Tandem mass spectrometry studies of acetone and acetone/water cluster ions

Ion clusters were formed in a temperature-variable high-pressure ion source from neat acetone and acetone/water mixtures and subjected to tandem mass spectrometry studies-unimolecular and collisionally activated mass-analyzed ion kinetic energy spectroscopy. The predominance of water loss from H⁺(H₂0)(A) _l=3, where A = acetone, suggests that the solvation sphere around H₃O⁺ does not close at l = 3, contrary to the case of acetonitrile or dimethyl ether. The results may be interpreted in terms of suggested ion structures which involve isomerization enroute to dissociation. The virtual absence of H/D scrambling in the collisionally activated dissociation of H₃O⁺(DA)₃, DA =acetone-d ₆, and of D₃O⁺(A)₃ means that if enolization takes place, it is a rate-determining step in an irreversible isomerization. The stability of H⁺(H₂O)(A)₃ is a dominant factor in the observation of acetone loss from H⁺(H₂0)(A)₄.     

Gas-phase ion/molecule reactions between dimethoxyphosphonium ions and aromatic hydrocarbons

Ion/molecule reactions between O=P(OCH(3))(2)(+) phosphonium ions and six aromatic hydrocarbons (benzene, toluene, 1,2,4-trimethylbenzene, naphthalene, acenaphthylene and fluorene) were performed in a quadrupole ion trap mass spectrometer. The O=P(OCH(3))(2)(+) phosphonium ions, formed by electron impact from neutral trimethyl phosphite, were found to react with aromatic hydrocarbons (ArHs) to give (i) an adduct [ArH, O=P(OCH(3))(2)](+) and (ii) for ArHs which have an ionization energy below or equal to 8.14 eV, a radical cation ArH(+ *) by charge transfer reaction. Collision-induced dissociation experiments, which produce fragment ions other than the O=P(OCH(3))(2)(+) ions, indicate that the adduct ions are covalent species. Isotope-labeled ArHs were used to elucidate fragmentation mechanisms. The charge transfer reactions were investigated using density functional theory at the B3LYP/6-311 + G(3df,2p)//B3LYP/6-31G(d,p) level of theory. The potential energy surface obtained from B3LYP/6-31G(d,p) calculations for the reaction between O=P(OCH(3))(2)(+) and benzene is described.     

Gas-phase NMR studies of chemical equilibria: 1—Methodology

Methods for obtaining ¹H NMR spectra of gases are discussed. Particular attention is paid to the nature of the tube and to the use of ‘second sample’ field/frequency locking. The question of the chemical shift reference is examined, and some results for tetramethylsilane gas are presented. Representative spectra are shown for three types of organic equilibria in the gas phase: keto-enol tautomerism, addition of methanol to acetaldehyde and Z-E isomerism of acetaldoxime.     

Structural and micro structural studies of PbO-doped SnO2 sensor for detection of methanol,propanol and acetone

In the present work the structural information of PbO-doped SnO2 thick film sensor has been investigated with X-ray diffractometer (XRD) and scanning electron microscope (SEM). Initially, SnO2 powder was derived using sol-gel process and was subsequently doped with PbO and ground up to nanosized particles. A suitable gas sensor structure was fabricated on 1′′×1′′ alumina substrate using thick film technology. The necessary paste for screen printing was also developed. SEM results showed sol-gel derived powder gets more agglomerated in the thick film form. The sensitivity of the sensor has been investigated at different temperatures (150 ?C?350 ?C) upon exposure to methanol, propanol and acetone, yielding a maximum at 250 ?C for acetone with 1 wt% PbO-doping while at 350 ?C for propanol with 3 wt% PbO-doping of the sensor. The reduction of particle size to nanometers (validated through XRD) leads to a dramatic improvement in sensitivity of sensors for the chosen organic vapors. The results also correlate well with the microstructural properties of the material and the dopant.     

Theoretical Van 't Hoff plots of gas-phase ion equilibria of chloride ion in water,methanol and acetonitrile

The gas-phase clustering reactions of chloride ion with water, methanol and acetonitrile molecules were investigated using a pulsed e-beam high-pressure mass spectrometer. Thermochemical data, −ΔH⁰ and −ΔS⁰, for these reactions agree with those reported previously. Theoretical van 't Hoff plots based on an ab initio MO calculation are compared with experimental ones.     

