<i>In Situ</i> Analysis of Copper Alloys by Femtosecond Laser Ablation Inductively Coupled Plasma Mass Spectrometry: Constrains on Matrix Effects

Abstract

Direct analysis of copper-base alloys using laser ablation techniques is an increasingly common procedure in cultural heritage studies. However, main discussions remain focused on the possibility of using non-matrix matched external reference materials. To evaluate the occurrence of matrix effects during in situ microanalysis of copper-base materials, using near infrared femtosecond laser ablation techniques (NIR fs-LA-ICP-MS), two bronzes, i.e., (Sn-Zn)-ternary and (Sn)-binary copper-matrix reference materials, as well as a reference synthetic glass (NIST-SRM-610) have been analyzed. The results have been compared to data obtained on a sulfide-matrix reference material. Similar values in relative sensitivity averages of 63Cu, 118Sn and 66Zn, as well as in 118Sn/63Cu and 66Zn/63Cu ratios were obtained, for all analyzed matrix types, i.e., copper-base-, silicate-, and sulfide-reference materials. Consequently, it is possible to determinate major and minor element concentrations in copper alloys, i.e., Cu, Sn and Zn, using silicate and sulfide reference materials as external calibrators, without any matrix effect and over a wide range of concentrations (from wt.% to ppm). Equally, Cu, Sn and Zn concentrations can be precisely determined in sulfides using homogeneous alloys (reference) materials as an external calibrator. Thus, it is possible to determine Cu, Sn and Zn in copper-base materials and their ore minerals, mostly sulfides, in a single analytical session, without requiring specific external calibrators for each matrix type. In contrast, immiscible elements in copper matrix, such as Pb and Fe show notable differences in their relative sensitivity values and ratios for different matrix-materials analyzed, implying that matrix-matched external calibrations remain to be applied for their trace quantification.