Thermodynamic study of gaseous vanadium phosphates by high-temperature mass spectrometry

Knowledge of the structures of gaseous oxyacid salts of the M_mXO_n type is of interest for understanding the nature of chemical bonds. Gaseous VPO₂ and VPO₃ have been identified by Knudsen effusion mass spectrometry during the vaporization of mixtures of V₂O₃ and alkali earth phosphates from molybdenum and tungsten effusion cells. The structures and molecular parameters of the gaseous vanadium phosphates under study were determined using quantum chemical calculations. On the basis of equilibrium constants measured for gas‐phase reactions, the standard formation enthalpies were determined to be ?273 ± 17 and ?615 ± 16 kJ?mol^–1 for VPO₂ and VPO₃, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Thermodynamic study of the vaporization of uracil

The vapour pressure of uracil was measured in the temperature range 452–587 K using different techniques and the pressure—temperature equation log P(kPa) = 12.13 ± 0.50 — (6823 ± 210)/T was derived. The thermodynamic functions of gaseous and solid uracil were also evaluated through spectroscopic and calorimetric measurements. The sublimation enthalpy of uracil, ΔH⁰₂₉₈ = 131 ± 5 kJ mole^?1, was derived from second and third law treatment of the vapour data.     

Thermodynamic study of some chromium-containing gaseous molecules by high-temperature mass spectrometry

A number of gaseous oxyacid salts have been identified by Knudsen effusion mass spectrometry, while vaporizing Cr(2)O(3) and mixtures of Cr(2)O(3)+Nb(2)O(5), Cr(2)O(3)+Ta(2)O(5), Cr(2)O(3)+BaO, and Cr(2)O(3)+Mg(2)P(2)O(7) from molybdenum and tungsten cells. The stabilities of the gaseous molecules CrMoO(3), CrMoO(4), CrMoO(5), CrWO(3), CrWO(4), CrWO(5), CrNbO(3), CrTaO(3), CrPO(2), CrPO(3), BaCrO(2) and BaCrO(3) were deduced from the measurements. The thermodynamic properties of this gaseous chromium-containing species are summarized. Prediction is tentatively made of the stability of as-yet unstudied gaseous molecules.     

Charging megadalton poly(ethylene oxide)s by electrospray ionization. A charge detection mass spectrometry study

Ions from compounds of megadalton (MDa) molecular weight were produced in an electrospray ionization source from solutions of poly(ethylene oxide) (PEO) samples with average molecular weights ranging from 1,000,000 to 7,000,000 Da. Charge detection mass spectrometry (CDMS) has been used to determine the mass of the MDa PEOs. Simultaneous measurement of the charge and velocity of individual ions allows the mass determination of the ion, after calibration of the instrument with independent samples. In addition to the mass spectra, CDMS generates charge-versus-mass plots, which allow investigation of the charging of electrosprayed ions over a broad range of masses. The experimental charging capacity of MDa PEOs is compared with a simple model based on the affinity of alkali cations for oxygen sites and on the electrostatic potential energy of the charged polymer. The charging capacity of PEOs was also investigated as a function of the concentration of and the type of alkali ions.     

An investigation of different modifiers in electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS)

The suitability of eleven modifiers (Pd-, Mg-, K-, Ca- and NH₄-salts) for electrothermal vaporization coupled to inductively coupled plasma mass spectrometry (ETV-ICP-MS) for the determination of Mn, Cu, Zn, Cd and Pb has been studied. Solutions containing varying quantities (10–2000 ng absolute) of these salts have been added to four different amounts of analyte to study their suitability as modifier and their mass dependent influence. The best sensitivity enhancement for all elements tested was achieved with IrCl₃ and PdCl₂. From a comparison of the effect of PdCl₂ vs. Pd(NO₃)₂ it could be concluded that the mechanism of matrix modification also depends on the chemical form of the modifier. Particularly, for the volatile elements Cd and Zn differences in the behavior of the different chemical compounds of one metal (e.g. Pd) is evident, which shows that the enhancement effect is a result of the stabilization of the analytes in the graphite tube prior to vaporization and the improvement of the transport efficiency after vaporization.     

