Metals
125
volume. An Eppendorf pipette was used to transfer 20 III of the sample into the
graphite cups. The cups were placed under an infrared light and heated until the
solvent had evaporated. They were then placed in the furnace and peak absorbances
were recorded. Spiking experiments in fish samples, originally containing 0.12, 0.77
and 1.81 mg kg- 1 lead, indicated recoveries of 95-102 %.
To overcome problems of contamination and non-reproducibility in the determination oflow levels oflead in fish, Harms [364] devised a method of sample pretreatment and enrichment, in which sample decomposition was performed in a closed
system based on Mattinson's two-bottle system, and followed by the addition of
internally purified nitric acid, followed by neutralization with ammonia and extraction with dithizone I toluene solution. After back extraction into aqueous hydrochloric acid, the aqueous phase was subjected to measurement of Pb-203 activity (recovery control) followed by electrothermal atomic absorption spectrometry for
determination of stable lead. Samples of fish muscle containing less than 0.5 J.,lg kg- 1
could be analysed by this procedure.
May and Brumbaugh [365] used ammonium dihydrogen phosphate matrix modifier and a modified L'vov platform to overcome matrix interference effects in the
determination of lead in fish tissues. The 283.3 lead line was used. They defined
required graphite furnace atomic absorption spectrometric conditions to obtain maximum improvement in the slope ratio. Precisions were between 0.8 and 1.7 % for fish
samples.
Fish sample digestions were performed in PTFE-capped glass pressure reaction
vessels, in which the sample was digested with concentrated nitric acid at 70°C for
48 h. The digestates were then made up to 50 ml with 1 % hydrochloric acid. This
procedure did not yield complete digestion, as lipids are not destroyed and remain as
a floating white solid in the digestate.
7.7.6
Mercury
Atomic Absorption Spectrometry. Various workers have discussed the application of
cold vapour atomic absorption spectrometry to the determination of mercury in fish
[366-378]. Various digestion procedures have been used, including concentrated
nitric acid in a Teflon-lined sealed bomb [366] or glass tube [369], mixtures of nitric
acid and sulphuric acid [375,376],50 % hydrogen peroxide [373,377], and sulphuric
acid-potassium permanganate [372] in open tubes. Wickbold combustion procedures
have also been used [378].
Hendzel and Jamieson [376] digested 0.1-0.5 g of fish sample with 5 mil: 1 v Iv
nitric acid-sulphuric acid in a glass digestion tube at 180°C until white fumes appeared. After reduction with a reagent comprising hydroxylamine sulphate and stannic
chloride, the elemental mercury was swept off with a stream of air and estimated at
253.7 nm by cold vapour atomic absorption spectrometry.
Louie [375] used concentrated hydrochloric acid-nitric acid-sulphuric acid in open
tube digestions followed by cold vapour atomic absorption spectrometry to determine down to 0.01 mg kg-l mercury in fish tissues. He claimed that this was an improvement over previous methods and that 3 g of fish was completely digested at 85-100 °c
125
volume. An Eppendorf pipette was used to transfer 20 III of the sample into the
graphite cups. The cups were placed under an infrared light and heated until the
solvent had evaporated. They were then placed in the furnace and peak absorbances
were recorded. Spiking experiments in fish samples, originally containing 0.12, 0.77
and 1.81 mg kg- 1 lead, indicated recoveries of 95-102 %.
To overcome problems of contamination and non-reproducibility in the determination oflow levels oflead in fish, Harms [364] devised a method of sample pretreatment and enrichment, in which sample decomposition was performed in a closed
system based on Mattinson's two-bottle system, and followed by the addition of
internally purified nitric acid, followed by neutralization with ammonia and extraction with dithizone I toluene solution. After back extraction into aqueous hydrochloric acid, the aqueous phase was subjected to measurement of Pb-203 activity (recovery control) followed by electrothermal atomic absorption spectrometry for
determination of stable lead. Samples of fish muscle containing less than 0.5 J.,lg kg- 1
could be analysed by this procedure.
May and Brumbaugh [365] used ammonium dihydrogen phosphate matrix modifier and a modified L'vov platform to overcome matrix interference effects in the
determination of lead in fish tissues. The 283.3 lead line was used. They defined
required graphite furnace atomic absorption spectrometric conditions to obtain maximum improvement in the slope ratio. Precisions were between 0.8 and 1.7 % for fish
samples.
Fish sample digestions were performed in PTFE-capped glass pressure reaction
vessels, in which the sample was digested with concentrated nitric acid at 70°C for
48 h. The digestates were then made up to 50 ml with 1 % hydrochloric acid. This
procedure did not yield complete digestion, as lipids are not destroyed and remain as
a floating white solid in the digestate.
7.7.6
Mercury
Atomic Absorption Spectrometry. Various workers have discussed the application of
cold vapour atomic absorption spectrometry to the determination of mercury in fish
[366-378]. Various digestion procedures have been used, including concentrated
nitric acid in a Teflon-lined sealed bomb [366] or glass tube [369], mixtures of nitric
acid and sulphuric acid [375,376],50 % hydrogen peroxide [373,377], and sulphuric
acid-potassium permanganate [372] in open tubes. Wickbold combustion procedures
have also been used [378].
Hendzel and Jamieson [376] digested 0.1-0.5 g of fish sample with 5 mil: 1 v Iv
nitric acid-sulphuric acid in a glass digestion tube at 180°C until white fumes appeared. After reduction with a reagent comprising hydroxylamine sulphate and stannic
chloride, the elemental mercury was swept off with a stream of air and estimated at
253.7 nm by cold vapour atomic absorption spectrometry.
Louie [375] used concentrated hydrochloric acid-nitric acid-sulphuric acid in open
tube digestions followed by cold vapour atomic absorption spectrometry to determine down to 0.01 mg kg-l mercury in fish tissues. He claimed that this was an improvement over previous methods and that 3 g of fish was completely digested at 85-100 °c