Determination of chlorine with radical emission using laser-induced breakdown spectroscopy coupled with partial least square regression

Chlorine is a crucial element which may cause the corrosion of reinforced concrete. However, the strongest chlorine atom/ion emission lines are in the UV region and the ground state atom is hard to excite by conventional single-pulsed laser-induced breakdown spectroscopy (SP-LIBS). Radical emission is a feasible alternative to atom/ion emission when detecting chlorine concentration. Here, Cl atomic emission and calcium chloride (CaCl) radicals were detected in SP-LIBS, the calibrations of both emissions were compared. To further improve the accuracy, partial least square regression (PLSR) was adopted to establish the calibrations. The results showed that CaCl radical signal is stronger than Cl atomic signal with low energy SP-LIBS in open air, achieving a LoD (limit of detection) of 0.0404 wt%. Meanwhile, CaCl calibration had a better accuracy with coefficient of determination (R²) and root mean square error of cross validation (RMSECV) of 0.9930 and 0.2016 wt% with the help of PLSR. In conclusion, this work provided a potential approach for Chlorine determination in industry.