Analysis of positional isomers of 2-3-4-alkoxyphenylcarbamic acid derivatives by a combination of TLC and IMS.

In this study, we have demonstrated a separation of positional isomers of some derivatives of alkoxyphenylcarbamic acid. These compounds belong to drugs with local anesthetics activity. The low volatility compounds were analysed by a Thin Layer Chromatography (TLC) and Ion Mobility Spectrometry (IMS) using diode laser desorption for sample introduction to IMS. This combined approach allowed the identification of compounds. Also, we have carried out IMS studies of all compounds and determined their ion mobilities The ion mobilities were increasing with the geometry change from position ortho to para of alkoxy chain, which is in agreement with their different collision cross section (CCS).

Low Energy Electron Attachment by Some Chlorosilanes.

In this paper, the rate coefficients (k) and activation energies (Ea) for SiCl4, SiHCl3, and Si(CH3)2(CH2Cl)Cl molecules in the gas phase were measured using the pulsed Townsend technique. The experiment was performed in the temperature range of 298-378 K, and carbon dioxide was used as a buffer gas. The obtained k depended on temperature in accordance with the Arrhenius equation. From the fit to the experimental data points with function described by the Arrhenius equation, the activation energies (Ea) were determined. The obtained k values at 298 K are equal to (5.18 ± 0.22) × 10-10 cm3·s-1, (3.98 ± 1.8) × 10-9 cm3·s-1 and (8.46 ± 0.23) × 10-11 cm3·s-1 and Ea values were equal to 0.25 ± 0.01 eV, 0.20 ± 0.01 eV, and 0.27 ± 0.01 eV for SiHCl3, SiCl4, and Si(CH3)2(CH2Cl)Cl, respectively. The linear relation between rate coefficients and activation energies for chlorosilanes was demonstrated. The DFT/B3LYP level coupled with the 6-31G(d) basis sets method was used for calculations of the geometry change associated with negative ion formation for simple chlorosilanes. The relationship between these changes and the polarizability of the attaching center (αcentre) was found. Additionally, the calculated adiabatic electron affinities (AEA) are related to the αcentre.

Study of atmospheric pressure chemical ionization of phthalates in air by ion mobility spectrometry/mass spectrometry.

RATIONALE: Phthalates are widely used in consumer products in the chemical industries. Due to their abundance in the milieu, their potentially harmful effect on the environment, human and animal health there is a need for sensitive and fast methods for their detection. METHODS: Positive polarity Corona Discharge Atmospheric Pressure Chemical Ionization (CD-APCI) in the air was applied for ionization of phthalates. The ionization method for the phthalates was studied by atmospheric pressure Ion Mobility Spectrometry (IMS) and hybrid IMS/orthogonal acceleration Time-of-Flight Mass spectrometry (IMS-oaTOF-MS). RESULTS: CD-APCI IMS and MS spectra of selected phthalates (dimethyl phthalate, diethyl phthalate, diethyl isophthalate, diethyl terephthalate, dipropyl phthalate, diisopropyl phthalate, dibutyl phthalate, diisobutyl phthalate, and dibutyl terephthalate) were recorded. In the case of the ortho- and "iso"-isomers exclusively the protonated molecular ions [M + H]+ were detected. In the case of the para- and meta-isomers and regioisomers, APCI resulted in the appearance of hydrated protonated molecular ions [M + H]+ ·(H2 O)0,1,2 . The ion mobilities, collision cross-sections of these ions in air, as well as the limits of detection (LODs) for the phthalate vapors, were determined. In the case of isomeric phthalates, we have demonstrated the potential of the IMS technique for their separation. CONCLUSIONS: The results show that CD-APCI in combination with IMS and IMS-oaTOF-MS is a suitable method for the fast and sensitive detection of phthalates with the potential to separate some isomers.

Low-energy electron interactions with chlorotrimethylsilane (Si(CH3 )3 Cl), dichlorodimethylsilane (Si(CH3 )2 Cl2 ) and chloromethyldimethylsilane (SiH(CH3 )2 (CH2 Cl)).

