LEd-SpEC: Spectroscopic detection of water contaminants using glow discharges from liquid microelectrodes

This paper reports on the detection of trace contaminants in water by spectroscopy of micro glow discharges that operate in air using liquid electrodes. A liquid electrode spectral emission chip (LEd-SpEC) has been developed to perform this function. Liquid from the cathode is sputtered into the discharge, and can be utilized for spectroscopic detection of impurities. Using a commercial spectrometer, we can measure Na concentrations <10 ppm (mg/l), and lead concentrations of 5 ppm. The relative intensity of certain spectral lines is shown to be a suitable measure of impurity concentration over several orders of magnitude. It is also shown that the addition of acids to lower the pH of the liquid solution increases the sensitivity of impurity detection. This device can also be used as a customizable optical source for UV and visible wavelengths.