Gas-phase ion chemistry in germane-propane and germane-propene mixtures

Germane-propane and germane-propene gaseous mixtures were studied by ion trap mass spectrometry. Variations of ion abundances observed under different partial pressure ratios and mechanisms of ion-molecule reactions elucidated by multiple isolation steps are reported. In addition, the rate constants for the main reactions were experimentally determined and compared with the collisional rate constants to obtain the reaction efficiencies. The yield of ions containing both Ge and C atoms is higher in the germane-propene than in the germane-propane system. In the former mixture, chain propagation takes place starting from germane ions reacting with propene and proceeds with the formation of clusters such as Ge(2)C(4)H(n) (+) and Ge(3)CH(n) (+).     

Gas-phase conformation-specific photofragmentation of proline-containing peptide ions

Singly-protonated proline-containing peptides with N-terminal arginine are photodissociated with vacuum ultraviolet (VUV) light in an ESI linear ion trap/orthogonal-TOF (LIT/o-TOF). When proline is the n^th residue from the N-terminus, unusual b _n + 2 and a _n + 2 ions are observed. Their formation is explained by homolytic cleavage of the C_α− C bond in conjunction with a rearrangement of electrons and an amide hydrogen. The latter is facilitated by a proline-stabilized gas-phase peptide conformation.     

Fluorescence reaction and complexation equilibria between norfloxacin and aluminium (III) ion in chloride medium

Norfloxacin, 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinoline carboxylic acid (NORH), reacts with aluminium(III) ion forming the strongly fluorescent complex [Al(HNOR)]³⁺, in slightly acidic medium. The complex shows maximum emission at 440 nm with excitation at 320 nm. The fluorescence intensity is enhanced upon addition of 0.5% sodium dodecylsulphate. Fluorescence properties of the Al-NOR complex were used for the direct determination of trace amounts of NOR in serum. The linear dependence of fluorescence intensity on NOR concentration, at a NOR to Al concentration ratio of 1:10, was found in the concentration range 0.001–2 μg/ml NOR with a detection limit of 0.1 ng/ml. The ability of aluminium (III) ion to form complexes with NOR was investigated by titrations in 0.1 M LiCl medium, using a glass electrode, at 298 K, in the concentration range: 2 × 10⁻⁴ ≤ [Al] ≤ 8 × 10⁻⁴; 5 × 10⁻⁴ ≤ [NOR] ≤ 9 × 10⁻⁴ mol/dm³; 2.8 ≤ pH ≤ 8.3. The experimental data were explained by the following complexes and their respective stability constants, log(β ± σ): [Al(HNOR)], (14.60 ± 0.05); [Al(NOR)], (8.83 ± 0.08); [A1(OH)₃(NOR)], (−14.9 ± 0.1), as well as several pure hydrolytic complexes of A1³⁺. The structure of the [Al(HNOR)] complex is discussed, with respect to its fluorescence properties.     

Gas-phase complexation of polyethers with halide ions

Gas-phase complexes of halide anions with a variety of crown ethers and acyclic analogs are formed by ion-molecule reactions in the chemical ionization source of a triple-quadrupole mass spectrometer. The ether complexes of iodide, bromide, and chloride dissociate on collisional activation by cleavage of the halide-ether electrostatic hydrogen bonds, resulting in the formation of bare halide anions. By contrast, the fluoride complexes dissociate by loss of HF, which may occur in conjunction or sequentially with losses of ethylene oxide units. This dissociation behavior is similar to that observed for collisionally activated dissociation of [M ? H]^? ions of the crown ethers and suggests that the fluoride ion is capable of promoting an intramolecular proton abstraction within the [M+F]^? complex. This type of dissociation chemistry is only observed for the fluoride ion complexes, and the fluoride ion is the most basic of all the halides. The kinetic method was used to establish orders of relative halide binding strengths, and the trends for the chloride and bromide affinities were 12-crown-4 < triethylene glycol dimethyl ether < 15-crown-5 < tetraethylene glycol dimethyl ether < 18-crown-6 < 21-crown-7 < tetraethylene glycol < pentaethylene glycol < 1,4,7,10,13-pentathiacyclopentadecane.     

Sorption of zinc complex ions from chloride solutions with ion exchangers

To characterize the reaction of zinc ions with anion exchangers of various types, the equilibrium compositions of all the components of the sorption system (zinc salt, hydrochloric acid, and water) and distribution of associated molecules in the resin phase were considered.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 9, 2004, pp. 1456–1461.Original Russian Text Copyright © 2004 by Skorokhodov, Radionov, Goryaeva.     

Solubility and equilibria of silver chloride

An hyperbolic cosine method for the study of the solubility equilibria of silver chloride in the presence of sodium chloride is reported in this paper. Various approximations are usually performed in a study of this kind of system in order to carry out single calculations. However, the method proposed considers all solubility data simultaneously, being as a result either more rigorous or simpler than the methods previously used.     

