Chemistry Reference
In-Depth Information
of which can lead to a decreased number of plates or a loss in efficiency. It is a
good idea, prior to setting specifications, or during column use, to be aware of these
effects and to take them into account so that chromatographic issues are not misin-
terpreted as product or sample issues.
4.3.6 l
IneArIty
And
r
Ange
Linearity is the ability of the method to provide test results that are directly propor-
tional to analyte concentration within a given range. Linearity generally is reported
as the variance of the slope of the regression line (e.g., standard error from an Excel
regression analysis). Range is the interval between the upper and lower concen-
trations of analyte (inclusive) that have been demonstrated to be determined with
acceptable precision, accuracy, and linearity using the method as written. The range
is normally expressed in the same units as the test results obtained by the method
(e.g., ng/mL). Guidelines specify that a minimum of five concentration levels be used
to determine the range and linearity, along with certain minimum specified ranges
depending upon the type of method. Table 4.6 summarizes typical minimum ranges
specified by the guidelines. Data to be reported generally includes the equation for
the calibration curve line, the coefficient of determination (
r
2
), and the curve itself,
and the residuals as illustrated in Figures 4.6 and 4.7, respectively.
tAble 4.6
example minimum recommended ranges
type of method
recommended minimum range
Assay
80%-120% of the target concentration
Impurities
From the reporting level of each impurity, to 120% of the specification
Content uniformity
70%-130% of the test or target concentration
Dissolution
±20% over the specified range of the dissolution test
Note:
For toxic or more potent impurities, the range should be commensurate with the controlled level.
1.5×10
6
Y = 5.39e+004 + 3.26e+004
R
2
= 0.999478
1.0×10
6
5.0×10
5
0.0
0.00
5.00
10.00
15.00
Amount
20.00
25.00
FIgure 4.6
Effect of column efficiency on DL and QL determinations. The higher-
efficiency column used to generate the chromatogram in Figure results in a higher S/N than
the lower-efficiency column used to generate the chromatogram in Figure.
