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
|
Measurement uncertainty
due to the matrix effect in LC-ESI-MS (LC-ESI-MSMS)
|
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 (LC-MS)
|
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 |
|
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
|
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: Tuesday, 22-May-2012 05:58:36 EEST