Haiyan Han

Determination of alcohol compounds using corona discharge ion mobility spectrometry.

Ion mobility spectrometry (IMS) is a very fast, highly sensitive, and inexpensive technique, it permits efficient monitoring of volatile organic compounds like alcohols. In this article, positive ion mobility spectra for six alcohol organic compounds have been systematically studied for the first time using a high-resolution IMS apparatus equipped with a discharge ionization source. Utilizing protonated water cluster ions (H2O)n H+ as the reactant ions and clean air as the drift gas, alcohol organic compounds, ethanol, 1-propanol, 2-propanol, 1-butanol, 1-pentanol and 2-octanol, all exhibit product ion characteristic peaks in their respective ion mobility spectrometry, that is a result of proton transfer reactions between the alcohols and reaction ions (H2O)n H+. The mixture of these alcohols, including two isomers, has been detected, and the results showed that they could be distinguished effectively in the ion mobility spectrum. The reduced mobility values have been determined, which are in very well agreement with the traditional 63Ni-IMS experimental values. The exponential dilution method was used to calibrate the alcohol concentrations, and a detection limit available for the alcohols is in order of magnitude of a few ng/L.

Control of solvent use in medical devices by proton transfer reaction mass spectrometry and ion molecule reaction mass spectrometry

A homemade proton transfer reaction mass spectrometer (PTR-MS) and a commercial ion molecule reaction mass spectrometer (IMR-MS) have been applied to detect volatile organic compounds (VOCs) in the packaging bags of infusion sets made of polyvinylchloride (PVC) plastic. The most abundant characteristic ions in the PTR-MS and IMR-MS measurements are observed at m/z 99 and 98 respectively, which are the results of soft ionizations that a residual chemical undergoes the proton transfer reaction in PTR-MS and the charge transfer reaction in IMR-MS. On the basis of ionic intensity dependence on the reduced-field in the PTR-MS investigation, the residue can be unambiguously identified as cyclohexanone, a commonly used adhesive agent in PVC medical device manufacture. Quantitative measurement by PTR-MS shows that concentrations of cyclohexanone in the packages of two types of infusion sets are 11 and 20 ppm respectively. Due to fast response, absolute concentration detection, and high sensitivity, the PTR-MS and IMR-MS detection methods are proposed for the quality control of medical devices including the detection of illegal or excessive uses of chemical solvents like cyclohexanone.

Discrimination of isomers and isobars by varying the reduced-field across drift tube in proton-transfer-reaction mass spectrometry (PTR-MS)

Proton-transfer-reaction mass spectrometry (PTR-MS) is a powerful technique for the real time trace gas analysis of volatile organic compounds (VOCs). However, quadrupole mass spectrometer (MS) used in PTR-MS has a relatively low mass resolution and is therefore not suitable for differentiating isobars. Furthermore, because of the lack of chemical separation before analysis, isomers can not be identified, either. In the present study, by varying the reduced-field E/N in the reaction chamber with a range of 50–180 Td in PTR-MS, we studied the product ion distribution (PID) of three sets of isobars/isomers, i.e. n-propanol/iso-propanol/acetic acid, propanal/acetone and four structural isomers of butyl alcohol. The profiles of the reduced-field dependence (PFD) of the PID under the chosen E/N-values show obvious differences which can be used to discriminate between these isobars/isomers thus enabling the titled method. Noticeably, we have observed that even the isomers, in the case of four structural isomers of butyl alcohol, which show little difference with each other at high reduced-field, can be discriminated easily at low reduced-field. Finally, two examples for the application of this method are discussed: (1) cyclohexanone was identified to be a major compound in the headspace of medical infusion sets; and (2) the differentiation and quantification of propanal and acetone in three synthetic mixtures with different ratios. This study presents a potential method to distinguish and quantify isobars/isomers conveniently in practical applications of PTR-MS analysis without additional instrumental configurations.

Corona Discharge Ion Mobility Spectrometry of Ten Alcohols

Ion mobility spectra for ten alcohols have been studied in an ion mobility spectrometry apparatus equipped with a corona discharge ionization source. Using protonated water cluster ions as the reactant ions and clean air as the drift gas, the alcohols exhibit different product ion characteristic peaks in their ion mobility spectra. The detection limit for these alcohols is at low concentration pmol/L level according to the concentration calibration by exponential dilution method. Based on the measured ion mobilities, several chemical physics parameters of the ion-molecular interaction at atmosphere were obtained, including the ionic collision cross sections, diffusion coefficients, collision rate constants, and the ionic radii under the hard-sphere model approximation.

Electron Attachment Studies for CHCl3 Using Ion Mobility Spectrometry

The dissociative electron attachment process for CHCl3 at different electric field have been studied with nitrogen as drift and carrier gas using corona discharge ionization source ion mobility spectrometry (CD-IMS). The corresponding electron attachment rate constants varied from 1.26×10−8 cm3/(molecules s) to 8.24×10−9 cm3/(molecules s) as the electric field changed from 200 V/cm to 500 V/cm. At a fixed electric field in the drift region, the attachment rate constants are also detected at different sample concentration. The ion-molecule reaction rate constants for the further reaction between Cl− and CHCl3 are also detected, which indicates that the technique maybe becomes a new method to research the rate constants between ions and neural molecules. And the reaction rate constants between Cl− and CHCl3 are the first time detected using CD-IMS.

A novel method to determine the concentration of VOCs at atmospheric pressure

A novel method to detect the concentration of electronegative VOCs based on the electron attachment rate at atmospheric pressure, through negative discharge in an ion drift tube, is introduced. When the carrier and drift gas in the drift tube are all high-purity nitrogen, electrons are formed by a negative discharge in the ion source, and are injected into the drift region through the shutter grid. When the electronegative sample molecules are continuously introduced into the drift tube from one end, the neutral molecules are ionized through a collision and capture process with the counterflowing swarm of electrons in the drift region. The electron swarm is exponentially diluted as it travels in the drift region. As a result, negative ions are formed in the drift region and a tail appears in the ion mobility spectrum. These spectra include information such as the intensity of the ions and electrons, the drift time, analyte concentration, the electron capture rate etc. The sample concentration can be calculated using the relative equation including information from the spectrum. As examples, in this work the concentration of electronegative samples of CCl4, CHCl3, and 1,1,1-C2H3Cl3 are studied when the electron energy is about 0.54 eV. The sample concentrations obtained in the experiment using this method are in good agreement with the initial concentrations created using a syringe pump. The comparison shows that the process of utilizing electron capture information to determine concentration is effective. This study provides a novel method to determine the concentrations of VOCs at atmospheric pressure.