47
solutions in the colorimeter tubes, was determined with a
Bausch and Lomb Spectronic 20 colorimeter and compared against
a set of standards in the range 0 - 2.5 wg of zinc,
for which
the dependence of transmittance upon concentration is linear.
Contamination from the resin and from the reagent solutions
was determined from blanks which were processed along with the
samples,
ani the sample values were corrected accordingly.
To determine the reliability of the method, 200 ug of
zinc
(as chloride) was added to each of 12 ion-exchange colums
prepared in the manner previously described,
and eluted in
exactly the same way as the zinc in the tissue samples.
The
zine in aliquots of 1/100 of the 0.005M eluate from each column
was then determined by the dithizone method described above.
From the data from this test
(Table 1),
ation was computed to be 20 per cent.
the coefficient of variThe recovery of zinc
separated by the same technique from 5 other transition elements
using ion-exchange columns of similar size and composition and
with the aid of a radioactive tracer was determined to be 100
per cent
(Joyner and Chakravarti,
1960).
The error,
therefore,
probably represented a composite of errors incurred in the
pipetting of aliquots and those involved in the several steps
of the dithizone determination.
ve