178
Crustacea and Molluscs
8.1.5
Mercury
Non-Dispersive Atomic Fluorescence Spectrometry. This technique has been applied
to the determination of mercury in shrimps [263] (see under mercury in sediments,
Sect. 4.2.6).
Cold Vapour Atomic Absorption Spectrometry. Various digestion procedures for
mussels and oysters, including wet oxidation with nitric-sulphuric acids [6], digestion
with concentrated nitric acid in a PTFE lined bomb [366], Wickbold combustion
[378], and digestion with concentrated nitric, sulphuric and nitric acids [547], have
been used to digest these materials prior to the determination of mercury by cold
vapour atomic absorption spectrometry. Recoveries of between 90 and 105 % (i. e. a
91.5 ± 1,5 %) are claimed with a detection limit of 0.01 mg kg-I.
The cold vapour atomic absorption spectrometric method [375] described in
Sect. 7.1.6 for the determination of mercury in fish has also been applied to the
determination of mercury in oysters. A 97 % recovery of mercury was obtained in
spiking experiments with oysters following open tube digestion with hydrochloric -
nitric and sulphuric acids at 70-95 °c.
Neutron Activation Analysis. The radiochemical neutron activation analysis procedure [545] described in Sect. 8.1.2 for the determination of cadmium in oysters has
also been applied to the determination of mercury in oysters. The final hydrochloric
acid extract containing nickel diethyl dithiocarbamate and mercury obtained in this
procedure was counted immediately after separation for the 67.0 keY Au Xray and the
77.5 keY combination gamma ray, and the Au Xray produced by the decay of
mercury-197 and/ or, after decay for several weeks, for the 279 keY gamma ray from
mercury-203.
Determined mercury contents obtained on an IAEA oyster homogenizate sample
MAM-1 of 0.15 ± 0.012 ~g kg- I obtained by this procedure are in reasonably good
agreement with the certified values of 0.20 ± 0.02 ~ kg-I.
Lo et al. [383] preconcentrated mercury with lead diethyldithiocarbamate prior to
its determination by neutron activation analysis in oyster. See Sect. 7.1.6, which
discusses the application of this method to the determination of mercury in fish.
8.1.6
Selenium
Cathodic Stripping Voltammetry. Ahmed et al. [548] determined selenium(IV) in
oysters by cathodic stripping voltammetry, arsenic(III), copper(II), lead(II), iron(III),
and zinc(II) did not interfere. The oyster sample was digested at 50 °c with aqueous
Lumatom (Hans Kurner, Neuberg, Germany), and then methanol was added and the
solution acidified with hydrochloric acid prior to polarography. Preelectrolysis was
carried out at -0.05 V for 120 s and the solution was then cathodically polarized and
quantified by standard addition and measurement of the peak heights of selenium at
Ep = -0.47 V vs SCE:
Se(IV) + 4e + Hg ~ HgSe (-0.05 V)
HgSe + 2W + 2e ~ HgSe + H2 (-0.47 V).
Crustacea and Molluscs
8.1.5
Mercury
Non-Dispersive Atomic Fluorescence Spectrometry. This technique has been applied
to the determination of mercury in shrimps [263] (see under mercury in sediments,
Sect. 4.2.6).
Cold Vapour Atomic Absorption Spectrometry. Various digestion procedures for
mussels and oysters, including wet oxidation with nitric-sulphuric acids [6], digestion
with concentrated nitric acid in a PTFE lined bomb [366], Wickbold combustion
[378], and digestion with concentrated nitric, sulphuric and nitric acids [547], have
been used to digest these materials prior to the determination of mercury by cold
vapour atomic absorption spectrometry. Recoveries of between 90 and 105 % (i. e. a
91.5 ± 1,5 %) are claimed with a detection limit of 0.01 mg kg-I.
The cold vapour atomic absorption spectrometric method [375] described in
Sect. 7.1.6 for the determination of mercury in fish has also been applied to the
determination of mercury in oysters. A 97 % recovery of mercury was obtained in
spiking experiments with oysters following open tube digestion with hydrochloric -
nitric and sulphuric acids at 70-95 °c.
Neutron Activation Analysis. The radiochemical neutron activation analysis procedure [545] described in Sect. 8.1.2 for the determination of cadmium in oysters has
also been applied to the determination of mercury in oysters. The final hydrochloric
acid extract containing nickel diethyl dithiocarbamate and mercury obtained in this
procedure was counted immediately after separation for the 67.0 keY Au Xray and the
77.5 keY combination gamma ray, and the Au Xray produced by the decay of
mercury-197 and/ or, after decay for several weeks, for the 279 keY gamma ray from
mercury-203.
Determined mercury contents obtained on an IAEA oyster homogenizate sample
MAM-1 of 0.15 ± 0.012 ~g kg- I obtained by this procedure are in reasonably good
agreement with the certified values of 0.20 ± 0.02 ~ kg-I.
Lo et al. [383] preconcentrated mercury with lead diethyldithiocarbamate prior to
its determination by neutron activation analysis in oyster. See Sect. 7.1.6, which
discusses the application of this method to the determination of mercury in fish.
8.1.6
Selenium
Cathodic Stripping Voltammetry. Ahmed et al. [548] determined selenium(IV) in
oysters by cathodic stripping voltammetry, arsenic(III), copper(II), lead(II), iron(III),
and zinc(II) did not interfere. The oyster sample was digested at 50 °c with aqueous
Lumatom (Hans Kurner, Neuberg, Germany), and then methanol was added and the
solution acidified with hydrochloric acid prior to polarography. Preelectrolysis was
carried out at -0.05 V for 120 s and the solution was then cathodically polarized and
quantified by standard addition and measurement of the peak heights of selenium at
Ep = -0.47 V vs SCE:
Se(IV) + 4e + Hg ~ HgSe (-0.05 V)
HgSe + 2W + 2e ~ HgSe + H2 (-0.47 V).