Search

The specific locations of the double bonds in linear olefins can facilitate olefin catalytic synthetic reactions to improve the quality of target olefin products. We developed a simple and efficient approach based on single photon ionization time-of-flight mass spectrometry (SPI-TOFMS) combined with online ozonolysis to identify and quantify the linear olefin double bond positional isomers. The online ozonolysis cleaved the olefins at the double bond positions that led to formation of corresponding characteristic aldehydes. The aldehydes were then detected by SPI-TOFMS to achieve unique spectrometric 'fingerprints' for each linear olefin to successfully identify the isomeric ones. To accurately quantify the isomeric components in olefin mixtures, an algorithm was proposed to quantify three isomeric olefin mixtures based on characteristic ion intensities and their equivalent ionization coefficients. The relative concentration errors for the olefin components were lower than 2.5% while the total analysis time was less than 2 min. These results demonstrate that the online ozonolysis SPI-TOFMS has the potential for real-time monitoring of catalytic olefin synthetic reactions. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

On-line monitoring of propofol in exhaled air is a potential way to evaluate the anaesthesia depth for patients during surgery. In this study, a negative Ni ionization high resolution ion mobility spectrometer with Bradbury-Nielsen-Gate-Grid structure was built to measure propofol with reactant ions Cl(HO) using dichloromethane as dopant. Instead of forming three propofol ions (M - H), M · O, and (M - H) with reactant ions O(HO), only product ion M · Cl was produced when introducing dichloromethane gas. The peak-to-peak resolution ( R) between reactant ions Cl(HO) and product ion M · Cl was 17.4, which was 1.6 times larger than that between O(HO) and product ion. Furthermore, the linear response range using reactant ions Cl(HO) was 3.5 times wider than that obtained with reactant ions O(HO). [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The hybrid quadrupole ion trap/time-of-flight mass spectrometry (QIT/TOFMS) device is popular because of its advantages of high sensitivity, high resolution, and MS/MS capability. However, the analytical performance of QIT/TOFMS is severely limited by the parameters of the ion trap, as QIT is typically used as a TOF pulser because the ion initial distributions of space, velocity, and angle change dynamically with the phase angle of rf voltage. In this work, a square waveform phase modulation strategy was proposed to eliminate the influence of the rf phase angle, and the dependence of QIT/TOFMS performance on the phase angle was studied. It was found that the mass resolution and signal intensity showed a "W" trend with the increase of the ion extraction phase angle from 0° to 360°, where the best resolution and sensitivity were obtained at 0°, 180°, and 360° while the worst resolution and sensitivity were obtained at 90° and 270°. Moreover, the optimum phase angle was independent of m / z . As a result, the mass resolution for m / z 106, 164, and 258 was improved by 162%, 160%, and 210% respectively, while the signal intensities for m / z 106, 164, and 258 were enhanced by 25 ± 1, 10 ± 1, and 21 ± 1 fold, respectively, and a limit of detection down to 0.015 ppbv for m / z 164 was obtained. The experiment results indicated that the square waveform phase modulation strategy could be used to simultaneously improve the resolution and sensitivity of QIT/TOFMS.