Qualitative & Quantitative Analysis
Energy dispersive X-ray fluorescence analysis (EDXRF) is a fast, qualitative elemental analysis technique. Typically all elements from sodium (Na) through to uranium (U) can be detected simultaneously, with good quality spectra obtained in minutes, or even seconds. Each element peak occurs at a known fixed position and generally concentrations from 100% down to sub-ppm are detectable with EDXRF. The lower limit depends on the particular instrument’s configuration.
XRF is mostly a quantitative technique – the peak-height for any element is directly related to the concentration of that element within the sampling volume. However, extreme care must be taken because two or more elements can interact with each other, resulting in contamination and thus skewed results. For example, chlorine atoms strongly absorb fluorescent X-Rays from lead – thus, if chlorine is present, the observed lead signal will be much less intense than expected for a particular concentration.
The ability of fluorescent X-rays to penetrate through and escape from the sample itself depends on their energy, which directly relates to which elements are being detected. The lighter elements all have very low energy X-rays (e.g. Na, Mg, Al and Si) and thus it is difficult to detect these even at relatively shallow depths within the sample. Heavier elements (e.g., Cu, Ag, and Au) have higher energy X-rays, which are able to traverse larger distances within the sample.
The sample composition itself is also an important factor- the higher the concentration of the heavier elements which absorb strongly, the lower is the chance of X-rays escaping from deep within the sample.
Physics of X-ray fluorescence, in a schematic representation