ASTM D2896 for base number of petroleum products
ASTM D2896 for base number of petroleum products by potentiometric perchloric acid titration
13. Quality Control Checks
13.1 Confirm the performance of the equipment or the procedure each day it is in use, by analyzing a quality control (QC) sample. It is advisable to analyze additional QC samples as appropriate, such as at the end of a batch of samples or after a fixed number of samples. Analysis of result(s) from these QC samples can be carried out using control chart techniques. When the result of a test on a QC sample exceeds the control limits of the laboratory, corrective action such as instrument recalibration, may be required. An ample supply of QC sample material shall be available for the intended period of use, and shall be homogeneous and stable under the anticipated storage conditions. If possible, the QC sample shall be representative of samples typically analyzed and the average value and control limits of the QC sample shall be determined prior to monitoring the measurement process. The precision for the QC sample must be compared against that given in the Precision and Bias section of this test method in order to verify that the instrument is functioning correctly.
NOTE 16 - Because the base number can vary while the QC sample is in storage, when an out-of-control situation arises, the stability of the QC sample can be a source of the error.
14. Calculation
14.1 For a manual titration, plot the volumes of the acid added against the corresponding meter readings.
14.2 Interpret the end point from the graph obtained from the manual or automatic titration. The end point is the midpoint of the inflection, that point at which the curve changes from concave to convex. A useful but not mandatory guide is that the end point is preceded and followed by a deflection of a least 50 mV/0.1 mL of titrant.
14.3 When there is no inflection point or only a very poor one, proceed to Section 16 or Section 17 on back titration. The inflection obtained during back titration preferably is to meet the criteria described in 14.2.
14.4 Calculate the base number, BN, as follows:
BN, mg KOH/g = [(E–F) • N(A) • 56.1]/S
where:
E= HClO4 solution used to titrate the sample to the inflection point on the titration curve, mL,
F= volume corresponding to E for blank titration at same potential as sample, mL
N(A) = normality of HClO4 solution, and
S= sample, g.
15. Report
15.1 Report the result as follows:
Base Number (D2896 - Procedure A or B) = Result
This report format may not be used when using the alternative solvent described in Appendix X2. Instead, use the format described in X2.4.
