Examples of Measurement Uncertainty
Budgets in Analytical Chemistry
If you do not have online access to
the cited publications, please contact ivo.leito
ut.ee
Measurement
|
Complexity
of measurement
|
Elaboration
level
|
Extent
of comments
|
Description
|
Available files
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Measurement uncertainty
due to the matrix effect in LC-ESI-MS
|
High |
High |
High |
This work
(A. Kruve, K. Herodes, I. Leito. J.
AOAC International 2010, 93, 306-314) presents an empirical
approach—the matrix effect graph approach—for estimating the
uncertainty due to the matrix effect in LC-MS (with the electrospray (ESI)
ion source) analysis of pesticide residues in fruits and vegetables. At
certain time intervals (1 month), a calibration graph using extracts of
different fruits/vegetables as calibration solutions is prepared, and a
regression line is fitted through these data. These fruits/vegetables may be
either from the commodity group of the samples or from different commodity
groups. The relative residuals of the calibration point peak areas are
calculated and plotted against the measurement time – the matrix effect
graph is then obtained. The root mean square of the relative residuals is
calculated and used as the estimate of relative uncertainty of the sample
peak areas caused by the matrix effect. The matrix effect graph obtained over
fruits/vegetables from different commodity groups can also be used to
identify fruits/vegetables with extreme matrix effects. |
Full text of the article
(please contact us if you do not have online access to this article) |
Measurement uncertainty of
measurement with amperometric sensors
|
Medium |
High |
High |
This
tutorial review (I. Helm, L. Jalukse, I. Leito Sensors 2010, 10,
4430-4455) focuses on measurement uncertainty estimation in amperometric
sensors (both for liquid and gas-phase measurements). The main uncertainty
sources are reviewed and their contributions are discussed with relation to
the principles of operation of the sensors, measurement conditions and
properties of the measured samples. The discussion is illustrated by case
studies based on the two major approaches for uncertainty
evaluation–the ISO GUM modeling approach and the Nordtest
approach. This tutorial is expected to be of interest to workers in different
fields of science who use measurements with amperometric sensors and need to
evaluate the uncertainty of the obtained results but are new to the concept
of measurement uncertainty. The tutorial is also expected to be educative in
order to make measurement results more accurate. |
Full text of the article (it is an open-access
article, so the full text is freely available) |
Electron probe
microanalysis (SEM-EDS)
|
High |
High |
High |
Determination
of iron in ink writing on paper manuscripts using electron probe
microanalysis (SEM-EDS). Full information, with detailed explanations on
uncertainty sources and their quantification is available in publication K.Virro,
E.Mellikov, O.Volobujeva,
V.Sammelselg, J.Asari, L.Paama, J.Jürgens, I.Leito Microchimica Acta, published online 06.08.2007. |
|
Analysis of gold alloys
by flame-AAS
|
High |
High |
High |
Detailed example,
covering not only uncertainty estimation but also validation and establishing
traceability |
Chapter 2 in Practical Examples on Traceability,
Measurement Uncertainty and Validation in Chemistry |
Determination of calcium
in serum by spectrophotometry
|
High |
High |
High |
Detailed
example, covering not only uncertainty estimation but also validation and
establishing traceability |
Chapter 3 in Practical Examples on Traceability,
Measurement Uncertainty and Validation in Chemistry |
Determination of radium
in water by a-spectrometry
|
High |
High |
High |
Detailed
example, covering not only uncertainty estimation but also validation and
establishing traceability |
Chapter 4 in Practical Examples on Traceability,
Measurement Uncertainty and Validation in Chemistry |
Determination of polar
pesticides by liquid chromatography mass spectrometry
|
High |
High |
High |
Detailed
example, covering not only uncertainty estimation but also validation and establishing
traceability |
Chapter 5 in Practical Examples on Traceability,
Measurement Uncertainty and Validation in Chemistry |
Determination of ammonium
in water by flow analysis (CFA) and spectrometric detection
|
High |
High |
High |
Detailed
example, covering not only uncertainty estimation but also validation and
establishing traceability |
Chapter 6 in Practical Examples on Traceability,
Measurement Uncertainty and Validation in Chemistry |
Simple weighing
|
Simple |
Medium |
Medium |
Uncertainty
of simple weighing |
|
Volume of 50 ml
volumetric flask
|
Simple |
Medium |
Medium |
Uncertainty
of volume of solution contained in 50 ml volumetric flask. |
|
Volume of 10 ml pipette
|
Simple |
Medium |
Medium |
Uncertainty
of volume of solution delivered by 10 ml bulb pipette. |
|
Nonvolatile matter by gravimetry
|
Medium |
Medium |
Medium |
Routine
determination of nonvolatile matter by gravimetry.