RATIONALE: Silane derivatives are widely used in industrial plasmas for manufacturing lighting devices, solar cells, displays, etc. Models of technological plasmas require quantitative data. The rate coefficients (k) and the activation energies (Ea ) of thermal electron attachment for chlorotrimethylsilane (Si(CH3 )3 Cl), dichlorodimethylsilane (Si(CH3 )2 Cl2 ) and chloromethyldimethylsilane (SiH(CH3 )2 (CH2 Cl)) are reported. This is important for understanding the basic processes occurring in plasmas. METHODS: The pulsed Townsend technique (known as the electron swarm method) has been applied for the measurements. In this technique, electrons generated by a laser, under a uniform electric field, traverse to an anode and induce a charge on it. In the buffer gas charge grows linearly, but in the presence of a scavenger, electrons are captured, and thus the rate of charge increase slows down with time. From the shape of the pulse, the kinetic parameters are determined. RESULTS: Kinetic parameters from the study of thermal electron attachment by Si(CH3 )3 Cl, Si(CH3 )2 Cl2 and SiH(CH3 )2 (CH2 Cl) were determined for the first time. The corresponding rate coefficients at 298 K are equal to (9.56 ± 0.02) × 10-11 , (6.62 ± 0.02) × 10-11 and (1.24 ± 0.05) × 10-11  cm3  s-1 and Ea values are equal to 0.29 ± 0.01, 0.24 ± 0.01 and 0.31 ± 0.01 eV for Si(CH3 )3 Cl, Si(CH3 )2 Cl2 and SiH(CH3 )2 (CH2 Cl), respectively. The experiment was performed in the 298-378 K temperature range. CONCLUSIONS: The presented results provide important new information about fundamental quantities such as rate coefficients and activation energies for thermal electron capture by chlorinated derivatives of silane. These data can further advance our understanding of thermal electron interactions with chlorosilanes that can be used to control the important species in the plasmas of many modern technologies.

Online detection and measurement of elemental mercury vapor by ion mobility spectrometry with chloroform dopant.

A rapid and simple method is proposed for detection of elemental mercury (Hg) vapor by ion mobility spectrometry (IMS). Negative corona discharge (CD) as the ionization source and chloroform as the dopant gas were used to produce Cl- reactant ion. A mass spectrum of the product ions confirmed that the mechanism of ionization is based on Cl- anion attachment to Hg and formation of HgCl- ion. It was found that the optimum drift gas temperature for Hg detection was about 160 °C and the drift gas flow rate should be minimized and just sufficient to clear contaminants and carry-over from the drift cell. The drift time of the HgCl- peak relative to that of the Cl- peak at 160 °C is 1.52 ms corresponding to the reduced mobility of 1.90 cm2/Vs. Because many volatile organic compounds (VOCs) such as alcohols, amines, aldehydes, ketones, and alkanes are not ionized in the negative mode of CD-IMS, these compounds do not interfere with the detection of Hg. Mercaptans peaks also did not show any interference with the Hg signal. Hence, the method is highly selective for detection of Hg in natural gas containing sulfur compounds. The detection limit of Hg obtained by the proposed method was 0.07 mg/m3. The method was successfully verified in determination of the mercury vapor content of a fluorescent lamp, as a real sample.

Ion chemistry of phthalates in selected ion flow tube mass spectrometry: isomeric effects and secondary reactions with water vapour.

Phthalates are widely industrially used and their toxicity is of serious environmental and public health concern. Chemical ionization (CI) analytical techniques offer the potential to detect and monitor traces of phthalate vapours in air or sample headspace in real time. Promising techniques include selected ion flow tube mass spectrometry (SIFT-MS), proton transfer reaction mass spectrometry (PTR-MS) and ion mobility spectrometry (IMS). To facilitate such analyses, reactions of H3O+, O2+ and NO+ reagent ions with phthalate molecules need to be understood. Thus, the ion chemistry of dimethyl phthalate isomers (dimethyl phthalate, DMP - ortho; dimethyl isophthalate, DMIP - meta; dimethyl terephthalate, DMTP - para), diethyl phthalate (DEP), dipropyl phthalate (DPP) and dibutyl phthalate (DBP) was studied by SIFT-MS. Reactions of H3O+, O2+ and NO+ with these phthalate molecules M were found to produce the characteristic primary ion products MH+, M+ and MNO+, respectively. In addition, a dissociation process forming the (M-OR)+ fragment was observed. For phthalates with longer alkyl chains, mainly DPP and DBP, a secondary dissociation channel triggered by the McLafferty rearrangement was also observed. However, this is dominant only for the more energetic O2+ reactions with phthalates, additionally resulting in a recognisable formation of the protonated phthalate anhydride. For the NO+ reagent ions, the McLafferty rearrangement makes only a minor contribution and for H3O+, it was not observed. Experiments on the effect of water vapour on this ion chemistry have shown that protonated DMIP and DMTP efficiently associate with H2O forming the DMIP·H+H2O, DMIP·H+(H2O)2 and DMTP·H+H2O cluster ions, whilst the protonated ortho DMP isomer as well as other ortho phthalates DEP, DPP and DBP does not associate with H2O. The results indicate that the degree of hydration can be used to identify specific phthalate isomers in CI.

Fast quantification of whisky lactone in oak wood by ion mobility spectrometer.

An Ion Mobility Spectrometry (IMS) apparatus has been used to detect the ß-methyl-γ-octalactone (Whisky Lactone - WL) standard in the air and as well WL vapours originating from the oak wood samples. The IMS was equipped with Atmospheric Pressure Chemical Ionisation (APCI) ion source based on a Corona Discharge (CD) and was operated in the positive polarity. The IMS spectrum of WL exhibits two peaks, a monomer with reduced ion mobility value K0 = 1.39 cm2V-1s-1 and dimer K0 = 1.09 cm2V-1s-1. Using Ion Mobility orthogonal acceleration Time of Flight mass spectrometer (IMS-oaTOF MS) these peaks were identified as protonated monomer M.H+.(H2O)0,1 and dimer M2.H+ ions respectively. The limit of detection study resulted in LOD for WL of 50 ppbv. Detection of WL from oak wood samples of different "Quality Level" (QL) categories (categories 1 to 10), indicated strong correlation between the QL category number and the response of the IMS.

