ASTM E1914-98
(Practice)Standard Practice for Use of Terms Relating to the Development and Evaluation of Methods for Chemical Analysis
Standard Practice for Use of Terms Relating to the Development and Evaluation of Methods for Chemical Analysis
SCOPE
1.1 This document covers terms and concepts used in developing and evaluating the performance of methods for determining chemical composition. Although useful with many types of methods, they are dealt with in this document in the context of chemical analysis of metals and related materials.
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
Designation:E1914–98
Standard Practice for
Use of Terms Relating to the Development and Evaluation
of Methods for Chemical Analysis
This standard is issued under the fixed designation E 1914; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
ASTM methods for determining the chemical composition of materials usually are developed in
four stages: (1) experimental development of procedures and techniques, (2) translation of research
into text suitable for analysts (in ASTM format), (3) demonstration of performance in an interlabo-
ratory study (ILS), and (4) acceptance as a method published for use in laboratories. Details of the
development processes may be complex, but the common concepts and terms needed to discuss them
are relatively simple. The concepts must be carefully defined and terms selected to represent them
unambiguously in the intended contexts.
Alist of terms and definitions does not guarantee clear communication. Many terms have different
common and technical meanings while representing different concepts when used in various contexts.
The use of important terms and concepts in the context of methods of chemical analysis is illustrated
by descriptions and by examples to help task group and subcommittee members communicate clearly.
1. Scope 3.1.2 analyte, n—in methods of chemical analysis, the
component determined by a method.
1.1 This document covers terms and concepts used in
3.1.3 matrix, n—in methods of chemical analysis, all com-
developing and evaluating the performance of methods for
ponents in a material except the analyte.
determiningchemicalcomposition.Althoughusefulwithmany
3.1.4 method, n—instructions used to produce a numerical
types of methods, they are dealt with in this document in the
result which are detailed in a document also referred to as “the
context of chemical analysis of metals and related materials.
method.”
2. Referenced Documents 3.1.5 precision, n—of methods of chemical analysis,a
characteristic manifested by agreement among individual re-
2.1 ASTM Standards:
sults at a given analyte content.
E 135 Terminology Relating to Analytical Chemistry for
3.1.6 result, n—value representing the quantity of analyte
Metals, Ores, and Related Materials
that is obtained by applying a method one time to a test
E 1601 Practice for Conducting an Interlaboratory Study to
material.
Evaluate the Performance of an Analytical Method
3.1.7 sample, n—in methods of chemical analysis, a portion
E 1763 Guide for Interpretation and Use of Results from
of a material selected and processed to render its composition
Interlaboratory Testing of Chemical Analysis Methods
representative of the composition of the whole. (Contrast
3. Terminology
specimen.)
3.1.8 specimen, n—in methods of chemical analysis, a piece
3.1 Definitions Relating to Analytical Methods:
of material selected to be typical of the whole under the
3.1.1 accuracy, n—of methods of chemical analysis,a
assumption that the whole is composed of pieces of similar
characteristic manifested by agreement between average re-
composition. (Contrast sample.)
sults and true analyte contents.
3.2 Definitions Referring to Statistics:
3.2.1 b-value, n—in statistics, the difference between the
This practice is under the jurisdiction of ASTM Committee E-1 on Analytical
mean of a set of results on a material and its accepted reference
Chemistry for Metals, Ores and Related Materials and is the direct responsibility of
value. (Compare error.)
Subcommittee E01.22 on Statistics and Quality Control.
Current edition approved May 10, 1998. Published July 1998. Originally
3.2.2 between-laboratory standard deviation, s , n—the
R
published as E 1914–97. Last previous edition E 1914–97.
standard deviation of results obtained on the same material in
Annual Book of ASTM Standards, Vol 03.05.
different laboratories (Synonym: reproducibility).
Annual Book of ASTM Standards, Vol 03.06.
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
E1914–98
3.2.3 detection limit, n—for an analytical instrument, the 4.2.1 Accuracy—When a method is applied to materials
minimum quantity of analyte expected to yield a response containing various quantities of analyte, it has the property of
greater than zero. accuracy if results equal the numerical values of the analyte
3.2.4 error, n—of a result, the difference between a result contents. This property relates solely to a method’s average
obtained on a material and its accepted reference value. response at each analyte level, ignoring random statistical
(Compare b-value.) fluctuations of individual results. Actual methods are never
3.2.5 interlaboratory study, ILS, n—a study undertaken to known to be perfectly accurate and this term is usually used in
demonstrate the precision and accuracy of a method. arelativesensetocomparedifferentmethodsorthebehaviorof
3.2.6 minimum standard deviation, s , n—the standard a single method under different conditions.