Investigation of the vaporization of boric acid by transpiration thermogravimetry and knudsen effusion mass spectrometry

The vaporization of H3BO3(s) was studied by using a commercial thermogravimetric apparatus and a Knudsen effusion mass spectrometer. The thermogravimetric measurements involved use of argon as the carrier gas for vapor transport and derivation of vapor pressures of H3BO3(g) in the temperature range 315-352 K through many flow dependence and temperature dependence runs. The vapor pressures as well as the enthalpy of sublimation obtained in this study represent the first results from measurements at low temperatures that are in accord with the previously reported near-classical transpiration measurements (by Stackelberg et al. 70 years ago) at higher temperatures (382-413 K with steam as the carrier gas). The KEMS measurements performed for the first time on boric acid showed H3BO3(g) as the principal vapor species with no meaningful information discernible on H2O(g) though. The thermodynamic parameters, both p(H3BO3) and Delta sub H degrees m(H3BO3,g), deduced from KEMS results in the temperature range 295-342 K are in excellent agreement with the transpiration results lending further credibility to the latter. All this information points toward congruent vaporization at the H3BO3 composition in the H2O-B2O3 binary system. The vapor pressures obtained from transpiration (this study and that of Stackelberg et al.) as well as from KEMS measurements are combined to recommend the following: log [p(H3BO3)/Pa]=-(5199+/-74)/(T/K)+(15.65+/-0.23), valid for T=295-413 K; and Delta sub H degrees m=98.3+/-9.5 kJ mol (-1) at T=298 K for H3BO3(s)=H3BO3(g).     

Electrothermal vaporization for the determination of halogens by reduced pressure inductively coupled plasma mass spectrometry

Trace level quantities of some halogen elements are determined by coupling tungsten filament electrothermal vaporization (ETV) with reduced pressure argon inductively coupled plasma mass spectrometry (ICP-MS). Microliter aqueous samples of chlorides, bromides and iodides were loaded on the tungsten wire, where they were dried at constant current and then vaporized by using a high-capacity condenser discharge. On decreasing the pressure of the plasma, analyte intensity increased sharply. The reduced pressure ICP is seen to give a much narrower, more intense signal profile. The detection limits for bromine and chlorine improved about 10 times compared with an atmospheric pressure ICP ionization source. An electron collision ionization mechanism may contribute most to halogen ionization for reduced pressure ICP. The linear dynamic range was over three orders of magnitude. The precision was generally between 3–8%. Matrix effect was investigated with Na as a matrix element. Absolute detection limits for the elements studied are in the picogram to subnanogram range.     

Determination of Mo, U and B in waters by electrothermal vaporization inductively coupled plasma mass spectrometry

A method for the determination of Mo, U and B in waters by inductively coupled plasma mass spectrometry, using an electrothermal vaporizer for sample introduction, is described. For Mo and U, NH(4)F was chosen as modifier and for B, synthetic sea water plus mannitol were used. The modifier effect was verified and the optimized pyrolysis and vaporization temperatures were obtained from pyrolysis and vaporization curves, together with the transient signals of the analytes. The masses of the modifiers added to the tube were also optimized. The detection limits were 0.018 or 0.30 ng ml(-1) for Mo, 0.03 ng ml(-1) for U and 0.68 ng ml(-1) for B. The analytes were determined in certified waters and the obtained results agree with the certified or recommended values or, in the case of B in sea waters, with the values obtained by other methods. Uranium could not be measured in the sea water samples due to strong memory effect.     

Synthesis,characterization, and blends of high temperature poly(arylether sulfone)s

The preparation of poly(4-oxy-1,4-phenylenesulfonyl-4,4′-biphenylene-4-sulfonylphenylene) (PBP) has been accomplished by the base mediated, polycondensation reaction between two biphenyl containing monomers. The bisphenol, 4,4′-bis[(4-hydroxyphenyl) sulfonyl]biphenyl (HSB), was reacted with 4,4′-bis[(4-chlorophenyl)sulfonyl]-biphenyl (CSB) in tetramethylene sulfone solvent. The highest mechanical properties and glass transition temperature was observed for polymer PBP with a reduced viscosity around 1.0 dL/g. Consequently, the current synthesis route provides polymer with higher properties than other historical preparative routes. Blends of PBP with a different poly(ether sulfone) were miscible based on the observance of a single glass transition temperature. The T_gs of the polymer blends exhibited an unusual positive deviation from the weighted linear averages of the components.     

A study of some imidazo[l,5-a]benzodiazepin-6-ones by electron impact mass spectrometry. characterization by tandem mass spectrometry of a distonic fragment ion

The mass spectra of several imidazo[l,5-a]benzodiazepin-6-one derivatives of neuropharmacological significance were determined in order to establish their decomposition paths under electron impact. A novel distonic fragment ion was observed and it was possible to demonstrate by consideration of metastable ions and by tandem mass spectrometry that it undergoes isomerization to the corresponding classical structure.     