The sample was weighed before and after drying in oven at a
specified temperature (please see the presentation ISO
GUM Uncertainty in Chemistry). |
In English: In
Estonian: |
pH measurement
|
Medium |
High |
Low |
The uncertainty
calculation for pH is available as a web application (server-based, written
in PHP). This means that calculation can be carried out immediately in the
browser and there is no need to install any software. The result can be
displayed either as a simple or as a detailed result. In the latter case the
measurement equation and detailed uncertainty budget are also displayed.
Additional information is available in the help file of the web application
and in the articles I.Leito, L.Strauss, E.Koort, V.Pihl
Accred. Qual. Assur. 2002,
7, 242-249 and E.Koort,
K.Herodes, V.Pihl, I.Leito. Anal. Bioanal. Chem. 2004,
379, 720-729. For more information
see also the PhD thesis of Eve Koort
(defended on June 20, 2006). |
In
English: |
Dissolved oxygen
concentration measurement
|
Medium |
High |
High |
This
uncertainty estimation procedure is intended for the mainstream dissolved
oxygen concentration measurement with the galvanic type of equipment. Details
can be found in the article: L.Jalukse,
I.Leito Measurement Science and technology 2007,
18, 1877-1886 and also in the PhD thesis of Lauri
Jalukse. |
In
English: |
Complexonometric titration
|
Medium |
Medium |
Medium |
Complexonometric determination (EDTA) of total hardness of water |
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Ammonium by Photometry
|
High |
High |
High |
A mainstream
measurement of NH4+ by photometry. Contains XLS import.
The corresponding SMU and XLS file must be placed in the same folder. The
method is based on ISO 7150-1:1984. This is a tricky example. After several
years of discussion and careful study we now believe that the uncertainty
estimate in this example is not underestimated if the determination is
carried out carefully and if there is no strong strong
chemical intereference. (please
see the presentation ISO
GUM Uncertainty in Chemistry). In any case, use with care! For deeper
coverage of uncertainty sources in photometric analysis see the paper L.Sooväli,
E.-I. Rõõm, A. Kütt, I. Kaljurand, I. Leito. Accred.
Qual. Assur. 2006, 11, 246-255 and the PhD thesis of Lilli Sooväli (defended on
June 20, 2006). |
In
English: |
Nitrite by Photometry
|
High |
High |
High |
Photometric
determination of nitrite using the NEDA-sulfanilamide method. For deeper coverage
of uncertainty sources in photometric analysis see the paper L.Sooväli,
E.-I. Rõõm, A. Kütt, I. Kaljurand, I. Leito. Accred.
