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

Cr 1.2 16 Sn 4.8 (Lα) 8
Mn 2.6 12 Sb 7.1 (Lβ) 8
Fe 2.2 12 Te 10
Co 6.0 I 13
Ni 6.0 5 Cs 24
Cu 4.8 6 Ba 5.1 (Lα) 40
Zn 5 Hg 7 (Lα)
Ga 4 Pb 21 (Mα) 8 (Lα)
II. Disturbing Effects
II.1 Interelement Radiation
By the term “interelements” we mean those elements in the sample which become
excited together with the wanted element under the influence of the primary radiation of the
source. The fluorescent radiation of interelements may disturb X-ray fluorescence
determination of the element of interest, or even make it completely impossible. These
disturbing effects can be classified as follows:
1. The K-series peak of the wanted element partially overlaps the K-series peaks of
interelements. Remember that if the difference between the atomic numbers of two
elements is lower than 3 (∆Z < 3), their characteristic peaks can be separated only by means
of a solid-state detector (Si(Li)) or appropriate absorption-edge filters.
2. The K-series peak of the wanted element overlaps the L-series peaks of some of the
interelements. As an example, let us consider zinc determination (ZnKα = 8.64 keV) in a
sample which also contains tungsten (WLα = 8.39 keV). From the energy values of the
ZnKα and WLα lines it is evident that the complete separation of two peaks may be a hard
task even if a solid-state detector is used.
3. The characteristic peak of the wanted overlaps the escape peaks of interelements. An
example of such a situation is the determination of vanadium (VKα = 17.47 keV) in a
sample which also contains tungsten (WLα = 8.39 keV).
It follows from these examples that the choice of optimum measurement conditions for
X-ray fluorescence determination of a particular element in a given material requires
information concerning the latter’s chemical composition and expected concentration ranges
of all the sample constituents in every analysed sample.
II.2 Matrix Effects
Generally speaking, the matrix effects in X-ray fluorescence analysis result from the
influence of the variations of chemical compositions of the sample matrix on the fluorescent
intensity of the wanted element. These effects can manifest themselves either via a difference
in the absorption of both the primary and fluorescence radiations in samples of different
matrix composition (absorption effect) or via an increase of the radiation intensity
(enhancement effect) due to the fluorescence radiation of some of the interelements. These
two phenomena will be discussed in detail in subsequent sections. The elements whose
varying concentrations in the analysed samples lead to the effects mentioned above will be
called disturbing elements.