EDS stands for Energy dispersive X-ray Spectroscopy. The fundamental principle of the method is that X-rays are generated as a result of the electron ejection of an inner level electron (low energy) by an energetic electron from an electron column. The ejected electron is replaced by an electron from a higher energy shell. The energy loss as it mov es from a high energy shell to a low energy shell is released in the form of X-rays. Each element has many energy levels and therefore many potential vacancy-filling mechanisms. As a consequence even pure elements emit X-rays at many energies. Because atomic structure of each element is different, it follows that each element will emit a different pattern of X-rays. These X-rays can be analyzed either by wavelength dispersive methods (WDS) or energy dispersive methods (EDS) depending on the equipment being used for the analysis.

An X-ray photon first creates a charge pulse in a semiconductor detector; the charge pulse is then converted into a voltage pulse whose amplitude reflects the energy level of the detected X-ray. This voltage pulse is converted into a digital signal which causes one count to be added to the corresponding voltage channel of a multichannel analyzer. Counting over some time, results in an X-ray spectrum.

In general, microanalysis is the easiest method (and sometime the only one) for analyzing microscopic samples, and in most cases, the technique practically nondestructive and requirements for sample preparation are minimal. It is sensitive to low concentrations - minimum detection limits(MDL) are below 0.1% in the best cases and typically less than 1% with relative precision of 1% to 5% throughout the range from MDL to 100%.