ASTM D3341 Test Method for Lead in Gasoline-Iodine Monochloride Method
8. Procedure
8.1 Transfer 50 mL of the iodine monochloride reagent and 25 mL of heavy distillate to the 250-mL separatory funnel. Measure the temperature of the sample to the nearest 0.5°C (1°F) (Note 4). Using a pipet (Warning - See Note 5), transfer 25 +/- 0.05 mL of the sample of the gasoline to the separatory funnel. Immediately stopper the funnel and shake the contents for 60 s. Allow the funnel to stand for several minutes, until the two phases have separated and run the lower aqueous phase into a 500-mL Erlenmeyer flask made of borosilicate glass. Wash the gasoline phase by shaking with three separate 20-mL portions of distilled water and add the washings to the Erlenmeyer flask.
NOTE 4 - For cool gasolines having a Reid vapor pressure above 7.0 lb cool the sealed sample container to approximately 60°F (15°C) before removing the sample for analysis.
NOTE 5 - Warning: Never suck leaded gasoline or corrosive liquids into a pipet by the mouth.
8.2 Place several glass beads in the flask, cover the mouth of the flask with a small ribbed watch glass, and place on a hot plate. Heat the contents and allow to boil until the volume of the solution is 15 to 20 mL. Without removing the flask from the hot plate, add 5 mL of concentrated nitric acid down the side of the flask and evaporate the contents almost to dryness to oxidize any organic material present. Repeat the nitric acid treatment, evaporating almost to dryness until all the organic matter has been removed and a white residue remains. Finally remove the watch glass and evaporate the solution to dryness. Remove the flask from the hot plate and allow the contents to cool.
8.3 Add about 200 mL of distilled water to the flask and swirl to dissolve the residue. The residue may be quickly dissolved by heating the solution, but this must be cooled before titrating. Add 5 drops of bromthymol blue indicator and titrate with 1 + 1 ammonia solution until the color just changes to blue; then add 10 mL of sodium acetate-acetic acid buffer solution and 5 drops of xylenol orange indicator solution. In the presence of lead, the solution will now have a rose color.
8.4 Titrate with the 0.005 M standard EDTA solution. The color of the solution changes to orange near the end point, the end point being indicated by a sharp change from orange to a permanent bright lemon-yellow. Note the titre. The addition of excess EDTA solution produces no further color change at the end point.
8.5 Carry out a blank determination on the reagents, excluding the heavy distillate and omitting the extraction stage and, if necessary, correct the sample titre accordingly.
9. Calculation
9.1 Calculate the concentration of lead by means of one of the following equations (see also Note 6):
Lead, g/US gal at 60°F (15.5°C) = 31.37 TM (1 + 0.00065 (t - 60))
Lead, g/UK gal at 60°F (15.5°C) = 37.68 TM (1 + 0.00065 (t - 60))
Lead, g/L at 15°C = 8.288 TM (1 + 0.0012 (tx - 15))
where:
T = volume of EDTA solution used to titrate the sample, mL,
M = molarity of EDTA solution,
t = the temperature of gasoline when pipeting sample, °F, and
tx = temperature of gasoline when pipeting sample, ° C.
NOTE 6 - The constant 31.37 is obtained from the expression 0.20721 x 3785.3/25, where 0.20721 is the number of grams of lead equivalent to 1 mL of M EDTA solution, 3785.3 is the number of millilitres in a US gal, and 25 represents the sample volume in millilitres. The constant 37.68 is obtained by multiplying 31.37 by 1.201 (the ratio of millilitres in 1 UK gal to millilitres in 1 US gal, 4546.0 and 3785.3 respectively). The constant 8.288 is obtained by dividing 31.37 by 3.7853.
NOTE 7 - The coefficient of expansion of gasolines is taken as 0.00065/°C at 60°F and 0.0012/°C at 15°C.
NOTE 8 - For gasoline containing only tetraethyl-lead (TEL) or tetramethyl-lead (TML), the grams of lead per unit volume can be converted to millilitres per unit volume by multiplying by the following factors:
For tetraethyl lead (TEL) = 0.946
For tetramethyl lead (TML) = 0.648
