Multi-elemental analysis of solder using ETV-ICPOES for applications in forensic science

Abstract

Improvised explosive devices (IEDs) are becoming increasingly common in modern terrorism. If solder from an IED recovered from the crime scene can be analyzed and compared to solder taken from a suspect's home, this may allow for the identification of the guilty party. Using electrothermal vaporization inductively coupled plasma optical emission spectrometry (ETV-ICPOES), a method of direct analysis of solder samples was developed for the determination of both trace (Ag, As, Bi, Cu, Sb) and bulk (Sn, Pb) elements. It requires only 1.5 mg of sample. Matrix-matched external calibration was performed with NIST 1131 Solder, and the accuracy of the method was evaluated using NIST C2416 Bullet Lead. Point-by-point internal standardization was performed with Ar I 763.511 nm to compensate for sample loading effects on the plasma. Many commercially available solders contain an organic rosin core to improve melting; the samples were analyzed with and without the inclusion of the core. Two of the samples were further sub-sampled to examine the consistency of solder composition; the effect of melting solder was also investigated. The results were compared to values previously obtained through sample digestion and analysis with inductively coupled plasma mass spectrometry. The developed method is robust and produces accurate results, allowing for the direct analysis of solder samples as well as their discrimination, whether melted or not, and with or without rosin. Furthermore, a spike in Cu concentration in melted solder indicates that a soldering gun with Cu tip was used.