ASTM D6920 Standard Test Method for Total Sulfur in Naphthas, Distillates, Reformulated Gasolines, Diesels, Biodiesels, and Motor Fuels by Oxidative Combustion and Electrochemical Detection
14. Calculation
14.1 For analyzers equipped with an automatic calibration, calculate the sulfur content of the sample in parts per million by weight (mg/kg) by either of the following equations:
Sulfur, mg/kg = (I - B) x K/(V x D)
Sulfur, mg/kg = (I - B) x K/M
where:
D = density of sample, g/mL,
K = dilution factor,
V = volume of sample, µL,
M = mass of sample, mg,
I = visual display reading of sample, and
B = average of visual display readings of blank.
14.2 For analyzers not equipped with automatic calibration, calculate the sulfur content of the sample in parts per million by weight (mg/kg) as follows:
Sulfur, mg/kg = I x S x K/(V x D)
where:
D = density of sample, g/mL,
S = slope of standard curve, mg S/count,
V = volume of sample, µL,
I = detector response, integration counts, and
K = dilution factor (when applicable).
15. Precision and Bias
15.1 Precision - The precision of this test method as determined by the statistical examination of the interlaboratory test results is as follows. These data were produced from an interlaboratory study involving 16 laboratories that analyzed a total of 16 samples for gasoline and 16 samples for diesel. Two instruments were used in this interlaboratory study, one from APS Technologies and one from Antek Instruments. Since the results from these instruments were statistically different, precision statements are provided for each of the instruments.
15.1.1 Repeatability - The difference between successive results obtained on the same day 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 values in Table 3 only in one case in twenty.
15.1.2 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, exceed the values in Table 4 only in one case in twenty.
15.2 Bias - Based on the analysis of NIST Standard Reference Materials (SRM), there was no significant bias for the test method on either instrument between the results by this test method and the certified values by NIST for diesel SRM 2723a. For gasoline SRMs, there was no bias for SRM 2299 containing 13.6 mg/kg sulfur. However, for gasoline SRM 2298 containing 4.6 mg/kg total sulfur there was a bias of -0.78 mg/kg for the test method on both instruments.
16. Quality Control
16.1 Confirm the performance of the instrument or the test procedure by regularly analyzing QC samples.
16.1.1 When QC/QA protocols are already established in the testing facility, these may be used so long as they can properly confirm the reliability of this test method's test results.
16.1.2 When there is no QC/QA protocol established in the testing facility, Appendix X1 can be used as a guide for acceptable QC/QA practices for this test method.
17. Keywords
17.1 diesel; diesel fuel; diesel fuel additives; electrochemical detection; gasoline; motor fuels; oxidative combustion; petroleum; sulfur
