The determination of lead in leaded gasoline

The method is suitable for the determination of Pb in gasoline in the range 1—lOOOpgml-1 (0.001—1 gl 1). The gasoline sample is diluted with MIBK and shaken with a solution of iodine in toluene. Iodo lead alkyl species are formed and these are stabilised with a liquid anion exchanger. Thus, the problem of the variable Pb response is overcome. This solution is compared with standards prepared in a similar fashion from Pb chloride in MIBK. 

The sample dilution required will depend on the concentration of Pb present in the gasoline. This should be chosen to fall within the range defined by the calibration standards. Pipette the chosen volume of gasoline into 100 ml volumetric flasks in duplicate. To this add approximately 50 ml of MIBK and 0.2ml (200pi) of a solution of iodine in toluene (see note 2). Swirl the mixture and allow to stand for two minutes. Add 5 ml of a 1% v/v solution of Aliquat 336 (see note 1), swirl to react and dilute to the mark with MIBK. 

A stock Pb standard must first be prepared. Place reagent-grade Pb chloride in an oven at approximately 100°C for a few hours. Accurately weigh 0.3355 g of this salt and dissolve in 200 ml of a 10% v/v solution of Aliquat 336 in a 250 ml volumetric flask. Dilute to the mark with 10% v/v Aliquat 336 solution. This standard contains 1000 pg ml-1 Pb. Store in a darkened bottle, tightly stoppered. 

Calibration standards are prepared by dilution of the stock standard. Choose an approximately linear range for Pb on the instrument to be used (normally 0—lOpgml-1). Into four 100 ml volumetric flasks place the following a volume of Pb free iso-octane (see note 3) equal to the volume of gasoline in the diluted sample 0.2ml of the iodine in toluene solution 5 ml of the l%v/v solution of Aliquat 336 and such volumes of the stock solution (after dilution, with MIBK, to lOOpgml-1 Pb if necessary) as are necessary to give the desired calibration concentrations. One standard must contain no Pb. Dilute to the mark with MIBK. Prepare these calibration standards freshly as required do not store. 

Adjust the instrumental parameters of spectral band pass, wavelength and lamp current in accordance with the manufacturer s recommended conditions. Use an air—acetylene flame and, aspirating the blank solution, adjust the acetylene flow rate to obtain a fuel-lean flame. 

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