7.13 Selected Parameters of Validation of the Measurement Procedure
105
7.13 Selected Parameters of Validation of the Measurement
Procedure
This chapter describes in detail how to evaluate the characteristic parameters of the
measuring procedure.
Warning! In this section, information on the evaluation of the individual parameters must be considered as guidelines rather than as definite recommendations.
For example, in many situations, the use of “at least 10 repetitions” is not
possible and/or economically justified. Common sense should be utilized.
7.14 Selectivity and Specificity
Selectivity and specificity of the measurement procedure are terms often used as
synonymous. Yet these terms are not synonymous; selectivity is the degree to which
other substances present in the sample affect the analytical signal, while specificity is
the ability to measure only the substance to be determined, without any interference
from other components. The concept of selectivity is related to the assessment of how
the received analytical signal is exclusively due to the presence of the analyte, and not
to the presence of other substances with similar physical or chemical characteristics.
Selectivity characterizes, therefore, the degree of disturbance of the measured
signal due to other substances present in the sample or other kinds of interferences.
It should be stressed that the most difficult situation occurs if the effect of potential
interfering substances is unknown.
Selectivity is a qualitative parameter, which may be graded or expressed descriptively; for example, it may be specified that the determination of selenium by ICP
MS, based on the measurement signal for the most abundant stable isotope
80 Se, is
selective in the presence of zwitterion argon containing an isotope of argon of mass
40 amu (
80 Ar 2 ).
Assessment of selectivity
– Testing of the matrix-free samples and those contains interfering substances;
– Evaluation of recovery for CRMs;
– Comparing the results for different analytical methods.
105
7.13 Selected Parameters of Validation of the Measurement
Procedure
This chapter describes in detail how to evaluate the characteristic parameters of the
measuring procedure.
Warning! In this section, information on the evaluation of the individual parameters must be considered as guidelines rather than as definite recommendations.
For example, in many situations, the use of “at least 10 repetitions” is not
possible and/or economically justified. Common sense should be utilized.
7.14 Selectivity and Specificity
Selectivity and specificity of the measurement procedure are terms often used as
synonymous. Yet these terms are not synonymous; selectivity is the degree to which
other substances present in the sample affect the analytical signal, while specificity is
the ability to measure only the substance to be determined, without any interference
from other components. The concept of selectivity is related to the assessment of how
the received analytical signal is exclusively due to the presence of the analyte, and not
to the presence of other substances with similar physical or chemical characteristics.
Selectivity characterizes, therefore, the degree of disturbance of the measured
signal due to other substances present in the sample or other kinds of interferences.
It should be stressed that the most difficult situation occurs if the effect of potential
interfering substances is unknown.
Selectivity is a qualitative parameter, which may be graded or expressed descriptively; for example, it may be specified that the determination of selenium by ICP
MS, based on the measurement signal for the most abundant stable isotope
80 Se, is
selective in the presence of zwitterion argon containing an isotope of argon of mass
40 amu (
80 Ar 2 ).
Assessment of selectivity
– Testing of the matrix-free samples and those contains interfering substances;
– Evaluation of recovery for CRMs;
– Comparing the results for different analytical methods.