PERFORMANCE OF TXRF and GI-XRF ANALYSES - Total-Reflection X-Ray Fluorescence Analysis and Related Methods - page 244

Figure4.14. Relative sensitivities of different elements in dependence on their atomic number Z .
Three excitation modes—(a), (b), and (c)—were applied as described in Section 4.2.1. The elements
were detected either by their K peaks (medium Z values) or by their L peaks (high Z values). Figure
from Ref. [4], reproduced with permission. Copyright1996, John Wiley and Sons.
energy E 0 . The constant, K , can be determined with the help of a reference
element for which S ref is set to be 1. The fundamental data— g , ω , f , and
( τ / ρ )—can be taken from tables. The efficiency of the detector and the
transmission of the air path between the sample and the detector are assumed
here to be equal for the individual elements, but they can easily be determined
and taken into consideration. The results correspond to the values experi-
mentally determined within a margin of 9%, in evidence of the validity of the
theory and the absence of matrix effects [51].
It can be concluded that the sensitivity values of those elements for which
standards are not available can be obtained by calculation or at least by
interpolation between known values. Relative sensitivities can even be trans-
ferred from one instrument to another if the equipment is the same.
4.4.2QuantificationbyInternalStandardization
In TXRF, quantification is generally carried out by internal standardization.
This easy and reliable method can be employed because small or minute
specimens are used for analysis. Two different methods can be chosen to this
end: the first is suitable for a quantitative determination of a single element and
the second is generally recommended for a multielement determination, which
is the actual task of TXRF.