ASTM D6810 Standard Test Method for Measurement of Hindered Phenolic 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 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 D6447. 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 this test method, from 0.10 to 0.50 mL.
5.4 Solvent Dispenser, or equivalent, capable of delivering volumes of analysis solution (see 7.3) required in this 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 +/- 100 µm.
6. Sampling
6.1 Obtain the sample in accordance with Practice D4057.
7. Reagents
7.1 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 sufficiently pure to permit its use without lessening the accuracy of the determination.
7.2 Purity of Water - Unless otherwise specified, references to water that conforms to Specification D1193, Type II.
7.3 Analysis Materials:
7.3.1 Alcohol Test Solution (Basic Test Solution) - Proprietary Yellow solution, ethanol solvent (1:10 ethanol solution/distilled water) containing a dissolved base electrolyte. (Warning - Corrosive, poison, flammable, skin irritant; harmful if inhaled.)
7.3.2 Alcohol Cleansing Pads - 70 % isopropyl alcohol saturated cleansing pads.
