21. Calculation
21.1 Calculate the saponification number, A, as follows:
where:
56.1 = molecular weight of KOH,
M = molarity of HCl,
VB = volume of acid used in titrating the blank, mL,
VS = volume of acid used in titrating the sample, mL,
and
W = sample weight, g.
21.2 The first inflection point is due to hydroxide and serves as the end point in the titration. If the added KOH titrant contains carbonate contamination, a second inflection point may be present (see Fig. 3). If this occurs, use the first inflection point as the titration end point for the blank (VB) and the sample (VS).
22. Report
22.1 For saponification numbers of less than 50, report the saponification number to the nearest 0.5 mg KOH/g of sample.
22.2 For saponification numbers of 50 or more, report to the nearest whole number.
22.3 For electrical insulating oils, report the values to the nearest 0.1 mg KOH/g sample.
22.4 Report the saponification test numbers as obtained by Test Methods D94, Method B.
23. Precision and Bias
23.1 Based on the round robin conducted using seven lube oil additives and automatic transmission fluids and 16 laboratories, the following precision estimates were obtained:
23.1.1 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 2.76 mg KOH/g saponification number only in one case in twenty.
23.1.2 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, in the normal and correct operation of the test method, exceed 10.4 mg KOH/g saponification number only in one case in twenty.
23.2 Bias - This is an empirical test method and there are no accepted standard reference materials that can be compared; hence, bias cannot be determined.
24. Keywords
24.1 additives; lubricating oils; potentiometric titration; saponification number