Trimethyllead in urban dust

One of the most critical points in organometallic chemistry analysis is the availability of calibrants of suitable purity and verified stoichiometry. This aspect was recognised at an early stage of the project and the purity of alkyllead compounds used in the feasibility study was carefully verified [25]. Additional experiments were performed on calibrants in the frame of the first interlaboratory exercise. Trimethyl- (TriML) and triethyllead (TriEL) compounds were obtained from Alfa products (Johnson Matthey) 

Some doubts were expressed on the procedure used by one laboratory which filtered the suspension and recovered TriML from the filtrate. Indeed, it was suspected that losses could have occurred by e.g, adsorption on the filter. The extraction recovery was not necessary as standard additions were performed prior to extraction recovery values of 66 and lT/ were obtained. At this stage, it was not possible to confirm the doubts expressed over the extraction recovery of TriML in this material. The participants recommended that emphasis be put on the verification of extraction recovery in a further exercise, i.e. that a small batch of candidate reference material of urban dust be spiked with a known amount of TriML, left to equilibrate, homogenised and made available to the participants so that the extraction recovery may be verified. Recommendation was made to spike the dust in a slurry which should be freeze-dried, rather than oven-dried, in order to avoid losses of TriML. 

Around 15 kg of surface road dust was collected from sweeping a lay-by in the central section of the Queensway tunnel in Birmingham (UK). The tunnel is approximately 850 m in length and is a major traffic route through Birmingham from the motorway system. The dust was passed through a 500 pm sieve to remove large particles of debris. 

the sample was treated by air drying at room temperature for five days, on a flat tray lined with clean paper, in a well-ventilated and dark place. Further, the dust was ground in a ballmill for a period of three minutes and sieved through a 125 pm sieve. 

The stability of the material upon storage was tested in the dark at -20°C, +20 C and +37°C and trimethyllead was determined at the beginning of the storage period and after 1, 3, 6, 12 and 37 months. Samples were analysed using the same procedures as for the homogeneity study. On the basis of the results obtained, no instability of the material could be demonstrated over a period of 37 months for the material stored at +20 C. However, a significant decrease in trimethyllead content was observed to occur at +37°C. It was hence concluded that the material is stable at +20 C whereas storage temperatures above this level should be strictly avoided. 

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