ASTM D5059 Standard Test Methods for Lead in Gasoline by X-Ray Spectroscopy
TEST METHOD C (LOW-LEAD METHOD)
17. Apparatus
17.1 X-ray Spectrometer, as described in 5.1. See Note 9.
18. Reagents and Materials
18.1 Reagents are described in Section 6.
18.2 Lead (Pb) Solution, Standard (0.500 g Pb/gal) - Dilute an aliquot of the standard prepared in 6.6 appropriately so that it contains 0.500 g Pb/US gal at 60°F (15.6°C). Keep refrigerated when not in use. (Warning - TEL is toxic by ingestion.)
19. Calibration
19.1 Make exact dilutions of the 0.500 g Pb/gal standards to give 0.30, 0.10, 0.050, 0.010, 0.005 and 0.001 g Pb/US gal at 60°F in toluene, iso-octane, or a mixture of these two solvents. Retain a 0.000 g Pb/gal standard as a blank.
19.2 Allow all solutions to come to room temperature.
19.3 Pipet accurately 20.0 mL of each standard (including the 0.500 g Pb/gal standard) and the blank into separate glass-stoppered bottles or flasks and add accurately 2.0 mL of the bismuth internal standard to each one. Mix thoroughly.
19.4 Place one of these solutions in the sample cell using techniques consistent with good operating practice for the spectrometer employed. Place the cell in the instrument, allow the atmosphere to reach equilibrium (if appropriate), and determine counting rates at the Pb L-a1 line (1.175 Å), the Bi L-a1 line (1.144 Å), and the background (1.194 Å).
NOTE 11 - If possible, collect at least 100 000 counts at each line. When sensitivity or concentration, or both, make it impractical to collect this many counts, the technique that allows the greatest statistical precision in the time allotted for each analysis should be used. Sample stability should also be considered in determining analysis time. Variation in counting rates should be observed and if the counting rate tends to go in one direction only, the sample is probably decomposing. If this occurs, shorter counting times should be used consistent with acceptable statistical precision.
19.5 Determine the ratio, R, for each standard and the blank as follows:
R = (A - C)/B
where:
A = counting rate at 1.175 Å,
B = counting rate at 1.144 Å, and
C = counting rate at 1.194 Å.
19.6 Determine the corrected ratio, Rc, as follows:
Rc = R - Rb
where: Rb = ratio for blank.
19.7 Plot a calibration curve (see Note 7) relating Rc to the grams of lead per gallon. Determine the slope, S, of the resulting line if it is straight as follows:
S = (g Pb/US gal)/Rc
20. Quality Control Checks
20.1 Follow the requirements specified in 8.1 for samples analyzed by Test Method C.
21. Procedure
21.1 Obtain sample in accordance with Practice D4057.
21.2 Prepare the samples to be analyzed and a blank as described in 19.3 and 19.4 for the standard lead solutions and determine the ratio, Rc, as described in 19.5 and 19.6 using the blank determined at the time of analysis.
22. Calibration
22.1 Calculate the lead content of the samples by relating Rc to the previously determined calibration curve. If S was calculated in 19.7 determine lead content as follows:
Pb, g Pb/US gal = Rc x S
23. Report
23.1 Report the lead content obtained in 10.2 as g Pb/US gal at 60°F (15.6°C) to the nearest 0.005 g.
