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)
10. Procedure
10.1 Pour 5 mL of Reagent 1 into a test tube and add a 5 mL aliquot of the test sample using Syringe 1. Stopper the test tube and vigorously shake the test tube for 10 +/- 2 s.
10.2 Remove the stopper and add 35 µL of Reagent 2 using Syringe 2. Stopper the test tube and vigorously shake the test tube for 10 +/- 2 s. Allow to settle for 30 to 35 min.
10.3 Switch on the spectrophotometer at least 2 min before the end of the 30 min period.
10.4 At the end of the 30 min period, use a pipette to draw the darker reagent layer (at the top) from the test tube and to transfer that liquid to the test cuvette. Fill the cuvette to within 5 mm of its top. (Warning - Hold the cuvette using the two ribbed sides to avoid affecting the optical path.)
10.5 Place the cuvette (with the ribbed side towards the drawer handle) in the spectrophotometer and close the drawer.
10.6 Record the results from the digital display every 60 +/- 5 s until two readings agree within 0.02 AU and report the second of these reading as the measured relative absorbance. Record a negative result as zero.
11. Report
11.1 Report the source, type, and identification of the material tested, plus the dates sampled and tested.
11.2 Refer to this test method and report any deviation, by agreement or otherwise, from the procedure specified.
11.3 Report the result of the test in absorbance units to the nearest 0.01 AU.
12. Precision and Bias
12.1 The precision of this test method, as determined by statistical analyses of interlaboratory results, is as follows:
12.2 Repeatability - The difference between two test results obtained by the same operator with the same apparatus under constant operating conditions, on identical test material would, in the long run, in the normal and correct operation of the test method, exceed the following only in one case in twenty.
r = 0.0876 (x + 0.2) AU
where:
x = average of results being compared.
12.3 Reproducibility - The difference between two single and independent results obtained by different operators working in different laboratories on identical test material would, in the long run, in the normal correct operation of the test method, exceed the following only in one case in twenty.
R = 0.1799 (x + 0.2) AU
where:
x = average of results being compared.
12.4 Bias - Since there is no accepted reference material suitable for determining the bias of the procedures in Test Method D6748, bias cannot be determined.
13. Keywords
13.1 absorbance units; burner fuel; diesel fuel; infrared; infrared spectrophotometer; marine fuel; middle distillate fuel; potential instability; spectrometer; spectrophotometer; storage stability; turbine fuel; visible spectrophotometer
