Unveiling the mechanisms behind the chemical vapor generation of plumbane for trace analysis of lead.

The mechanisms controlling the generation of PbH4 by reaction of inorganic Pb(II) with aqueous NaBH4 were investigated both in the presence and in the absence of the additive K3Fe(CN)6. For the first time PbH4 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 NaBH4. In the presence of K3Fe(CN)6, deuterium labelled experiments clearly indicated that the generated PbH4 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 K3Fe(CN)6 by NaBH4, the rate of hydrolysis of NaBH4 both in the presence and in the absence of K3Fe(CN)6, and the rate of dihydrogen evolution following NaBH4 hydrolysis. The effect of delayed addition of Pb(II) to NaBH4-HCl- K3Fe(CN)6, and K3Fe(CN)6 to NaBH4-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 K3Fe(CN)6 additive.

Ionic Liquids as Working Fluids for Heat Storage Applications: Decomposition Behavior of N-Butyl-N-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate.

Ionic liquids (ILs) represent promising working fluids to be used in thermal energy storage (TES) technologies thanks to their peculiar properties, such as low volatility, high chemical stability, and high heat capacity. Here, we studied the thermal stability of the IL N-butyl-N-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate ([BmPyrr]FAP), a potential working fluid for TES applications. The IL was heated at 200 °C for up to 168 h either in the absence or in contact with steel, copper, and brass plates to simulate the conditions used in TES plants. High-resolution magic angle spinning nuclear magnetic resonance spectroscopy was found to be useful for the identification of the degradation products of both the cation and the anion, thanks to the acquisition of 1H, 13C, 31P, and 19F-based experiments. In addition, elemental analysis was performed on the thermally degraded samples by inductively coupled plasma optical emission spectroscopy and energy dispersive X-ray spectroscopy. Our analysis shows a significant degradation of the FAP anion upon heating for more than 4 h, even in the absence of the metal/alloy plates; on the other hand, the [BmPyrr] cation displays a remarkable stability also when heated in contact with steel and brass.

Determination of thiocyanate in saliva by headspace gas chromatography-mass spectrometry, following a single-step aqueous derivatization with triethyloxonium tetrafluoroborate.

A novel method for the determination of salivary thiocyanate is presented. Thiocyanate was converted into ethyl thiocyanate by single-step aqueous derivatization based on triethyloxonium tetrafluoroborate and measured by gas chromatography-mass spectrometry (15 min runtime). The ethyl thiocyanate derivative is volatile and can be sampled from the headspace. The derivatization chemistry proposed allows for separation of the analyte from saliva matrix whose introduction in the measurement system is avoided. Quantitation of the analyte was obtained by isotope dilution, employing a (13)C-enriched thiocyanate as internal standard. Technical details and fundamental aspects of derivatization chemistry and calibration strategy are presented. The method was validated by comparison with a standard method based on ion chromatography. The two independent methodologies produced results in agreement within 3%. Also a three level spike recovery test was carried out for validation purpose and quantitative recoveries were attained. The method is fast, simple, safe, and sensitive. Measurement of a 1 mL volume 50 ng/g of thiocyanate standard produced a signal-to-noise ratio of 250 for the analytical peak. This method is therefore suitable for ultra-trace determination of thiocyanate (low part-per-billion range). For the application described the full detection potential of the method was not required and the sample preparation presented has been designed for quantitation of saliva samples containing 1-400 µg/g of thiocyanate with a combined standard uncertainty of 2% relative for saliva samples containing 25 µg/g of thiocyanate. This method was applied for the determination of thiocyanate in human saliva samples.

Chemical generation of arsane and methylarsanes with amine boranes. Potentialities for nonchromatographic speciation of arsenic.

