186
4 The Measurement Process in Chemistry
Annex III
Determination methylmercury in fish and shellfish
Learning objective:
To exemplify the speciation of pollutants in samples used as environmental indicators.
Reference:
Official Methods of Analysis of AOAC. 15th Edition
AOAC, Arlington, MA, 1990, pp 268, 269.
988.11 Mercury (Methyl) in Fish and Shellfish Rapid Gas Chromatographic Method First Action 1988
A. Principle
Organic interferences are removed from
homogenized seafood by acetone wash followed by toluene wash. Protein-bound Me Hg
is released by addition of HCl and extracted
into toluene. Toluene extract is analysed for
CH2HgCl by electron capture Gc.
B. Reagents
Equivalent reagents may be used.
(a) Solvents. Acetone, toluene and isopropanol, all distilled in glass (Burdick and
Jackson Laboratories, Inc., or EM Science
OmniSolv ® reagents). Caution: toluene is
harmful if inhaled and is flammable; conduct
all operations with toluene in laboratory
hood.
(b) Hydrochloric acid solution (1 + 1). Add
concentrated HCl to equal volume distilled
or de-ionized H20 and mix. Use 2 volumes
toluene to extract potential interferences
from 1 volume HCl solution by vigorously
shaking mixture 15 s in separator. Discard
toluene extract. Repeat extraction step 4
times. Solution may be mixed in advance.
However, extraction must be performed
immediately before HCl solution is used to
avoid formation of electron-capturing compounds which produce extraneous peaks in
chromatograms.
Before beginning analysis, check quality
of reagents by chromatographing blank
taken through method. Do not use HCl and
solvents which produce extraneous peaks at
retention time of Me Hg.
(c) Carriergas. GCquaiity Ar-CH4 (95+5).
(d) Sodium sulphate. Anhydrous reagent
grade. Heat overnight in 600°C furnace, let
cool, and store in capped bottle. Line cap with
acetone-washed Al foil to prevent contamination from cap. Peaks appearing at 14-15 min
may be eliminated by refiring Na2S04 (600 °C
overnight) .
(e) Methyl mercuric chloride standard
solutions. Keep tightly stoppered. Seal stopper with Teflon tape. (I) Stock standard
solution. - 1000 Jlg Hg/mL. Weigh 0.1252 g
CH3HgCl (ICN-K&K Laboratories, Inc., PO
Box 28050, Cleveland, OH 44128-0250) into
100 mL volumetric flask. Dilute to volume
with toluene. (2) High level intermediate
standard solution. - 40 Jlg Hg/mL. Dil. 10.0
mL stock standard solution to 250.0 mL with
toluene. (3) Low level intermediate standard
solution. - 2.0 Jlg Hg/mL. Dil. 10.0 mL high
level intermediate standard solution to 200.0
mL with toluene. (4) Working standard solutions. - 0.005-0.10 Jlg HglmL. Prepare monthly by diluting with toluene in volumetric
flasks as follows: Dilute 10.0 mL of 2.0 Jlg HgI
mL solution to 200.0 mL for 0.10 Jlg Hg/mL.
Dilute 20.0 mL of 0.10 Jlg HglmL solution to
25.0 mL, 15.0 mL to 25.0 mL, 10.0 mL to 25.0
mL, 10.0 mL to 50.0 mL, 10.0 mL to 100.0 mL,
and 10.0 mL to 200.0 mL for 0.080, 0.060,
0.040,0.020, 0.010, and 0.005 Jlg Hg/mL, respectively.
(f) Mercuric chloride column treatment
solution. -1000 ppm HgCI2. Dissolve 0.1 g
HgCl2 in 100 mL toluene.
(g) Fortification solutions. (I) Stock solution. -1000 Jlg Hg/mL. Weigh 0.1252 g
CH3HgCl into 100 mL volumetric flask. Dil. to
volume with H20. (2) Working fortification
solution. - 15 jlg Hg/mL. Dilute 1500 JlL stock
fortification solution to 100.0 mL with H20.
