La Micro-fluorescència de raigs X en estudis forènsics : anàlisi d’aliatges de metalls nobles d’acord amb la norma ISO/DIS 23345/(2020)

Abstract

The objective of this final degree project is to develop a new methodology for the analysis of the

elemental composition of noble metal alloys, according to the recently approved ISO DIS 23345

regulation. This new methodology is intended to be put into practice in common forensic

analyses to intervene in expert trials of crimes of counterfeiting or theft of jewellery or gold

objects. The motivation to develop this new method has been the multiple advantages that it allegedly

presented over cupellation, the current official method of gold analysis according to the laws

established by Spanish legislation. The official method presents significant drawbacks: high

analysis time, destruction of the sample, generation of waste, high energy cost and

consumption of reagents, among others. Since the X-ray spectroscopy technique could overcome these drawbacks, it was proposed to develop the new methodology. The analysis is carried out thanks to the energy dispersive X-ray microfluorescence technique (ED-XRF). Likewise, first of all, a general calibration was developed, which included the elements commonly found in jewellery. For this, appropriate reference materials were used, a total of 33 standards of different composition. Subsequently, a specific calibration for the Au-Ag-Cu alloy was carried out and all

of this was subjected to a study to confirm that the methodology complied with the ISO DIS

23345 regulation. The results of these calibrations were satisfactory, so the study continued

Forward. Thus, the next step was the quantitative analysis of different privately owned jewels to

determine if they were legal gold, plated or counterfeit, also being able to determine their

composition precisely, fulfilling the proposed objective.

It was possible to determine that, of the seven jewels analysed, only four were legal gold, so the

remaining three did not present the minimum amount of gold required by the BOE, 18K