Qual. Assur. 2006, 11, 246-255 (published online on 25.04.06) and the PhD thesis of Lilli Sooväli (defended on June 20, 2006). |
|
Butanol in acetone by GC
|
High |
High |
Medium |
Measurement
of butanol content in acetone by GC. Very small
solution volumes are used in this method and all solutions are prepared by
weighing. The largest uncertainty contributions are due to the imperfections of
integrating peaks on the chromatogram and drift of the balance, which is
mainly due to the volatility of acetone. |
In
English: |
Sorbic acid by HPLC
|
High |
Low |
Medium |
Mainstream
liquid chromatography (HPLC) method for determination of preservatives (Sorbic acid in this example). Main parameters of the
method: Isocratic elution (Acetate buffer : MeOH, 70:30), RP C18 column, UV-Vis photometric detection
at 235 nm. |
In
English: In
Estonian: |
Quality control of a
drug product by HPLC
|
High |
High |
High |
Liquid
chromatography (HPLC) determination of Simvastatin
in tablets. The method is a mainstream HPLC method with UV-Vis photometric
detection at 238 nm. Two varieties are provided: 5-point calibration and single
point calibration. This uncertainty estimation has been published in the
following paper: S.
Leito, K. Mölder, A. Künnapas,
K. Herodes, I. Leito J.
Chrom. A 2006, 1121, 55-63. |
In English: 5-point
calibration: Single-point
calibration: |
Phosphorus Content in
Feed by Photometry
|
High |
High |
High |
Measurement
uncertainty estimation example on photometric determination of phosphorus in
feed using the molybdatovanadate reagent. The
largest uncertainty contribution is due to the sample preparation. For deeper
coverage of measurement uncertainty sources in photometric analysis see the
following paper: L.Sooväli, E.-I. Rõõm, A. Kütt, I. Kaljurand, I. Leito. Accred. Qual.Assur.
2006, 11, 246-255. |
|
Lead in Soil by AAS
|
High |
High |
High |
Measurement
of Lead content of soil by graphite furnace atomic absorption spectrometry. |
Comments
Files
|
The
uncertainty budgets are available in files of following types:
Most of
the files are in English. In some cases files in other languages are also
available. |
Complexity, elaboration
level and extent of comments
|
The
“complexity of measurement” refers to the intrinsic
complexity of the measurement itself (the more there are operations and
measurements, the higher the complexity) The
“elaboration level” refers to the extent to which various
uncertainty sources have been identified and taken into account. Low
elaboration level does not necessarily mean that there are important
uncertainty sources that have not been taken into account: instead it usually
means that here and there several different uncertainty sources have been
grouped. For example, instead of identifying all the repeatability
contributions, they may have been grouped to give the general repeatability
of the procedure that can be estimated from overall repeatability studies. The
“extent of comments”: indicates how much comment is added
to the file to increase the readability by users. |
Estimates of uncertainty
components
|
Generally
the uncertainty components have been estimated according to the particular
equipment and working practices used in our lab. In some cases reasonable
estimates (based on experience or literature data) are used. The obtained
uncertainty values have proved to be adequate for those conditions. However,
these uncertainty values are not directly applicable to results obtained in
other laboratories using different instrumentation and working practices
(even if exactly the same measurement procedures are used) because they are
dependent on the conditions. These values should thus be used for guidance
only. The users of the examples are strongly recommended to do their own
estimation of uncertainty components based on their own equipment and working
practices and then insert the uncertainty data into the files from this page.
Also, it is strongly recommended to see the presentations ISO
GUM Uncertainty in Chemistry (presented in 2004 in Stockholm on MiC teaching workshop) and Different Approaches to Estimation
of Measurement Uncertainty in Analytical Chemistry (presented in
2010 in Tel Aviv at IsrAnalytica XIII). |
Feedback
|
Any
feedback (comments, error reports, criticism) is most welcome! The feedback
should be sent to Ivo Leito (ivo.leito[at]ut.ee, +372
5 184 176, University of Tartu, Testing Centre, Ravila
14a, 50411 Tartu, Estonia). You can also submit your own examples for posting
on this site. The examples will be examined and then decision will be made,
whether they are suitable. Preference will be given to detailed and fully
commented examples. |
Other topics
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See also
other research topics |
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This page has been created at University of Tartu
with support from the EC JRC Institute for Reference Materials and
Measurements in the framework of the TrainMiC programme. |
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Last edited: Sunday, 13-Nov-2011 23:33:13 EET