ASTM D6748 for Determination of Potential Instability of Middle Distillate Fuels
ASTM D6748 Standard Test Method for Determination of Potential Instability of Middle Distillate Fuels Caused by the Presence of Phenalenes and Phenalenones (Rapid Method by Portable Spectrophotometer)
6. Apparatus
6.1 Spectrophotometer, double beam, capable of measuring absorbance at one visible wavelength in the range 600-800 nm and one near infrared wavelength in the range 800-850 nm with a spectral bandwidth of 10 +/- 2 nm and an accuracy of +/-3 nm (see Fig. 1). The display shall have a resolution of 0.01 of AU, and a repeatability of measurement of +/-0.02 AU for ranges up to 1.00 AU. See Practice E 275.
NOTE 2 - The two wavelengths used are proprietary and are not adjustable.
6.1.1 Zero Adjustment, a facility shall be incorporated to allow the absorbance measured at the two individual wavelengths to be set to zero when using Reagent 1 as a control.
6.1.2 Absorbance Display, the relative absorbance, in AU, shall be the instantaneous difference between the absorbance measured at the two wavelengths. The peak wavelength represents the absorption due to the colored indolylphenalene salts which are formed, and the baseline wavelength is for normalizing the result.
6.2 Timer, capable of measuring 35 min to an accuracy of +/-0.2 min.
6.3 Dispenser, for Reagent 1 made of polyethylene, polypropylene, or glass and capable of dispensing 5 mL of reagent with an accuracy of +/-0.5 mL.
6.4 Syringe 1, for test portion, 5 mL, polyethylene, polypropylene, or glass, with an accuracy of +/-0.25 mL.
6.5 Syringe 2, for Reagent 2, preset at 35 µL, glass, with an accuracy of +/-0.35 µL.
6.6 Test Tube with Stopper, nominally 15 mL, polyethylene, polypropylene, or glass.
6.7 Pipette, 5 mL, polyethylene, polypropylene, or glass.
6.8 Test Cuvette, 4.5 mL volume, optical methacrylate, disposable, with two opposite ribbed sides. Dimensions shall be 45 mm high, 12.5 by 12.5 mm in width with a test portion pathlength 10 +/- 0.25 mm.
7. Reagents and Materials
7.1 Reagent 1, proprietary, methanol solvent containing a Lowry-Bronsted acid 7 (Warning - Acidic, flammable, toxic, irritant).
7.2 Reagent 2, proprietary solution containing potassium permanganate an oxidizing agent (Warning - Oxidizing agent, toxic, irritant).
7.3 Water, distilled or deionized, for flushing Syringe 2 used for Reagent 2.
