L A B O R A T O R Y M A N A G E M E N T
■
© A O A C I N T E R N A T I O N A L
■
N O V E M B E R / D E C E M B E R 2 0 1 4
24
the likeliness that a validated method
will provide equivalent results in the
hands of multiple independently operat-
ing users at different laboratories. It
is sometimes assumed that validated
methods can be implemented “straight
off the shelf” and achieve the published
performance data straight away by
whomever uses the method. In truth,
the analytical performance of any given
method, validated or not, is not known
until the method has been verified on-
site where the method will be used with
the existing equipment and analysts.
It is reasonable to expect that a vali-
dated method with lower RSD
(R)
should
perform better than a method with an
unknown RSD
(R)
. A collaborative study,
although it involves multiple laborato-
ries and many factors, does not include
all potential sources of variation. So a
laboratory must verify a new method
to ensure that there are no factors in
its laboratory or with its samples that
negatively impact the behavior of the
new method.
On-site verification became a
requirement for laboratory accredita-
tion after the adoption of ISO 25, a
precursor to ISO 17025, in 1999. Today,
all accredited laboratories have adopted
the practice of on-site verification.
AOAC maintains a method verification
guideline on its website that describes
how to meet the method verification
requirements of ISO 17025 (20).
With the prevalence of on-site veri-
fication of analytical methods, one must
wonder if the role of the collaborative
study is still as relevant as it once was
30 years ago. Perhaps it is time for
another paradigm shift that embraces
measurement uncertainty and the on-
site verification process.
Conclusions and Recommendations
Collaborative studies are not
always practical. There are several
alternative procedures that might
be used to estimate reproducibility
that include use of proficiency test-
ing data, intermediate reproducibility,
and measurement uncertainty.
PT data has been found to be equiv-
alent to collaborative study data, and a
properly designed PT program could be
used to determine reproducibility with-
out interfering with the principles of PT.
Measurement uncertainty is a widely
used convention to describe the pos-
sible range of results represented by an
analytical result. All accredited labora-
tories are required to determine and,
where applicable, report measurement
uncertainty. Measurement uncertainty
can be considered equivalent in concept
to RSD
(R)
. ISO has provided guidance for
using single-laboratory data to deter-
mine the measurement uncertainty of a
method. Weitzel and others have dem-
onstrated that single-laboratory data
can be used to determine measurement
uncertainty with proper planning.
On-site verification is a common
practice for accredited laboratories. It is
widely understood that a method cannot
be used “out of the box” based on its
RSD
(R)
, but must be verified. The practice
of on-site verification reduces the reli-
ance on reproducibility results [RSD
(R)
].
—Scott Coates and
Deborah McKenzie
Contributing Writers
—M.L.J. Weitzel
Contributing Writer
Independent Consultant
References
(1) AOAC INTERNATIONAL, Guidelines for
Collaborative Study Procedure to Validate
Characteristics of a Method of Analysis, J.
Assoc. Off. Anal. Chem.
72,
694–704(1989)
(2) Pure and Applied Chemistry
67
(2),
331-333(1995)
(3) J. AOAC Int.
78
(5), 143A–160A(1995)
(4) AOAC INTERNATIONAL (July 2011)
“Alternative Pathway to Official First Action
Method Status Requirements”
(5) AOAC INTERNATIONAL (May/June 2011)
“AOAC Implements Alternative Pathway
to First Action Status,” Inside Laboratory
Management, Vol. 15, No. 3, pp 22-24
(6) Youden, W., & Steiner, E. (1975) Statistical
Manual of the AOAC, AOAC INTERNATIONAL
(reprinted 1987)
(7) Weitzel, M.L.J., & Johnson, W.M. (2012)
“Using Target Measurement Uncertainty to
Determine Fitness-for-Purpose,” Accred.
Qual. Assur. doi: 10.1007/s00769-012-0899-x
(8) International Vocabulary of Metrology–
Basic and General Concepts and Associated
Terms (VIM) (2008) JCGM 200:2008, Joint
Committee for Guides in Metrology, www.
bipm.org
(9) Ellison, S.L.R., Thompson, M., Westwood,
D., & Wood, R. (2010) “The Role of Proficiency
Testing in Method Validation,” Accred. Qual.
Assur.
15,
73-79
(10) Thompson, M., & Lowthian, P.J. (1995)
Analysts
120,
271-272
(11) Guidelines for the Assessment of the
Competence of Testing Laboratories Involved
in the Import and Export Control of Food
(CAC/GL 27-1997)
(12) Ellison, S.L.R., Rösslein, M., & Williams,
A. (Eds) (2000) Eurachem/CITAC Guide:
Quantifying Uncertainty in Analytical
Measurement, 2nd Ed., ISBN 0 948926 15 5,
(13) Measurement Uncertainty Revisited:
Alternative Approaches to Uncertainty
Evaluation (2007) Eurolab 2007/1, www.
eurolab.org
(14) Guidance for the Use of Repeatability,
Reproducibility and Trueness Estimates in
Measurement Uncertainty Estimation (2010)
ISO 21748:2010, International Organization
for Standardization (ISO), Geneva,
Switzerland
(15) Horwitz, W. (1998) “Uncertainty—A
Chemist’s View,” J. AOAC Int.
81,
785-794
(16) Federal Agency for the Safety of the
Food Chain (Belgium) (November 2008)
Estimating Measurement Uncertainty in
Quantitative Chemistry Analysis,
.
favv.be/laboratories/approvedlaboratories/
officecircular/_documents/03-11-2008-proce-
dureENLAB-P-508-Measurement-uncertainty-
v.01_en.pdf
(17) Weitzel, M.L.J. (2012) “The Estimation
and Use of Measurement Uncertainty for a
Drug Substance Test Procedure Validated
According to USP,” Accred. Qual. Assur.
17,
139-146
(18) Weitzel, M.L.J. (January 10, 2012)
personal communication
(19) Barwick, V., & Ellison, S. (2000) “The
Evaluation of Measurement Uncertainty from
Method Validation Studies,” Accred. Qual.
Assur.
5,
47-53
(20) How to Meet ISO 17025 Requirements
for Method Verification (2007) AOAC
INTERNATIONAL,
.
org/iMIS15_Prod/AOAC/PUBS/GAR/
AOAC_Member/PUBSCF/GARCF/GUIDE_A.
aspx?hkey=965b2306-1083-404c-b41a-
bf159216a610
■
Alternative Approaches to the Traditional Collaborative Study
84
