Selective measurement of Cl2 and HCl based on dopant-assisted negative photoionization ion mobility spectrometry combined with semiconductor cooling.

This study presents an efficient approach for the precise detection of chlorine gas (Cl2) and hydrogen chloride (HCl), harmful pollutants frequently emitted from chlor-alkali and various industrial processes. These substances, even in trace amounts, pose significant health risks. Ion mobility spectrometry (IMS), known for its sensitivity in pollutant detection, traditionally struggles to differentiate between Cl2 and HCl due to the similarity of their product ions, Cl-. To overcome this limitation, we introduce a novel technique combining dopant-assisted negative photoionization ion mobility spectrometry (DANP-IMS) with an automatic semiconductor cooling system. This unique combination utilizes the differential cryogenic removal efficiencies of Cl2 and HCl to segregate these gases before analysis. By applying DANP-IMS, we achieved selective measurement of Cl- ion signal intensities under both standard and cryogenic conditions, facilitating the accurate quantification of total chlorine and Cl2 levels. We then determined HCl concentrations by deducting the Cl2 signal from the total chlorine readings. Our approach demonstrated detection limits of 2.0 parts per billion (ppb) for Cl2 and 0.8 ppb for HCl, across a linear detection range of 0-200 ppb. Moreover, our method's capability for real-time atmospheric monitoring of Cl2 and HCl near industrial sites underscores its utility for environmental monitoring, offering a robust solution for the separate and precise measurement of these pollutants.

Real-time monitoring of atmospheric ammonia based on modifier-enhanced vacuum ultraviolet photoionization ion mobility spectrometry.

Ammonia (NH3) plays an important role in the atmospheric environment such as the formation of PM2.5, the concentration monitoring of which could hence help in the air quality assessment. In this study, a method for quantitative monitoring of atmospheric NH3 was developed based on modifier-enhanced selectivity detection using a homemade vacuum ultraviolet photoionization ion mobility spectrometry (VUV-PI-IMS). To enhance the resolution and sensitivity of measuring NH3, 2-butanone as the gas modifier was introduced into the drift tube with the drift gas. Atmospheric NH3 can be selectively detected, where the peak-to-peak resolution (RP-P) of 7.69 was obtained. The product ions were identified to be [C4H8O]2NH4+ by using a homemade time-of-flight mass spectrometer. The calculated limit of detection (LOD) was 0.39 ppbv improving about 10 times. For the most common concentration variation of atmospheric NH3 in the range of 10-100 ppbv, the linear curve was obtained with R2 of 0.997. Lastly, the VUV-PI-IMS was used to monitor the evolution of atmospheric NH3 near our laboratory and mounted on a car for monitoring the regional distribution of atmospheric NH3 in Dalian, China. The results also showed that VUV-PI-IMS has a promising application prospect in monitoring the concentration of atmospheric NH3 and supporting the air quality assessment.

Study of Coulombic broadening in stand-alone ion mobility spectrometry.

This paper proposes a method for investigating the Coulombic broadening, tcou, in an ambient pressure ion mobility spectrometer based on the analysis of peaks originating from O2 -(H2O)n and electrons. It showed that the full width at half maximum (FWHM) of electrons was independent of electron density and remained at a constant contribution from the initial width of ion packets, tg, and amplifier broadening, tamp; in contrast, the FWHM of O2 -(H2O)n increased with the rise of O2 -(H2O)n density due to additional contributions from tcou and diffusion broadening tdiff. The tcou of O2 -(H2O)n was extracted from the FWHM by subtracting tg, tamp, and tdiff. The tcou of O2 -(H2O)n was found to increase from 0.14 ms to 0.24 ms as the O2 -(H2O)n density increased from 7.35 × 105 to 1.22 × 107 cm-3. The percentage of tcou in the FWHM was in the range of 45%-80%, and the Coulomb-limited resolving power decreased from 70 to 40 as the ion density increased, which indicated that the Coulomb effect was dramatic.

