Organometallic compounds in non-saline sediments 173
Chau et al [5] have described a simple and rapid extraction procedure to extract
the five tetraalkyllead compounds (Me 4 Pb, Me 3 EtPb, Me 2 Et 2 PB, MeEt 3 Pb, Et 4 Pb)
from sediment. The extracted compounds are analysed in their authentic forms by
a gas chromatographic-atomic absorption spectrometry at 217 mg. Other forms of
inorganic and organic lead do not interfere. The detection limits for sediment (5 g) was
0.01 mg kg
−1 . In this method the sediment is digested with EDTA and a hexane extract
gas analysed by chromatography. Concentrations found in a sediment ranged from
8.3 mg kg
−1 (tetramethyl and methyltriethyl lead) and 12 mg kg
−1 (dimethyl diethyl
lead and tetraethyl lead). Recoveries in spiking experiments were between 81 and 84%.
Determination of the ionic forms of alkyllead compounds is difficult because of
the incomplete extraction of the dimethyl and trimethyl species from sample matrices.
A chelation extraction method followed by derivatisation to their butyl homologues
has overcome all the previous difficulties to achieve quantitative extraction of the
dialkyl- and trialkyllead (R = Me, Et) from water samples at nanogram levels [7].
The application of a combination of gas chromatography and atomic absorption
spectrometry to the determination of tetraalkyllead compounds has been studied by
Chau et al [6] and by Segar et al [9]. In these methods the gas chromatography flame
combination showed a detection limit of about 0.1 µg Pb. Chau et al [6, 7, 50] have
applied the silica furnace in the atomic absorption unit and have shown that the sensitivity limit for the detection of lead can be enhanced by three orders of magnitude.
They applied the method to the determination of tetramethyllead in sediment systems.
The relative standard deviation was in the range of 10–15% at the 5 ng level
(as Pb). When the absorbances were plotted against lead concentrations, each of the
five tetraalkyl compounds gave similar calibration curves; the response was linear
up to at least 200 ng Pb, above which overlapping of the peaks occurred. If only one
compound was present (e.g. tetramethyllead), the plot was linear up to at least 2000 ng.
For determination at the microgram level, the flame atomic absorption spectrometric
technique [6] is more suitable.
Chau et al [8] have described the optimum conditions for extraction of alkyllead
compounds from sediments originating in non-saline waters and in saline waters [9].
Analyses of some environmental samples revealed for the first time the occurrence of
diakyl- and trialkyllead in sediments in areas of lead contamination.
The various alkyllead species and lead (II) are isolated quantitatively by chelation extraction with sodium diethyldithiocarbamate, followed by n-butylation to their
corresponding tetraalkyl forms, R, PbBu (4−n) , and Bu 4 Pb, respectively (R = Me, Et)
all of which can be determined by a gas chromatograph using an atomic absorption
detector. The method determines simultaneously the following species in one sample; tetraalkyllead (Me 4 Pb, Me 3 EtPb, Me 2 Et 2 Pb, MeEt 3 Pb, Et 4 Pb); ionic alkyllead
(Me 2 Pb
2+ , Et 2 Pb
2+ ; Me 3 Pb
+ , Et 3 Pb
2+ , Pb
2+ . Detection limits expressed for lead were
15 µg kg
−1 for sediment samples.
Ressinger et al used the gas chromatographic-atomic adsorption technique to
demonstrate that bio methylation of inorganic lead does not account for the presence of organolead compounds in sediments. Sulphide induced chemical conversation
of organic lead (IV) salts into alkyl lead compounds is, however, possible.
Wong et al [11] on the other hand, claims that the conversation of inorganic lead to
tetramethyllead in river and marine sediments is purely a microorganism induced biological process. These workers demonstrated that incubation of some lead-containing
Chau et al [5] have described a simple and rapid extraction procedure to extract
the five tetraalkyllead compounds (Me 4 Pb, Me 3 EtPb, Me 2 Et 2 PB, MeEt 3 Pb, Et 4 Pb)
from sediment. The extracted compounds are analysed in their authentic forms by
a gas chromatographic-atomic absorption spectrometry at 217 mg. Other forms of
inorganic and organic lead do not interfere. The detection limits for sediment (5 g) was
0.01 mg kg
−1 . In this method the sediment is digested with EDTA and a hexane extract
gas analysed by chromatography. Concentrations found in a sediment ranged from
8.3 mg kg
−1 (tetramethyl and methyltriethyl lead) and 12 mg kg
−1 (dimethyl diethyl
lead and tetraethyl lead). Recoveries in spiking experiments were between 81 and 84%.
Determination of the ionic forms of alkyllead compounds is difficult because of
the incomplete extraction of the dimethyl and trimethyl species from sample matrices.
A chelation extraction method followed by derivatisation to their butyl homologues
has overcome all the previous difficulties to achieve quantitative extraction of the
dialkyl- and trialkyllead (R = Me, Et) from water samples at nanogram levels [7].
The application of a combination of gas chromatography and atomic absorption
spectrometry to the determination of tetraalkyllead compounds has been studied by
Chau et al [6] and by Segar et al [9]. In these methods the gas chromatography flame
combination showed a detection limit of about 0.1 µg Pb. Chau et al [6, 7, 50] have
applied the silica furnace in the atomic absorption unit and have shown that the sensitivity limit for the detection of lead can be enhanced by three orders of magnitude.
They applied the method to the determination of tetramethyllead in sediment systems.
The relative standard deviation was in the range of 10–15% at the 5 ng level
(as Pb). When the absorbances were plotted against lead concentrations, each of the
five tetraalkyl compounds gave similar calibration curves; the response was linear
up to at least 200 ng Pb, above which overlapping of the peaks occurred. If only one
compound was present (e.g. tetramethyllead), the plot was linear up to at least 2000 ng.
For determination at the microgram level, the flame atomic absorption spectrometric
technique [6] is more suitable.
Chau et al [8] have described the optimum conditions for extraction of alkyllead
compounds from sediments originating in non-saline waters and in saline waters [9].
Analyses of some environmental samples revealed for the first time the occurrence of
diakyl- and trialkyllead in sediments in areas of lead contamination.
The various alkyllead species and lead (II) are isolated quantitatively by chelation extraction with sodium diethyldithiocarbamate, followed by n-butylation to their
corresponding tetraalkyl forms, R, PbBu (4−n) , and Bu 4 Pb, respectively (R = Me, Et)
all of which can be determined by a gas chromatograph using an atomic absorption
detector. The method determines simultaneously the following species in one sample; tetraalkyllead (Me 4 Pb, Me 3 EtPb, Me 2 Et 2 Pb, MeEt 3 Pb, Et 4 Pb); ionic alkyllead
(Me 2 Pb
2+ , Et 2 Pb
2+ ; Me 3 Pb
+ , Et 3 Pb
2+ , Pb
2+ . Detection limits expressed for lead were
15 µg kg
−1 for sediment samples.
Ressinger et al used the gas chromatographic-atomic adsorption technique to
demonstrate that bio methylation of inorganic lead does not account for the presence of organolead compounds in sediments. Sulphide induced chemical conversation
of organic lead (IV) salts into alkyl lead compounds is, however, possible.
Wong et al [11] on the other hand, claims that the conversation of inorganic lead to
tetramethyllead in river and marine sediments is purely a microorganism induced biological process. These workers demonstrated that incubation of some lead-containing