Organometallic compounds in non-saline sediments 183
and the organomercury species are isolated as their bromoderivaties. Total mercury
recovery was in the range of 75–90% and down to 1 µg kg
−1 of specific compounds
can be determined.
Ealy et al [76] determined methyl-, ethyl-, and methoxyethylmercury compounds
in sediments by leaching the sample with sodium iodide for 24 hours and then extracting the alkylmercury iodides into benzene. These iodides are then determined by
gas chromatography of the benzene extract with electron capture detection (
3 H foil).
Good separation of chromatographic peaks is obtained for the mercury compounds
as chloride.
Andren and Harris et al [77] have reported a methylmercury concentration of
0.02–0.1 ng Hg g
−1 in unpolluted sediments by using a gas chromatograph with an
electron capture detector.
A procedure has been described by Lee et al [78] in which 20 L of water containing
alkylmercury compounds is concentrated with sulfydryl cotton fibre. The alkylmercury
compounds adsorb on to the fibre quantitatively. The cotton fibre is then removed
and extracted with a few millilitres (say, 10 mL) of dilute hydrochloric acid/sodium
chloride i.e. the preconcentration stage in which a concentration factor of 20.000/1= 2000 is achieved. The alkyl mercury content of the extract is then determined by gas
chromatography using an electron capture detector. A detection limit of 0.04 ng L
−1
alkylmercury is achieved in this procedure.
Spectrometric methods
In a Standard procedure [79] the sediment is wet oxidised with dilute sulphuric acid and
nitric acids in an apparatus in which the vapour from the digestion is condensed into a
reservoir from which it can be collected or returned to the digestion flask as required.
The combined oxidised residue and condensate are diluted until the acid concentration is 1 N and nitrate is removed by addition of hydroxylammonium chloride with
boiling. Fat is removed from the cooled solution with a carbon tetrachloride solution
of dithizone. The extract is shaken with 0.1 N hydrochloric acid and sodium nitrite
solution and, after treatment of the separated aqueous layer with hydroxylammonium
chloride a solution of urea and then EDTA solution are added to prevent subsequent
extraction of copper. The liquid is then extracted with a 0.101% solution of dithizone
in carbon tetrachloride and mercury estimated in the extract spectrophotometrically
at 485 nm.
Miscellaneous
Jurka and Carter et al [57] have described an automated determination of down to
0.1 µg 1
−1 mercury in river sediment samples. This method is based on the automated
procedure of El-Awady et al [80] for the determination of total mercury in waters and
wastewaters, in which potassium persulphate and sulphuric acid were used to digest
samples for analysis by the cold vapour technique. These workers proved that the use
of potassium permanganate as an additional oxidizing agent was unnecessary.
There was no significant interference due to sulphide in the solutions containing 10 mg sulphide 1
−1 . However, a negative interference was observed for both
organic and inorganic standards containing 100 mg sulphide 1
−1 which is equivalent to
25,000 mg sulphide kg
−1 in the sediment. This interference was overcome by ensuring
that an excess of dichromate was present during the automated analysis.
and the organomercury species are isolated as their bromoderivaties. Total mercury
recovery was in the range of 75–90% and down to 1 µg kg
−1 of specific compounds
can be determined.
Ealy et al [76] determined methyl-, ethyl-, and methoxyethylmercury compounds
in sediments by leaching the sample with sodium iodide for 24 hours and then extracting the alkylmercury iodides into benzene. These iodides are then determined by
gas chromatography of the benzene extract with electron capture detection (
3 H foil).
Good separation of chromatographic peaks is obtained for the mercury compounds
as chloride.
Andren and Harris et al [77] have reported a methylmercury concentration of
0.02–0.1 ng Hg g
−1 in unpolluted sediments by using a gas chromatograph with an
electron capture detector.
A procedure has been described by Lee et al [78] in which 20 L of water containing
alkylmercury compounds is concentrated with sulfydryl cotton fibre. The alkylmercury
compounds adsorb on to the fibre quantitatively. The cotton fibre is then removed
and extracted with a few millilitres (say, 10 mL) of dilute hydrochloric acid/sodium
chloride i.e. the preconcentration stage in which a concentration factor of 20.000/1= 2000 is achieved. The alkyl mercury content of the extract is then determined by gas
chromatography using an electron capture detector. A detection limit of 0.04 ng L
−1
alkylmercury is achieved in this procedure.
Spectrometric methods
In a Standard procedure [79] the sediment is wet oxidised with dilute sulphuric acid and
nitric acids in an apparatus in which the vapour from the digestion is condensed into a
reservoir from which it can be collected or returned to the digestion flask as required.
The combined oxidised residue and condensate are diluted until the acid concentration is 1 N and nitrate is removed by addition of hydroxylammonium chloride with
boiling. Fat is removed from the cooled solution with a carbon tetrachloride solution
of dithizone. The extract is shaken with 0.1 N hydrochloric acid and sodium nitrite
solution and, after treatment of the separated aqueous layer with hydroxylammonium
chloride a solution of urea and then EDTA solution are added to prevent subsequent
extraction of copper. The liquid is then extracted with a 0.101% solution of dithizone
in carbon tetrachloride and mercury estimated in the extract spectrophotometrically
at 485 nm.
Miscellaneous
Jurka and Carter et al [57] have described an automated determination of down to
0.1 µg 1
−1 mercury in river sediment samples. This method is based on the automated
procedure of El-Awady et al [80] for the determination of total mercury in waters and
wastewaters, in which potassium persulphate and sulphuric acid were used to digest
samples for analysis by the cold vapour technique. These workers proved that the use
of potassium permanganate as an additional oxidizing agent was unnecessary.
There was no significant interference due to sulphide in the solutions containing 10 mg sulphide 1
−1 . However, a negative interference was observed for both
organic and inorganic standards containing 100 mg sulphide 1
−1 which is equivalent to
25,000 mg sulphide kg
−1 in the sediment. This interference was overcome by ensuring
that an excess of dichromate was present during the automated analysis.