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Critical review of analytical methods for determination of inorganic mercury and methylmercury compounds.

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APPLIED ORGANOMETALLIC CHEMISTRY, VOL. 8, 293-302 (1994)
REVIEW
Critical Review of Analytical Methods for
Determination of Inorganic Mercury and
Methylmercury Compounds
Richard Puk and James H. Weber*
University of New Hampshire, Chemistry Department, Parsons Hall, Durham, NH 03824, USA
This review describes determinations of mercury
compounds under three categories: total mercury;
separate determinations of inorganic mercury(I1)
and organomercury compounds by selective
reduction; and speciation of inorganic mercury(II), monomethylmercury cation, and dimethylmercury. Topics described for each category
include sample treatment, separation, detection,
and limit of detection. Finally, we note that most
methods would not detect dimethylmercury if it
were present.
Keywords: Analytical methods, mercury, monomethylmercury, dimethylmercury
ETAA
EXT
GC
GFAA
HCL
Hg"
Hg(I1)
Hg,,,
HOM
HPLC
ICP
LOD
MeHg
Me,Hg
MIP
ox
NOTATl0N
AA
AF
APDC
Carbo trap
cc
Conc
Cry-PC
CVAA
CVAF
DER
DIG
DME
DMF
ECD
Et,Hg
Atomic absorption
Atomic fluorescence
Ammonium pyrrolidine dithiocarbamate
Graphitized carbon-black column
Column chromatography
Concentrated
Cryogenic packed column
Cold vapor atomic absorption
Cold vapor atomic fluorescence
Derivatization
Digestion
Dropping mercury electrode
Dimethylformamide
Electron capture detector
Diet h ylmercury
' Author to whom correspondence should be addressed.
CCC 02hX-2605/94/040293- 10
0 1994 by John Wiley & Sons. Ltd
PRE
RED
RHg
RSD
SAMP
STOR
Electrothermally heated atomic
absorption
Extraction
Gas chromatography
Graphite furnace atomic absor;tior.
Hollow-cathode lamp
Elemental mercury
Mercury(I1)
Total mercury
Homogenization
High-performance liquid chromatography
Inductively coupled plasma
Limit of detection
Monomethylmercury cation
Dimethylmercury
Microwave-induced plasma detector
Oxidation
Pretreatment
Reduction
Organomercury (R = M e or Me,)
Relative standard deviation
Sample
Sample storage
GENERAL INTRODUCTION
Long-term and increasing interest in the speciation of inorganic mercury [ Hg(ll)], monomethylmercury cation (MeHg), and occasionally dimethylmercury (MezHg) in environmental and
biological samples has resulted in a large number
of published analytical methods. A recent interlaboratory study on the determination of methylmercury (MeHg) in fish and mussels' clearly
shows the importance of a methods review. The
Receioed 16 Fehruury I994
Accepied I April 1994
R. PUK AND J. H. WEBER
294
Table 1 Scheme for the determination of mercury compounds.
~
Sample
treat men t
Homogenization
Digestion
Oxidation
Extraction
Reduction
Derivatization
DETERMINATION OF TOTAL MERCURY
Introduction
Separation
Detection
Gold
GC
HPLC
Cry-PC
Carbo trap
CVAA
WAF
ECD
GFAA
MIP
ETAA
DME
cc
results were a relative standard deviation between
laboratories in the range of 20-25%, indicating a
lack of reproducibility of existing methods and
the urgent need for improvements in MeHg
determinations.
It is clearly impossible for us in a short review
to describe hundreds of publications using dozens
of analytical methods and their variations. We
will summarize only major themes and organize
existing methods into three major categories: (1)
determination of total mercury (Hgt,,,), (2) separate determination of Hg(I1) and organomercury
compounds (RHg) by selective reduction; and (3)
speciation of Hg(II), MeHg, and MezHg. Within
each category we emphasize originators of methods and newest applications.
Most environmental samples require a
sequence of three analytical steps (Table 1)
namely sample treatment, separation and
detection '.' Each step is futher divided into one
or more specific techniques depending on the
mercury compound(s) of interest. Tables 2-4 list
analytical methods for determining Hg(I1) and
methylmercury compounds. They include sample
type and treatment, separation method, detection
method, and limit of detection (LOD). LOD is
the lowest concentration that is statistically different from the blank." ' The tables list LOD based
on the mass of mercury per sample weight (fresh
weight or dry weight are not always mentioned)
or volume. Missing information in some papers
made it impossible to calculate LOD as the absolute mass of mercury in samples.