Isomer and conformer selective atmospheric pressure chemical ionisation of dimethyl phthalate.

In this work we have studied the ionisation mechanism of Atmospheric Pressure Chemical Ionisation (ACPI) for three isomers of dimethyl phthalate (dimethyl phthalate - DMP (ortho- isomer), dimethyl isophthalate - DMIP (meta) and dimethyl terephthalate - DMTP (para)) using Ion Mobility Spectrometry (IMS) and IMS combined with an orthogonal acceleration Time of Flight Mass Spectrometer (oa-TOF MS). The molecules were chemically ionised using reactant ions H+·(H2O)n (n = 3 and 4). The positive IMS and IMS-oaTOF mass spectra of the isomers showed significant differences in the ion mobilities and in the ion composition. The IMS - oaTOF spectra consisted of clusters of ions M·H+·(H2O)n with different degrees of hydration (n = 0, 1, 2, 3) for different isomers. In the case of the DMP isomer, we have observed almost exclusive formation of M·H+ by proton transfer ionisation, while in the case of DMIP and DMTP, hydrated ions M·H+·(H2O)n (n = 1, 2, 3) and M·H+·(H2O)n (n = 0, 1, 2) respectively were detected, formed via adduct formation reactions. This behaviour was elucidated by differences in ionisation processes. In order to elucidate the ionisation processes we have carried out DFT calculations of the structures and energies of the neutral and protonated and hydrated isomers (for different conformers) and their corresponding proton affinities (PA) and hydration energies.

Effect of Basicity and Structure on the Hydration of Protonated Molecules, Proton-Bound Dimer and Cluster Formation: An Ion Mobility-Time of Flight Mass Spectrometry and Theoretical Study.

Protonation, hydration, and cluster formation of ammonia, formaldehyde, formic acid, acetone, butanone, 2-ocatanone, 2-nonanone, acetophenone, ethanol, pyridine, and its derivatives were studied by IMS-TOFMS technique equipped with a corona discharge ion source. It was found that tendency of the protonated molecules, MH+, to participate in hydration or cluster formation depends on the basicity of M. The molecules with higher basicity were hydrated less than those with lower basicity. The mass spectra of the low basic molecules such as formaldehyde exhibited larger clusters of MnH+(H2O)n, while for compounds with high basicity such as pyridine, only MH+ and MH+M peaks were observed. The results of DFT calculations show that enthalpies of hydrations and cluster formation decrease as basicities of the molecules increases. Using comparison of mass spectra of formic acid, formaldehyde, and ethanol, effect of structure on the cluster formation was also investigated. Formation of symmetric (MH+M) and asymmetric proton-bound dimers (MH+N) was studied by ion mobility and mass spectrometry techniques. Both theoretical and experimental results show that asymmetric dimers are formed more easily between molecules (M and N) with comparable basicity. As the basicity difference between M and N increases, the enthalpy of MH+N formation decreases.

Study of Atmospheric Pressure Chemical Ionization Mechanism in Corona Discharge Ion Source with and without NH3 Dopant by Ion Mobility Spectrometry combined with Mass Spectrometry: A Theoretical and Experimental Study.

Ionization of 2-nonanone, cyclopentanone, acetophenone, pyridine, and di- tert-butylpyridine (DTBP) in a corona discharge (CD) atmospheric pressure chemical ionization (APCI) ion source was studied using ion mobility (IMS) and time-of-flight mass spectrometry (TOF-MS). The IMS and MS spectra were recorded in the absence and presence of ammonia dopant. Without NH3 dopant, the reactant ion (RI) was H+(H2O) n, n = 3,4, and the MH+(H2O) x clusters were produced as product ions. Modeling of hydration shows that the amount of hydration ( x) depends on basicity of M, temperature and water concentration of drift tube. In the presence of ammonia (NH4+(H2O) n as RI) two kinds of product ions, MH+(H2O) x and MNH4+(H2O) x, were produced, depending on the basicity of M. With NH4+(H2O) n as RI, the product ions of pyridine and DTBP with higher basicity were MH+(H2O) x while cyclopentanone, 2-nonanone, and acetophenone with lower basicity produce MNH4+(H2O) x. To interpret the formation of product ions, the interaction energies of M-H+, H+-NH3, and H+-OH2 in the M-H+-NH3 and M-H+-OH2 and M-H+-M complexes were computed by B3LYP/6-311++G(d,p) method. It was found that for a molecule M with high basicity, the M-H+ interaction is strong leading in weakening of the H+-NH3, and H+-OH2 interactions in the M-H+-NH3 and M-H+-OH2 complexes.