The efficiency of chemical generation of arsanes from inorganic arsenic, monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA), to arsane, AsH3, monomethylarsane, CH3AsH2 (MMA), and dimethylarsane, (CH3)2AsH (DMA), has been investigated in different reaction media with the aim to better elucidate the mechanisms controlling their generation process and to find the experimental conditions to implement a nonchromatographic arsenic speciation analytical method, which is based on the selective determination of some arsenic species. Studies were performed by continuous flow hydride generation coupled with atomic spectrometry (CF-HG-AS), using different reductants such as borane-ammonia (AB), borane-tert-butylamine (TBAB), and sodium tetrahydridoborate (THB) in HCl and HClO4 media, in the presence or absence of L-cysteine (Cys). The efficiency of HG processes for MMA and DMA is mainly controlled by the reactivity of the substrates with the borane, which could be strongly influenced by the formation of ion couples. The protonation of arsane did not play a significant role in the employed reaction system. By taking advantage of the different reactivity pattern of As species in selected generation conditions, DMAA and MMAA could be selectively determined in 0.5 and 10 M HClO4 solutions, respectively, in the presence of Cys, with AB as the reducing agent. The presence of Cys as a masking agent and the peculiar reducing properties of AB ensured a good control of interferences, as far as it has been observed for Co(II), Ni(II), Cu(II), Fe(II), Fe(III). The overall time needed to complete the prereduction step has been verified for MMAA and DMAA at different acidities in order to achieve the best selectivity. The selective determination of DMAA with AB/Cys in HClO4 has been optimized and applied to certified reference materials (CRMs) of natural waters CASS-4, SLRS-4, and NASS-4 (NRCC). The estimation of DMAA concentration allows us to correct the concentration of As(III) for the interference of DMAA in the selective determination of As(III) according to a selective HG method recently reported.

A multidisciplinary approach for assessing the toxicity of marine sediments: analysis of metal content and elutriate bioassays using metal bioavailability and genotoxicity biomarkers.

The goal of this article is to verify the applicability of two different biological assays for studying a coastal area that is subject to anthropogenic inputs. Phytochelatins in the marine diatom Thalassiosira weissflogii were used as a biomarker of metal bioavailability. The frequency of genetic damage in the sensitive D7 strain of the yeast Saccharomyces cerevisiae was used to estimate the mutagenic potential. Biological assays were carried out using sediment elutriates. Sediments were collected at three selected sites located in the Gulf of Follonica (Tuscany, Italy), during a 2-year sampling period: Cala Violina (reference site) and the mouths of the rivers Pecora and Cornia, named sites V, P and C, respectively. The chemical characterization of each site was determined in terms of metal concentrations (As, Cd, Cr, Cu, Ni, Pb), measured in 11 sediment samples for each site. The results showed that metal concentrations in sediments from sites C and P were 2-10 times higher than the reference values (site V, year 2004). In addition, we found generally higher metal concentrations in the 2007 sediments than in the 2008 ones, including those of site V, due to the occurrence of an unexpected pollution event. This enabled us to obtain a pollution gradient to validate the proposed bioassays. In fact, the bioassays showed a potential biological hazard in the 2007 elutriates. Significant mutagenic effects were found in samples exhibiting higher concentrations of Cd and Cr. The induction of phytochelatins in T. weissflogii correlated positively with the Cd concentration in the elutriates.

Glutathione transferase omega 1-1 (GSTO1-1) plays an anti-apoptotic role in cell resistance to cisplatin toxicity.

Several lines of evidence correlate the overexpression of glutathione S-transferase omega 1-1 (GSTO1-1) with the onset of drug resistance of cancer cells; however, no direct evidence is yet available. In order to investigate the mechanisms involved, stable transfection with GSTO1-1 complementary DNA was performed in HeLa cells, which spontaneously express very low levels of GSTO1-1. When transfected cells were seeded at low density, a sharp increase in GSTO1-1 expression was observed as compared with controls, along with an increased resistance against cisplatin cytotoxicity. When seeded at increasing densities, control untransfected cells also presented with an increase in GSTO1-1 expression, again accompanied by cisplatin resistance; the latter was significantly reduced after transfection with GSTO1-1 small interfering RNA. Cisplatin resistance of transfected cells was not accounted for by changes in the intracellular drug concentration nor in the amount of DNA cross-links or content of glutathione. Rather, transfected cells presented with a marked decrease of apoptosis as compared with controls, suggesting that GSTO1-1 overexpression may prevent cisplatin toxicity by interfering with the apoptotic process. Cisplatin treatment was in fact followed at early times (1-2 h) by activation of both Akt kinase and extracellular signal-regulated kinase (ERK)-1/2 in the transfected cells but not in controls. Conversely, in transfected cells, the strong activation of Jun N-terminal kinase (JNK)-1 induced by cisplatin at later times (10-20 h) was completely prevented. In conclusion, GSTO1-1 overexpression appears to be associated with activation of survival pathways (Akt and ERK1/2) and inhibition of apoptotic pathways (JNK1), as well as protection against cisplatin-induced apoptosis.

