ASTM D7058 Standard Test Method for Determination of the Red Dye Concentration and Estimation of Saybolt Color of Aviation Turbine Fuels and Kerosine 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 with the estimation of Saybolt color, are selected for analysis using selective bandpass filters. A multivariate mathematical analysis converts the detector response for the selected wavelengths to the red dye concentration and the estimated Saybolt color.
5. Significance and Use
5.1 In the United States, high sulfur content distillate products and diesel fuel used for off-road purposes, other than aviation turbine fuel, are required to contain red dye. A similar dye requirement exists for tax-free distillates. Contamination of aviation turbine fuel by small quantities of red dye has occurred. Such contamination presents major problems because airframe and engine manufacturers have severely limited operation on aviation turbine fuel containing red dye.
5.2 An alternate methodology for the determination of the presence of red dye in aviation turbine fuel is the observation of the color of the fuel when placed in a white bucket. The presence of the dye can be masked in aviation turbine fuels having dark Saybolt color. This test method provides an objective means of quickly measuring red dye concentration, but to avoid confusion with trace levels of other materials which will be indicated by the instrument, the method requires that instrument readings below 0.026 mg/L be reported as No Dye Present.
5.3 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 aviation turbine fuel and kerosine in the presence of red dye.
6. Interferences
6.1 The presence of colorants resulting from the refining process or crude oil or the presence of red dye other than the quantified types (alkyl derivatives of azobenzene-4-azo-2-naphthol) can interfere with the accurate determination of the red dye concentration reported as Solvent Red 26 equivalent, or the accurate estimation of the base fuel color. If there is controversy over whether the indicated dye concentration is from the alkyl derivatives ofazobenzene-4-azo-2-naphthol, the procedure described in Annex A5 shall be used to confirm the presence of a red dye.
