110
7 Validation of the Measurement Procedure
Table 7.10 How to evaluate detection limit: recommendation and examples
Kind of sample
How to proceed*
Blank for the matrix-free standards (only
solvent and reagents used for the preparation of
matrix free standards)
For 10 independently prepared blanks, perform
10 repetitive measurements
Calculate the mean value and the standard
deviation of the mean
Procedural blank (as above + all reagents used
for the test samples preparation; execute the
entire analytical process)
For 10 independently prepared procedural
blanks, perform 10 repetitive measurements
Calculate mean value and standard deviation of
the mean
Test samples with low but above detection
limit content of analyte
For 10 independently prepared test
sub-samples, perform 10 repetitive
measurements
Calculate the mean value and standard
deviation of the mean
*The recommended number of repetitive values allows the use of sound statistical evaluation.
However, one should be aware that there are situations when this is not possible due to the lack of
a sufficient amount of sample or the high cost of a single measurement
7.20 The Limit of Quantitation
Limit of quantitation (LoQ) indicates the lowest concentration/content of an analyte
that can be determined with the accepted uncertainty, using a given measurement
procedure. The LoQ is most commonly calculated as six or ten times the standard
deviation for a blank sample or a sample containing a low but above LoQ concentration of the analyte. The numerical value of LoQ has the dimension of the
concentration/content of the analyte.
There are several methods used for the calculation of LoQ; it can be calculated
as a sum of average signal for the blank and six or ten standard deviation or can be
calculated from the slope of the calibration curve, so the detection limit is calculated
as six or ten of s/b, where b is the slope of the graph.
The limit of quantitation: perform measurements as described for limit of
detection.
7.21 Robustness
One of the important features of validation is the robustness of the analytical procedure, meaning the stability of analytical results under the minor deviation in the
procedure or environmental conditions. The robustness is usually evaluated for the
7 Validation of the Measurement Procedure
Table 7.10 How to evaluate detection limit: recommendation and examples
Kind of sample
How to proceed*
Blank for the matrix-free standards (only
solvent and reagents used for the preparation of
matrix free standards)
For 10 independently prepared blanks, perform
10 repetitive measurements
Calculate the mean value and the standard
deviation of the mean
Procedural blank (as above + all reagents used
for the test samples preparation; execute the
entire analytical process)
For 10 independently prepared procedural
blanks, perform 10 repetitive measurements
Calculate mean value and standard deviation of
the mean
Test samples with low but above detection
limit content of analyte
For 10 independently prepared test
sub-samples, perform 10 repetitive
measurements
Calculate the mean value and standard
deviation of the mean
*The recommended number of repetitive values allows the use of sound statistical evaluation.
However, one should be aware that there are situations when this is not possible due to the lack of
a sufficient amount of sample or the high cost of a single measurement
7.20 The Limit of Quantitation
Limit of quantitation (LoQ) indicates the lowest concentration/content of an analyte
that can be determined with the accepted uncertainty, using a given measurement
procedure. The LoQ is most commonly calculated as six or ten times the standard
deviation for a blank sample or a sample containing a low but above LoQ concentration of the analyte. The numerical value of LoQ has the dimension of the
concentration/content of the analyte.
There are several methods used for the calculation of LoQ; it can be calculated
as a sum of average signal for the blank and six or ten standard deviation or can be
calculated from the slope of the calibration curve, so the detection limit is calculated
as six or ten of s/b, where b is the slope of the graph.
The limit of quantitation: perform measurements as described for limit of
detection.
7.21 Robustness
One of the important features of validation is the robustness of the analytical procedure, meaning the stability of analytical results under the minor deviation in the
procedure or environmental conditions. The robustness is usually evaluated for the