168
Fish
Table 7.18 Determination of methylmercury (MeHg) in fish and shellfish (in I1g Hg/ g) by the
heated graphite furnace (Authors' Lab), with comparative analyses data (from [516])
Shum et al S16 lab
MeHg in
MeHg
MeHg in
Na 2 S 2 0 3
by
Total Inorganic Total
Sample
toluene ext.
ext.
Total Hg
GLC Hg
Hg
Freeze-dried
Oyster
N.D."
0.06.0.06 0.18 ± 0.02b 0.02 0.25
Halibut
5.37,5.68
5.49,5.55 5.79 ± 0.07 4.55 4.77 0.200
5.85
Canned tuna
0.76 ± 0.05 (6) 0.78,0.74 0.92 ± 0.03 0.60 0.80 0.034
0.95
Scallop muscle
N.D.
0.06,0.06 0.06 ± 0.02 0.05 0.11
Lobster tomalley
N.D.
0.05,0.06 0.74 ± 0.02 0.09 0.64
Swordfish muscle 1 0.43 ± 0.06
0.40,0.42 0.41 ± 0.02 -
0.022
0.42
Swordfish muscle 2 2.37 ± 0.06
2.52,2.48 2.54 ± 0,07 -
0.109
2.45
Swordfish muscle 3 3.00 ± 0.10
3.34 ± 0.06 2.75 3.03 0.143
3.31
Canned tuna 1
0.40,0.40
0.41,0.42 0.50 ± 0.01
Canned tuna 2
1.90, 1.95
2.23 ± 0.19
Frozen
Swordfish liver 1
0.41,0.42
1.05, 1.00
Swordfish liver 2
8.67,8.25
9.14, 8.39 19.1 ± 0.72
Swordfish liver 3
1.50, 1.62
1.38, 1.81 2.27 ± 0.12
Swordfish muscle 1 1.96 ± 0.15 (4) -
2.02, 1.99
Swordfish muscle 2 3.98,4.22
4.40,4.41
Swordfish muscle 3 1.60, 1.50
1.71, 1.70
Swordfish muscle 4 0.87,0.87
0.92 ± 0.12
" Not detectable
b Figures are the mean and standard deviation of triplicate analyses except otherwise indicated
cury than muscle. This was not surprising, because the liver had been suggested as
one of the sites for demethylation of methylmercury.
Gas Chromatography; Sodium Hydroxide Digestion - Toluene Extraction. In this
method [510] 5 g of the homogenised sample is placed in a centrifuge tube and 25 ml
of sodium hydroxide added. The tube is heated at 100°C for 30 min, then 8 ml of
hydrochloric acid (specific gravity 1.18), 25 ml of freshly distilled toluene, and 1 ml of
1 mol 1-1 copper(II) sulphate added and the mixture shaken, then centrifuged. The
toluene layer is syphoned into a 125 ml separating funnel.
The combined toluene extracts are shaken successively with 3 and 2-ml portions of
cysteine hydrochloride reagent solution and the extracts combined in a 25-ml separating funnel. Then 1 ml of hydrochloric acid, (specific gravity 1.18) is added prior to
extraction with 10 ml of toluene. The cysteine solution is run into a second 25- ml
separating funnel, retaining the toluene layer in a separate container. The toluene
extracts are combined and made up to 25 ml. This solution is now ready for gas
chromatography on a Carbosorb 20 M - Chrosorb G column at 160°C using "a nickel63 electron capture detector and nitrogen as carrier gas.
Kamps and McMahon [522] determined methylmercury in fish by gas chromatography. The method involves the partitioning of methylmercury chloride in benzene,
and analysis with electron capture detection. Down to 0.02 ppm of methylmercury
chloride were detected in a 10 g sample. Longbottom et al. [523] used the Westoo
Fish
Table 7.18 Determination of methylmercury (MeHg) in fish and shellfish (in I1g Hg/ g) by the
heated graphite furnace (Authors' Lab), with comparative analyses data (from [516])
Shum et al S16 lab
MeHg in
MeHg
MeHg in
Na 2 S 2 0 3
by
Total Inorganic Total
Sample
toluene ext.
ext.
Total Hg
GLC Hg
Hg
Freeze-dried
Oyster
N.D."
0.06.0.06 0.18 ± 0.02b 0.02 0.25
Halibut
5.37,5.68
5.49,5.55 5.79 ± 0.07 4.55 4.77 0.200
5.85
Canned tuna
0.76 ± 0.05 (6) 0.78,0.74 0.92 ± 0.03 0.60 0.80 0.034
0.95
Scallop muscle
N.D.
0.06,0.06 0.06 ± 0.02 0.05 0.11
Lobster tomalley
N.D.
0.05,0.06 0.74 ± 0.02 0.09 0.64
Swordfish muscle 1 0.43 ± 0.06
0.40,0.42 0.41 ± 0.02 -
0.022
0.42
Swordfish muscle 2 2.37 ± 0.06
2.52,2.48 2.54 ± 0,07 -
0.109
2.45
Swordfish muscle 3 3.00 ± 0.10
3.34 ± 0.06 2.75 3.03 0.143
3.31
Canned tuna 1
0.40,0.40
0.41,0.42 0.50 ± 0.01
Canned tuna 2
1.90, 1.95
2.23 ± 0.19
Frozen
Swordfish liver 1
0.41,0.42
1.05, 1.00
Swordfish liver 2
8.67,8.25
9.14, 8.39 19.1 ± 0.72
Swordfish liver 3
1.50, 1.62
1.38, 1.81 2.27 ± 0.12
Swordfish muscle 1 1.96 ± 0.15 (4) -
2.02, 1.99
Swordfish muscle 2 3.98,4.22
4.40,4.41
Swordfish muscle 3 1.60, 1.50
1.71, 1.70
Swordfish muscle 4 0.87,0.87
0.92 ± 0.12
" Not detectable
b Figures are the mean and standard deviation of triplicate analyses except otherwise indicated
cury than muscle. This was not surprising, because the liver had been suggested as
one of the sites for demethylation of methylmercury.
Gas Chromatography; Sodium Hydroxide Digestion - Toluene Extraction. In this
method [510] 5 g of the homogenised sample is placed in a centrifuge tube and 25 ml
of sodium hydroxide added. The tube is heated at 100°C for 30 min, then 8 ml of
hydrochloric acid (specific gravity 1.18), 25 ml of freshly distilled toluene, and 1 ml of
1 mol 1-1 copper(II) sulphate added and the mixture shaken, then centrifuged. The
toluene layer is syphoned into a 125 ml separating funnel.
The combined toluene extracts are shaken successively with 3 and 2-ml portions of
cysteine hydrochloride reagent solution and the extracts combined in a 25-ml separating funnel. Then 1 ml of hydrochloric acid, (specific gravity 1.18) is added prior to
extraction with 10 ml of toluene. The cysteine solution is run into a second 25- ml
separating funnel, retaining the toluene layer in a separate container. The toluene
extracts are combined and made up to 25 ml. This solution is now ready for gas
chromatography on a Carbosorb 20 M - Chrosorb G column at 160°C using "a nickel63 electron capture detector and nitrogen as carrier gas.
Kamps and McMahon [522] determined methylmercury in fish by gas chromatography. The method involves the partitioning of methylmercury chloride in benzene,
and analysis with electron capture detection. Down to 0.02 ppm of methylmercury
chloride were detected in a 10 g sample. Longbottom et al. [523] used the Westoo