ASTM D5059 Standard Test Methods for Lead in Gasoline by X-Ray Spectroscopy
3. Summary of Test Method
3.1 There are three alternative test methods, as follows.
3.1.1 Test Method A (Bismuth Internal Standard Method High Concentration) - One volume of sample is mixed thoroughly with an equal volume of bismuth internal standard solution. The mixture is placed in the X-ray beam and the intensities of the lead L-a1 radiation at 1.175 Å and the bismuth L-a1 radiation at 1.144 Å are determined. The lead concentration of the sample is measured by comparing the ratio of gross counting rate at 1.175 Å with the gross counting rate at 1.144 Å to a previous prepared calibration curve of concentration versus the same ratios.
3.1.2 Test Method B (Scattered Tungsten Radiation Method) - The ratio of the net X-ray intensity of the lead L-a1 radiation to the net intensity of the incoherently scattered tungsten L-a1 radiation is obtained on a portion of the sample. The lead content is determined by multiplying this ratio by a calibration factor obtained with a standard lead solution of known concentration.
3.1.3 Test Method C (Bismuth Internal Standard Method, Low Concentration) - Twenty millilitres of sample is mixed thoroughly with two milliliters of bismuth internal standard solution. The mixture is placed in the X-ray beam of a spectrometer and the intensities of the lead L-a1 radiation at 1.175 Å, the bismuth L-a1 radiation at 1.144 Å, and a background at 1.194 Å are determined. A blank, made with iso-octane and bismuth internal standard, is run using the same procedure. The lead concentration is measured by determining the ratio of the net counting rate at 1.175 Å to the gross counting rate at 1.144 Å for the sample, subtracting the comparable ratio found for the blank, and comparing to a previously prepared calibration curve of concentration versus the same ratios.
4. Significance and Use
4.1 These test methods determine the concentration of lead (from alkyl addition) in gasoline. These alkyl additives improve the antiknock properties.
4.2 Test Method C is used to ensure compliance of trace lead as required by federal regulations for lead-free gasoline (40 CFR part 80).
