7.10. Interpretation of Requirements
Analytical results observed in the laboratory (or calculated from experimental measurements) are compared with stated acceptance criteria to determine whether the article conforms to compendial requirements.
The reportable value, which often is a summary value for several individual determinations, is compared with the acceptance criteria. The reportable value is the end result of a completed measurement procedure, as documented.
Where acceptance criteria are expressed numerically herein through specification of an upper and/or lower limit, permitted values include the specified values themselves, but no values outside the limit(s). Acceptance criteria are considered significant to the last digit shown.
7.10.10. Equivalence Statements in Titrimetric Procedures
The directions for titrimetric procedures conclude with a statement of the weight of the analyte that is equivalent to each mL of the standardized titrant. In such an equivalence statement, the number of significant figures in the concentration of the titrant should be understood to correspond to the number of significant figures in the weight of the analyte. Corrections to calculations based on the blank determination are to be made for all titrimetric assays where appropriate (see Titrimetry 541).
7.20. Rounding Rules
The observed or calculated values shall be rounded off to the number of decimal places that is in agreement with the limit expression. Numbers should not be rounded until the final calculations for the reportable value have been completed. Intermediate calculations (e.g., slope for linearity) may be rounded for reporting purposes, but the original (not rounded) value should be used for any additional required calculations. Acceptance criteria are fixed numbers and are not rounded.
When rounding is required, consider only one digit in the decimal place to the right of the last place in the limit expression. If this digit is smaller than 5, it is eliminated and the preceding digit is unchanged. If this digit is equal to or greater than 5, it is eliminated and the preceding digit is increased by 1.
Illustration of Rounding Numerical Values
for Comparison with Requirements
Compendial Requirement Unrounded Value Rounded Result Conforms
Assay limit 98.0% 97.96% 98.0% Yes
97.92% 97.9% No
97.95% 98.0% Yes
Assay limit 101.5% 101.55% 101.6% No
101.46% 101.5% Yes
101.45% 101.5% Yes
Limit test 0.02% 0.025% 0.03% No
0.015% 0.02% Yes
0.027% 0.03% No
Limit test 3 ppm 3.5 ppm 4 ppm No
3.4 ppm 3 ppm Yes
2.5 ppm 3 ppm Yes