On-line measurement of propofol using membrane inlet ion mobility spectrometer.

The concentration of propofol in patient's exhaled air is an indicator of the anesthetic depth. In the present study, a membrane inlet ion mobility spectrometer (MI-IMS) was built for the on-line measurement of propofol. Compared with the direct sample introduction, the membrane inlet could eliminate the interference of moisture and improve the selectivity of propofol. Effects of membrane temperature and carrier gas flow rate on the sensitivity and response time have been investigated experimentally and theoretically. Under the optimized experimental conditions of membrane temperature 100 °C and carrier gas flow rate 200 mL min(-1), the calculated limit of detection (LOD) for propofol was 1 ppbv, and the calibration curve was linear in the range of 10-83 ppbv with a correlation coefficient (R(2)) of 0.993. Finally, the propofol concentration in an anaesthetized mouse exhaled air was monitored continuously to demonstrate the capability of MI-IMS in the on-line measurement of propofol in real samples.

Note: Design and construction of a simple and reliable printed circuit board-substrate Bradbury-Nielsen gate for ion mobility spectrometry.

A less laborious, structure-simple, and performance-reliable printed circuit board (PCB) based Bradbury-Nielsen gate for high-resolution ion mobility spectrometry was introduced and investigated. The gate substrate was manufactured using a PCB etching process with small holes (Φ 0.1 mm) drilled along the gold-plated copper lines. Two interdigitated sets of rigid stainless steel spring wire (Φ 0.1 mm) that stands high temperature and guarantees performance stability were threaded through the holes. Our homebuilt ion mobility spectrometer mounted with the gate gave results of about 40 for resolution while keeping a signal intensity of over 0.5 nano-amperes.

[Automatic continuous monitoring of volatile organic compounds using ion mobility spectrometer array].

An ion mobility spectrometer array was designed, in order to broaden the detection range of ion mobility spectrometer and improve the accuracy of compound identification. This instrument was based on the combination of ionization sources of 63Ni positive ion mode, 63Ni negative ion mode and photoionization mode with vacuum UV lamp, and it can continuously monitor the volatile organic compounds in air. With the automatic system of sampling and injection of this instrument, the positive ion of dimethyl sulfoxide and negative ion of dichloromethane were detected simultaneously. By comprehensive analysis of spectra with ion mobility spectrometer array, acrylonitrile, m-xylene and acetone were identified, which were difficult to be distinguished under the 63Ni positive ion mode. Acetone samples were determined quantitatively within four days continuously, and the results indicated that the linear range of acetone in this instrument was 2 orders of magnitude. The linear correlation coefficient R was higher than 0.995, and the relative standard deviations were controlled in the range of 4.0%-18.3%. Methacrylate leaked in simulation was monitored on-line for 24 h continuously, using the method of dynamic tracking, and the result showed the leaking time and the concentration of methacrylate directly.

Quartz crystal microbalance sensor array for the detection of volatile organic compounds.

A sensor array system consisting of five quartz crystal microbalance (QCM) sensors (four for measuring and one for reference) and an artificial neural network (ANN) method is presented for on-line detection of volatile organic compounds. Three ionic liquids, 1-butyl-3-methylimidazolium chloride (C(4)mimCl), 1-butyl-3-methylimidazolium hexafluorophosphate (C(4)mimPF(6)), 1-dedocyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C(4)mimNTf(2)), and silicone oil II, which is widely used as gas chromatographic stationary phase, have been selected as sensitive coatings on the quartz surface allowing the sensor array effective to identify chemical vapors, such as toluene, ethanol, acetone and dichloromethane. The success rate for the qualitative recognition reached 100%. Quantitative analysis has also been investigated, within the concentration range of 0.6-6.1 mg/L for toluene, 0.9-7.5 mg/L for ethanol, 2.8-117 mg/L for dichloromethane, and 0.7-38 mg/L for acetone, with a prediction error lower than 8%.