3.5 Analytical Chemical Standards
129
that the result assessed is acceptably accurate and precise. There are, however,
more rigorous chemometric methods available for comparing results.
Using a pure substance (an RM or CRM) not subjected to the whole but only
part of the CMP, and a single, treated aliquot of the standard sample to obtain
several portions for insertion into the measuring instrument, are two frequently made mistakes in evaluating CMPs; the results will obviously be spurious as
they will be based on incomplete information.
The quantitative evaluation of a laboratory involves examining the results it
produces by using suitable RMs or CRMS to implement specific CMPs. Control
graphs (internal evaluation) and interlaboratory exercises (proficiency testing)
are two typical approaches to the problem (see Box 3.15).
__ Box 3. 15
The role of standards in assessing the quality of an analytical laboratory
Standards can be used in three different ways to evaluate the performance of a laboratory
depending on the type of personnel engaged in the evaluation - in any case, the analytical
process will always be cond ucted by laboratory staff.
Internal evaluation: This is carried out by laboratory personnel.
Example: Control graphs, which can be constructed by using a CRM (expensive) or an
internal reference material (IRM) prepared by the laboratory itself. The CRM (or IRM) is subjected to the whole analytical sequence, under reproducible conditions, and the statistica l
parameters that allow calculation of
_
s
X=r -
rn
are obtained. Next, the control graph is constructed between two limits:
5
1) WARNING ±2rn
+l~
.rn
5
2) ACTION ± 3 rn
•
•
+2~
.rn
• •
Xf - - - - -- - - -
-22.rn
-2 2•
•
n
Batches (Days)
The same sample (CRM or IRM) in each batch is subjected to the CM? each day and the result
obtained is plotted on the graph .
Mixed (internal and external) evaluation. This is carried out by the Quality Management
Department of the parent body, which submits samples (blind or otherwise) to the laboratory
for delivery of specific results.
129
that the result assessed is acceptably accurate and precise. There are, however,
more rigorous chemometric methods available for comparing results.
Using a pure substance (an RM or CRM) not subjected to the whole but only
part of the CMP, and a single, treated aliquot of the standard sample to obtain
several portions for insertion into the measuring instrument, are two frequently made mistakes in evaluating CMPs; the results will obviously be spurious as
they will be based on incomplete information.
The quantitative evaluation of a laboratory involves examining the results it
produces by using suitable RMs or CRMS to implement specific CMPs. Control
graphs (internal evaluation) and interlaboratory exercises (proficiency testing)
are two typical approaches to the problem (see Box 3.15).
__ Box 3. 15
The role of standards in assessing the quality of an analytical laboratory
Standards can be used in three different ways to evaluate the performance of a laboratory
depending on the type of personnel engaged in the evaluation - in any case, the analytical
process will always be cond ucted by laboratory staff.
Internal evaluation: This is carried out by laboratory personnel.
Example: Control graphs, which can be constructed by using a CRM (expensive) or an
internal reference material (IRM) prepared by the laboratory itself. The CRM (or IRM) is subjected to the whole analytical sequence, under reproducible conditions, and the statistica l
parameters that allow calculation of
_
s
X=r -
rn
are obtained. Next, the control graph is constructed between two limits:
5
1) WARNING ±2rn
+l~
.rn
5
2) ACTION ± 3 rn
•
•
+2~
.rn
• •
Xf - - - - -- - - -
-22.rn
-2 2•
•
n
Batches (Days)
The same sample (CRM or IRM) in each batch is subjected to the CM? each day and the result
obtained is plotted on the graph .
Mixed (internal and external) evaluation. This is carried out by the Quality Management
Department of the parent body, which submits samples (blind or otherwise) to the laboratory
for delivery of specific results.