Some definitions for terms used in Analytical
Chemistry* (cont)
Replicates: Samples taken from
the same object that are carried through the same analytical procedures
to test for the reproducibility and/or repeatability of the analytical
procedures. Replication can start at many points within the analytical
procedure.
Precision: The closeness of data
to each other.
Repeatability: A measure of the
precision of data all collected at the same time using the same
laboratory facilities.
Reproducibility: A measure of
the precision of data collected at different times and possibly
using different facilities, equipment, chemicals, etc.
Accuracy: The closeness of data
to the true or accepted value.
Systematic or determinate errors:
Errors that result from procedural or instrumental sources that
can normally be detected and subsequently avoided. Such errors
can be positive or negative (but not both from any one source)
and affect the accuracy of the data.
Random or indeterminate errors:
Errors resulting from the inherent limitations of the measurement
procedure which cannot be avoided (but can possibly be reduced).
Such errors, which from each source can be either positive or
negative, affect the precision of the data.
Gross errors: Mistakes made by
the laboratory personnel.
Standard Reference Material (SRM):
A material, purchased from a reputable supplier, which has been
analysed for selected analytes by several laboratories and by
several methods and whose composition has been agreed upon, quantified
(concentrations plus precisions) and documented. The material
is supplied with a certificate stating the concentrations and
precisions and the analytical methods used to determine them.
SRMs are used to test for the accuracy of analytical methods.
In-house Reference Material: A
material produced by a laboratory and analysed by it along with
batches of samples so as to test for the repeatability and reproducibility
(precision) of its analytical methods.
Analytical Method Validation: Confirmation
and provision of objective evidence that the defined analytical
method can be performed satisfactorily using existing laboratory
conditions (personnel, equipment, chemicals, …) and that
all requirements for its specific intended use or application
have been fulfilled.
Standard Method: An analytical
method that has been shown by several analysts and analytical
laboratories to produce reliable results when applied correctly
and has been accepted by a professional analytical organization
as an appropriate method for its defined use.
Quality Assurance: Documented procedures
in place within an analytical laboratory that define how the laboratory’s
work is to be conducted so as to be confident that the obtained
data are of the required quality. QA consists of quality control
and quality assessment activities.
Quality Control: The practices
and procedures that lead to the achievement of quality analytical
data (suitable facilities, staff competence and training, good
laboratory practices, standard operating and reporting procedures).
Quality Assessment: The practices
and the data generated by them that illustrate that the QC activities
have been effected and that the data generated are of the quality
required (SRMs, spiking, replicates, inter-laboratory comparisons,
control charts, auditing, statistical analyses).
Quality: The ability of the qualitative
(analyte identification) and quantitative (accuracy, precision)
data to satisfy the requirements of their purpose.
The QA/QC programme: The part of
the laboratory management system that focuses on the quality of
the data generated by the laboratory.
Laboratory Quality Management System:
The operations or processes of the laboratory which define its
policies and objectives and the manner in which they are implemented
to ensure that the objectives are met.
* see also Glossary in Skoog West and Holler,
Fundamentals of Analytical Chemistry, 7th Edition
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