Cracking study of pentakis(dimethylamino)tantalum vapors by Knudsen cell mass spectrometry

Organometallic molecules are commonly used as gaseous precursors in Atomic Layer Deposition/Chemical Vapor Deposition (ALD/CVD) processes. However, the use of these molecules, which are generally thermally unstable at temperatures close to the deposition temperature, requires an understanding of their gas‐phase chemical behavior. The thermal cracking of the gaseous precursor, pentakis(dimethylamino) tantalum (PDMAT), generally adopted in the ALD/CVD TaN deposition processes, has been studied in the temperature range from 343 to 723K using a specific reactor coupled with a high‐temperature mass spectrometer. This reactor – built as tandem Knudsen cells – consists of two superimposed cells. The first stage reactor – an evaporation cell – provides an input saturated vapor flow operating from room temperature to 333K. The second stage cell, named the cracking cell, operated from 333 to 723K in the present study. Experiments showed the appearance of many gaseous species when the cracking temperature increased and, in particular, dimethylamine, corresponding to the saturated organic branches of PDMAT. Decomposition products of the HNC₂H₆ branch were observed at relatively high temperature, namely above 633K. This gas‐phase study – as for the preceding saturated one – shows the presence of oxygen‐containing molecules in PDMAT cracked vapor. Thus, it explains the systematic presence of oxygen contamination in the deposited TaN films observed in ALD/CVD industrial processes. Copyright © 2010 John Wiley & Sons, Ltd.     

The role of modifiers in electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for the determination of B,La and U

The role of modifiers in electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for the determination of refractory elements such as La or U and carbide forming elements such as B has been studied. Solutions of NH₄F, NH₄Cl, NH₄Br, NaCl, NaF, NH₄HSO₄, (NH₄)₂HPO₄, the gaseous halogenated hydrocarbons CHF₃ and CCl₂F₂ and HCl have been used as modifiers.The mechanism of the modifier effect and the influence of modifiers on sensitivity enhancement have been investigated. The sensitivity enhancements are great enough to achieve absolute detection limits of 2–6 pg for boron and 10 fg for La and U. The signal reproducibility is 0.5–3.0% for a concentration of 1 μg 1⁻¹ La and U, and 20 μg 1⁻¹ boron. Therefore, by adding modifiers, the use of ETV-ICP-MS can be extended to trace element determination of refractory and carbide forming elements in μl amounts of sample.     

Characterization of pyrene end-labeled poly(ethylene glycol) by high resolution MALDI time-of-flight mass spectrometry

We report the characterization of a sample of poly(ethylene glycol) (PEG, M _n = 3841, M _w/M _n = 1.01), and its derivative end-labeled with pyrenebutyrate groups, using high resolution MALDI time-of-flight mass spectrometry. A matrix of 2-(4-hydroxyphenyl-azo)benzoic acid containing a trace of either sodium chloride or potassium chloride was employed for laser desorption. Peaks due to the sodium or potassium cationized polymers were obtained, equally spaced at 44 mass units apart. For the pyrenebutyrate diester, the analysis shows that 80 ± 2% of the chains were doubly labeled, with the ramaining chains containing only a single pyrene group. Molecular weight determinations for both sets of samples were entirely consistent with size-exclusion chromatography measurements, but were obtained with greater accuracy and less ambiguity about the influence of the end groups on the hydrodynamic radius of the polymer.     

Desorption sonic spray ionization for (high) voltage-free ambient mass spectrometry

Sonic spray ionization is shown to create a supersonic cloud of charged droplets able to promote efficient desorption and ionization of drugs directly from the surfaces of commercial drug tablets at ambient conditions. Compared with desorption electrospray ionization (DESI), desorption sonic spray ionization (DeSSI) is advantageous since it uses neither heating nor high voltages at the spray capillary. DeSSI therefore provides a more friendly environment in which to perform ambient mass spectrometry (MS). DeSSI-MS is herein evaluated for the analysis of drug tablets, and found to be, in general, as sensitive as DESI-MS. The (high) voltage-free DeSSI method provides, however, cleaner mass spectra with less abundant solvent cluster ions and with enough abundant analyte signal for tandem mass spectrometry (MS/MS). These features may therefore facilitate the DeSSI-MS detection of low molar mass components or impurities, or both. The higher-velocity supersonic DeSSI spray also facilitates matrix penetration thus providing more homogenous sampling and longer lasting ion signals.