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.