Thc first entry in Table 2 exemplifies the interpretation of Tables 2-4. Hatch and Ott' determined Hg,,,, in metal, rock, or soil by a sample
treatment of digestion and reduction followed by
detection by cold vapor atomic absorption
(CVAA). Their method has an LOD of
1 ng Hg g - ' .
Determination of Hg,,,, (Table 2) requires conversion of all forms of mercury to Hg(I1). Since
samples may contain Hg(I1) bound to other molecules such as proteins o r humic matter, it must be
liberated from ligands present. In addition, sample treatment must convert bound or free MeHg
and Me2Hg to free Hg(I1). Researchers usually
convert all mercury compounds to free Hg(1I) by
an acidic, oxidative digestion (Eqns [l] and [2]).
DIG/OX
Bound Hg(I1)-Free
RED
Hg(1I)-Hg"
DIG/OX
MeHg(or Me2Hg)-Free
[ 11
RED
H g ( I I ) - - H g " [2]
The final two steps are reduction of Hg(I1) to Hg"
by Sn(I1) or NaBH, and detection of Hg", typically by atomic absorption (AA) or atomic fluorescence (AF).
Sample treatment
Researchers have digested and clxidized samples
in various ways to release mercury compounds
from binding substances, or have sometimes
omitted this ~ t e p . Bricker9
~.~
oniitted the digestion and storage steps by using a field method for
reduction and volatilization of mcrcury and purging Hg" onto a gold column. Match and Ott"
digested samples with the oxidizing acid HNO,.
Other researchers used acid digestion and
oxidation."'-'h with or without heating.
The digestion procedure (if any) is followed by
reduction of Hg(I1) with tin(II)'? (Eqn [3]).
''
Hg(I1)
+ Sn(II)-tHg''+
Sn(lV)
[31
Hatch and Ott,h Rezende et ul.," Bloom and
Crecelius"' I t and Robinson and !$humani5added
hydroxlyamine (NH20H) as a preliminary reducing agent before adding the tin(I1) solution.
NaBH, also reduces Hg(1I) to Hg" (Eqn [4]).
Hg(I1) + 2NaBH,
+ 6 H 1 0 - +Hg"+ 7H2
+ 2H,BO, + 2Na'
141
Bricker" and Tsalev et ul.'" usecl NaBH, alone.
Two group^^.^ used a transition-metal catalyst
with NaBH,.
DETERMINATION OF INORGANIC MERCURY AND METHYLMERCURY
295
Table 2 Method summary for the determination of total mercury (Hg,,,J
Sample typc
and treatment
Separation
Detection
LOD
Reference
6
SAMP:
DIG:
RED:
Metal, rock, soil
7 M HNO1/4.S M HZSO,
NH,OH/NaCI/Sn(lI)
Air purge
None
CVAA
1 ngg-'
SAMP:
DIG:
RED:
Urine
None
N:IBH,/CLI(II)/~H6.5 buffer
Ar purge
None
ETAA
1-2 ng mt
SAMP:
River water, rainwater,
pond water, sewage effluent
None
NaBH, (in the field)
Air purge
Gold
Helium-dc
plasma emission
SAMP:
DIG:
RED:
Water, waste water
None
NaBH,IFe(III)/S M HCI
Ar purge
Gold
CVAA
SAMP:
DIG:
Fish
Hot cone HNO;/H,SO,
(reflux)
0.2 M BrCl
Sn(1l)
He purge
Gold
CVAF
1.0ngg
Urine, river, lake water.
rain water
Microwave (SO-90 "C)
KBrO,/KBr/HCI
NaBH,/O. I M HCI
Ar purge
Gold or without
Gold
CVAA
0.0 1 ng ml I
(with gold)
0.2 ng ml
Seawater. sediment, sewage effluent
2% HNO,
Conc HNO,/H,SO,
(sediment only)
0.2 M BrCl
NH,OH/Sn(lI)
N, purge
Gold
CVAA
Stream water. river water
HNO,/K,Cr,O,/cysteine
Hot (60°C) HISOJHNO?
