DIFFERENT FIELDS OF APPLICATIONS - Total-Reflection X-Ray Fluorescence Analysis and Related Methods - page 327

identical or similar behavior could be built: (1) K and Br; (2) Ca, Fe, and Ni;
(3) P and S, Cu and Zn.
Tissue samples of 15 patients with breast cancer were investigated and eight
elementsdetected(P,S,K,Ca,Fe,Ni,Cu,Zn,andBr).Absoluteprecision
and accuracy are strongly improved with higher concentrations; however, the
relative reliability is nearly constant for concentrations significantly above the
detection limits. Consequently, a logarithmic plot for all net intensities was
chosen so that a constant relative reliability is demonstrated by a constant
scatter. Furthermore, the logarithmic plot reflects the log-normal distribution
of elements in the earth's crust. For cluster analysis, three-dimensional plots
for the combinations of three elements were demonstrated as two-dimen-
sional figures [110]. Altogether, 83 different combinations are feasible; four of
them with specific results are shown in Figure 5.11. Each of them is repre-
sentingdataofnearly75healthyand75canceroustissuesamplesfrom15
patients. Two or three clusters can be distinguished depending on the
individual element combination. Figure 5.11a and b for Br, Fe, and S, and
for Br, Zn, and S show two clusters. Apart from some outliers, they can be
separated by the presence or absence of bromine. However, the clusters with
high Br values can be split into two subgroups with cancerous and healthy
tissue. Figure 5.11c and d for S, P, and Fe and for S, P, and Zn represent two
clusters apart from some outliers: one cluster with higher Fe or Zn concen-
trations for cancerous tissues and another cluster with lower Fe or Zn values
for healthy tissues. Further studies on cancerous tissues carried out by
XANES are presented in Section 7.3.3.
5.3.4MedicinesandRemedies
Several investigations of TXRF applied to medicines and remedies have been
carried out. The method is suitable for the determination of inorganic
impurities, especially heavy metals in drugs and also identifying a poisoning
due to an improper use of remedies. Two examples are given here.
The quality control of drugs with regard to inorganic impurities was
proposed by Wagner etal . [112,113]. Arsenic, zinc, and heavy metals are
suspected to cause toxic effects. Of course, the toxicity depends on the daily
dose and the duration of treatment. The main spectrometric methods for
testing drugs are AAS, ICP-OES, and conventional XRF. However, TXRF
is a method especially recommended in cases where only a small mass is
available. For that purpose, aliquots of only ∼ 10 mg could be dissolved in nitric
acid and rubidium added as internal standard (1 mg/l). A droplet less than 50 μ l
has to be pipetted on a clean quartz-glass disc and dried. Insoluble substances
should be decomposed by high-pressure digestion. Several substances were
investigated: lecithin used as an emulsifier in pharmaceutical products and also
in foodstuffs, human insulin as an essential drug for people suffering from
diabetes, procaine used as an anesthetic and neural therapeutic, and trypto-
phan from barbiturates or antidepressants. Human insulin could be analyzed