Organometallic Compounds
169
clean-up procedure to detect down to 10 ~g kg- I of methylmercury. They improved
the Westoo clean-up procedure by replacing cysteine with the more stable sodium
thiosulphate when forming the methylmercury adduct. For the gas chromatography
of methylmercury iodide, these workers recommend the use of a 63Ni electron capture
detector as it does not form an amalgam at 280°C, the temperature at which it is
used.
Cappon and Crispin Smith [524] have described a method for the extraction,
clean-up, and gas chromatographic determination of organic (alkyl and aryl) and
inorganic mercury in fish. Methyl-, ethyl-, and phenylmercury are first extracted as
the chloride derivatives. Inorganic mercury is then isolated as methylmercury upon
reaction with tetramethyltin. The initial extracts are subjected to thiosulphate cleanup and the organomercury species are isolated as the bromide derivatives. Total
mercury recovery ranges between 75 and 90 % for both forms of mercury, and is
assessed by using appropriate 203Hg labelled compounds for liquid scintillation spectrometric assay. Specific gas chromatographic conditions allow detection of mercury
concentrations of 1 !1g kg-lor lower. Mean deviation and relative accuracy average 3.2
and 2.2 % respectively.
Uthe et al. [525] have described a rapid semi-micro method for determining
methylmercury in fish. The procedure involves extracting the methylmercury into
toluene as methylmercury(II) bromide, partitioning the bromide into aqueous ethanol as the thiosulphate complex, re-extracting methylmercury(II) iodide into benzene
followed by gas chromatography on a glass column (4 ft x 0.25 in) packed with 7 % of
Carbowax 20 M on Chromosorb W and operated at 170°C with nitrogen as carrier gas
(60 ml min-I), and electron capture detection. Down to 0.01 mg kg- I of methylmercury in a 2 g sample could be detected.
Callum et al. [527] used the proteolytic enzyme subtilisin Carlsberg Type A for the
breakdown of fish tissues prior to release of methylmercury. The finely chopped
tissue is homogenized with 1 mol 1-1 tri(hydroxymethyl)-amino methane-hydrochloric acid buffer (pH 8.5) and then incubated with the subtilisin for 1 h at 50°C. Then
2 ml of 40 % w / v sodium hydroxide solution and 1 ml of 1 % w / v cysteine hydrochloride solution were added and the samples stirred for 5 min at 50°C. When cool, 1 ml
of 0.5 mol 1-1 copper(II) bromide and 10 ml of acidic sodium bromide were added.
The methylmercury(II) bromide was then extracted with two 5 ml portions of toluene. In each extraction, the mixtures were shaken for 2 min then centrifuged at 6000 g
for 10 min. The two toluene extracts were removed and combined, and the methylmercury was extracted twice with 1 ml of ethanolic sodium thiosulphate solution (a
1:1 mixture of 95 % ethanol and 0.005 mol 1-1 sodium thiosulphate solution). During
each extraction, the solutions were vortex mixed and centrifuged at 4000 g for 2 min.
The lower aqueous layers were removed and combined, then 0.5 ml of 3 mol I-I
potassium iodide was added to these combined aqueous extracts followed by 0.5 ml of
benzene (pesticide grade, distilled in glass) containing ethylmercury(II) iodide as an
internal standard. These solutions were shaken and then centrifuged at 3000 g for 1
min. Standard solutions of methylmercury(II) iodide were prepared in the benzene
containing the internal standard. Samples were analysed by gas chromatography on a
column comprising 5 % w /w ethylene glycol adipate polyester on 80-100-mesh GasChrom G at 155°C with electron capture detection.
169
clean-up procedure to detect down to 10 ~g kg- I of methylmercury. They improved
the Westoo clean-up procedure by replacing cysteine with the more stable sodium
thiosulphate when forming the methylmercury adduct. For the gas chromatography
of methylmercury iodide, these workers recommend the use of a 63Ni electron capture
detector as it does not form an amalgam at 280°C, the temperature at which it is
used.
Cappon and Crispin Smith [524] have described a method for the extraction,
clean-up, and gas chromatographic determination of organic (alkyl and aryl) and
inorganic mercury in fish. Methyl-, ethyl-, and phenylmercury are first extracted as
the chloride derivatives. Inorganic mercury is then isolated as methylmercury upon
reaction with tetramethyltin. The initial extracts are subjected to thiosulphate cleanup and the organomercury species are isolated as the bromide derivatives. Total
mercury recovery ranges between 75 and 90 % for both forms of mercury, and is
assessed by using appropriate 203Hg labelled compounds for liquid scintillation spectrometric assay. Specific gas chromatographic conditions allow detection of mercury
concentrations of 1 !1g kg-lor lower. Mean deviation and relative accuracy average 3.2
and 2.2 % respectively.
Uthe et al. [525] have described a rapid semi-micro method for determining
methylmercury in fish. The procedure involves extracting the methylmercury into
toluene as methylmercury(II) bromide, partitioning the bromide into aqueous ethanol as the thiosulphate complex, re-extracting methylmercury(II) iodide into benzene
followed by gas chromatography on a glass column (4 ft x 0.25 in) packed with 7 % of
Carbowax 20 M on Chromosorb W and operated at 170°C with nitrogen as carrier gas
(60 ml min-I), and electron capture detection. Down to 0.01 mg kg- I of methylmercury in a 2 g sample could be detected.
Callum et al. [527] used the proteolytic enzyme subtilisin Carlsberg Type A for the
breakdown of fish tissues prior to release of methylmercury. The finely chopped
tissue is homogenized with 1 mol 1-1 tri(hydroxymethyl)-amino methane-hydrochloric acid buffer (pH 8.5) and then incubated with the subtilisin for 1 h at 50°C. Then
2 ml of 40 % w / v sodium hydroxide solution and 1 ml of 1 % w / v cysteine hydrochloride solution were added and the samples stirred for 5 min at 50°C. When cool, 1 ml
of 0.5 mol 1-1 copper(II) bromide and 10 ml of acidic sodium bromide were added.
The methylmercury(II) bromide was then extracted with two 5 ml portions of toluene. In each extraction, the mixtures were shaken for 2 min then centrifuged at 6000 g
for 10 min. The two toluene extracts were removed and combined, and the methylmercury was extracted twice with 1 ml of ethanolic sodium thiosulphate solution (a
1:1 mixture of 95 % ethanol and 0.005 mol 1-1 sodium thiosulphate solution). During
each extraction, the solutions were vortex mixed and centrifuged at 4000 g for 2 min.
The lower aqueous layers were removed and combined, then 0.5 ml of 3 mol I-I
potassium iodide was added to these combined aqueous extracts followed by 0.5 ml of
benzene (pesticide grade, distilled in glass) containing ethylmercury(II) iodide as an
internal standard. These solutions were shaken and then centrifuged at 3000 g for 1
min. Standard solutions of methylmercury(II) iodide were prepared in the benzene
containing the internal standard. Samples were analysed by gas chromatography on a
column comprising 5 % w /w ethylene glycol adipate polyester on 80-100-mesh GasChrom G at 155°C with electron capture detection.