X-ray fluorescence analysis (XRF) is a method of quantitative analysis of the chemical composition, which is actively used in many areas of science and industry. XRF is one of the most common methods for elemental composition analysis, since it allows you to quickly (less than a minute) obtain accurate quantitative results with little or no sample preparation required.
Measurement time and precision
The accuracy of the XRF method largely depends on the conditions and parameters of a particular measurement. First of all, precision (convergence of the results of parallel measurements) is determined by the measurement time and the workload of the spectrometer. To obtain an accurate result, it is necessary to collect the spectrum over a period of time sufficient to achieve good statistics of the energy distribution of X-ray quanta. The measurement time can be reduced by increasing the load on the spectrometer, although this may complicate the processing of the spectrum due to parasitic effects associated with the finite processing time of each particular sample. Modern high-speed XRF spectrometers are able to determine the alloy grade in 1-3 seconds of measurement.
Accuracy for different elements
The accuracy may vary depending on the task. For example, the accuracy of determining the main metal elements of the alloy (iron, nickel, copper) is usually hundredths of a percent, but as the atomic number decreases, the accuracy deteriorates, and for aluminum it will already be tenths of a percent. This is especially true for hand-held analyzers due to the strong absorption of quanta corresponding to the characteristic lines of light elements in air. In desktop spectrometers, to improve the accuracy for light elements, the measuring chamber is purged with helium. The presence of heavy metals such as lead, mercury, chromium and arsenic in a light matrix can be detected with an accuracy of 1 ppm (part per million). In general, XRF has a low sensitivity to light elements and a high sensitivity to heavy elements. It should also be noted that the accuracy of determining a particular element depends on the presence of other elements in the sample and may vary depending on the composition of the sample.
Method Precision
An important quality characteristic of a method is precision, i.e. reproducibility of measurements. This characteristic of the XRF analyzer primarily depends on its calibration. The results of successive measurements of the same sample with a well-calibrated spectrometer will always differ from the true value by no more than the statistical error of determining a particular element. The quality of the test sample also affects the correctness of the results obtained. The ideal sample for analysis is a smooth surface of a homogeneous solid sample, a homogeneous liquid, or a very finely divided powder sample. In case of significant inhomogeneity of the test sample, the result will depend on the point at which the measurement was taken. To determine the integral composition in this case, it is possible to average the results of many measurements made at different points, however, the accuracy will be worse than in the case of a homogeneous sample.
