Introduction

This application note gives all recommended data for the described analytical task including the list of measured values based on certified reference samples.

Alloy system       Au-Ag-Pd-Cu-Zn
                             Au-Ag-Cu-Zn-Ni

The Analytical problem

Analysis of gold alloys is an important task in the jewellery industry for determination of alloy composition and monetary value.

The five component alloys examined here are typical for white gold, although Nickel is now unusually as it is allergenic. However, many older alloys did contain Nickel.

Palladium white golds are common and have higher content of „precious“ elements. From the analytical point of view the overlapping of Au, Cu, Zn- and Ni-peaks and also of the Ag- and Pd-lines are the essential problems.

The analytical instrument

Measurements are made with the benchtop spectrometers

A low power tube is used in either instrument in excitation mode. A special collimator reduces the exciting beam down to 0.5 mm diameter. In this way, analysis of irregular or filigree samples will be possible. This is very important for jewellery manufacturers.

Energy dispersive measurement is made with a proportional counter. Despite the limited resolution of this type detector, highly precise analysis is possible if the qualitative composition of the sample is known. Good statistical measurement guarantees high reproducibility.

Max. Layer Thickness: approx. 10 µm

Sample preparation

The surface of the samples should be thoroughly cleaned free of contaminants. This will enable the irradiated area to be representative of the whole.

Further preparation is not necessary as the very small excited area and the use of normalised intensities reduce the geometric influence on the signal.

The irradiated area must be homogeneous. Non-homogenities can produce insufficient reproducibility of measurement.

Excitation conditions

Program Parameters

Au-Ag-Pd-Cu-Zn

Au-Ag-Cu-Zn-Ni

Calibration

Calibration is made in one range. Ten reference samples were used.

Analytical results

Accuracy

Au-Ag-Pd-Cu-Zn:

Calibration curve

Error of fit

In the calibration of different elements, there are the following errors of the fit, σ:

That means, that the analytical error for the described analytical problem is in the range of 0.20 Wt.% for gold.

The strong overlapping of the peaks of Ag and Pd reduced the limit of detection for these elements to 1%.

Au-Ag-Cu-Zn-Ni:

Calibration curve

Error of fit

In the calibration of different elements, there are the following errors of the fit, σ:

This means, that the analytical error for the described analytical problem is in the range of 0.20 Wt % for gold.

Reproducibility

Repeated measurements on the same sample with measuring times of 120 s give the following results:

Standard deviation