Visual observations of an atmospheric-pressure solution-cathode glow discharge

The solution-cathode glow discharge (SCGD) is an optical emission source for atomic spectrometry comprised of a moderate-power atmospheric-pressure DC glow discharge sustained directly upon the surface of an electrically conductive solution. The SCGD boasts a simple, inexpensive design and has demonstrated detection limits similar to those of more conventional excitation sources used in atomic spectrometry. Although the analytical performance of the SCGD as an optical emission source is well characterized, the mechanism through which the discharge atomizes and excites analyte from the sample solution remains a point of debate. The current paper presents visual observations of the SCGD from a variety of imaging techniques. The implications of the images regarding the mechanism of analyte solution-to-plasma transport and excitation in the SCGD are discussed. ► Droplets appear to be ejected from the surface of the discharge. ► Droplets are drawn downward toward the cathodic solution. ► Hot spots appear on the solution surface in the presence of the discharge. ► Optical emission is particularly strong in the region of the hot spots.