Detection of zinc and lead in water using evaporative preconcentration and single-particle laser-induced breakdown spectroscopy

•Metals in a water sample are preconcentrated inside drying salt water droplets.•LIBS measurement from a single 5 μm dry salt particle using low laser pulse energy.•Stable sodium matrix can be utilized in the signal processing.•0.3 ppm and 0.1 ppm detection limits in water obtained for Zn and Pb respectively.

A novel laser-induced breakdown spectroscopy (LIBS)-based measurement method for metals in water is demonstrated. In the presented technology a small amount of sodium chloride is dissolved in the sample solution before spraying the sample into a tubular oven. After water removal monodisperse dry NaCl aerosol particles are formed where trace metals are present as additives. A single-particle LIBS analysis is then triggered with a scattering based particle detection system. Benefits are the highly increased metal concentration in the LIBS focal volume and the static NaCl-matrix which can be exploited in the signal processing procedure. Emitted light from the emerged plasma plume is collected with wide angle optics and dispersed with a grating spectrometer. In an aqueous solution, the respective limits of detection for zinc and lead were 0.3 ppm and 0.1 ppm using a relatively low 14 mJ laser pulse energy. Zn/Na peak intensity ratio calibration curve for zinc concentration was also determined and LIBS signal dependence on laser pulse energy was investigated.