Ivory or Bone? discrimination using ATR-FTIR spectroscopy and chemometrics

Abstract

Elephant ivory is one of the most priced items/products in the illegal wildlife trade. Its increased demand and the dwindling population of elephants have led to a heavy influx of many natural and artificial elephant ivory substitutes in the illegal wildlife market. Identification of genuine elephant ivory and distinguishing it from substitutes is mandatory for subsequent legal proceedings and successful implementation of the related laws. In this study, 30 Asian elephant (Elephas maximus) ivory and 29 cattle (Bubalus bubalis) bone samples were evaluated using ATR-FTIR spectroscopy with chemometrics. ATR-FTIR spectra of ivory and bone samples in the mid-IR range were visually compared and subjected to advanced chemometric analysis. The developed PCA model differentiated the ivory and cattle bone samples, with 98.30 % accuracy. PLS-DA model successfully differentiated ivory and bone samples into discrete classes with a calibration R square value of 0.99. A PLSDA-V model was also developed utilizing X-variables with a VIP score > 1 that distinguished ivory and bone samples into discrete classes. It was observed that the PLS-DA model outperformed the PLSDA-V model in terms of high accuracy and low error rates. Subsequently, the PLS-DA model was employed solely for external validation and blind tests. Furthermore, resin-based fake ivory samples were also differentiated from genuine ivory samples through visual comparison of their ATR-FTIR spectra. The findings of the study showed that ATR-FTIR spectroscopy could identify and differentiate ivory and bone samples, even when they are in powdered form and have lost their morphological characteristics in a quick, precise, non-destructive manner.