Chemical vapor generation of arsane in the presence of L-cysteine. Mechanistic studies and their analytical feedback.

The complex reactivity of the system As-AH-RSH-THB (As=As(III), As(V); AH=HCl, HClO4, CH3COOH; RSH=L-cysteine (Cys); THB=NaBH4) was investigated using continuous flow (CF) hydride generation (HG) coupled either with atomic absorption (AAS) or atomic fluorescence spectrometry (AFS). AsH3 generation was examined in the presence of Cys by varying acidity and the type of acid, the mixing sequence, and the reaction time of reagents. The strong depression of arsane generation, which is typically observed in the range of acidity of 0.2-2 M HCl, can be addressed to the low reaction rate of thiol-borane, hydroboron complexes, or both toward those As(III) substrates that are formed in the same reaction environment. The simultaneous presence of Cys-borane and As(III)-Cys species is at the origin of the gap of the arsane generation efficiency in the 0.2-2 M HCl acidity range. The selective formation of Cys-borane complexes, which are formed faster than As(III)-thiol complexes, can be achieved by a careful choice of the mixing sequence of the reagents. The simultaneous mixing of sample, Cys, and THB is able to reduce substantially the gap of the arsane generation efficiency in the 0.2-2 M HCl acidity range. These properties were employed to implement a simple method for selective determination of As(III) in samples containing inorganic arsenic: (i) Total inorganic arsenic is determined by sample treatment with 0.2 M Cys for 30 min, acidity 0.1 M HCl, followed by CF-HG-AFS; (ii) As(III) is selectively determined in 0.005 M CH3COOH in the presence of Cys using a chemifold setup allowing the simultaneous mixing of sample, 0.2 M Cys and 0.1 M THB. The selectivity, measured from the ratio between the slopes of calibration graphs As(III)/As(V), is 220. The interference effects of Cu(II), Fe(III), Ni(II), Co(II), Ag(I), Pd(II), and Pt(IV) can be kept under control using the simultaneous mixing of all the reagents. The tolerance toward the interferences was almost the same as that obtained by allowing the formation of As(III)-Cys complexes (offline sample pretreatment with Cys for 30 min). The method was tested with the application to the natural waters and mineral well waters analysis employing CF-HG-AFS.

Effect of additives on the chemical vapour generation of bismuthane by tetrahydroborate(III) derivatization.

The effect of mM concentrations of K(3)[Fe(CN)(6)], Fe(III), Mo(VI), KSCN and KMnO(4) on the generation of BiH(3) by the reaction of 0.2-10 microg ml(-1) Bi(III) with 0.2 M tetrahydroborate(III) at 1 M acidity (HCl or HNO(3)) was investigated. Chemical vapour generation (CVG) of BiH(3) was investigated by atomic absorption spectrometry using a continuous flow reaction system (CF-CVG-AAS) and different mixing sequences and reagent reaction times. Gas chromatography-mass spectrometry (GC-MS) was employed in batch generation experiments with NaBD(4). In the absence of additives, the formation of Bi(0) at high concentrations of Bi(III) caused rollover of calibration curves and limited the linear range to less than 1 microg ml(-1) Bi(III). In the presence of additives, the formation of Bi(0) was not observed and the linear range was increased to 5 microg ml(-1) of Bi(III) while rollover was completely removed. GC-MS experiments indicated that the presence of additives did not affect the direct transfer of H from boron to bismuth. Experiments with CF-CVG-AAS and different mixing sequences and reagent reaction times suggest that additives act by preventing the formation of Bi(0) through the formation of reaction intermediates which evolve towards the formation of BiH(3) at elevated Bi(III)/NaBH(4) ratios.