4 The Measurement Process in Chemistry
Annex III
Determination methylmercury in fish and shellfish
Learning objective:
To exemplify the speciation of pollutants in samples used as environmental indicators.
Reference:
Official Methods of Analysis of AOAC. 15th Edition
AOAC, Arlington, MA, 1990, pp 268, 269.
988.11 Mercury (Methyl) in Fish and Shellfish Rapid Gas Chromatographic Method First Action 1988
A. Principle
Organic interferences are removed from
homogenized seafood by acetone wash followed by toluene wash. Protein-bound Me Hg
is released by addition of HCl and extracted
into toluene. Toluene extract is analysed for
CH2HgCl by electron capture Gc.
B. Reagents
Equivalent reagents may be used.
(a) Solvents. Acetone, toluene and isopropanol, all distilled in glass (Burdick and
Jackson Laboratories, Inc., or EM Science
OmniSolv ® reagents). Caution: toluene is
harmful if inhaled and is flammable; conduct
all operations with toluene in laboratory
hood.
(b) Hydrochloric acid solution (1 + 1). Add
concentrated HCl to equal volume distilled
or de-ionized H20 and mix. Use 2 volumes
toluene to extract potential interferences
from 1 volume HCl solution by vigorously
shaking mixture 15 s in separator. Discard
toluene extract. Repeat extraction step 4
times. Solution may be mixed in advance.
However, extraction must be performed
immediately before HCl solution is used to
avoid formation of electron-capturing compounds which produce extraneous peaks in
chromatograms.
Before beginning analysis, check quality
of reagents by chromatographing blank
taken through method. Do not use HCl and
solvents which produce extraneous peaks at
retention time of Me Hg.
(c) Carriergas. GCquaiity Ar-CH4 (95+5).
(d) Sodium sulphate. Anhydrous reagent
grade. Heat overnight in 600°C furnace, let
cool, and store in capped bottle. Line cap with
acetone-washed Al foil to prevent contamination from cap. Peaks appearing at 14-15 min
may be eliminated by refiring Na2S04 (600 °C
overnight) .
(e) Methyl mercuric chloride standard
solutions. Keep tightly stoppered. Seal stopper with Teflon tape. (I) Stock standard
solution. - 1000 Jlg Hg/mL. Weigh 0.1252 g
CH3HgCl (ICN-K&K Laboratories, Inc., PO
Box 28050, Cleveland, OH 44128-0250) into
100 mL volumetric flask. Dilute to volume
with toluene. (2) High level intermediate
standard solution. - 40 Jlg Hg/mL. Dil. 10.0
mL stock standard solution to 250.0 mL with
toluene. (3) Low level intermediate standard
solution. - 2.0 Jlg Hg/mL. Dil. 10.0 mL high
level intermediate standard solution to 200.0
mL with toluene. (4) Working standard solutions. - 0.005-0.10 Jlg HglmL. Prepare monthly by diluting with toluene in volumetric
flasks as follows: Dilute 10.0 mL of 2.0 Jlg HgI
mL solution to 200.0 mL for 0.10 Jlg Hg/mL.
Dilute 20.0 mL of 0.10 Jlg HglmL solution to
25.0 mL, 15.0 mL to 25.0 mL, 10.0 mL to 25.0
mL, 10.0 mL to 50.0 mL, 10.0 mL to 100.0 mL,
and 10.0 mL to 200.0 mL for 0.080, 0.060,
0.040,0.020, 0.010, and 0.005 Jlg Hg/mL, respectively.
(f) Mercuric chloride column treatment
solution. -1000 ppm HgCI2. Dissolve 0.1 g
HgCl2 in 100 mL toluene.
(g) Fortification solutions. (I) Stock solution. -1000 Jlg Hg/mL. Weigh 0.1252 g
CH3HgCl into 100 mL volumetric flask. Dil. to
volume with H20. (2) Working fortification
solution. - 15 jlg Hg/mL. Dilute 1500 JlL stock
fortification solution to 100.0 mL with H20.