Handheld laser-induced breakdown spectroscopy (LIBS) as a fast and easy method to trace gold

Abstract

Gold is traded in virtually every country around the world. Consequently, tracing gold provenance is a difficult but necessary task to ensure a responsible supply chain from deposit to consumer. Measuring the silver content is often the first step in characterizing gold to retrace its origin. In this study, laser-induced breakdown spectroscopy (LIBS) using a handheld instrument was evaluated as a fast and easy method to analyse the silver content in natural gold. Six commercial gold alloys and natural gold from French Guiana were used. Our results demonstrate that handheld LIBS is relevant to gold traceability and is simple to use in the field. The micron-scale focused laser beam allows in situ analyses of small gold grains with acceptable reproducibility. Univariate and multivariate regression modelling was performed to assess the best calibration model for quantification of the Ag content. The quadratic univariate model was selected for its good predictive ability, with a coefficient of determination R² of 0.99 and a mean average error of 0.36 wt% Ag for prediction. The LIBS analyses of natural gold were compared to the EPMA data using a statistical test that allow distinct gold populations to be discriminated (or matched) and the results indicate it would be suitable for identifying unknown samples. We were able to successfully trace the origin of our “unknown” samples, a promising first step in the goal of delivering a low-cost field-based tool for responsible supply chain management.