Nebulization assisted molecular LIBS for sensitive and fast fluorine determination in aqueous solutions

Abstract

The determination of halogen content in liquid samples by conventional laser induced breakdown spectroscopy (LIBS) is a difficult task due to the high excitation threshold of these elements. The indirect detection of these elements via molecular emission, product of recombination with an alkali-earth metal, is a well-known method to overcome this problem. However, current LIBS methods for halogen detection in liquid samples are scarce and based on the deposition of solutions on a CaCO₃ substrate using a pipetting gun, followed by an annealing process, resulting in a relatively slow sample preparation method. In this work, a novel approach based on online nebulization of different concentrations of an aqueous solution of NaF towards a CaCO₃ pellet is employed to obtain fluorine calibration curves from molecular emission of CaF. Operating parameters were optimized considering signal intensity, repeatability and analysis time (which determines the amount of consumed sample). Moreover, three fluorine calibration curves were built using different operating configurations and then tested by carrying out fluorine determination of mouthwash samples diluted in water. The optimized microanalysis configuration provided LODs of 10 mg kg⁻¹ with a linear range of 900 mg kg⁻¹ as well as accurate determination of the F-content in the mouthwash samples, which were validated by ion chromatography.