KMnO,/ K&O,
NH,OH/Sn(lI)
N ? purge
Gold
CVAA
0.02 ng ml
Fish
HNOJHTSO, (4.5 M)
KMnO,
NH,OH.HCI/Sn(II) in
IS'%, HCI
Air purge
None
CVAA
2Sngg
DIG:
RED:
ox:
RED:
SAMP:
DIG/OX:
RED:
SAMP:
STOR:
DIG:
ox:
RED:
SAMP:
STOR:
DIG:
ox:
RED:
SAMP:
DIG:
ox:
RED:
~
8
'
13. 14
(without gold)
10. I I
I
I
1s
12
R . PUK A N D J. H. WEBER
296
Table 3
Method summary lor the determination of (Hg(I1) and RHg by selective reduction
-
Sample typc
and treiitment
Fish, niisc. biological samples
35'% NaOH/ I '%cysteind
20%) NaCI/ 100 "C
Separation
Detection
LOD
Relerence
None
CVAA
1 0 ng mt
None
CVAA
~).003-0.0~)5
ng rid
None
CVAA
25ngg
22
I
Sn(II)/X M
H?SO,/cysteine/NaCI
Air purge (NaOH added)
KH s
RED:
Sn(ll)-Cd(ll)/X M
HISO,/cystcine/NaCI
Air purge (NaOlI added)
H g ( I I ) + R H g= Hg,,,,
SAMP:
DIG:
OX:
Txp water, tuna, hair, urine
10 M KOH (90 "C)
0.24 M HNO,/O.Ol'%
K,CrlO,/ 1 '%NaCl
'
Sn( II)/HNO:/K,Cr20,
N? purge
R I i(:
RED:
NsBH,/HNOJ K?Cr@,
N? purge
lish
water/4.5 M H:SO,/KBr
'
wiiter phase after
extraction with
CHCli/NaHH,
Air purge
,is McHgBr i n t o
RED:
CHCI,
NaBH,/DMF/HNO,
Air purge
Hg,,,,- Iig(lI) = RHg
SAMP:
SI'OR:
I i S ("1
RED:
Sn(ll)/O.OS M HCL
NaBH,:
mi
'
0. 192
iig
21
DETERMINATION OF INORGANIC MERCURY AND METHYLMERCURY
291
Table 3 continued
~~~~~
Sample type
and treatment
~
Separation
Detection
LOD
Reference
standards, tap water, river water
0.16 M HN03/KMn04
Sn(II)/O.12 M HCI
Air purge
None
CVAA
0.001 ng mt-'
2s
seawater, rain water,
estuarine water, river water
None
0.06 M HNO,
Sn(I1)
N, purge
Gold
CVAA
0.042 ng m1-I
24
Hg(1t)~'
SAMP:
ox:
RED:
H g (1)'
SAMP:
DIG:
STOR:
RED:
Hg,,,,- Hg(I1) = MeHg: this Hg(I1) method is used with a Hg,,,, method in Table 1 to determine MeHg by difference.
Separation/concentration
The high 1.2 x lo-' mm Hg vapor pressure of Hgo
at 20°C simplifies its detection by AA. Hgo
formed during the reduction step is often concentrated on a gold ~ o I u m n ~ - I I ,and
~ ~ -then
' ~ thermally desorbed prior to detection. Water, volatile
organic compounds, sulfides or CI, can sometimes
interfere with the amalgamation of Hg".''~"
Concentration of Hg' on the gold column can
decrease LOD by 20-fold. For example, Tsalev et
a/." had an LOD of 0.2ngml-I without a gold
column and of 0.01 ng ml-l with it.
Detection
M~~~ groups6. 8 . 10. 12. 15. 16 used CVAA for the
detection of Hg". CVAA avoids problems with
nebulization and atomization that occur in classical flame AA." Cold vapor atomic fluorescence
(CVAF) detection for Hg" often has improved the
LOD relative to A A detection.13 Other types of
detection include a electrothermally heated atomic absorption cell (ETAA)' and helium-dc
plasma emission.'
