Energy Dispersive Spectroscopy

Energy dispersive spectroscopy (also called energy dispersive x-ray spectroscopy) is an analysis technique that can be of great value in the forensic examination of samples. The technique utilizes a scanning electron microscope, a type of high magnification microscopy in which the sample is bombarded by electrons. The resultant pattern of electron reflection by the sample is used to generate a detailed three-dimensional appearing surface view.

At the heart of energy dispersive spectroscopy are x rays. During electron bombardment, electrons are also ejected from surface atoms of the sample. The resulting electron vacancy is filled by a higher energy electron. To maintain the energy balance of the atom, some energy must be released. The energy is released as x rays.

Released x rays are gathered by a detector positioned above the sample. Because the energy of the x rays will vary, depending on the element from which they were released, analysis of the x-ray spectrum can permit the various elements comprising a sample to be identified.

The x-ray spectrum is graphically displayed as a series of peaks. The pattern of peaks is a fingerprint of the specific elements in a specimen. Thus, blood will produce a different and characteristic pattern of peaks from gasoline.

Fluid samples such as the aforementioned cannot be examined directly. This is because the electron microscope operates in the absence of air, which would otherwise deflect the electron beam from the sample. During sample preparation, fluids can be dried down onto the surface. This residue is sufficient for analysis and identification.

Fluids can thus be identified and differentiated from each other using the spectroscopy technique. Furthermore, solids can also be analyzed, as the electron beam of the microscope can be focused to a small point on the sample surface. Indeed, various areas of a solid can be independently analyzed. This is advantageous when trying to identify the presence of a component on a solid object (i.e., blood on a knife tip). As well, different types of solid materials can be differentiated from one another.

Energy dispersive spectroscopy requires a dedicated laboratory equipped with a scanning electron microscope and ancillary equipment to conduct the x-ray analysis, as well as trained personnel. Thus, the analysis is typically done at regional or state facilities that will accept samples from local agencies.