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Sample preparation for speciation of lead
Chapter 34
Sample preparation for speciation of lead Freddy C. Adams and Monika Heisterkamp
34.1
INTRODUCTION
Tetraalkyllead (TeAL) compounds are used worldwide as anti-knock agents in leaded fuel to prevent premature ignition of the compressed air–gasoline mixture, which is detected as knocking of the motor. During the firing process, the majority of the lead–carbon bonds are broken and the organolead is converted into inorganic lead halides that leave the engine via the exhaust pipe. Depending on the motor type and the velocity, a small fraction of organolead (,2%) enters the atmosphere because of incomplete combustion. In view of the enormous consumption of leaded gasoline, this is by far the most important source of organolead in the atmosphere. TeAL is also released into the environment by evaporation during production, transport and storage of both anti-knock agents and leaded gasoline. Distribution of the latter at petrol stations is also a considerable source due to liberation of the volatile organolead compounds during the tanking process. Once released into the atmosphere, these TeAL compounds can be transported over great distances as free molecules or adsorbed on particles, so that they can even be detected in remote areas, such as Greenland or Antarctica [1]. These species (tetramethyllead [TeML], tetraethyllead [TeEL] or mixed tetra-ethylmethyllead) decompose via their ionic trialkyllead (TAL: trimethyllead [TML] and triethyllead [TEL]), dialkyllead (DAL: dimethyllead [DML] and diethyllead [DEL]) into inorganic lead (Pbi). The breakdown reaction is initiated by reactive species such as hydroxyl radicals generated by photochemical activity or by direct photolysis. The ionic organolead is washed out of the atmosphere by precipitation and transported to the hydrosphere. Sunlight and the components present in the aqueous medium determine the rate of the decomposition, as many metals catalyze this process. Table 34.1 presents a survey of the compounds on which this section is mainly focused. The question of whether methyllead is also formed by biological methylation of inorganic lead is still controversial. At this time, it is not clear Comprehensive Analytical Chemistry XLI Mester and Sturgeon (Eds.) q 2003 Elsevier B.V. All rights reserved
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Sample preparation for speciation of lead Freddy C. Adams and Monika Heisterkamp
34.1
INTRODUCTION
Tetraalkyllead (TeAL) compounds are used worldwide as anti-knock agents in leaded fuel to prevent premature ignition of the compressed air–gasoline mixture, which is detected as knocking of the motor. During the firing process, the majority of the lead–carbon bonds are broken and the organolead is converted into inorganic lead halides that leave the engine via the exhaust pipe. Depending on the motor type and the velocity, a small fraction of organolead (,2%) enters the atmosphere because of incomplete combustion. In view of the enormous consumption of leaded gasoline, this is by far the most important source of organolead in the atmosphere. TeAL is also released into the environment by evaporation during production, transport and storage of both anti-knock agents and leaded gasoline. Distribution of the latter at petrol stations is also a considerable source due to liberation of the volatile organolead compounds during the tanking process. Once released into the atmosphere, these TeAL compounds can be transported over great distances as free molecules or adsorbed on particles, so that they can even be detected in remote areas, such as Greenland or Antarctica [1]. These species (tetramethyllead [TeML], tetraethyllead [TeEL] or mixed tetra-ethylmethyllead) decompose via their ionic trialkyllead (TAL: trimethyllead [TML] and triethyllead [TEL]), dialkyllead (DAL: dimethyllead [DML] and diethyllead [DEL]) into inorganic lead (Pbi). The breakdown reaction is initiated by reactive species such as hydroxyl radicals generated by photochemical activity or by direct photolysis. The ionic organolead is washed out of the atmosphere by precipitation and transported to the hydrosphere. Sunlight and the components present in the aqueous medium determine the rate of the decomposition, as many metals catalyze this process. Table 34.1 presents a survey of the compounds on which this section is mainly focused. The question of whether methyllead is also formed by biological methylation of inorganic lead is still controversial. At this time, it is not clear Comprehensive Analytical Chemistry XLI Mester and Sturgeon (Eds.) q 2003 Elsevier B.V. All rights reserved
1081