Chemistry Reference
In-Depth Information
Figure5.9.
(a) Freezing microtome: (1) tissue sample; (2) stretcher with a thin section; (3) scalpel.
(b) A thin section of mussel tissue is placed on a quartz-glass carrier. Figure from Ref. [98],
reproduced with permission. Copyright1989, Elsevier.
absolutely recommended for cooling down to room temperature and condi-
tioning of the section.
Finally, the individual sections are analyzed by TXRF within a counting time
of 100-1000 s. Afterward, the dry mass of the section has to be determined. For
this purpose, a difference weighing is carried out by means of a microbalance
with a precision of 0.1
μ
g. Every carrier is weighed twice, first
with
the deposited
section and then
without
the section, after it was scraped off with a scalpel. The
carriers must not be touched by hand, and gloves must be used in order to
precisely determine dry masses of only 100
μ
g or so. The mass fractions are
finally determined by Equation 4.12.
The reliability of the method was checked by the analysis of different
reference materials [98]: NIST 1573“Tomato Leaves”; NIST 1566“Oyster
Tissue”; NIST 1577“Bovine Liver”; and NIES
2
No. 6“Mussel Tissue”.
Because these materials are only available as powders, 100 mg was first mixed
with several
μ
l of ultrapure water and then this powder mash was freeze-cut and
analyzed by TXRF. The detection limits were found to be about 1
μ
g/g. The
relative deviations between certified and measured values were about 10% for
elements with a mass fraction
>
10
μ
g/g. A possible Fe contamination by the
iron scalpel was precluded by control tests.
The freeze-cut technique can be applied to the analysis of human tissues, for
example, of kidney, liver, and lung. Within a project on occupational hazards,
Wiecken and colleagues studied the dust stress caused by the inhalation of
heavy-metal particles [96]. A first group of 12 persons with exposure to normal
dust stress was examined. The spectra obtained from their lung tissue differed
2
NIES stands for the National Institute for Environmental Studies (Tsukuba, Japan).
Search WWH ::
Custom Search