DETERMINATION OF Hg(ll) AND RHg BY
SELECTIVE REDUCTION
Introduction
Separate determinations of Hg(I1) and RHg
(Table 3 ) combine two reactions that are carried
out sequentially on one or more sample aliquots.
The first reaction is typically reduction by the
mild reducing agent tin(I1) that reduces free
Hg(1I) to Hg* (Eqn [ 3 ] ) , but not C-Hg bonds in
RHg. After complete purging of the resulting
Hgo, the same aliquot is treated under acid and
oxidizing conditions to break C-Hg bonds in
RHg and form Hg(I1) which is reduced to Hg"
(Eqn [2]). The separation and detection steps are
similar to those described above.
A disadvantage of selective reduction techniques is the impossibility of confirming the identity of RHg. For example, the selective reduction
method does not permit researchers to distinguish
MeHg from Me2Hg. The typical assumption is
that RHg is predominant MeHg since it is the
nearly exclusive form of RHg in fish.I4
Researchers have used selective reduction on
samples such as fish,'2.20-'2 hair and urine,"
animals,, and blood.23
Sample treatment for mercury(l1)
The sample treatment used to determine Hg(I1)
should separate free Hg(I1) from any chemical
that binds it without breaking C-Hg bonds.
Digestion with NaOH and cysteine" or KOH"
leaves the C-Hg bond intact but frees any bound
Hg(I1). Determination of Hg(I1) in aquatic
matrices involves sample treatment with tin(I1) in
aqueous dilute hydrochloric acid (HCI) to reduce
Hg(I1) to Hg".24,25HCI prevents adsorption of
mercury compounds on the sam le container
Pused NaBH4
prior to reduction. Rezende ef u1.Irather than tin(I1) with air purging to reduce the
Hg(I1) in the aqueous phase to Hg".
R. PUK AND J. H. WEBER
298
Table4 Method summary for speciating Hg(I1). M eHg and Me,Hg
~
~~~
~
Sample type
and treatment
Separation
Detection
LOD
Reference
MeHg
SAMP:
DIG:
HOM:
EXT:
Fish, eggs, meat, liver
None
WaterIHCI
Benzene, cysteine, HCI, benzene
GC
ECD
70-400 ng g -I
27, 28
MeHg
SAMP:
DIG:
DER:
Fish, biological tissue
Conc H2S04
Iodoacetic acid
GC
MIP
20 ng g-'
36
Fish
Water16 M HCV
Celite 545
Elute with CC14,
Na2S203(to eluate)
Air or N2 purge
HPLC
HeatICVAA
or DME
0.37-0.6 ng g-'
33
Fish
KOHlMeOH (70 "C)/neutralize
NaBEt,/pH 4.5 acetate buffer
N, or air purge to Carbo trap
He purge to Cry-PC
Carbo trap/
Cry-PC
CVAF
MeHg: 0.5 rig g - '
Me2Hg:0.1 ng g- '
13, 14
MeHg
SAMP:
DIG:
HOM:
EXT:
Fish, eggs, meat, liver
None
WaterIHCI
Benzene, cysteine, HCI, benzene
GC
ECD
70-400 ng g
27,28
Hg(ll), MeHg
SAMP:
HOM:
Fish, biological materials
WaterlNaClIl M HCI
GFAA
3.0 ng m L - '
34
NaBH,ICVAA
(on eluted
MeHg: 0.5 ng ml-'
Hg(I1):
0.015 ng ml-'
43
MeHg
SAMP:
HOM:
EXT:
MeHg, Me,Hg
SAMP:
DIG:
RED:
Hg(W
DERIEXT:
I
Me,Sn/MeOH (100 "C)
Benzene/Na2SZ03/
benzene
MeHg
EXT:
Benzene, Na2S203/Cu(II)Ibenzene
H g ( l l ) , MeHg
SAMP:
DER:
Standards, tap water
Hg-APDC complex formed on
RED:
column
Elute with APDC
Eluent with NaBH,
HPLC
sample)
DETERMINATION O F INORGANIC MERCURY AND METHYLMERCURY
~
-
~~~
299
~~
Table 4 continued
Sample type
and treatment
Separation
Hg(ll), MeHg
SAMP:
River water, tap water
cc
STOR:
0.08 M HNO,
Hg(lI)
Pre:
Pass through sulfhydryl
cotton column with 0.01 M
HCI
ox:
KBr/KBrO,
RED:
Eluate with Sn(II)/HCI
MeHg
PRE:
RED:
Elute column with 3 M HCI
KBr/KBrO,
Sn(II)/HCI
Me2Hg
SAMP:
Seawater
ox:
H g ( I l ) , M e H g , MerHg
SAMP:
Fish, seawater
HOM:
KOH/MeOH
RED:
NaBEt,/pH 4.5 acetate
buffer
He purge
M e H g , Me,Hg
SAMP:
Sediment
EXT:
Acetic acid
DER:
