126
Fish
within 30 min. Using this procedure, Louie [375] obtained a mercury content on NBS
Albacore Tuna Research Material 50 Reference Sample of 0.94 ± 0.05 mg kg- I against
a certified value of 0.95 ± 0.01 mg kg-I. Levels found in various fish samples ranged
between 0.1 and 0.4 mg kg-I.
Davidson [373] used digestion on a hot plate with 4: 1 50 % sulphuric acidhydrogen peroxide to digest tissue prior to the determination of mercury at 253.7 nm
by cold vapour atomic absorption spectrometry.
An approximately 0.100-0.200 g portion (less if high mercury levels are known to
exist) of homogenised, freeze-dried, and ground tissue (or 0.500-1.00 g wet mass) was
weighed into each reaction tube. Then 10 ml of 4 + 1 sulphuric acid was added and
the tubes were covered and left to stand overnight. At this stage, 4 ml of cold (4°C)
50 % w I v hydrogen peroxide was mixed in and the tubes were placed on the hot
block, set so that the sample temperature did not exceed 80°C. When the solutions
were clear and colourless, tubes were removed from the hot block. They were cooled
in a cold water-bath and 46.0 ml of cold (4°C) 0.1 % w Iv potassium permanganate
solution were added in a steady stream to ensure complete mixing. The required final
volume was 60 ml. With argon flowing through the solution, a hydroxylamine sulphate-hydrazine sulphate-stannous chloride reductant was added and the elemental mercury swept into the atomic absorption spectrometer.
Nine replicate samples of NBS reference tuna (Research Material No. 50) were
analysed by the 50 % hydrogen peroxide method to determine the repeatability of the
method. The mean and standard deviations were 1.00 ~-I and 0.02 ~-I dry mass,
respectively against the reported value of 0.95 ± 0.1 ~g-I and indicated that 80-90 %
of the mercury content is present as methylmercury. Between 0.24 and 1.11 mg kg- I of
mercury was found in pike and lake trout samples by this method.
Konishi and Takahashi [377] have described a method for the determination of
inorganic mercury in fish in the presence of organic mercury. This is based on the fact
that hydrogen peroxide oxidatively liberates inorganic mercury from organic substances in strong alkali, and reduces it to the metallic state without decomposing
organic materials concomitantly present. The metallic mercury, vaporised with a
nitrogen stream, is trapped by gold amalgamation, and then released for electrothermal atomisation atomic-absorption spectrometry. The detection limit is 1 ng of inorganic mercury, and the coefficient of variation for 40 ng of inorganic mercury is
2.8 %. A 92 % recovery of mercury was obtained in this procedure.
Gas Chromatography. Jones and Nickless [379] converted inorganic mercury in fish
samples to its methyl derivative using 2,2'dimethyl-2-silapentane-5-sulphonate (DSS)
as a reagent, prior to the determination of inorganic mercury in benzene extracts of
the reaction product by gas chromatography. The highest yield was obtained by
digesting the fish sample at 100°C with 5 N nitric acid in the presence of sodium
nitrite and then extracting with benzene. Between 2.8 and 8.6 mg kg-I mercury were
found in fish samples by this method.
Pyrolysis Ultraviolet Spectroscopy. Thomas et al. [380] described a rapid pyrolytic
procedure to determine the total mercury content in fish. A weighed amount of
homogenized fish tissue is combusted in a flowing air stream at 900°C, and then over
copper oxide at 850 °c to ensure complete combustion. Elemental mercury vapour is
Fish
within 30 min. Using this procedure, Louie [375] obtained a mercury content on NBS
Albacore Tuna Research Material 50 Reference Sample of 0.94 ± 0.05 mg kg- I against
a certified value of 0.95 ± 0.01 mg kg-I. Levels found in various fish samples ranged
between 0.1 and 0.4 mg kg-I.
Davidson [373] used digestion on a hot plate with 4: 1 50 % sulphuric acidhydrogen peroxide to digest tissue prior to the determination of mercury at 253.7 nm
by cold vapour atomic absorption spectrometry.
An approximately 0.100-0.200 g portion (less if high mercury levels are known to
exist) of homogenised, freeze-dried, and ground tissue (or 0.500-1.00 g wet mass) was
weighed into each reaction tube. Then 10 ml of 4 + 1 sulphuric acid was added and
the tubes were covered and left to stand overnight. At this stage, 4 ml of cold (4°C)
50 % w I v hydrogen peroxide was mixed in and the tubes were placed on the hot
block, set so that the sample temperature did not exceed 80°C. When the solutions
were clear and colourless, tubes were removed from the hot block. They were cooled
in a cold water-bath and 46.0 ml of cold (4°C) 0.1 % w Iv potassium permanganate
solution were added in a steady stream to ensure complete mixing. The required final
volume was 60 ml. With argon flowing through the solution, a hydroxylamine sulphate-hydrazine sulphate-stannous chloride reductant was added and the elemental mercury swept into the atomic absorption spectrometer.
Nine replicate samples of NBS reference tuna (Research Material No. 50) were
analysed by the 50 % hydrogen peroxide method to determine the repeatability of the
method. The mean and standard deviations were 1.00 ~-I and 0.02 ~-I dry mass,
respectively against the reported value of 0.95 ± 0.1 ~g-I and indicated that 80-90 %
of the mercury content is present as methylmercury. Between 0.24 and 1.11 mg kg- I of
mercury was found in pike and lake trout samples by this method.
Konishi and Takahashi [377] have described a method for the determination of
inorganic mercury in fish in the presence of organic mercury. This is based on the fact
that hydrogen peroxide oxidatively liberates inorganic mercury from organic substances in strong alkali, and reduces it to the metallic state without decomposing
organic materials concomitantly present. The metallic mercury, vaporised with a
nitrogen stream, is trapped by gold amalgamation, and then released for electrothermal atomisation atomic-absorption spectrometry. The detection limit is 1 ng of inorganic mercury, and the coefficient of variation for 40 ng of inorganic mercury is
2.8 %. A 92 % recovery of mercury was obtained in this procedure.
Gas Chromatography. Jones and Nickless [379] converted inorganic mercury in fish
samples to its methyl derivative using 2,2'dimethyl-2-silapentane-5-sulphonate (DSS)
as a reagent, prior to the determination of inorganic mercury in benzene extracts of
the reaction product by gas chromatography. The highest yield was obtained by
digesting the fish sample at 100°C with 5 N nitric acid in the presence of sodium
nitrite and then extracting with benzene. Between 2.8 and 8.6 mg kg-I mercury were
found in fish samples by this method.
Pyrolysis Ultraviolet Spectroscopy. Thomas et al. [380] described a rapid pyrolytic
procedure to determine the total mercury content in fish. A weighed amount of
homogenized fish tissue is combusted in a flowing air stream at 900°C, and then over
copper oxide at 850 °c to ensure complete combustion. Elemental mercury vapour is