Gas-phase reactions of organic radicals and diradicals with ions

Reactions of polyatomic organic radicals with gas phase ions have been studied at thermal energy using a flowing afterglow-selected ion flow tube (FA-SIFT) instrument. A supersonic pyrolysis nozzle produces allyl radical (CH2CHCH2) and ortho-benzyne diradical (o-C6H4) for reaction with ions. We have observed: [CH2CHCH2 + H3O+ --> C3H6+ + H2O], [CH2CHCH2 + HO- --> no ion products], [o-C6H4 + H3O+ --> C6H5+ + H2O], and [o-C6H4 + HO- --> C6H3- + H2O]. The proton transfer reactions with H3O+ occur at nearly every collision (kII approximately with 10(-9) cm3 s(-1)). The exothermic proton abstraction for o-C6H4 + HO- is unexpectedly slow (kII approximately with 10(-10) cm3 s(-1)). This has been rationalized by competing associative detachment: o-C6H4 + HO- --> C6H5O + e-. The allyl + HO- reaction proceeds presumably via similar detachment pathways.     

Gas-phase electrophilic addition reactions of chlorinated alkyl ions

Chemical ionization was used to study gas-phase electrophilic addition reactions of chloromethyl ions ([CH_xCl_3-x]⁺, x = 0, 1, 2) with a number of substituted benzenes (C₆H₅Y, Y = NH₂, OH, CHO, CN, NO₂). Mass-analyzed ion kinetic energy spectrometry was used to characterize the reaction products with respect to the site of electrophilic addition (ring v. substituent). In some cases, examination of secondary reaction products (ion–molecule adduct which has undergone an elimination reaction in the ion source) aided in establishing the original site of electrophilic addition. Aniline, benzonitrile and nitrobenzene exhibited preferential substituent interaction, while phenol and benzaldehyde gave a mixture of ring and substituent reaction products. These gas-phase results differ considerably from solution-phase Friedel–Crafts alkylation; however, they are consistent with the notion of preferential σ-bond formation at polarizable centers of negative charge.     

Gas-phase ion chemistry in the ternary silane-propyne-phosphine system

The gas-phase ion chemistry of propyne-phosphine and silane-propyne-phosphine mixtures was studied by ion trap mass spectrometry. For the binary mixture, the effect of different partial pressures of the reagents on the yield of C and P-containing ions was evaluated. Reaction sequences and rate constants were determined and reaction efficiencies were calculated from comparison of experimental and collisional rate constants. In the ternary silane-propyne-phosphine systems, the reaction pathways leading to formation of Si(m)C(n)P(p)H(q) (+) ions were determined and the rate constants of the most important steps were measured. For some ion species, selected by double isolation procedures (MS/MS), the low ion abundances prevented determination of the reaction rate constants. Si, C and P-containing ions are mainly produced in reactions of Si(m)P(p)H(q) (+) ions with propyne, while the reactivity of the Si(m)C(n)H(q) (+) ions towards PH(3) and of the C(n)P(p)H(q) (+) ions towards SiH(4) is very low. The formation of hydrogenated Si--C--P ions is interesting for their possible role as precursors of amorphous silicon carbides doped with phosphorus, obtained in a single step, by deposition from properly activated silane-propyne-phosphine mixtures.     

Gas-phase ion chemistry of the allene-phosphine and silane-allene-phosphine systems

The gas-phase ion chemistry of allene-phosphine and silane-allene-phosphine mixtures was studied by ion trap mass spectrometry. Rate constants of the main processes were measured and compared with the collisional rate constants to determine the reaction efficiencies. For the binary mixture, the highest yield of C- and P-containing ions is obtained with a 1 : 1 partial pressure ratio among the reagents. In the ternary mixture, formation of ion species containing Si, C and P together is mainly achieved in reactions of Si/P ions with allene, with a lower contribution from reactions of Si/C and C/P ions with phosphine and silane, respectively. The formation of ternary ion clusters is related to their possible role as precursors of amorphous silicon carbides doped with phosphorus, obtained by deposition from properly activated silane-allene-phosphine mixtures.     

Condensation of ammonium ion with acetone

Recrystallization of ammonium anthranilate or ammonium salicylate from acetone-hexane results in conversion of the ammonium salts to diacetoneammonium salts. The reaction is general for the ammonium salts of amino- and hydroxy-substituted benzoic acids, all of which are converted at least in part to diacetoneammonium salts when treated with acetone. Under similar conditions ammonium benzoate is converted to the triacetoneammonium salt. These reactions constitute convenient laboratory procedures for the preparation of diacetoneammonium and triacetoneammonium salts, and explain the frequent incursion of diacetoneamine and triacetoneamine as artifacts when natural systems are extracted with acetone.