Rapid dissolution of metal in aqueous media using a modified commercial spark source unit

In this preliminary study the feasibility of a modified spark source was investigated as a method of rapidly dissolving solid conductive samples in aqueous media prior to analysis by atomic spectroscopy. The spark source, originally designed for spark emission spectroscopy in air, was modified by the installation of a spark ablation vessel. This spark ablation vessel was designed for spark ablating samples in aqueous solution, such as deionised water. Samples such as mild steel and brass were ablated in 5–10 ml of deionised water for 2–30 s producing a colloidal suspension. The suspension was readily dissolved by adding 100 μl of concentrated HCl or HNO3. In this paper the spark ablation vessel is described as well as some of the properties of spark ablation in aqueous solutions. Spark ablation rates on mild steel were measured with respect to spark ablation parameters such as applied current (power), polarity and spark time. Using mild steel as a test sample, spark ablation rates varied from 40 μg s−1, with 2.5 A of applied current, to 70 μg s−1 with 10 A of applied current to the electrodes. The feasibility of using this technique for analysing trace levels (μg g−1) of elements in solid samples was also demonstrated for elements such as Ni in brass with inductively coupled plasma mass spectrometry (ICP-MS). Quantification of selected elements (Cr, Ni, Mn and Cu) in a certified alloy (SRM 663) and a non-certified stainless steel showed good agreement between the measured values using spark ablation and the accepted values.