Abstract

A low-power (100–300 W) spark ablation device for rapid sample dissolution in aqueous solutions is described. In this device two closely spaced conductive samples were used as electrodes and placed in an aqueous solution. When a large enough potential is applied between the electrodes, a spark is formed and metal is removed from the sample surface, resulting in the formation of a colloidal suspension in the aqueous phase which is stable at neutral pH. The colloidal suspension can be readily dissolved, prior to the analysis, by adding 100–200 µl of concentrated HNO₃. Total sample preparation time was approximately 5–10 min, depending on the type of sample and the concentration of the target element. The samples used for this study included brass, mild steel, stainless steel and an aluminium alloy. Properties such as the rate of ablation of metal as well as the change in rate of ablation over time were measured. In general, the rate of metal ablated gradually decreases over time as metal is removed from the electrode surface; however, as more material is ablated, properties of the spark ablation medium also change (e.g. conductivity). Further experiments revealed that the rate of ablation decreased as the conductivity of the spark ablation medium increased. Other properties, such as relative permittivity and temperature of the spark ablation medium, did not seriously affect the rate of ablation of the metal. Spark ablation was also used for the determination of trace levels (0.002–0.7%) of Ni, Al, Si, Ag, Cu, Pb, As and Ti in a standard vanadium–chrome steel sample using ETAAS.