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

Abstract

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.