170
Fish
Methylmercury recoveries of 96-97 % from tuna were obtained by this procedure.
The coefficient of variation was in the range 3.6 to 5.5 %.
Fischer et al. [761] determined methylmercury, diethylmercury and methylethylmercury in fish using gas chromatography - atomic absorption spectrometry, following derivativization with sodium tetramethyl borate. The sample was dissolved in
alcoholic potassium hydroxide, then reacted with sodium tetramethyl borate, and
then subjected to cryogenictrapping of reaction products passing through a chromatographic column. Down to 4 pg CH 3 Hg+g- I (a mercury) could be determined.
Hight [532] and Corcoran [528] extracted methylmercuric chloride from homogenized, acetone-washed, acid-digested (hydrochloric acid) fish tissue using toluene.
Toluene extracts were the analysed by gas chromatography with electron capture
detection, using a 5 % DEGS-PS column pretreated with mercuric chloride. Samples
of swordfish, shark, shrimp, oysters, clams, and tuna were analysed for methylmercury. The detection limit for the method was 0.25 mg kg-I.
Bye and Paus [526] determined alkylmercury compounds in fish tissues, using an
atomic absorption spectrometer tuned in at the mercury wavelength as a specific gas
chromatographic detector.
Bache and Lisk [533] used emission spectrometry in a helium plasma to detect
organomercury compounds separated by gas chromatography of benzene extracts of
hydrochloric acid digests of fish.
High Performance Liquid Chromatography. Holak [529] has developed a method
that uses a simplified sample preparation procedure and atomic absorption or electrochemical detection of HPLC eluents for the determination of methylmercury in
fish. Methylmercury is isolated from the blended sample by chloroform elution from a
diatomaceous earth-hydrochloric acid column. The organomercury compound is
then extracted into a small volume of 0.0 1 N sodium thiosulphate solution. An aliquot
of this solution is injected on to a Zorbax ODS column and eluted with methanolammonium acetate solution (3:2) buffer, pH 5.5 containing mercaptoethanol. Detection can be accomplished by atomic-absorption spectrophotometry with the aid of a
specially designed apparatus for the generation of mercury vapour. Alternatively, a
commercially available electrochemical detector equipped with a dropping-mercury
electrode may be used.
Linearity was maintained for up to 5 Ilg ml- I solution of methyl mercury(II) chloride (when 100 J.Ll are injected). The reproducibility of multiple injections of2.95 Ilg mII of methylmercury(II) chloride was 3.2 % in terms of relative standard deviation. The
sensitivity, i. e. amount of methylmercury(II) chloride that gave an adsorption of 1 %
(0.0044 absorbance units), was 0.0037 Ilg. The detection limit was 0.6 ng.
Table 7.19 shows the results and the recovery of spikes of a number of fish samples
analysed by this proposed method for methylmercury. The recoveries ranged from 96
to 106 %, (i. e. 101 ± 5 %). Precision was, in terms of the relative standard deviation,
4.1 %. In the majority of instances, atomic-absorption detection was used. When
determining mercury compounds, this is the preferred mode of detection because of
the ease with which mercury vapour can be generated.
MacCrehan and Durst [530] also used an electrochemical detector in the high
performance liquid chromatography of extracts of fish. Down to 2 J.Lg kg-I methylmer-
Fish
Methylmercury recoveries of 96-97 % from tuna were obtained by this procedure.
The coefficient of variation was in the range 3.6 to 5.5 %.
Fischer et al. [761] determined methylmercury, diethylmercury and methylethylmercury in fish using gas chromatography - atomic absorption spectrometry, following derivativization with sodium tetramethyl borate. The sample was dissolved in
alcoholic potassium hydroxide, then reacted with sodium tetramethyl borate, and
then subjected to cryogenictrapping of reaction products passing through a chromatographic column. Down to 4 pg CH 3 Hg+g- I (a mercury) could be determined.
Hight [532] and Corcoran [528] extracted methylmercuric chloride from homogenized, acetone-washed, acid-digested (hydrochloric acid) fish tissue using toluene.
Toluene extracts were the analysed by gas chromatography with electron capture
detection, using a 5 % DEGS-PS column pretreated with mercuric chloride. Samples
of swordfish, shark, shrimp, oysters, clams, and tuna were analysed for methylmercury. The detection limit for the method was 0.25 mg kg-I.
Bye and Paus [526] determined alkylmercury compounds in fish tissues, using an
atomic absorption spectrometer tuned in at the mercury wavelength as a specific gas
chromatographic detector.
Bache and Lisk [533] used emission spectrometry in a helium plasma to detect
organomercury compounds separated by gas chromatography of benzene extracts of
hydrochloric acid digests of fish.
High Performance Liquid Chromatography. Holak [529] has developed a method
that uses a simplified sample preparation procedure and atomic absorption or electrochemical detection of HPLC eluents for the determination of methylmercury in
fish. Methylmercury is isolated from the blended sample by chloroform elution from a
diatomaceous earth-hydrochloric acid column. The organomercury compound is
then extracted into a small volume of 0.0 1 N sodium thiosulphate solution. An aliquot
of this solution is injected on to a Zorbax ODS column and eluted with methanolammonium acetate solution (3:2) buffer, pH 5.5 containing mercaptoethanol. Detection can be accomplished by atomic-absorption spectrophotometry with the aid of a
specially designed apparatus for the generation of mercury vapour. Alternatively, a
commercially available electrochemical detector equipped with a dropping-mercury
electrode may be used.
Linearity was maintained for up to 5 Ilg ml- I solution of methyl mercury(II) chloride (when 100 J.Ll are injected). The reproducibility of multiple injections of2.95 Ilg mII of methylmercury(II) chloride was 3.2 % in terms of relative standard deviation. The
sensitivity, i. e. amount of methylmercury(II) chloride that gave an adsorption of 1 %
(0.0044 absorbance units), was 0.0037 Ilg. The detection limit was 0.6 ng.
Table 7.19 shows the results and the recovery of spikes of a number of fish samples
analysed by this proposed method for methylmercury. The recoveries ranged from 96
to 106 %, (i. e. 101 ± 5 %). Precision was, in terms of the relative standard deviation,
4.1 %. In the majority of instances, atomic-absorption detection was used. When
determining mercury compounds, this is the preferred mode of detection because of
the ease with which mercury vapour can be generated.
MacCrehan and Durst [530] also used an electrochemical detector in the high
performance liquid chromatography of extracts of fish. Down to 2 J.Lg kg-I methylmer-