Forensic discrimination of lead-tin solder based on the trace impurity analysis by ICP-AES

Trace impurities in lead-tin solders were determined using inductively coupled plasma atomic emission spectrometry (ICP-AES) for the forensic discrimination of solder samples from different origins by a comparison of the concentration for each element. After about 10 mg of sample was accurately measured and taken into a glass tube, 1 ml of HNO3 was added. The tube was capped and heated at 80 degrees C for 10 min. After cooling to the room temperature, 1 ml of HCl and 2 ml of purified water were added. It was then agitated until the sample was completely dissolved, followed by dilution to 10 ml. Five elements (Sb, Bi, Cu, As and Ag) in this solution were determined by ICP-AES. The observed values for these elements in the NIST Standard Reference Material 1131 showed good agreement with the certified ones. Eighteen kinds of solder samples could be distinguished from each other, since all of the pairs among these samples provided remarkable difference in the concentration of the trace elements. The copper concentration should have been excluded from the comparison when it increased after melting by a soldering iron made of copper.