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
8. Sampling
8.1 Samples shall be taken in accordance with Practice D4057 or D4177.
8.2 Precautions must be taken to shield the samples from light prior to analysis.
9. Calibration and Standardization of the Apparatus
9.1 The instrument is calibrated according to the procedure described in Annex A2.
NOTE 1 - The DT100C instruments are calibrated at the factory by the vendor.
9.2 The instrument is qualified according to the procedure described in Annex A3.
NOTE 2 - The DT100C instruments are qualified at the factory by the vendor.
9.2.1 If the qualification procedure is performed by the vendor, then the user shall perform a quality control check according to the procedure described in Section 10.
10. Quality Control Check
10.1 To confirm the performance of the instrument, periodically measure the red dye concentration and the ASTM color of three control samples using the procedure outlined in Section 11. The quality control check standards should be analyzed at least once a week or before the sample analysis if the instrument is used less frequently than weekly or if the instrument is moved to a different laboratory or field location.
NOTE 3 - Quality control samples are available from DT100C.
10.1.1 A standard of known dye concentration and ASTM color is made according to the information in A1.4. The set of quality control samples shall have a low, medium, and high red dye concentration (0 mg/L to 14 mg/L +/- 2 mg/L) and a low, medium, and high ASTM color (0 to 5 ASTM color units).
10.1.2 The standards are stable for at least one year when stored in the dark in tightly sealed bottles.
10.2 If the red dye concentration determined for one of the quality control samples differs from the known value by more than 1.0 mg/L or if the estimated ASTM color for one of the quality control samples differs from the known value by more than 0.5 units, then the measurement system is out-of-control and cannot be used to determine the red dye concentration or used to estimate the ASTM color until the cause of the out-of-control behavior is corrected.
10.3 If correction of out-of-control behavior requires repair to the instrument or recalibration of the instrument, the qualification of instrument performance described in Annex A3 shall be performed before the system is used to measure red dye concentration or used to estimate ASTM color.
