ASTM D6756 Standard Test Method for Determination of the Red Dye Concentration and Estimation of the ASTM Color of Diesel Fuel and Heating Oil Using a Portable Visible Spectrophotometer
4. Summary of Test Method
4.1 A sample is introduced into the liquid specimen cell. The cell is placed into the light path of the apparatus. A beam of visible light is imaged through the sample onto a detector, and the detector response is determined. Wavelengths of the spectrum, which correlate highly with the red dye concentration and the ASTM color, are selected for analysis using selective bandpass filters. A multivariate mathematical model converts the absorption values from the filters to the red dye concentration and the estimated ASTM color.
5. Significance and Use
5.1 In the United States, high sulfur content (defined by the United States Environmental Protection Agency (USEPA)) middle distillate products and diesel fuel used for off-road purposes, other than aviation turbine fuel, are required by government agencies to contain red dye. The dye concentration required to be present in high-sulfur and off-road diesel products is regulated by the United States Environmental Protection Agency and the United States Internal Revenue Service, respectively.
5.2 Some fuels that are readily exchanged in the market have a color specification. The color of the base fuel is masked by the presence of the red dye. This test method provides a means of estimating the base color of Number 1 and Number 2 diesel fuel and heating oil in the presence of red dye.
5.3 The test method provides a means to indicate conformance to contractual and legal requirements.
6. Interferences
6.1 The presence of colorants other than the hydrocarbons typical of Number 1 and 2 diesel fuel and heating oils, or the presence of red dye other than the specified types, can interfere with the accurate determination of the red dye concentration reported as Solvent Red 26 equivalent or the base fuel ASTM color.