Role of hydroboron intermediates in the mechanism of chemical vapor generation in strongly acidic media.

Unknown and controversial aspects related to the mechanisms of hydrolysis of borane complexes and to the mechanisms of chemical vapor generation for trace element determination in strongly acidic media (0.01-10 M HCl) have been investigated and clarified. The overall hydrolysis rates of borane complexes (BH(4)(-), H(3)N-BH(3)) in the acidity range of 0.2-10 M HCl were several orders of magnitude lower than those predicted by kinetics laws and obtained in the pH range of 3.8-14. The decomposition of the borane complexes takes place stepwise and proceeds through the formation of hydroboron intermediates, L(x)()BH(4)(-)(x)()(n)() (x = 1, 2, 3), where L could be one or more species among the donor groups H(2)O, NH(3), OH(-), and Cl(-) and n is the charge of the hydroboron species (n = 0, +1, -1, depending on L). Some intermediates present surprisingly long lifetimes at elevated acidities and play a key role in determining both the overall hydrolysis rates of borane complexes and the reactivity of Hg(II), As(III), Sb(III), Bi(III), Se(IV), Te(IV), and Sn(IV) in chemical vapor generation for trace element determination. Atomic absorption experiments demonstrated that almost all trihydroboron species (LBH(3)(n)()), dihydroboron species (L(2)BH(2)(n)()), and monohydroboron species (L(3)BH(n)()) play an active role in the generation of elemental mercury and stibine. Some of these intermediates are inactive or play a marginal role in the generation of arsine, bismuthine, and hydrogen selenide. Hydrogen telluride is preferentially formed by those hydroboron species, which are stable in strongly acidic conditions, while the same species are unreactive in the generation of stannane. The collected experimental evidence is in agreement with the general reactivity of the elements in chemical vapor generation techniques and, together with other literature data, definitely rule out the hypothesis of "nascent hydrogen" as a possible mechanism of chemical vapor generation by borane complex derivatization.

Chemical vapor generation atomic spectrometry using amineboranes and cyanotrihydroborate(III) reagents.

Amineboranes of the type L-BH3 (L = NH3; tert-BuNH2; Me2NH; Me3N) and sodium cyanotrihydroborate(III) (NaBH3CN) have been tested as derivatization reagents in the generation of volatile hydrides and elemental mercury following aqueous phase reaction with ionic species of Hg(II), As(III), As(V), Sb(V), Sb(III), Bi(III), Se(IV), Se(VI), Te(IV), and Te(VI). Continuous flow generation atomic absorption spectrometry coupled with a flameless quartz tube atomizer (T = 25 degrees C) and a miniature argon-hydrogen diffusion flame atomizer were employed for the detection of mercury vapors and volatile hydrides, respectively. All of the reductants were able to reduce Hg(II) to the elemental state, giving sensitivities comparable to NaBH4 reduction. Under reaction conditions giving maximum sensitivity for hydride generation with NaBH4, only some amineboranes are able to produce volatile hydrides from all the elements. No evidence of hydride formation was observed from the Se(VI) and Te(VI). In general, the reducing power decreased in the order NaBH4 > H3N-BH3 > tert-BuNH2-BH3 > NaBH3CN > or = Me2HN-BH3 > Me3N-BH3. In comparison with THB, amineboranes and NaBH3CN allowed, in general, a better control of interference effects of Fe(III), Ni(II), Co(II), and Cu(II). Application to determination of mercury in certified reference material is reported. The most likely mechanism of reaction of borane complexes in chemical vapor generation is based on the direct action of hydrogen bound to boron.