X-Ray Fluorescence Analytical Techniques - CNSTN : Centre ...

factor of 2, because also the reflected beam contributes to sample excitation. Figure III.1
shows both effects as function of the angle of incidence.
Figure III.1: Effect on spectral line and background of total reflection.
III. Principle of Total Reflection X-Ray Fluorescence Analysis
Total reflection X-ray fluorescence analysis (TXRF) is basically an energy dispersive
analytical technique in special excitation geometry (Figure III.2). This geometry is achieved
by adjusting the sample carrier, not inclined under 45° to the incident beam, as for standard
EDXRF, but with angles of about 1 mrad (0.06°) to the primary beam. The incident beam thus
impinges at angles below the critical angle of (external) total reflection for X-rays onto the
surface of a plane smooth polished reflector.
Figure III.2: Scheme of total reflection X-ray fluorescence (TXRF).
Usually a liquid sample, with a volume of only 1 – 100 µL, is pipetted in the center of
this surface and the droplet will cover an area of a few millimetres in diameter. As result of
the drying process where the liquid part of the sample is evaporated, the residual is irregularly
distributed on the reflector (within the above stated diameter), forming a very thin sample.
The simplified equation (valid above the highest K absorption edge of the reflector
material) for the critical angle of total reflection ϕcrit (in mrad) depends on the energy E (in
keV) of the incident photons and the density ρ (in g/cm 3 ) of the reflector material: