Determination of Silver Carat using X-ray Fluorescence

Abstract

Jewellery has attracted humans of all cultures and civilization since times immemorial. Silver for example, has a beautiful colour, excellent corrosion and oxidation resistance, superior malleability, and ease of fabrication. Its limited availability together with these other characteristics is collectively responsible for the unique place silver has in the family of metals. As a consequence much thought and extensive research have been devoted to develop non destructive method for analyzing silver metal in general materials and from Jewellery in particular. In the present research, the application of X- ray fluorescence, which is classified as non-invasive technique, to analysis two kinds of silver samples in two silver parcels have been undertaken. The two silver samples used in this experiment were purchased from Sudan. As a result of radiation X-ray fluorescence (XRF) spectroscopy, only three elements, silver, zinc and copper were observed in XRF spectrum of both silver parcel samples. The peak intensity showed good correlation with the concentration of silver in the samples. The analytical line for analysis silver which is Kα is fully resolved from the other lines within the sample components. Nevertheless, there are spectral interferences within the other sample component, copper and zinc. This could be due to similarity in the X- ray energy since they have closely atomic number (Cu = 29, Zn = 30). In addition, the variation of silver peak intensity for sample 1 (designated as Carat 925) were sufficiently higher compared with corresponding one in sample -2 (designated as Carat 800). Therefore, the comparison of the intensity can be effective method to discriminate different silver samples originating from different type of silver parcel. The silver III concentration (w/w%) in sample -1 (Carat 925) and sample -2 (Carat 800) were found to be 94.79% and 84.45%, respectively. In order to validate the over mention method, other wet analysis was performed by atomic absorption spectroscopy (AAS). The obtained result from XRF analysis and the one from AAS were correlated using statistical method (t-test). The results indicate that there is no significant different between the results obtained by the two methods. Therefore, XRF can be successfully utilized for analyzing material containing silver, particularly Jewellery objects.