Quantitative Analysis

XRF is a quantitative technique – the peak height for any element is directly related to the concentration of that element within the sampling volume. However, care must be taken, because two or more elements can interact with each other, resulting in skewed results. For example, chlorine atoms strongly absorb fluorescent X-Rays (Ka) from lead – thus, if chlorine is present, the observed lead signal will be much less intense than expected for a particular concentration.

Quantitative analysis is usually carried out using two main methods, both of which are usually fully incorporated within typical instrument software.

Fundamental Parameters Method (FPM)

Comprehensive software algorithms based on theoretical X-Ray beam intensity, detector solid angle, matrix effects (element-element interactions), band overlap and spectral backgrounds are used to calculate element concentrations based on the observed peak intensities. FPM provides a very fast, robust quantification method, which will work well for various matrices and experimental conditions (eg, voltage, current, beam size etc).

Calibration with standards

Calibration standards with accurately known element concentrations are used to generate calibration curves (XRF peak intensity versus concentration). These curves are then used to calculate concentrations from observed spectra. This method works extremely well, and would be recommended for best accuracy. However, matrix effects are not taken into account, so calibration standards can only be used for analysis of samples with similar (if not identical) matrices. As an example, a calibration curve generated with a set of metal alloys will most likely yield incorrect values when analyzing mineralogical samples.

Quantitative Analysis