Application of Fluorescence Spectroscopy in Identification of Ivory and Mammoth Tusk

For protection of elephant populations, the trade of ivory is prohibited, but the trade of mammoth tusk is allowed in international trade.Therefore, it is a great significant to identify ivory and mammoth tusk accurately.It is easy to distinguish the whole ivory and mammoth tusk.However, the current challenge is to identify the jewelry made of them.In this paper, the FTIR and fluorescence spectrophotometer are used to distinguish the ivory and mammoth tusk samples.The epidermis and Retzius layer of mammoth tusk and the Retzius layer of ivory are tested by FTIR.The result shows that the ivory and mammoth tusk are mainly composed of collagen and hydroxyapatite.Due to the strong fossilization, the infrared spectra have a remarkable difference between the epidermis of ivory and mammoth tusk samples.However, the infrared spectra of interior parts of both samples are almost same.So FTIR has a certain limitation in identification of ivory and mammoth tusk jewelry.According to different emission spectra or excitation spectra of substances under the external excitation light, fluorescence spectra can be used for nondestructive, accurate and convenient analysis.Testing samples are slices from the Retzius and the fine concentric layers of the ivory and mammoth tusk.In the test, the slit width is set as 5nm and the angle between incident light and sample surface is 45°.By 280nm exciting light, the emission peak of the ivory is at 307nm, but that of mammoth tusk is at 315nm.Moreover, the former one's intensity is higher than the latter one.Fossilization caused damage to the collagen in the mammoth tusk partially and the micro-environment of amino acids changed.There are obvious differences in the occurrence state of amino acids between ivory and mammoth tusk.The difference between fluorescence spectra of the two samples is caused by the amino acids.The synchronous fluorescence spectrum analysis of the samples is further carried out.△λis set at 15nm and 60nm and the tyrosine and tryptophan of both mammoth tusk and ivory are measured.The spectrograms of both materials show the same profile, but there are significant differences in the intensity.Tyrosine and tryptophan appear in both samples, but contents of them in mammoth tusk are less than those in ivory, and mirco-environment are different from each other.This is the main reason that caused the difference in synchronous fluorescence spectra of the samples.The result of the synchronous fluorescence spectra conforms to the fluorescence spectra.Fluorescence spectroscopy can provide useful information of identification of ivory and mammoth tusk.