Fast detection of hazardous chlorinated volatile organic compounds via laser-induced breakdown spectroscopy

Abstract

Chlorinated volatile organic compounds (Cl-VOCs) have severe toxicity and low biodegradability, and are listed as priority pollutants in most countries. However, air pollution occurs intermittently, which is difficult to monitor by traditional methods with low temporal resolutions (1–24 h). With the specific advantages of fast and in situ detection, laser-induced breakdown spectroscopy (LIBS) has been regarded as a viable technology for Cl-VOCs analysis. However, strong atomic lines of Cl are easily absorbed by oxygen in air. To solve this problem, some researchers set the whole or part LIBS instrument in a vacuum or inert environment, and other researchers focus on increasing plasma temperature and electron number density. These methods can achieve satisfactory results for Cl detection, but they present the problems of the complex device, harsh detection conditions, and high cost, which weaken the simplicity and fast detection ability of LIBS technology. Fortunately, the molecular spectra can be detected in air, but the intrinsic molecules in Cl-VOCs are weak. In this regard, a novel approach is proposed for realizing the controllable formation of high-intensity CaCl molecules, in which calcite is selected as the substrate to supply sufficient Ca. The results show that Cl can be sensitively detected using LIBS assisted with molecular spectra, and the limit of detection was 12.74 ppm, which meets the occupational exposure limits recommended by the American Conference of Governmental Industrial Hygienists (ACGIH). What's more, the prediction performance, generalization ability, and analytical efficiency (below 5 s) of the established calibration model were evaluated. It can be confirmed that the precise formation of LIBS molecular spectra shows great potential for the real-time and in situ analysis of Cl-VOCs.