Geographical origin classification of gem corundum using elemental fingerprint analysis by laser ablation inductively coupled plasma mass spectrometry

Abstract

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was applied to study source identification by using elemental fingerprint analysis combined with the use of multivariate statistical analysis of gem corundum samples with different colors (red, blue, purple, yellow) from six countries (Kenya, Madagascar, Nigeria, Tanzania, Cambodia and Thailand). With LA-ICP-MS, the element concentrations in the samples were calculated using NIST 612 standard glass reference material as the external standard, with Al being used as the internal standard. The optimum conditions of laser ablation, i.e., 9 mJ laser power, 100% laser energy, a spot size of 200 μm and a repetition rate of 20 Hz, were selected to improve the signal intensities. The multivariate data analysis, including principal component analysis (PCA) and linear discriminant analysis (LDA) was used for classification study of samples. Two categories of gem corundum were analyzed including the gem corundum of the same color and the gem corundum of different colors. In the case of gem corundum of the same color classification, the LDA provided good scatter plot that could differentiate rubies between South East Asia and African countries and blue sapphires from Madagascar and Nigeria. For the classification of gem corundum with different colors, the LDA with the use of normalization factor was effective for the identification of the origin of corundum samples with 80% accuracy. © 2011 Elsevier B.V. All rights reserved.