 2017, Pisa

The aim of our study was to investigate how denaturing agents commonly used in protein analysis influence the labeling between a reactive molecule and proteins. For this reason, we investigated the labeling of ovalbumin (OVA) as a globular model protein with p-hydroxymercurybenzoate (pHMB) in its native state (phosphate buffer solution) and in different denaturing conditions (8 mol L-1 urea, 3 mol L-1 guanidinium thiocyanate, 6 mol L-1 guanidinium chloride, 0.2% sodium dodecyl sulfate, and 20% methanol). In addition to chemical denaturation, thermal denaturation was also tested. The protein was pre-column simultaneously denatured and derivatized, and the pHMB-labeled denatured OVA complexes were analyzed by size exclusion chromatography (SEC) coupled online with chemical vapor generation-atomic fluorescence spectrometry (CVG-AFS). The number of-SH groups titrated greatly depends on the protein structure in solution. Indeed, we found that, depending on the adopted denaturing conditions, OVA gave different aggregate species that influence the complexation process. The results were compared with those obtained by a common alternative procedure for the titration of -SH groups that employs monobromobimane (mBBr) as tagging molecule and molecular fluorescence spectroscopy as detection technique. We also investigated the labeling kinetics for denatured OVA and pHMB, finding that the 4 thiolic groups of OVA have a very different reactivity toward mercury labeling, in agreement with previous studies. (C) 2015 Elsevier Inc. All rights reserved.

The naturalized dyes (ND) and the traditional acid dyes (ADs) were compared by studying the different behavior during the leather dyeing process. NDs are glyconjugated compounds synthesized by the covalent union of a dye species with a natural sugar (e.g. lactose) able to confer water-soluble properties to the dye molecule as a whole. The interactions between the dyes and the leather proteins were studied by FT-IR spectroscopy and thermogravimetric (TG) analyses. The protein cross-linking of the dyed leather samples was investigated by studying the 1654/1690 cm(-1) peak height ratio and a deconvolution procedure of the amide I peak. The helix secondary structure was the predominant component of the leather proteins of the samples dyed with low concentrations of NDs (2%), while the beta-sheets prevailed when leather samples were dyed with the traditional ADs and high concentrations of NDs (>5%). The data were discussed with respect to TG results. (C) 2015 Elsevier Ltd. All rights reserved.

The chemical vapor generation of H2Se has been investigated in the presence and in the absence of either Nal or NaSCN as additives (0.5 mol L-1), in HCLO4 media (0.1-5.0 mol L-1) and using a low concentration of NaBH4 (0.02 mol L-1). The enhancement of generation efficiency of H2Se produced by iodide and thiocyanate was measured by a continuous flow reaction system coupled with a miniature argon hydrogen diffusion flame and atomic absorption detection. The chemifold of the continuous flow reactor was designed in order to change the mixing sequence and the interaction time of the reagents. By this way it has been possible to evaluate the contribution of additive selenium and additive-borane species to the mechanism producing the increase of generation efficiency of H2Se. Both the iodide complexes of selenium and borane contribute to enhance generation efficiency of H2Se, whereas the thiocyanate complexes of selenium rather than thiocyanate-borane complexes play a major role in the enhancement of the efficiency. At elevated acidities (2 < [H+] < 5 mol L-1), only thiocyanate continues to maintain its properties to increase H2Se generation efficiency while iodide causes a marked signal depression unless its addition is performed after the starting of Se-IV - [BH4-] reaction with an appropriate time delay. Both iodide and thiocyanate caused marked depression of H2Se generation when NaBH4 was replaced by the amine boranes, NH3-BH3 and tert-ButylNH(2)-BH3. (C) 2018 Elsevier B.V. All rights reserved.

The abandoned mining area of Valdicastello Carducci (Tuscany, Italy) is characterized by the massive presence of thallium in the acid mine drainages and in the valley stream crossing the region. We previously found that Tl(III), generally considered the less stable oxidation state of thallium, is present both in the stream and in tap water distributed in the area, whereas acid mine drainages only contain Tl(I). These findings posed some concern related to the reactivity and dispersion of this toxic element in the environment. Since the valence state of thallium determines its toxicity, distribution and mobility, the study of thallium redox speciation appears crucial to understand its environmental behaviour. In this work, water samples collected from the mine drainages and the contaminated stream were adopted as model to study the distribution of aqueous Tl(I)/Tl(III) as a function of light exposure and solution properties and composition. The influence of three light sources and organic acids was evaluated. Thallium speciation was also assessed in tap water after treatment with common oxidizing agents, and in the rust crust collected from the public waterworks.

Since1971, Chemical Vapor Generation (CVG) by aqueous borane reagents has been employed as an analytical derivatization technique for the conversion of aqueous ions of several metals and semi-metals to their volatile derivatives. At present CVG is a popular technique and it has been widely employed in the determination and speciation of several elements at ultratrace level by atomic and mass spectrometry. More recently, starting since 2003, dedicated studies were developed with the aim to clarify the mechanisms governing the chemistry of CVG. In a first phase, the attention was focused on the removal of erroneous concepts and the clarification of controversial aspects of CVG of volatile hydrides. The studies developed during this step served to reconcile CVG with the evidence reported in the fundamental chemistry literature concerning the mechanisms of hydrolysis of boranes, NaBH4 (THB) and amine-boranes (ABs), and the mechanism of hydrogen transfer from borane to analytical substrate [1,2]. Due to the particular conditions in which analytical CVG operates i.e., elevated acidities, high borane to analyte molar ratios, presence of foreign species and chemical additives, the use of dedicated experiments is necessary, in particular to investigate the mechanism of action of additives and the mechanisms of hydrolysis of ABs [3,4]. Some of the evidences obtained under analytical conditions for the hydrolysis of amine-boranes cannot be explained in the light of the current knowledge and suggests the needing of a revision of the mechanism of acid-catalyzed hydrolysis which is currently accepted in the literature for ABs.

Chemical vapor generation of cadmium (CVG) by aqueous NaBH4 was investigated with the aim to individuate the mechanisms controlling the generation of volatile cadmium species in the absence of any additive. A continuous flow reactor was employed in combination with atomic absorption spectrometry. An electro-thermal quartz tube atomizer (293–1200 K) and a miniature argon–hydrogen diffusion flame were employed as the atomizers. The reactor system can be used with various chemifold setups which allow different mixing strategies of the sample (2.5–50 μg L−1 of CdII in 0.25 mol L−1 HCl) and reductant (1–3% m/v NaBH4 in 0.1–1.2 mol L−1 NaOH) solutions. The molar ratios of the reagents HCl, NaBH4 and NaOH play a decisive role in determining both the nature of CdII substrates and the hydrolysis products of BH4−, which strongly affected the generation efficiency of volatile Cd species. For the first time the interference effect of dissolved oxygen and the use of BH3OH− in CVG of Cd have been demonstrated. The interference of dissolved oxygen, causing liquid phase interference during the derivatization step, can be removed by degassing the solution with argon. The on-line generation of BH3OH− in a quenched flow reactor indicates that it is more efficient than that of BH4− and it might play a role in CVG of Cd. The combination of BH3OH− derivatization and degassed solutions allows obtaining about 20 and 5 fold increase of sensitivity using a quartz tube and miniature flame, respectively. Volatile cadmium vapors are composed of both atomic and molecular species, and the oxygen removal and/or the use of BH3OH− favors the formation of atoms with respect to molecular species.