124
Fish
this method is that both the natural copper content of the fish organs and the
concentration of added tracers are determined on the same sample by making two
measurements of isotopic ratio - one before and one after the addition of the standard
63CU spike. Both of these isotopes constitute ideal tracers, being readily available at
low cost and being free from radiation hazards. A spark source mass spectrometer is
an ideal way of carrying out isotopic ratio measurements.
In this procedure, the wet fish sample was weighed before and after vacuum freeze
drying, then transferred to a Tracerlab LTA 600 low temperature asher to remove
organic matter. The residue was then digested in 0.5 mol I-I hydrochloric acid-30 %
hydrogen peroxide, ascorbic acid being added to destroy residual hydrogen peroxide,
and copper extracted from the solution with a carbon tetrachloride solution of
dithizone. This extract was then evaporated directly onto graphite prior to spark
source mass spectrometric evaluation.
Table 7.2 illustrates the type of data obtained in a typical experiment and it can be
seen that the amount of copper available for analysis varied appreciably from one type
of tissue to another (column C). Thus, as far as possible, the size of sample taken for
analysis was adjusted by sub-sampling (muscle, bone, skin, etc.) or by bulking organs
from more than one fish (heart, spleen, kidney, etc.). In this way, a constant amount
(200 ng) of 63CU standard could be added to all samples, thus greatly simplifying the
procedure at that stage.
7.1.5
Lead
The molybdenum- and lanthanum-treated pyrolytically coated graphite furnace atomic
absorption spectrometric method described by Poldoski [360] under cadmium earlier
in this section has also been applied to the determination of lead in fish tissue. Lead
results were reported obtained in spiking recovery experiments, carried out on fish
tissue samples and on an authenticated reference sample (NBS SRM 1577 bovine liver)
under specified conditions of analysis. It is seen that the determined lead content on
NBS SRM 1577 (0.33 ± 0.01 mg kg-I) is in good agreement with the nominal value
(0.34 ± 0.08 mg kg-I). Average analytical recoveries on the fish samples are 91-93 %.
Down to 4 pg lead in the injected portion of sample can be determined. Lead contents
obtained by this procedure are in good agreement with those obtained by anodic
scanning voltammetry. Using this method, 0.26 mg kg- I and 0.32 mg kg- I of lead were
found, respectively, in whole catfish and blue gill samples.
Pagenkopf et al. [363] also employed graphite furnace atomic absorption spectrometry to determine lead in fish. They were able to determine down to 0.15 J,Lg kg-I lead
in fish. In this procedure 1-5 g fish muscle tissue were removed by dissection and
freeze-dried by a Thermovac lypholizer. Approximately 1 g of the dried tissue was
weighed and then digested in a mixture of 7.00 ml of concentrated nitric acid and
5.00 ml of concentrated perchloric acid. The solutions were slowly heated until all
foaming had stopped and dissolution was achieved. At this point, the temperature was
increased so as to reduce the volume to about 1 ml. This was accompanied by copious
fuming of perchloric acid. The maximum temperature was 88°C. The colourless
samples were then transferred to cleaned 100-ml volumetric flasks and diluted to
Fish
this method is that both the natural copper content of the fish organs and the
concentration of added tracers are determined on the same sample by making two
measurements of isotopic ratio - one before and one after the addition of the standard
63CU spike. Both of these isotopes constitute ideal tracers, being readily available at
low cost and being free from radiation hazards. A spark source mass spectrometer is
an ideal way of carrying out isotopic ratio measurements.
In this procedure, the wet fish sample was weighed before and after vacuum freeze
drying, then transferred to a Tracerlab LTA 600 low temperature asher to remove
organic matter. The residue was then digested in 0.5 mol I-I hydrochloric acid-30 %
hydrogen peroxide, ascorbic acid being added to destroy residual hydrogen peroxide,
and copper extracted from the solution with a carbon tetrachloride solution of
dithizone. This extract was then evaporated directly onto graphite prior to spark
source mass spectrometric evaluation.
Table 7.2 illustrates the type of data obtained in a typical experiment and it can be
seen that the amount of copper available for analysis varied appreciably from one type
of tissue to another (column C). Thus, as far as possible, the size of sample taken for
analysis was adjusted by sub-sampling (muscle, bone, skin, etc.) or by bulking organs
from more than one fish (heart, spleen, kidney, etc.). In this way, a constant amount
(200 ng) of 63CU standard could be added to all samples, thus greatly simplifying the
procedure at that stage.
7.1.5
Lead
The molybdenum- and lanthanum-treated pyrolytically coated graphite furnace atomic
absorption spectrometric method described by Poldoski [360] under cadmium earlier
in this section has also been applied to the determination of lead in fish tissue. Lead
results were reported obtained in spiking recovery experiments, carried out on fish
tissue samples and on an authenticated reference sample (NBS SRM 1577 bovine liver)
under specified conditions of analysis. It is seen that the determined lead content on
NBS SRM 1577 (0.33 ± 0.01 mg kg-I) is in good agreement with the nominal value
(0.34 ± 0.08 mg kg-I). Average analytical recoveries on the fish samples are 91-93 %.
Down to 4 pg lead in the injected portion of sample can be determined. Lead contents
obtained by this procedure are in good agreement with those obtained by anodic
scanning voltammetry. Using this method, 0.26 mg kg- I and 0.32 mg kg- I of lead were
found, respectively, in whole catfish and blue gill samples.
Pagenkopf et al. [363] also employed graphite furnace atomic absorption spectrometry to determine lead in fish. They were able to determine down to 0.15 J,Lg kg-I lead
in fish. In this procedure 1-5 g fish muscle tissue were removed by dissection and
freeze-dried by a Thermovac lypholizer. Approximately 1 g of the dried tissue was
weighed and then digested in a mixture of 7.00 ml of concentrated nitric acid and
5.00 ml of concentrated perchloric acid. The solutions were slowly heated until all
foaming had stopped and dissolution was achieved. At this point, the temperature was
increased so as to reduce the volume to about 1 ml. This was accompanied by copious
fuming of perchloric acid. The maximum temperature was 88°C. The colourless
samples were then transferred to cleaned 100-ml volumetric flasks and diluted to