M
deviationofresultsonatestmaterialobtainedunderconditions
4.2.2 Precision—When a method is applied a number of
of minimum variability.
times to a homogeneous sample, it has the property of
3.2.7 repeatability, n—see within-laboratory standard de-
precision if the result is always the same. This property relates
viation.
solely to time-related variations in the response of a method
3.2.8 repeatability standard deviation, n—see within-
and ignores systematic (averaged) differences between results
laboratory standard deviation.
and analyte content that may occur at various analyte levels.
3.2.9 repeatability index, r, n—an estimate of the maximum
Actual methods are never perfectly precise and this term is
difference expected for results on the same test material on
usuallyusedinarelativesensetocomparedifferentmethodsor
different days in the same laboratory, a difference not expected
the behavior of a single method under different conditions.
to be exceeded an average of more than once in 20 compari-
4.3 Written methods must satisfy two criteria: (1) they shall
sons (95 % probability.)
have the form and editorial style specified in the latest edition
3.2.10 reproducibility, n—see between-laboratory standard
of Form and Style for ASTM Standards, and (2) the technical
deviation.
contentshallbestatedintermsthatconveyprecisemeaningsto
3.2.11 reproducibility standard deviation, n—see between-
laboratory personnel using the method. The language used in
laboratory standard deviation.
the method must direct users (who may not have the same
3.2.12 reproducibility index, R, n—an estimate of the maxi-
technical knowledge or experience as the developer) to repeat
mum difference expected for results on the same material in
the procedural steps in the manner that produced satisfactory
two laboratories, a difference not expected to be exceeded an
results in the development laboratory. Unless the method
average of more than once in 20 comparisons (95 % probabil-
conveys this information, users will not achieve the potential
ity.)
accuracy and precision of the method.
3.2.13 set, n—of results, a group of results collected under
4.4 The ILS demonstrates the performance of the method in
specified conditions for statistical analysis.
a group of laboratories typical of those expected to use the
3.2.14 standard deviation, between-laboratory, n—see
method; whereas the accuracy and precision of the analytical
between-laboratory standard deviation.
techniques and procedures employed are defined by the statis-
3.2.15 standard deviation, minimum, n—see minimum stan-
tics obtained in the development laboratory. ILS statistics are
dard deviation.
influenced by three additional factors: (1) the success of the
3.2.16 standard deviation, within-laboratory, n—see
translationoftheresearchfindingsintothemethodtestedinthe
within-laboratory standard deviation.
ILS, (2) the care with which the ILS experimental design was
3.2.17 within-laboratory standard deviation, s , n—the
r
followed, and (3) the quality of the test materials employed
standard deviation of results collected on the same material in
during the ILS.
the same laboratory on different days (Synonym: repeatabil-
4.5 The published method contains a summary of the ILS
ity).
statistics that a user may interpret, based upon the user’s own
3.3 The terms mean, standard deviation, random (as in
experience. A task group observing a relationship between the
random error), and systematic error, in their statistical senses,
method’s precision and analyte content as described in Guide
are adequately defined in Webster’s Collegiate Dictionary,
E 1763E 1763, may choose to provide more detailed descrip-
Tenth Edition.
tions of the method’s performance, for example, an equation or
table predicting approximate standard deviations at various
4. Analytical Science and Analytical Methods
analyte levels.
4.1 Analytical science deals with the development and use
of methods for determining chemical composition of materials.
5. Statistics and Statistical Methods
Chemical analysis is the application of written analytical
methods. 5.1 Statistics deals with the collection, analysis, interpreta-
4.2 Analytical method development consists of selecting tion,andpresentationofnumericaldatasets.Themathematical
chemical and physical systems that respond to a specific proceduresemployedintheseprocessesarestatisticalmethods.
analyte in a defined suite of material types. The purpose is to Statistic is a generic term for the variable represented by a
define a process that produces a physical change proportional statistical procedure, but it also refers to the numerical value
to analyte content unaffected by other sample components.The obtained when a statistical procedure is applied to a data set.
measurementsystem(instrument)yieldsanumericalresultthat For example, mean is a statistic, but the value 6 is the mean of
represents the quantity of analyte. A good analytical method {3, 5, 10}.Astatistic is definable by a
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