ASTM D2622 for sulfur in petroleum products
ASTM D2622 standard test method for sulfur in petroleum products by wavelength dispersive X-ray fluorescence spectrometry
11. Calculations
11.1 When using the drift correction monitor described in 7.3, calculate a correction factor for changes in daily instrument sensitivity as follows:
F = A/B
where:
F = correction factor,
A = counting rate of the drift correction monitor as determined at the time of calibration (see 9.4), and
B = counting rate of the drift correction monitor as determined at the time of analysis.
11.2 Determine the corrected net counting rate (intensity) as follows:
R = [(Np/S1) – (NbF'/S2)] F
where:
R = corrected net counting rate,
Np = total counts collected at 0.5373 nm,
Nb = total counts collected at the background location chosen in 10.8,
S1 and S2 = seconds required to collect Np and Nb counts, respectively,
F' = the ratio of counts/s at 0.5373 nm to the counts/s at background using a sample containing no sulfur, and
F = optional factor (see Note 16).
NOTE 16 - The inclusion of the factor F in Eq 8 may not be necessary or desirable with some instrumentation. In this case F is set to unity. It is recommended that the user chart the F factor and develop criteria for its application based on the stability of the instrumentation and standard SQC principles.
11.2.1 The inclusion of the factor F8 in Eq 8 is optional. In general it is needed for multi-channel spectrometers, which use different spectrometer channels to measure peak and background intensities.
NOTE 17 - Charting the F' factor, even if it is not used in Eq 8, will alert the user to changes in instrument operation due to contamination of system elements, such as crystals, collimators, and fixed windows.
11.3 Calculate the sulfur content of the sample by inserting the corrected net counting rate from Eq 8 in the chosen calibration model from Section 9. In many cases the instrument vendor will provide software for the required calculations.
11.4 Calculate the concentration of sulfur in samples, which have been diluted, as follows:
S = Sb[(Ws + Wo)/Ws]
where:
S = mass % total sulfur in the sample,
Sb = mass % sulfur in diluted blend,
Ws = mass of original sample, g, and
Wo = mass of diluent, g.
11.4.1 The instrument vendor may have provided software to perform this calculation when required masses are input.
11.5 When analyzing fuels containing high levels of ethanol or methanol (Table 1) with a calibration determined with white oil based standards, divide the result obtained in 11.3 as follows (see Note 15):
S(Fuel) = M/F
where:
S(Fuel) = mass % sulfur present in the fuel sample, wt.%,
M = measured mass percent, wt.%, and
F = correction factor, for example, equals 0.59 for M-85 and 0.55 for M-100
11.5.1 This correction is not required if the standards are prepared in the same matrix as the samples, as described in 5.2.
11.6 Additional information regarding regression calculations may be found in Practice D7343.
