Improving Cl determination in cements by molecular LIBS using noble gas-enriched atmospheres and new approaches for interference removal

Abstract

Nowadays, emission from diatomic molecules is frequently used for multiple purposes within laser-induced breakdown spectroscopy (LIBS). However, these spectrally broad signals are often found to be interfered with by other spectral emissions, which can be detrimental for analytical purposes. In the particular case of chlorine determination in cements via CaCl emission (∼593 nm), the spectral interferences are caused by molecular CaO (∼590–620 nm) and atomic Na I (∼590 nm) emissions. In this work, a methodology to remove both CaO and Na interferences was developed and critically evaluated, overcoming the problematics associated with the absence of a Cl-blank cement sample and the variability of Na concentration in the analyzed samples. Moreover, the generation of a plasma in Ar- and He-enriched atmospheres was also investigated, concluding that the use of Ar is recommended to improve Cl determination since it yields a higher sensitivity while maintaining a lower contribution of Na interferences. The suitability of the developed protocol was demonstrated through the successful determination of Cl content in real cement samples, with concentrations ranging between 0.23 and 1.5 wt% of Cl.