176
Crustacea and Molluscs
variability of ± 0.4 Ilg / g was found in a group of 100 individuals, ranging in size from
2 to 5 g dry weight, with no correlation in cadmium concentration with size.
Inductively Coupled Plasma Atomic Emission Spectrometry. The wavelength modulation inductively coupled plasma echelle spectrometric technique [251], described in
Sect. 4.2.3 for the determination of cadmium in sediments, has also been applied to
the determination of cadmium in crab tissue. Freeze dried crab tissue was digested in
open tubes with nitric and perchloric acids. Spectrometric evaluation was carried out
using the cadmium 226.502 nm line, which is not subject to arsenic interference as is
the cadmium 228.803 nm line, but does need a two point background correction. Very
good agreement was obtained in determinations of cadmium in crab by three different methods of analysis, these being ICPAES 0.76 ± 0.6 mg kg, IDSSMS 0.83 ±
0.08 mg kg and GFAAS 0.71 ± 0.08 mg kg-I.
Mazzucotelli et al. [544] point out that interference by inorganic elements frequently occurs in the determination of cadmium in mussels by methods based on electrothermal atomic absorption spectrometry and inductively coupled plasma atomic
emission spectrometry. Electrothermal atomic absorption spectrometry of cadmium
in solutions containing 50 Ilg kg-I plus increasing amounts (0.5-500 mg kg-I) of interfering elements showed that sodium, potassium and calcium acted as enhancing
agents, whereas iron and magnesium did not. In similar experiments using inductively coupled plasma atomic emission spectrometry (wavelengths 228.802 and
214.438 nm), calcium and iron acted as enhancing agents at both wavelengths whereas
sodium and potassium acted as enhancing agents at 228.802 nm but depressive agents
at 214.438 nm. Liquid anion exchange extraction was suggested as a way of overcoming metal interaction (only applicable to electrothermal atomic absorption spectrometry) but separation was necessary when an absolute cadmium value was required.
Neutron Activation Analysis. Greenberg [545] has developed a radiochemical neutron activation procedure for the determination of cadmium in oysters. The procedure is based on irradation of the sample in a quartz tube with neutrons. Then, following
a 3 day decay period, the sample is digested with concentrated nitric and sulphuric
acids in a sealed PTFE-lined bomb at 140°C for 2 h, followed by treatment with
hydrofluoric acid to remove silica and hydrogen peroxide to destroy nitrogen oxides.
Zinc nitrate is added as a holdback carrier, and a chloroform solution of nickel
diethyldithiocarbamate added to extract mercury into the organic phase (which can
also be determined by this procedure - see under mercury in this section). The
remaining aqueous fraction is extracted with a chloroform solution of zinc diethyldithiocarbamate. Back extraction of this organic phase with aqueous hydrochloric acid
provides an extract containing cadmium. The hydrochloric acid solution is allowed to
decay for 24 h to establish the equilibrium between cadmium-lIS and its daughter,
indium-lIS m. The 336-keV line from indium-lIS m and the 528 keV line from
cadmium-lIS were both used to evaluate the cadmium content of the sample.
Table 8.2 shows the determined cadmium contents of NBS reference samples
contents and some oyster homogenizates obtained by this procedure.
Crustacea and Molluscs
variability of ± 0.4 Ilg / g was found in a group of 100 individuals, ranging in size from
2 to 5 g dry weight, with no correlation in cadmium concentration with size.
Inductively Coupled Plasma Atomic Emission Spectrometry. The wavelength modulation inductively coupled plasma echelle spectrometric technique [251], described in
Sect. 4.2.3 for the determination of cadmium in sediments, has also been applied to
the determination of cadmium in crab tissue. Freeze dried crab tissue was digested in
open tubes with nitric and perchloric acids. Spectrometric evaluation was carried out
using the cadmium 226.502 nm line, which is not subject to arsenic interference as is
the cadmium 228.803 nm line, but does need a two point background correction. Very
good agreement was obtained in determinations of cadmium in crab by three different methods of analysis, these being ICPAES 0.76 ± 0.6 mg kg, IDSSMS 0.83 ±
0.08 mg kg and GFAAS 0.71 ± 0.08 mg kg-I.
Mazzucotelli et al. [544] point out that interference by inorganic elements frequently occurs in the determination of cadmium in mussels by methods based on electrothermal atomic absorption spectrometry and inductively coupled plasma atomic
emission spectrometry. Electrothermal atomic absorption spectrometry of cadmium
in solutions containing 50 Ilg kg-I plus increasing amounts (0.5-500 mg kg-I) of interfering elements showed that sodium, potassium and calcium acted as enhancing
agents, whereas iron and magnesium did not. In similar experiments using inductively coupled plasma atomic emission spectrometry (wavelengths 228.802 and
214.438 nm), calcium and iron acted as enhancing agents at both wavelengths whereas
sodium and potassium acted as enhancing agents at 228.802 nm but depressive agents
at 214.438 nm. Liquid anion exchange extraction was suggested as a way of overcoming metal interaction (only applicable to electrothermal atomic absorption spectrometry) but separation was necessary when an absolute cadmium value was required.
Neutron Activation Analysis. Greenberg [545] has developed a radiochemical neutron activation procedure for the determination of cadmium in oysters. The procedure is based on irradation of the sample in a quartz tube with neutrons. Then, following
a 3 day decay period, the sample is digested with concentrated nitric and sulphuric
acids in a sealed PTFE-lined bomb at 140°C for 2 h, followed by treatment with
hydrofluoric acid to remove silica and hydrogen peroxide to destroy nitrogen oxides.
Zinc nitrate is added as a holdback carrier, and a chloroform solution of nickel
diethyldithiocarbamate added to extract mercury into the organic phase (which can
also be determined by this procedure - see under mercury in this section). The
remaining aqueous fraction is extracted with a chloroform solution of zinc diethyldithiocarbamate. Back extraction of this organic phase with aqueous hydrochloric acid
provides an extract containing cadmium. The hydrochloric acid solution is allowed to
decay for 24 h to establish the equilibrium between cadmium-lIS and its daughter,
indium-lIS m. The 336-keV line from indium-lIS m and the 528 keV line from
cadmium-lIS were both used to evaluate the cadmium content of the sample.
Table 8.2 shows the determined cadmium contents of NBS reference samples
contents and some oyster homogenizates obtained by this procedure.