Spectral Standard-Free Laser Microanalysis of Gold Alloys

Abstract

A standard-free variant of spectral laser microanalysis of the material of gold alloys for determining the standard of fineness of the specimens investigated has been implemented experimentally. A good correspondence of the results of measurements of the concentrations of gold in the materials analyzed to the specified data is shown. The basic stages and characteristic features of the procedures of the standard-free analysis are considered.Introduction. Articles made from gold alloys as well as native gold are the objects of routine technological, criminalistic, art, and other investigations. The methods and equipment used to analyze the material of gold alloys were considered to a quite satisfactory extent in [1]. The most widespread traditional method of determining the content of gold in alloys is assaying. The main drawbacks of this method are the following: the absence of information on doping components; a comparatively large mass of the laboratory sample, usually exceeding 200 mg; the slow operation of the analysis (not less than 2 h), and the necessity of recovering wastes. The most rapid method of determining the content of gold in alloys remains assaying on an assay stock. This technique has still another important advantage, that is, the mass of the sample used is fairly small (0.01-0.10 mg). The main disadvantages are the impossibility of determining the content of the remaining elements in the material and the necessity of having a highly competent operator. The simplest technique is the measurement of the material density (densitometry). Usually pure metals are suitable for the purpose. Moreover, this method cannot be used for investigating hollow specimens and articles with fragments made from other materials. Analysis of the composition of precious metals can be performed by the classical methods of "wet" chemistry. Although highly accurate, these techniques are very laborious in the case of a complete elemental analysis, and the main thing is that they require a relatively high expenditure of material.An effective investigation of the composition of the alloys of precious metals is ensured by the methods of spectral analysis: atomic absorption analysis involving a flame or electrothermal atomizer and an emission or mass spectrometric analysis with an inductively confined plasma. The procedure of measurement with the aid of the indicated methods eventually requires that the test sample be converted into a solution or a finely divided powder, although laser samples can be used for initial sampling. Here, among the drawbacks are a comparatively large expenditure of the material (except for electrothermal atomizers) and the high labor content of the full cycle of the procedure. One of the most promising methods that makes it possible to carry out a nondestructive analysis is the xray fluorescent one (XF). However, XF spectrometers yield quantitative information on the composition of the surface layers of a sample (on the order of several micrometers) and, moreover, the geometric shape of the investig...

Calibration-Free Laser-Induced Breakdown Spectroscopy: State of the art

“…Most frequently, the CF-LIBS analysis has been applied to solid materials: aluminum alloys [7,[15][16][17][18][19], steel and iron alloys [15,[18][19][20], precious alloys for jewelry [21,22], copper alloys [19,[23][24][25][26][27][28], archaeological copper artifacts [24,29], glasses [23], pigments on roman frescoes [30] and on parchments [31], soils and rocks [32][33][34], meteorites [35], coral skeletons [36], human hair [37].…”

Quantitative analysis of alloys and glasses by a calibration-free method using laser-induced breakdown spectroscopy

“…Such approach is based on the application of a complete optical diagnostic procedure of pulsed plasma. Recent achievements in instrumentation and data processing of pulsed ablation plasma have provided a possible way to overcome the matrix effects, yielding precise and accurate quantitative results on elemental composition of materials without using calibration curves, CRM, and internal standards [21][22][23][24][25][26][27]. The theoretical background underlying this approach has been described in the pertinent literature and will not be repeated here.…”

State of the art and problems in determining high gold contents in alloys and articles (Review)

“…The stan dard deviation of repeatability is of the order of 0.1%, which is close to the accuracy of cupellation. In other studies using this method [78][79][80][81], however, this level of accuracy was not obtained; the absolute error of gold determination was 0.8-2.5%.…”

“…The achieved level of accuracy is moderate; therefore, many studies considered evalua tion and methods of improving the metrological char acteristics of the LIBS method, especially in analysis of modern jewelry alloys and items, where high accuracy of gold determination (fineness) is required. In recent studies, jewelry gold alloys were analyzed by LIBS by two procedures: partial least squares (PLS) using ade quate standard samples [71][72][73][74][75][76] and a standardless method based on the analysis of emission spectra and their treatment with specially developed mathematical models [77][78][79][80][81].…”

“…They are almost nondestructive (the crater on the surface of the sample after the action of laser is shaped like a sphere with a depth of ~50 µm and a volume of 5 × 10 -9 cm 3 [78]). 4.…”