NaBH,/acetic acid (pH 3.5)
He purge
LOD
Reference
CVAF
6 ng g-'
35
Carbo trap/Cry-PC HeatICVAF
GoldlCarbo trap/
Cry-PC
Heat/CVAF
13
Seawater: 0.2 ng I- I
(Hg(lI), 0.003 ng I-'
(MeHg and MeZHg)
13, 14
Fish: 0.5 ngg-' (MeHg),
0.1 ngg-l
(Me&)
Cry-PC
Hg(Il), MeHg
SAMP:
Fish, lobster
Cry-PC
DIG:
KOH/MeOH
DER:
NaBEtJpH 4.5 acetate buffer
He purge
H g ( I I ) , M e H g , MerHg
SAMP:
S . alterniflora, eelgrass
EXT:
0.1 M HCI, MeOH
DERIRED: NaBHJ0.01 M HCI
He purge
Detection
Cry-PC
Hz/Oz/ETAA
39
ETAA
MeHg: 4 ng g-'
Hg(I1): 75 ng g-'
44
ETAA
Hg(I1): 0.11 ngg-'
42
MeHg: 0.05 ng g-
Sample treatment for RHg
Separation and detection
Under most conditions, NaBH, does not reduce
MeHg. However, NaBH, and air purge in the
presence of dimethylformamide,'2 NaBH, and
nitric acid," or tin(1I) plus metal-ion c a t a l y d 2
reduce RHg left in the sample aliquot after the
removal of Hg( 11).
A separation using a gold trap is generally
unnecessary since both Hg(I1) and RHg are
separately reduced to volatile Hg".". 'I."
However, Gill and Bruland'h and Gill and
F i t ~ g e r a l ddid
~ ~use a gold trap. The usual detectors for H ~ I I are CVAAI?.
21, ??. 24.25 and CVAF.2h
R. PUK AND J. H. WEBER
300
SPECIATION OF Hg(ll), MeHg AND
Introduction
Speciation of Hg(II), MeHg, and Me,Hg (Table
4) generally requires extraction and derivatization
(not all methods), separation and concentration
(not all methods), and detection. This speciation
section differs from the selective reduction
section (Table 3) by identifying RHg compounds
and confirming that the organomercury compound most commonly observed in the environment is MeHg.
Sample treatment
Extraction
Hundreds of papers on the determination of
MeHg in the environment have appeared during
the past 25 years. Most researchers use a variation
of the original extraction method reported by
Westooj.?l.?X Researchers have applied the
method to a wide variety of sample types including fish, food, seawater, sediment, blood and
urine. One goal of these extraction methods is to
separate Hg(I1) from MeHg. A second goal is to
concentrate MeHg and separate it from chemicals
such as proteins and humic matter to avoid interferences during the detection step. Extraction
methods are commonly used before separation
and detection by gas chromatography (GC).2X.2y
In the W e ~ t o o ~ ’ method
.~’
samples are typically
homogenized in water, acidified with hydrochloric acid and treated with benzene to extract
MeHgCl from the aqueous phase into benzene.
After extraction of MeHgCl from the benzene
phase with aqueous cysteine, the intitial benzene
layer is discarded. The aqueous solution is acidified to break up the cysteine-MeHg complex and
MeHg is again extracted into benzene.
Many determinations of MeHg in environmental samples are performed by variations of the
Westoo extraction method in which bound Hg(I1)
and MeHg are converted to free forms using HCI
or HBr .30. 31 Free MeHg halide is extracted into an
organic solvent such as benzene,2X
di~hloromethane’~,”
or CC14.33MeHg halide is
extracted from the organic phase by aqueous
or cysteine.2X.2y
Other sample
thiosulfate
treatments requiring separation have been
accomplished on microcolumns of sulfhydryl
cotton,”” which binds MeHg but not Hg(I1). The
eluted Hg(I1) is treated with an oxidizing agent
and reduced to Hg” with tin(I1). MeHg is eluted
from the column with 3 M HCI, an oxidizing agent
is added to the solution, and Hgi:II) is reduced to
Hg” with tin(I1) before its detection.
