Quality Assurance and Method Validation - Forensic Applications of Gas Chromatography - page 54

they do not meet the accepted criteria, the method would have to be modified
until the acceptance criteria for linearity are met.
5.6.3.2 Range
This is the interval between upper and lower concentrations of analyte in a
sample for which it has been demonstrated that analytical procedure has a
suitable level of precision, accuracy and linearity.
5.6.3.3 Accuracy
This is a measure of the difference between expectation of test result and
the accepted reference value due to systematic method and laboratory error,
or closeness of agreement of results between the true value and the value
found. The accuracy is typically established by using nine determinations
of the analyte in question (i.e., at least three replicates over a minimum of
three concentrations). Accuracy is usually expressed as a percentage and is
sometimes termed trueness.
5.6.3.4 Precision
This is the closeness of agreement between a series of measurements obtained
from multiple sampling of the same homogeneous sample under the pre-
scribed conditions.
• Repeatability expresses the precision under the same operating con-
ditions over a short period of time. (It can also be referred to as intra-
assay precision. )
• Intermediate precision expresses the within-laboratories variation.
This is established by carrying out precision tests on different days,
with different analysts, and using different instruments.
• Reproducibility expresses the precision between laboratories (col-
laborative studies are generally used, for standardisation). This is
an optional parameter that requires demonstration of lab-to-lab
variation only if multiple laboratories use the same procedure.
The reproducibility data can be obtained during method transfer
between laboratories.
5.6.3.5 Robustness
This is a measure of a method's capacity to remain unaffected by small but
deliberate variations in method parameters and provides an indication of the
method's reliability during normal usage. This may include solvent manu-
facturer, temperature, flow rate etc. Typically, the method will be assessed
against predefined acceptance criteria established in the standard operating
procedure by the company and/or by the accrediting body.