20.3 Record the QC results and analyze by control charts or
other statistically equivalent technique to ascertain the statistical
control status of the total testing process.4 Any out-ofcontrol
data should trigger investigation for root cause(s). The
results of this investigation may, but not necessarily, result in
instrument recalibration.
20.4 The frequency of QC testing is dependent on the
criticality of the quality being measured, the demonstrated
stability of the testing process, and customer requirements.
Generally, a QC sample should be analyzed each testing day.
The QC frequency should be increased if a large number of
samples are routinely analyzed. However, when it is demonstrated
that the testing is under statistical control, the QC
testing frequency may be reduced. The QC precision should be
periodically checked against the precision listed in the Precision
and Bias Section of this test method to ensure data quality.
20.5 It is recommended that a QC standard be routinely
analyzed at a concentration level in the same range as the
samples analyzed. An ample supply of QC sample material
should be available for the intended period of use, and must be
homogeneous and stable under the anticipated storage conditions
21. Report
21.1 Report acid number of biodiesel and blends to the 0.01
as mg KOH/g of sample (Test Method D664, Test Method B).
22. Precision and Bias6
22.1 The precision of this test method is based on an
interlaboratory study of D664 conducted in 2009. Seven
laboratories participated in this study, however the results from
one laboratory were excluded from the precision calculations
due to a fairly consistent bias in their reported values. Each of
the laboratories was asked to report replicate test results for
eleven different diesel and biodiesel blends and a blank. Every
“test result” reported represents a single determination or
measurement. D2PP was used for the analysis of the study
data; the details are given in ASTM Research Report RR:D02-
1727.
22.1.1 Repeatability Limit (r)—Two test results obtained
within one laboratory shall be judged not equivalent if they
differ by more than the “r” value for that material; “r” is the
interval representing the critical difference between two test
results for the same material, obtained by the same operator
using the same equipment on the same day in the same
laboratory. Repeatability limits are listed in Table 2.
22.1.2 Reproducibility Limit (R)—Two test results shall be
judged not equivalent if they differ by more than the “R” value
for that material; “R” is the interval representing the critical
difference between two test results for the same material,
obtained by different operators using different equipment in
different laboratories. Reproducibility limits are listed in Table
2.
22.1.3 The above terms (repeatability limit and reproducibility
limit) are used as specified in Practice E177.
22.1.4 Any judgment in accordance with statements 22.1.1
and 22.1.2 would have an approximate 95% probability of
being correct.
22.2 The precision statement was determined through statistical
examination of 138 results, from six laboratories, on a
total of eleven different petroleum blends and a blank.
22.3 Bias—At the time of the study, there was no accepted
reference material suitable for determining the bias for this test
method, therefore no statement on bias is being made.
23. Keywords
23.1 acid number; B5; B10; B20; B100; biodiesel; biodiesel
blend; lubricants; petroleum products; potentiometric; strong
acid number; titration