Analysis of Mexican Amber and Natural Resins Using Fourier Transform Infrared Spectroscopy (FTIR) and Raman Spectroscopy

Abstract

Amber is a semi-precious gemstone, it is a natural resin formed as a fossil and consists of labdanoid diterpenes. This study involves a compositional analysis of Mexican amber using FTIR Spectroscopy and Raman Spectroscopy, comparing it with resins mixed with sulphur, copal, and rosin, to determine the main spectral features of Mexican amber and identify differences from other fake amber resins. Samples of yellow, red, and green amber were utilised. The equipment used included an ATR FTIR spectrometer and a Raman spectrometer with a 785 nm laser source. In the FTIR analysis, the results reveal that the colour variations in Mexican amber do not reflect structural differences. The ester group is identified in amber through the C=O carbonyl bond at 1727 cm-1, confirmed by a band at 1243 cm-1 and a set of bands between 1200-1060 cm-1 corresponding to C-O-H and O-C-C bonds, respectively. The range between 1000-600 cm-1 is identified as the most crucial for distinguishing authentic amber and determining whether the resin is young or fossilised. In Raman, the main peaks to identify amber are at 1646 cm-1 and 1450 cm-1 with which the ratio of intensities was quantified to determine the maturity of the fossil resin.