DIFFERENT FIELDS OF APPLICATIONS - Total-Reflection X-Ray Fluorescence Analysis and Related Methods - page 304

of HNO 3 and H 2 O 2 (4 : 1) within 6 h at 150 ° C. The clear solutions were diluted
to 5 ml with ultrapure water. Nitrous gases were evaporated and an aliquot of
1 ml was spiked with yttrium as internal standard (1 μ g/ml). Finally, a portion of
20 μ l was pipetted onto a clean quartz-glass carrier, polyvinyl alcohol (5 μ l) was
added, and the liquid drop was gently evaporated to dryness. The mass of the
residue was determined by triplicate weighing on a microbalance (57 ± 3 μ g).
For TXRF analysis, Mo excitation and a Si(Li) detector at 500-1000 s
measuring time were chosen. The method was first checked by the application
to the certified reference materials CRM 414“Trace elements in plankton”and
NIST 1643c“Trace elements in water.”Parallel analyses of three independent
samples showed a good precision of about 7% and an accuracy of about 9% for
nine different elements. The analyses of the biofilm samples grown on exposed
plates showed that K, Ca, Cr, Mn, Fe, Ni, Cu, Zn, and Pb are enriched by a
“bioconcentration factor”between about 100 and 60 000 in comparison to
typical values of the river Elbe water (total water phase). The bioaccumulation
on natural stones is two to three times smaller.
Mages etal . showed that a newly developed portable TXRF spectrometer
(PicoTAX, Bruker, Berlin, Germany) is even suitable for in-field trace element
analyses of biological materials and applied this instrument for a further
example of biomonitoring [42]. Daphnia is a genus of microcrustaceans with
the colloquial name“water fleas”living in zooplankton. They were collected
from a reservoir of the river Tisza, near Kisköre (Hungary) with the help of a
zooplankton net and washed with lake water. Single specimens with a length of
some millimeter and a mass of some milligrams were selected by a stereo-
microscope, deposited on a quartz-glass carrier and digested with 5 μ l HNO 3 —
spiked with a Ga standard—on a hot plate at 100 ° C. The dried residue was
analyzed by TXRF and the relative amount of several accumulated elements
could be determined. This is a fast and easy possibility to select polluted
sampling sites by a field study. It was also shown that a polycarbonate substrate
is best suited for biofilm production [43].
In a further example of biomonitoring, Wagner and Boman used tissue
samples of freshwater fish [44] to check the potential impact of a coal
combustion power plant in Vietnam. For that purpose, catfish (genus Clarias
fuscus ) of similar age and size were sampled from two places: (1) from a lake
11 km southwest of the power plant situated in an agricultural area and (2) from
a freshwater channel only 1 km apart and south of the power plant. During the
sampling period, this channel was exposed to the emissions of the plant
distributed by the monsoon wind, whereas the lake far away from the plant
was considered to be unaffected.
The catfish ( C.fuscus ) were dissected and muscle and liver tissues were
chosen, heated, dried, and sent to a laboratory in Sweden for analysis. Aliquots
of 50 mg were digested with 2.5 ml HNO 3 in a microwave oven at 350 W for 30 s.
TXRF analyses were carried out with Mo excitation, a Si(Li) detector, and 500 s
lifetime. Aliquots of 5 μ l were pipetted onto hydrophobic quartz-glass discs;
10 μ l of a Ga solution was added as internal standard, dried on a hot plate at