Organometallic Compounds
165
Stuart [511] used mercury-203 labelled methylmercury chloride for invivo labelling
of fish to study the efficacy of various wet ashing procedures, and obtained 93 %
recovery of activity in digestions of fish with concentrated sulphuric acid and fuming
nitric acid.
Sodium Hydroxide Digestion. Magos [499] has described a simple method for the
determination of total mercury in biological samples contaminated with inorganic
mercury and methylmercury. The method is based on the rapid conversion of organomercurials, first into inorganic mercury and then into atomic mercury suitable for
aspiration through the gas cell of a mercury vapour concentration meter, by a
combined tin(II) chloride-cadmium chloride reagent. It was found that, if 100 mg of
tin(II) chloride alone were added instead of the tin(II) chloride-cadmium chloride
reagent, only the release of inorganic mercury influenced the peak deflection of the
potentiometer, thus permitting the selective determination of inorganic mercury, and
then, after re-acidification of the reaction mixture, methylmercury, by adding the
tin(II) chloride-cadmium chloride reagent and sodium hydroxide. When total mercury and inorganic mercury were determined separately, the difference between results
gave the methylmercury content of the sample.
Sulphuric Acid-Nitric Acid-Hydrogen Peroxide Digestion. In this method [510] the
fish sample is treated with boiling sulphuric acid, nitric acid, and hydrogen peroxide,
excess peroxide being removed by boiling and the addition of potassium permanganate. A portion of the digest is reduced with hydroxylammonium chloride solution
and stannous chloride, aerated through a cell in an atomic absorption spectrometer
fitted with a cold cathode mercury lamp, and the absorption measured at 253.7 nm.
Some results obtained by this and other methods in round robin determinations of
total mercury and methyl mercury in tuna are shown in Table 7.16. Total mercury was
determined by the atomic absorption method discussed above, whilst methyl mercury
was determined by the gas chromatographic method discussed below [510].
Hydrochloric Acid Digestion. In this procedure [509], the fish sample is digested with
2 moll-I hydrochloric acid, then organic mercury is extracted into benzene. Organic
mercury is then extracted from the benzene phase with 3 x 10- 4 % glutathione in
0.1 moll-I ammonia solution.
To a gas washing bottle is added 150 ml of water, 10 ml of 10 mol I-I sodium
hydroxide, 2 ml of 1000 ppm copper solution, and 5 ml of 5 % tin(II) chloride dihydrate solution. Nitrogen gas at a flow rate of 1.41 min-I is passed for 6 min to eliminate
any mercury in the reagent solutions. Then the aqueous back-extract from the sample
is added. Mercury is concentrated on 1.5 g of gold granules (about 1 mm diameter)
packed in a glass tube (4 mm i.d.) by passing nitrogen gas for 6 min. The gold
granules are heated in a boat to 500°C in a furnace for 2 min, and the absorbance at
253.7 nm measured by passing nitrogen gas at a flow rate of 1.21 min-I. Between 0.1
and 1.0 mg kg-I mercury in rockfish samples were determined by this method.
Hydrobromic Acid Digestion-Toluene Extraction. Capelli et al. [517] have described a
procedure for the determination of down to 0.7 ng kg-I mercury in fish.
A sample of 5.00-10.00 g of fish flesh is homogenised with 10 ml of water in a
mortar and then transferred into a centrifuge tube with water; 14 ml of 47 % mlm
165
Stuart [511] used mercury-203 labelled methylmercury chloride for invivo labelling
of fish to study the efficacy of various wet ashing procedures, and obtained 93 %
recovery of activity in digestions of fish with concentrated sulphuric acid and fuming
nitric acid.
Sodium Hydroxide Digestion. Magos [499] has described a simple method for the
determination of total mercury in biological samples contaminated with inorganic
mercury and methylmercury. The method is based on the rapid conversion of organomercurials, first into inorganic mercury and then into atomic mercury suitable for
aspiration through the gas cell of a mercury vapour concentration meter, by a
combined tin(II) chloride-cadmium chloride reagent. It was found that, if 100 mg of
tin(II) chloride alone were added instead of the tin(II) chloride-cadmium chloride
reagent, only the release of inorganic mercury influenced the peak deflection of the
potentiometer, thus permitting the selective determination of inorganic mercury, and
then, after re-acidification of the reaction mixture, methylmercury, by adding the
tin(II) chloride-cadmium chloride reagent and sodium hydroxide. When total mercury and inorganic mercury were determined separately, the difference between results
gave the methylmercury content of the sample.
Sulphuric Acid-Nitric Acid-Hydrogen Peroxide Digestion. In this method [510] the
fish sample is treated with boiling sulphuric acid, nitric acid, and hydrogen peroxide,
excess peroxide being removed by boiling and the addition of potassium permanganate. A portion of the digest is reduced with hydroxylammonium chloride solution
and stannous chloride, aerated through a cell in an atomic absorption spectrometer
fitted with a cold cathode mercury lamp, and the absorption measured at 253.7 nm.
Some results obtained by this and other methods in round robin determinations of
total mercury and methyl mercury in tuna are shown in Table 7.16. Total mercury was
determined by the atomic absorption method discussed above, whilst methyl mercury
was determined by the gas chromatographic method discussed below [510].
Hydrochloric Acid Digestion. In this procedure [509], the fish sample is digested with
2 moll-I hydrochloric acid, then organic mercury is extracted into benzene. Organic
mercury is then extracted from the benzene phase with 3 x 10- 4 % glutathione in
0.1 moll-I ammonia solution.
To a gas washing bottle is added 150 ml of water, 10 ml of 10 mol I-I sodium
hydroxide, 2 ml of 1000 ppm copper solution, and 5 ml of 5 % tin(II) chloride dihydrate solution. Nitrogen gas at a flow rate of 1.41 min-I is passed for 6 min to eliminate
any mercury in the reagent solutions. Then the aqueous back-extract from the sample
is added. Mercury is concentrated on 1.5 g of gold granules (about 1 mm diameter)
packed in a glass tube (4 mm i.d.) by passing nitrogen gas for 6 min. The gold
granules are heated in a boat to 500°C in a furnace for 2 min, and the absorbance at
253.7 nm measured by passing nitrogen gas at a flow rate of 1.21 min-I. Between 0.1
and 1.0 mg kg-I mercury in rockfish samples were determined by this method.
Hydrobromic Acid Digestion-Toluene Extraction. Capelli et al. [517] have described a
procedure for the determination of down to 0.7 ng kg-I mercury in fish.
A sample of 5.00-10.00 g of fish flesh is homogenised with 10 ml of water in a
mortar and then transferred into a centrifuge tube with water; 14 ml of 47 % mlm