IS 1448 (Part 173): 2020 Methods of test for petroleum and its products [P:173] Determination of lead content in motor gasoline — energy dispersive x-ray fluorescence spectrometry method
Lead is a toxic metal that interferes with anti-pollution devices in motor gasoline (petrol) vehicles and contributes to lead poisoning. Addition of lead in moto gasoline is banned in our country way back in 2000. Though lead is not being added by our refiners after the ban, in motor gasoline specifically, there is a possibility of contamination due to accidental or incidental mixing. Further imported motor gasoline may sometimes have little amount of lead content in it, in the way of addition of tetraethyl lead, an anti-knocking agent, by some of the countries still. Indian Standard for motor gasoline, IS 2796 specifies the requirement of lead content as 0.005 mg/l, maximum, to ensure the product is free from lead.
This standard, IS 1448 Part 173, describes the procedure for determination of lead content in motor gasoline using X-ray Fluorescence Spectrometry (XRF) technique, where the lead is present as lead alkyl. The detailed calibration analysis in both low range and high range is also described in this standard. A test portion is exposed to an X-ray beam and the intensity of specified excited lines of lead is measured and compared with calibration curve of intensity versus lead content. For the high range analysis the intensity of lead L line is measured, whereas for the low range analysis, the low power X-ray tube instrument measures a region of the spectrum centered on the Lα line together with one set to the high energy back-scatter to calculate a net intensity. This method can determine lead as low as 0.002 g Pb/l to 0.50 g Pb/l.