Derivatization
Some researchers have emphasized methods of
volatizing MeHg to avoid extractions. For example, Lansens and B a e y e n ~anti
~ ~ Decadt et a!.’’
separated MeHg from biological tissue by treatment with concentrated sulfuric acid in a closed
vial and conversion of MeHg into volatile MeHgI
by addition of iodoacetic acid.
Bloom‘3 developed based on ethylation of
Hg(I1) and MeHg to produce volatile compounds. The digested sample is reacted with
sodium tetraethylborate (NaBEt,) to convert
MeHg to methylethylmercury (MeEtHg) (Eqn
[ 5 ] ) and Hg(I1) into diethylmercury (Et,Hg) (Eqn
[61).
MeHg’
Hg(I1)’’
+ NaBEt,+
+ ‘BEt,’ + Na’
EtzHg+ 2 BEt,’ + 2Na’
MeEtHg
+ 2NaBEt,+
[5]
[6]
In both equations ‘BEt,’ represents unstable BEt,
which reacts with air and water.
More recently two g r o ~ p s ’ ~ -reported
~’
a hydride derivatization method in which NaBH, converts MeHg into volatile MeHgH (Eqn [7]).
+ NaBH, + 3HzO+ h4eHgH + 3H2
+ H,B03 + Na’
[71
MeHg’
NaBH, also reduces Hg(1I) to Hg” (Eqn [4]) and
Me,Hg is purged unchanged. Quevauviller et af.”
used this hydride generation method for detection
of MezHg in sediment samples. Puk and Weber42
further developed the method fclr determinations
of Hg(II), MeHg, MezHg and EtzHg.
Separation by GC, HPLC or cryogenic
packed column (Cry-PC)
GC2X.29.34 or derivatization followed by GC” is
often used for separation of MeHg after extraction. HPLC has an advantage over G C in that
formation of volatile derivatives is not
necessary .33. 43
The volatile products formed by reactions with
NaBEt, or NaBH, can be separated in several
ways. H i ’ , Me2Hg, MeEtHg (Eqn IS]) and EtzHg
(Eqn [6]) are separated sequentially with a gra-
DETERMINATION OF INORGANIC MERCURY A N D METHYLMERCURY
phite carbon column, gold column and
Cry-PC"." or Cry-PC alone.14 Hg" (Eqn [4]),
MeHgH (Eqn [7]), and Me,Hg from the NaBH,
reaction can be separated on a Cry-PC.""'
Detection
MeHg from an extracted sample can be separated
by G C and detected by an electron capture detector (ECD)?~.
ZL).4i.46 , helium microwave induced
plasma emission spe~trometry,~".".'~ mass
spectrometry.'" inductively coupled plasma-mass
spectometry5"or graphite furnace atomic absorption (GFAA).jJ
Hgl can be detected after Cry-PC separation by
atomic spectrometry either by CVAFl3 or by
ETAA."." CVAA is a sensitive enough method
for determining MeHg in environmental samples,
provided it is converted into Hg" before detection.
The eluate from a high-performance liquid
chromatography (HPLC) separatiod3.'" must be
reduced by N a B H P or atomized by thermal
decomposition33for determination of MeHg and/
or Me,Hg as Hg".
Hg" is detected after HPLC by atomic spectrometry using CVAA,33.U atomic emission
or CVAF after separation on a
microcolumn .35
Critique of the possible presence of
Me&
Recently Baldi er al." reported formation of
Me,Hg from MeHg by sulfate-reducing
Desuffouibrio desuffulricans strains. This result
suggests that Me,Hg may be more common in the
aquatic environment that was generally believed.
Despite this possibility, only Mason and
Fitzgerald," Quevauviller et af.,'" Puk and
Weber" and Bloom13 have observed Me,Hg in
environmental samples. Virtually all known procedures for speciating RH, in environmental and
biological matrices have emphasized MeHg
because MeHg was considered the sole RHg synthesized by bacteria in the aquatic environment.
