ASTM D6447 Test Method for Hydroperoxide Number of Aviation Turbine Fuels
ASTM D6447 Standard Test Method for Hydroperoxide Number of Aviation Turbine Fuels by Voltammetric Analysis
5. Apparatus
5.1 Voltammetric Analyzer - The instrument used to quantify the liberated iodine is a voltammetric analyzer equipped with a three electrode system and a digital or analog output. The combination electrode system (see Fig. 1) consists of a glassy carbon disc (3-mm diameter) working electrode, a platinum wire (0.5 mm diameter) auxiliary electrode, and a platinum wire (0.5 mm diameter) reference electrode. The voltammetric analyzer applies a linear voltage ramp (0 to -1 V range with respect to the reference electrode) at a rate of 0.1 V/s to the auxiliary electrode. The current output of the working electrode is converted to voltage by the voltammetric analyzer, using the gain ratio of 1V/20µA. The peak height or peak area of the voltammetric response to iodine is outputted to an analog or digital recording device (0 to 1 V full scale).
5.2 Vortex Mixer, with a 2800 to 3000 rpm motor and a pad suitable for mixing test tubes and vials.
5.3 Pipette, or equivalent, capable of delivering volumes required in the test method, such as 0.2, 1, and 2 mL.
5.4 Volumetric Flasks (optional), 100 and 500 mL capacity.
5.5 Glass Vials, 5 or 10 mL capacity.
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's purity suffices 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 II of Specification D1193.
6.3 Acetic Acid Solution - Mix 0.5 g of concentrated hydrochloric acid (HCl), (Warning: Poison. Corrosive. Can be fatal if swallowed. Causes severe burns. Harmful if inhaled. See Annex A1.1), 0.5 g of water, and 24 g of glacial acetic acid (CH3COOH) (Warning: Poison. Corrosive. Combustible. Can be fatal if swallowed. Causes severe burns. Harmful if inhaled. See Annex A1.2) in a suitable container. Store in a closed container. The acetic acid solution shall be prepared bi-weekly.
6.4 Potassium Dichromate Solution, Standard (0.1 N) - Recrystallize twice from an aqueous solution of potassium dichromate (K2Cr2O7) (Warning: Poison. Can be fatal if swallowed. Avoid contact with eyes and skin, and avoid breathing of dust, possible cancer hazard, strong oxidizer. See Annex A1.2) Dry at 120°C to constant mass. Dissolve 2.452 g of the purified K2Cr2O7 in water and dilute to 500 mL in a volumetric flask. This solution is 0.1 N. Commercially available solutions certified to this standard can also be used.
6.5 Potassium Dichromate Solution, Standard (0.002N) (Warning: Avoid contact with eyes and skin.) - Dilute 2.0 mL of 0.1 N K2Cr2O7 solution with water to 100 mL in a volumetric flask. Store in a closed container.
6.6 Potassium Iodide Solution - Dissolve 6 g of potassium iodide (KI) in 5 g of water. Store in a closed container. Do not use if the solution shows any color or is cloudy.
6.7 Potassium Chloride Solution - Dissolve 4 g of potassium chloride (KCl) in 20 g of water. Store in a closed container.
7. Sampling
7.1 Samples shall be taken in accordance with the procedures described in Practice D4057.
