Characteristic X-ray generated with high energy X-ray irradiation is called as “fluorescent X-ray”. Each element has unique energy level sets of electrons; therefore, emitted X-ray energies are characteristic of each element. Table 2 shows examples of characteristic X-rays energies emitted from various elements [1]. Characteristic X-rays can be used to perform an elemental analysis by electron or X-ray irradiation. EPMA and SEM/EDS are popularly used for micro-elemental analysis because they simultaneously provide electron microscopic images and elemental distribution images. However, there are some requirements for specimens in

electron microscopy observation. The specimen should have electroconductivity RO4929097 cell line (or an electroconductive coating) and kept under a high vacuum during observation. Therefore, wet specimens (e.g., cells or wet tissue) Baf-A1 in vitro and specimens with a low heat resistance (e.g., paraffin-embedded tissue) are hard to analyze using EPMA or SEM/EDS methods. In addition, there is some possibility that electron irradiation can damage the specimens. Thus, high skills are required for the specimen preparation and observation for the EPMA or SEM/EDS analyses of scarce specimens [2]. X-ray fluorescence analysis (XRF) uses characteristic X-rays (called “fluorescence X-rays”) emitted under high-energy X-ray irradiation. XRF has some advantages over EPMA and EDS as follows. (1) X-ray irradiation

and fluorescence X-ray detection can be carried out in air, because X-rays are easily transmitted in an air layer. Therefore, XRF analysis can be performed in air and evacuation of the specimen chamber is not Exoribonuclease necessary, as it is in electron microscopy methods. In dental and medical analyses, specimens that are wet and/or have low heat resistance are often requested for elemental analysis. Additionally, scarce

pathological specimens should be analyzed non-destructively. The features of XRF are quite appropriate for such specimens. Conventional XRF irradiates an unfocused, wide beam onto the specimen. Therefore, a large specimen surface was required for analysis. Recently, a micro-focused X-ray source has been developed; thus, micro-sample analysis and elemental distribution analysis have become available. The optics for visible light are created by transparent materials with refractive indices greater than 1. However, for X-rays, materials have a refractive index almost equal to 1; therefore, different optics are required for X-ray focusing. Capillary focusing is widely used for XRF focusing optics. The inner surface of the capillary is designed to be the paraboloid of revolution, and the total reflection from the inner surface guides the X-ray to the focus. XRF analysis while scanning the specimen additionally provides elemental distribution images. A schematic diagram of micro-focused XRF equipment is shown in Fig. 2. Spatial resolution, which depends on the focus size, is 10–100 μm.