In this section we will attempt to convince the
reader that with many common analytical methods for speciation of mercury compounds, Me,Hg
would not be observed even if it were present.
There for several reasons for non-observance
of Me,Hg in environmental samples:
(1) Volatilization of Me,Hg may occur during
30 I
storage, homogenization, hot digestion or
other means of sample preparation.
(2) Me,Hg may be lost during extraction of
toluene or benene phases with aqueous
cysteine or S20:-. We confirmed (unpublished results) that Me,Hg sometimes
remains in the original organic phase which
is usually discarded.
(3) Me,Hg may not be detected when
GC-ECD is used. The ECD is very sensitive to compounds like MeHgCl that contain at least one electronegative element,
but it is not very sensitive to Me'Hg. In
addition, the absence of a retention time
from Me,Hg standards would accentuate
the difficulties of identifying it.
(4) Me,Hg may not be seen because of its high
density and low solubility in H 2 0 . We
sometimes observed significant amounts of
Me,Hg after extraction of plant material
with 0.1 M HCl, and sometimes saw none in
the same extract. The reason was that
Me,Hg was insoluble and at the bottom of
the water layer. Addition of MeOH (1 : 1)
to the 0.1 M HCI solubilized Me,Hg and
allowed its determinati~n.~'
( 5 ) Determination of Me2Hg during extractions requires sufficient acidity to free it
from ligands in the matrix, but not enough
to convert it to MeHg or Hg(I1). Papers
have estimated the maximum concentration of acid that leaves C-Hg bonds
intactl3.53".S
but the results are inconsistent.
Our unpublished work tested the stability
of Me,Hg in aqueous HCI solutions while
sonicating 1 h at 40°C. Under these conditions Me'Hg is stable in 0.1 M HCI, partially decomposed in 1 M and 3 M HCl, and
unstable in 6~ HCI. Many researchers
used sufficiently strong acidic solutions for
extractions, etc., to decompose Me,Hg.
REFERENCES
I . P . Ouevauviller. I . Drahaek. H. Muntau. B . Griepink,
Appl. Organomer. Cliern. 7. 413 (1993).
2. 0. F. X . Donard and F. M. Martin, Trmds Atid. Chrm.
11- 17 (1992).
3. D. E. Wclls, Mikrochim. Ac/u 109. 13 (1992).
4. L. H. Kcith. W. Crummctt. J . Dcegan Jr. R. A . Lihhy.
J . K . Taylor and G . Wcntlcr, A n d . Chem. 55. 2210
(1983).
302
R. PUK. A N D J . H. WEBER
5. Anon. AriuIv.st (London) 112, 199 (1987).
6. R, Hatch and W. L. Ott. Anul. Chem. 40,2085 (1968).
7. J. Toffaletti and J. Savory, Anal. Chem. 47 , 2091 (1975).
8. B. Welz and M. Schubert-Jacobs, Fres. Z . Anal. Chem.
331. 324 (1988).
9 , J. L. Bricker, Anal. Chem. 52, 492 (1980).
10. N. S . Bloom and E. A . Crecelius, Mar. Chem. 14, 49
(1983).
I I . N. S. Bloom and E. A . Crecelius, Mar. Chem. 21, 377
(1987).
12. M. R. Rezende, R. C. Compos and A. J. Curtius, J . Anal.
Atom. Sprctrom. 8 , 247 (1993).
13. N. S. Bloom. Cun. J . Fish. Ayuat. Sci. 46, 1131 (1989).
14. N. S. Bloom, Cun. J . Fish. Ayuat. Sci. 49, 1010 (1992).
15. K . G. Robinson and M. S. Shuman, In[. J . Enuiron. Anal.
Chem. 36. I 1 I (1989).
16. D . L. Tsalev. M . Sperling and B. Welz, Analysf (London)
117. 1729 (1092).
17. M. H . Bothner and D . E. Robertson, Anal. Chem. 47,
592 (1975).
18. W . F. Fitzgerald and G . A. Gill. 51, 1714 (1979).
19. A . M. Ure. Anal. Chim. Acta76, l(1975).
20. K. Fukushi. S . N. Willie and R. E. Sturgeon, A n d . Lelt.
26. 325 (1993).
