Electrospray deposition followed by laser-induced breakdown spectroscopy (ESD-LIBS): a new method for trace elemental analysis of aqueous samples

Abstract

The combination of electrospray deposition with laser-induced breakdown spectroscopy (ESD-LIBS) was investigated as a potential approach to the detection and quantification of Zn, Cd, Cr and Ni, at trace levels, in aqueous samples. In this analytical procedure, the aqueous samples were first converted into solids in an electrospray system. To this end, micro-volumes of liquids were electro-sprayed onto a heated substrate, leading to the generation of solid residues. Afterwards, the as-obtained residues were analysed by LIBS. Three calibration methodologies were tested with the proposed ESD-LIBS methodology, namely external calibration, conventional standard addition calibration and on-line standard addition calibration. In all cases, the analytical features of the ESD-LIBS method were assessed. The obtained limits of detection ranged from 9 μg kg−1 to 57 μg kg−1, depending on the element and on the calibration modality used. Method trueness, evaluated from the analysis of a real sample of tap water, was highly dependent on the calibration method. The use of external calibration led to recovery values in the range of 18–123%, indicating the existence of strong matrix effects. This drawback was overcome with the application of conventional standard addition and on-line standard addition calibration modalities, for which recovery values were improved to the ranges 91–110% and 90–105%, respectively. Among them, the use of on-line standard addition provides a sensitive and accurate methodology with possibilities of automation.