11. Calculation
11.1 Prepare a calibration curve, plotting the amplitude difference for each working calibration standard on the y axis versus the dye concentration on the x axis.
11.2 Determine the concentration of dye in the sample by comparing the amplitude difference measured in 10.3 for the sample against the calibration curve.
11.2.1 Computer systems/software having appropriate multi-point calibration program capabilities may be used instead of a manual interpolation from calibration curves.
11.3 Report the dye concentration results for the sample in mg/L to one decimal place, for example, 11.1 mg/L.
12. Precision and Bias
12.1 Precision - The precision of the test method, as obtained by statistical examination of inter- and intra-laboratory test results obtained in accordance with the requirements of Practice E 691, is as follows:
12.1.1 Repeatability - Within-laboratory precision, a quantitative expression of the random error associated with a single operator in a given laboratory obtaining repetitive results with the same apparatus under constant operating conditions on identical test material. It is defined as the difference between two such results at the 95 % confidence level.
where:
x = mean dye concentration (mg/L) of two results from the same laboratory.
12.1.2 Reproducibility - Between-laboratory precision, a quantitative expression of the random error associated with different operators using different test apparatus in different laboratories and obtaining test results when applying the same method. It is defined as the 95 % confidence limit for the difference between two such single and independent results.
where:
x = mean dye concentration (mg/L) of two results from different laboratories.
12.2 Bias - Bias cannot be determined because there was no acceptable reference material suitable for determining bias for this test method.
13. Keywords
13.1 dyed diesel fuel; second derivative spectroscopy; Solvent Red 26 Dye; Solvent Red 164 Dye; tax-exempt diesel fuels; visible spectroscopy