ASTM D3341 Test Method for Lead in Gasoline-Iodine Monochloride Method
5. Apparatus
5.1 Separatory Funnel, borosilicate glass, capacity 250 mL, glass-stoppered with preferably an iodine flask type of neck.
5.2 Erlenmeyer Flask, borosilicate glass, capacity 500 mL.
6. Reagents and Materials
6.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.
6.2 Purity of Water - Unless otherwise indicated, references to water shall be understood to mean reagent water as defined by Type III or Type IV of Specification D1193.
6.3 Ammonia Solution (1 + 1) - Mix 1 volume of concentrated ammonia solution (rel dens 0.90) with 1 volume of distilled water.
6.4 Bromthymol Blue Indicator Solution - Dissolve 0.1 g of bromthymol blue in 50 mL of ethanol and dilute to 100 mL with distilled water.
6.5 EDTA, Standard Solution (0.005 M) - Dissolve approximately 3.75 g of diaminoethanetetra-acetic acid, disodium salt, in 2-L of distilled water. Determine the molarity of the solution by standardization with lead nitrate solution as follows:
6.5.1 Using a pipet, transfer 25.0 mL of the standard lead nitrate solution to a 250-mL Erlenmeyer flask. Dilute to about 75 mL with distilled water and add several drops of bromthymol blue indicator solution. Titrate with 1 + 1 ammonia solution until the color of the solution 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 have a rose color. Titrate with the EDTA solution. The color changes near the end point, this being indicated by a sharp change from orange to a permanent bright lemon-yellow.
6.5.2 Record the titre and calculate the molarity of the EDTA solution. The addition of excess EDTA produces no further color change at the end point.
6.6 Heavy Distillate - A straight-run, lead-free, petroleum distillate of low bromine number, with approximately 10 % distilling at 400°F 205°C and 90 % at 460°F 240°C (Warning - See Note 1).
NOTE 1 - Warning: Combustible.
6.7 Iodine Monochloride Reagent (1.0 M) (Warning - see Note 2) - Dissolve 111.0 g of potassium iodide (KI) in approximately 400 mL of distilled water. Add 445 mL of concentrated hydrochloric acid (sp gr 1.18) and cool to room temperature. Add 75.0 g of potassium iodate (KIO3) slowly and with stirring, until all the free iodine initially formed has just redissolved to give a clear orange-red solution (the amounts of KI and KIO3 are calculated to give a slight excess of iodate; if a greater excess is present, this will cause precipitation of lead and indifferent end points in the EDTA titration). Cool to room temperature and dilute to 1 L with distilled water. Store in a glass-stoppered bottle (Note 3).
NOTE 2 - Warning: Iodine monochloride will react with ammonium ions under certain conditions to yield nitrogen triiodide, which is explosive. Take care, therefore, that this reagent does not come into contact with ammonia or ammonium salts.
NOTE 3 - Do not use rubber stoppers to stopper vessels containing iodine monochloride solutions.
6.8 Lead Nitrate, Standard Solution (0.005 M) - Weigh with an accuracy of +/-0.001 g about 1.7 g of lead nitrate (Pb(NO3)2) that has been dried at 105°C and cooled in a desiccator. Dissolve it in distilled water and add 10 mL of concentrated nitric acid. Dilute to 1 L with distilled water in a volumetric flask and shake thoroughly to mix. Calculate the molarity of the solution according to the equation:
Molarity = wt (g) of lead nitrate/331.23
6.9 Nitric Acid, concentrated (rel dens 1.42).
6.10 Sodium Acetate, Acetic Acid Buffer Solution - Dissolve 23.0 g of anhydrous sodium acetate in about 500 mL of distilled water. Using a buret, add 6.2 mL of glacial acetic acid. Dilute to 1 L with distilled water in a 1-L volumetric flask and shake to mix.
6.11 Xylenol Orange Indicator Solution - Dissolve 0.2 g of xylenol orange, sodium salt, in 100 mL of distilled water and add 1 drop of 1 + 1 hydrochloric acid. (Prepare freshly each week.)
7. Sampling
7.1 Samples shall be taken in accordance with the instructions in Practice D4057.
