ASTM D6971 Standard Test Method for Measurement of Hindered Phenolic and Aromatic Amine Antioxidant Content in Non-zinc Turbine Oils by Linear Sweep Voltammetry
5. Apparatus
5.1 Voltammetric Analyzer - The instrument used to quantify the hindered phenol and aromatic amine antioxidants is a voltammograph equipped with a three-electrode system and a digital or analog output. The combination electrode system 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, as described in Test Method D6810. The voltammetric analyzer applies a linear voltage ramp (0 to -1.8 V range with respect to the reference electrode) at a rate of 0.01 to 0.5 V/s (0.1 optimum) to the auxiliary electrode. The current output of the working electrode is converted to voltage by the voltammetric analyzer, using the gain ratio of 1 V/20 µA, and is outputted to an analog or digital recording device (0 to 1 V full scale) as shown in Figs. 1 and 2.
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 sample volumes required in the test method, from 0.10 to 0.50 mL.
5.4 Test Solution Dispenser, or equivalent, capable of delivering volumes of analysis test solution (see 6.3) required in the test method, such as 3.0 and 5.0 mL.
5.5 Glass Vials, with caps, 4 or 7 mL capacity and containing 1 g of sand. White quartz suitable for chromatography, within the size range of 200 to 300 µm +/- 100 µm.
6. Reagents
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 specified, references to water that conforms to Specification D1193, Type II.
6.3 Analysis Materials:
6.3.1 Acetone Test Solution (Neutral) - Proprietary Green Test Solution, Acetone test solution (1:10 distilled water/acetone test solution) containing a dissolved neutral electrolyte. (Warning - Corrosive, poisonous, flammable, and a skin irritant. Harmful if inhaled.)
6.3.2 Alcohol Test Solution (Basic) - Proprietary Yellow Test Solution, Ethanol test solution (1:10 distilled water/ethanol test solution) containing a dissolved base electrolyte. (Warning - Corrosive, poisonous, flammable, and a skin irritant. Harmful if inhaled.)
6.3.3 Alcohol Cleansing Pads - 70 % isopropyl alcohol saturated cleansing pads (alcohol prepared skin cleansing pads, for the preparation of the skin prior to injection (antiseptic)).
7. Sampling
7.1 Obtain the sample in accordance with Practice D4057.
