Chapter 5 Flashcards
The degree to which the data produced by a measurement process
enables a user to make sound decisions for a stated purpose
The cost of producing data can be reduced by selecting analytical
methods that generate data in accordance with the stated
objectives of carrying out the analysis or test
FITNESS FOR PURPOSE
▪ Staff competence (training)
▪ Matrix interferences
▪ Contamination of sample and/or
equipment
▪ Inappropriate sampling protocol/ sample
pre-treatment (needs to be agreed with
your client)
Causes of “unfit for purpose” results
(water analysis)
A method’s performance is defined by a number of important
individual characteristics. There are:
Sensitivity Precision
Accuracy Limit of Detection (LoD)
Limit of Determination Bias
Selectivity Linear Range
Dynamic range
“ THE PROCESS OF
PROVIDING
DOCUMENTED
EVIDENCE THAT
SOMETHING DOES
WHAT IT IS INTENDED
TO DO”
* the process of demonstrating or confirming the
performance characteristicsof a method of analysis.
* A process of evaluating method performance and
demonstrating that it meets a particular
requirement.
* applies to a specific operator, laboratory, and
equipment utilizing the method over a reasonab
VALIDATION
- Is the confirmation by examination and the provision of
objective evidence that the particular requirements for
the a specific intended use are fulfilled (ISO/IEC 17025:2005 cl. 5.4.5.1) - A process of evaluating method performance and
demonstrating that it meets a particular requirement
(agreed between lab and customer) - In essence, it is knowing what your method is capable of
delivering, particularly at low concentrations
METHOD VALIDATION
What does it require a method to be capable of?
➢Performance characteristics should be
adequate to meet the needs of the user/
regulatory agency as appropriate
➢Should be specific to the analyte of interest
(interferences known)
➢Determining actual performance and not just
that stated by the supplier/ manufacturer
Why Do Method Validation?
✓To minimize analytical and instrumental errors
✓To give reliable and reproducible results in
accordance with the given specifications of the test
method
✓To ensure the quality of the test results
✓To meet accreditation requirement
✓Objective evidence for defense against challenges
✓To be assured of the correctness of results
When should methods be validated?
✓ New method developed for a particular problem- no
previous performance history
✓ Established method revised to incorporate improvements
or extended to a new problem
✓ When quality control indicates an established method is
changing with time
✓ Established method used in a different laboratory, or with
different analysts or different instrumentation
✓ To demonstrate equivalence between two methods, e.g., a
new method and a standard method
Method validation- carried out on:
➢ the whole method including sample preparation and
actual determination of the analyte
➢ over whole range of concentrations where the
method will be applied
➢ over whole range of matrices where the method will
be applied
Strictly speaking, validation should refer to an analytical
system rather than an analytical method, the analytical
system is comprised of:
a defined method protocol
a defined concentration range for the analyte
a specified type of material
a method is validated with participation
of a number of laboratories
a method is validated in a laboratory
before use to prove that the method
performs adequately.
Collaborative validation
Internal validation
How to do validation of an analytical
method:
Use of spiked samples
Use of Certified Reference
Materials
Comparison of the performance
of a method with a reference
method whose performance has
been well-establishe
Selectivity Extent to which a method can determine
a particular analyte in a complex mixture
without interference from other
components
Parameters for Validation
1. Accuracy
2. Precision
3. Selectivity (Specificity)
4. Limit of Detection (LOD)
5. Limit of Quantitation (LOQ)
6. Linearity Range
7. Robustness (Ruggedness)
The lowest amount of analyte in a
sample that can be detected, but not
necessarily quantitated as an exact
value
The lowest amount of analyte in a
sample that can be quantitated with
suitable accuracy and precision
Detection
Limit
Limit of
Quantitation
% RECOVERY
(Spiked value – unspiked value) X 100
(theoretical value)
Mean of the results (Observed result) X 100
Target value (Expected result
The range of concentrations of analyte
for which the procedure provides test
results that are in direct correlation to
the amount of analyte in the sample
Measure of a method’s capacity to
remain unaffected by small but
deliberate variations in method
parameters (temp, extraction time,
batch of reagents)
Linearity
Robustness
(Ruggedness)
obtained when the analysis is performed in
one laboratory by one analyst using the same
equipment at the same day
expresses within laboratories’ variation,
different days, different analysts, different
equipment, etc.
represents the precision obtained
between different laboratories
(collaborative studies, usually
applied to standardization and
methodology)
REPEATABILITY (intra-day precision)
INTERMEDIATE PRECISION (interday precision
REPRODUCIBILITY
(between laboratories
precision)
Limit of Detection (LoD)
It is the smallest amount or concentration of an analyte
that can be estimated with acceptable reliability.
An alternative definition of the limit of detection and
limit of determination is based upon the variability of
the blank.
The blank value plus three times the standard
deviation of the blank is taken as the detection limit
(LOD) and the blank value plus 10 times the standard
deviation of the blank is taken as the determination
limit (LOQ)
LINEARITY includes:
* Slope of the line
* Intercept
* Correlation coefficient data
( r > 0.9 over the working
range)
The interval between the upper and lower
concentrations of analyte in the sample for
which it has been demonstrated that the
analytical procedure has a suitable level of
precision, accuracy and linearity.
Normally derived from linearity studies
RANGE
property of the result of a measurement or the value of a
standard whereby it can be related to stated
references, usually national and international standards,
through an UNBROKEN CHAIN OF COMPARISONS all
having stated uncertainties.
TRACEABILITY
the ability to discriminate between the analyte or species
to be determined and other materials in the test sample
the ability to assess the analyte in the presence of
components that may be expected to be present in the
sample such as degradation products
Need to be aware of potential interferences… especially for inhouse developed methods. These are usually well documented
for “standard” methods
Selectivity
Specificity
- the degree of reproducibility of results obtained
under a variety of conditions, such as different
laboratories, analysts, instruments, environmental
conditions, operators and materials (U.S. Pharmacoepia) - a measure of reproducibility of test results under
normal, expected operational conditions from
laboratory to laboratory and from analyst to analyst.
Ruggedness
Degree of reproducibility of test results under a variety of
conditions such as
* Different Analysts
* Different Laboratories
* Different Instruments
* Different Reagents
* Different Days
RUGGEDNESS
Measure of the capacity to remain
unaffected by small (deliberate) variations
in method parameters
examines the effect that operational parameters have
on the analysis results.
If the influence of the parameter is within a previously
specified tolerance, the parameter is said to be within
the method’s robustness range.
Obtaining data on these effects helps to assess whether
a method needs to be revalidated when one or more
parameters are changed, for example, to compensate
for Flame photometer performance over time.
ROBUSTNESS
General requirements
* Qualified and calibrated instruments
* Documented methods
* Reliable reference standards
* Qualified analysts
* Sample integrity
VALIDATION
TRACEABILITY
MEASUREMENT
UNCERTAINTY
The Famous Trio
