ISO 13759 Petroleum products - Determination of alkyl nitrate in diesel fuels - Spectrometric method
7 Test procedure
7.1 Pipette 1.0 ml of the test diesel fuel into a 10-ml volumetric flask (5.5) and dilute to the mark with propan-2-ol (4.8).
7.2 Pipette 1.0 ml of the test specimen prepared in 7.1 into a separating funnel (5.3). Add 1.0 ml of propan-2-ol to another funnel as a blank test.
NOTE - A more accurate test would be obtained if the same base fuel as that of the test specimen, diluted with propan-2-ol, were used as the blank solution.
7.3 Carry out the procedure described in 6.5 to 6.10.
NOTE - If an absorbance is too intense to remain on-scafe, dilute an aliquot of the test specimen (7.1) five-fold with blank fuel (4.6), repeat the procedure, and correct the calculations accordingly.
8 Calculation
8.1 Subtract the absorbance of the blank from the absorbance of the sample, and calculate the concentration of the alkyl nitrate, N, as a percentage by volume, by inserting the value for the slope of the calibration curve, as calculated in 6.11, in the following equation (see also 8.2):
N = CD
where
C is the slope of the calibration curve;
D is the absorbance of the test sample.
8.2 For some additive/fuel combinations, the response is not linear. If, after checking, this is confirmed, the calculation in equation (1) is not carried out, and the calculation in equation (2) is replaced by locating the measured corrected absorbance obtained in 6.10 on the best-fit curve and reading off the alkyl nitrate concentration.
