ASTM D5386 Test Method for Color of Liquids Using Tristimulus Colorimetry
5. Apparatus
5.1 Instrument, with the following provisions:
5.1.1 Instrument Sensor, shall provide a beam for illuminating the sample cell in transmission. The instrument shall be capable of converting light measured in total transmission through the sample cell to CIE X Y Z tristimulus color values for the measurement conditions of CIE illuminant C and the CIE 1931 2 degree standard observer as described in Guide E 179 and Practice E 308.
5.1.2 The CIE X Y Z tristimulus color values shall be convertible to the instrumental yellowness index (YI) defined by Practice E 308 and Practice E 313. A correlation between measured yellowness index (YI) (Practice E 313) values and the Pt-Co standard solutions shall be used to yield an equivalent instrumental Pt-Co rating for liquid hydrocarbon samples.
5.1.3 Sample Cells, shall have clear, colorless, parallel entrance and exit windows. Internal distance between faces shall be selectable. Pathlengths from 20 mm to 150 mm have been used for near-clear liquid hydrocarbons. If measuring samples using cells of the same pathlength, a pathlength tolerance of more or less 3 % or less would be appropriate. Matched cells would be beneficial but not required.
6. Reagents
6.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests.
6.2 Purity of Water - References to water shall be understood to mean colorless distilled water, conforming to Type IV of Specification D1193.
6.3 Cobalt Chloride, (CoCl2•6H2O).
6.4 Hydrochloric Acid (sp gr 1.19) - Concentrated hydrochloric acid (HCl).
6.5 Potassium Chloroplatinate, (K2PtCl6).
6.6 Platinum-Cobalt Stock Solution - Dissolve 1.245 g of potassium chloroplatinate (K2PtCl6) and 1.00 g of cobalt chloride (CoCl2 H2O) in water. Carefully add 100 mL of hydrochloric acid (HCl sp gr 1.19) and dilute to 1 L with distilled water. The absorbance of the 500 platinum-cobalt stock solution in a cell having a 10-mm light path with distilled water in a matched cell as the reference solution must fall within the limits given in Table 1.
7. Materials
7.1 Platinum-Cobalt Standards - From the stock solution prepare color standards in accordance with Table 2 by diluting the required volumes to 100 mL with water in volumetric flasks. When properly sealed and stored these standards are stable for at least one year.
