Tetramethyllead determination

Temperature programming packed-capillary and open capillary HTLC-ICP-MS (up to 200 °C) has been reported [738]. //.HTLC-ICP-MS instrumental coupling has been applied to organotin (tetraethyltin, tributyltin chloride and triphenyltin chloride) and organolead (tetramethyllead and tetraethyllead) compounds [756]. HTLC-ICP-MS can be used for the determination of organometallic compounds at low concentrations. The observed limit of detection (LOD) was 5pg for Pb in... 

Samples for determination of ionic alky Head species in marine fauna were homogenized in the presence of salts and the alkyllead component was extracted with toluene and oxidized with HN03. Determination was by DPASV115. A method based on oxidation on Hg electrode has been described116 for analysis of alkylleads in gasoline. Alkylation of Hg is involved, of course, but as an oxidation the method does not suffer from the background of atmospheric oxygen. The peak potentials Ev for oxidation of tetramethyllead and tetraethyllead on various cathodes are well resolved (Table 5). 

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. [f 7] and by Segar [20], In these methods the gas chromatography flame combination showed a detection limit of about O.lpg Pb. Chau et al. [f 7, 18] 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. 

This experiment showed that some volatile component was formed in the thermal decomposition of tetramethyllead and that this compound consumed a cold lead mirror with formation of a volatile product. If, instead, a zinc mirror was first deposited and allowed to be consumed by the volatile product from decomposition of tetramethyllead, dimethylzinc could be identified as the product. Paneth concluded that free methyl radical was formed in the thermal reaction and could determine its half-life to be 0.006 seconds under the reaction conditions employed. Also, free ethyl radicals could be formed in... 

Bond AM, McLachlan NM. 1986. Direct determination of tetraethyllead and tetramethyllead in gasoline by high-performance liquid chromatography with electrochemical detection at mercury electrodes. Anal Chem 58 756-758. 

Chemical shifts for lead u-complexes are given in Table XVII. Coupling constants for tetramethyllead have been determined by several workers (76,... 

The absorbance of the chloroform layer in each tube at 520 nm in the spectrophotometer is measured against air as a reference. Applying blank corrections, refer to a standard curve of absorbance versus micrograms of lead to determine the amount of lead in the total sample and in the eluted tetramethyllead sample. The difference represents the amount of lead as tetraethyllead. 

To analyse mixtures of tetraethyllead, triethyImethyHead, di-ethyldimethyllead, ethyltrimethyllead and tetramethyllead by this procedure, Parker et al first prepared a mixture of the five pure compounds in toluene and obtained the retention indices and concentrations of the pure compounds (Figure 133) (petroleum unlike toluene did not interfere in the gas chromatographic procedure). They then chromatographed a mixture of known concentrations of the five lead alkyls in deleaded petroleum and using the previously determined retention indices, determined the concentrations of each component by the dithizone procedure. 

Finally, pure tetramethyllead and pure tetraethyllead were added to gasoline so that a 50- yl sample would contain approximately 50 yg of each calculated as lead. Table 122 shows the results of determining known amounts of tetramethyllead-tetraethyllead in gasoline. 

Laveskag has described a gas chromatographic mass-spectro- metric method for the determination of tetramethyllead and tetramethyl-lead in air. 

Kramer used an electron capture detector for the determination of lead alkyls in petroleum. He claims that a complete analysis for tetramethyllead and tetraethyllead in petrol can be achieved on a column (3 metres) of 10% of Apiezon L on Chromosorb W at 120°C with bromobenzene as internal standard. To separate the mixed alkyls (ethyltrimethyllead, diethyldimethyllead and triethylmethyHead, tetramethyllead and tetraethyllead) it is necessary to combine the above analysis with use of a pre-column (5 cm) of 20% of Carbowax 400 saturated with silver nitrate on Chromosorb W impregnated with 8% of potassium hydroxide. The pre-column retains halogen-containing scavengers in the petrol, which would otherwise mask the ethyltrimethyllead peak. As little as 0.002 g of tetramethyllead and tetraethyllead can be detected in 1 litre of petroleum in a 45 minute analysis. 

Chau et al pointed out that as the authenticity of the compounds to be analyzed must be preserved, any of the digestion methods with acids or alkalis are not suitable, and that extraction seemed to be the method of choice for removing these compounds from samples. For this traction, they adopted benzene as recommended by Sirota and Uthe for the quantitative extraction of tetramethyllead and tetraethyllead from fish homogenates suspended in aqueous EDTA solution. Although ionic forms of lead such as Pb(II), diethyllead dichloride, and trimethyllead acetate do not extract in the benzene phase, any lead compounds that distribute into the benzene phase as tetraalkyllead will be determined. Chau et al421 found that environmental samples can contain other forms of organolead compounds that are extractable into benzene but which are not volatile enough to be analyzed by the GC-AAS technique, hence the need for a speciation specific analytical system. 

Chau et al have applied gas chromatography atomic absorption to the determination of tetraalkyllead compounds in water, sediments and fish samples in high lead areas. Of some 50 fish samples analyzed, only one sample was found to contain detectable amounts (0.26 g/g) of tetramethyllead in the fillet. Since there is no known tetraalkyllead industry and tetramethyllead is not used in gasoline in this area, the source of tetramethyllead is not yet known. The possibility that... 

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