21. C . E. Oda and J . D . Ingle Jr, Anal. Chem. 53, 2305
(1981).
22. I-. Magos. Analyst (London) 96, 847 (1971).
23. I-. Magos and T. W. Clarkson. J . Assoc. Off. Anal. Chem.
55. 966 (1972).
24. G . A . Gill and W. F. Fitzgerald, Mar. Chem. 20, 227
(1987).
25. J. E. Hawley and J . D. Ingle Jr. Anal. Chem. 47, 719
(1975).
26. G . A . Gill and K. W. Bruland, Enoiron. Sci. Technol. 24,
1392 (1990).
27. G . Wcstoii. Actu Chem. Scand. 20. 2131 (1966).
28. G . Westiiii. Actu Chern. Scund. 21. 1790 (1967).
29. M . Uorvat. A . R . Byrne and K. May, Talantu 37. 207
( 199(1).
30. C . Mculeman, C. C. Lairio, P. Lansens and W. Baeyens,
Wuter Res. 27. 1431 (1993).
31. G. Cerrati, M. Bernhard and J. H. Weber, Appl.
Orgunornet. Chem. 6 , 587 (1992).
32. Y. Thibaud and D. Cossa. Appl. Organomet. Chem. 3,
257 (1989).
W . Holak, Analyst (London) 107, 1457 (1982).
M. Filippelli, Anal. Chem. 59, 1 I6 (1987).
W. Jian and C . W . McLeod, Talunra 39, 1537 (1992).
P. Lansens and W. Baeyens, Anar. Chim. Acta 228, 93
( 1990).
37. G . Decadt, W. Baeyens, D . Bradley and L. Goeyens,
Anal. Chem. 57, 2788 (1985).
38. M. Filippelli, F. Baldi, F. E. Brinckman and G . J. Olson,
Enoiron. Sci. Technol. 26, 1457 (1942).
39. P. Quevauviller, 0. F. X . Donard, J . C . Wasserman,
F. M. Martin and J. Schneider, Appl. Organomet Chem.
6 , 221 (1992).
40. P. J . Craig, D. Mennie, N. Ostah, 0. F. X. Donard and F.
Martin, Analysl (London) 117, 823 :l992).
41. P. J. Craig, D. Mennie, M. Needham. N. Ostah.
0. F. X. Donard and F. Martin, J . Orgonomet. Chem.
447. 5 (1993).
42. R. Puk and J. H. Weber, Anal. Chim. Acta (1994). in
press.
43. C. Sarzanni, G . Sacchero, M. Aceto, 0. Abollino and E.
Mentasti, J . Chromatogr. 1992, 626, 151 (1992).
44. R . Fischer. S. Rapsomanikis and M. 0. Andreae. Anal.
Chem. 65, 763 (1993).
45. C. J . Cappon and J. C . Smith, Anul. Chem. 49, 365
(1977).
46. V. Zelenko and L. Kosta, Talantu 21). I15 (1973).
47. Y. Talmi, Anal. Chim. Acla 74, I07 (1975).
48. K. Chiba, K. Yoshida, K. Tanabe, 11. Haraguchi and K.
Fuwa, Anal. Chem. 55, 450 (1983).
49. B. Johansson, R. Ryhage and G. \Yestiiii. Acta Chem.
Scand. 24, 2340 ( 1970).
50. D. Beauchemin, K. W. M. Siu and <. S . Bcrman. Anul.
Chem. 60, 2587 (1988).
51. M. Fujita and E. Takabatake, Anul. Chem. 55, 454
(1983).
52. F. E. Brinckman, W. R. Blair, K. 1.. Jewett and W . P.
Iverson, J . Chromatogr. Sci. 15, 493 (1977).
53. F. Baldi, M. Pepi and M. Filippclli, Appl. Etiuirori.
Microbiol. 59, 2479 ( 1993).
54. R. P. Mason and W . F. Fitzgerald, I?/a/. Air Soil Pollut.
56, 779 (1991).
55. N. Imura, E. Sukewaga, S. K. Pan, K . Nagao. J. K. Kim,
T . Kwan and T. Ukita. Science 172. !23K (1972).
33.
34.
35.
36.
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