ASTM D4127-12
(Terminology)Standard Terminology Used with Ion-Selective Electrodes
Standard Terminology Used with Ion-Selective Electrodes
SCOPE
1.1 This terminology covers those terms recommended by the International Union of Pure and Applied Chemistry (IUPAC),2 and is intended to provide guidance in the use of ion-selective electrodes for analytical measurement of species in water, wastewater, and brines.
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Designation: D4127 − 12
Standard Terminology Used with
1
Ion-Selective Electrodes
This standard is issued under the fixed designation D4127; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope alkaline error, n—in alkaline solutions, where hydrogen ion
activity becomes very small, some glass electrodes respond
1.1 This terminology covers those terms recommended by
to other cations, such as sodium.
the International Union of Pure and Applied Chemistry
DISCUSSION—AnegativeerrorinthepHreadingresults.Bychanging
2
(IUPAC), and is intended to provide guidance in the use of
thecompositionoftheglass,theaffinityoftheglassforsodiumioncan
ion-selective electrodes for analytical measurement of species
be reduced. Such electrodes are known as lithium glass, high-pH, or
in water, wastewater, and brines.
full-range electrodes.
2. Referenced Documents
analate, n—the sample being analyzed; used in the terms
3
“analate addition” and “analate subtraction.”
2.1 ASTM Standards:
DISCUSSION—This term differs from the term “analyte,” which
D1129Terminology Relating to Water
describes the chemical species of interest in an analytical test.
3. Terminology
asymmetry potential, n—the potential across a glass pH
3.1 Definitions—For other definitions used in this
electrode membrane when the inside and outside of the
terminology, refer to Terminology D1129.
membrane are in contact with solutions of identical pH.
DISCUSSION—This term has also been used to define the observed
3.2 Definitions of Terms Relevant to Ion-Selective Electrode
potential differences between identical electrode pairs placed in iden-
Technology:
tical solutions.
acid error, n—in very acid solutions, the activity of water is
calibration curve, n—a plot of the potential (emf or E) of a
reduced (less than unity) causing a non-Nernstian response
given ion-selective electrode cell assembly (ion-selective
in glass electrodes.
DISCUSSION—A positive error in the pH reading results. electrode combined with an identified reference electrode)
versus the logarithm of the ionic activity (or concentration)
activity, n—the thermodynamically effective concentration of
of a given species.
a free ion in solution.
DISCUSSION—For uniformity, it is recommended that the potential be
DISCUSSION—In dilute solutions, ionic activity, and concentration are
plotted on the ordinate (vertical axis) with the more positive potentials
practically identical, but in solutions of high ionic strength, or in the
at the top of the graph and that pa (−log activity of the species
A
presence of complexing agents, activity may differ significantly from
measured, A)orpc (−log concentration of species measured, A)be
A
concentration. Ionic activity, not concentration, determines both the
plotted on the abscissa (horizontal axis) with increasing activity to the
rate and the extent of chemical reactions.
right. See Fig. 1 and Fig. 2. Region I of Fig. 1 represents the segment
of the curve where the potential no longer changes in response to
activity coefficient, n—afactor, γ,thatrelatesactivity, A,tothe
changes of the measured species activity and the electrode no longer
concentration, C of a species in solution:
demonstrates Nernstian response.
A 5 γC
IUPAC
DISCUSSION—The activity coefficient is dependent on the ionic
strength of the solution. Ions of similar size and charge have similar activity standard, n—a standardizing solution whose value is
activity coefficients.
reported in terms of ionic activity.
DISCUSSION— If the electrode is calibrated using activity standards,
1
the activity of the free, unbound ion in the sample is determined.
This terminology is under the jurisdiction ofASTM Committee D19 on Water
and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents
concentration standard, n—a standardizing solution whose
in Water.
Current edition approved Aug. 1, 2012. Published August 2012. Originally value is reported in terms of total concentration of the ion of
approved in 1982. Last previous edition approved in 2006 as D4127–06. DOI:
interest.
10.1520/D4127-12.
DISCUSSION—If the electrode is calibrated using pure-concentration
2
Recommendations for Nomenclature of Ion-Selective Electrodes, IUPAC Com-
standards and measurements made on untreated samples, results must
mission on Analytical Nomenclature, Pergamon Press, Oxford, 1976.
be corrected for the sample ionic strength and the presence of
3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
complexingagents.Morecommonly,areagentisaddedtoallstandards
contact ASTM Customer Service at service@astm.org. F
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D4127 − 06 D4127 − 12
Standard Terminology Used with
1
Ion-Selective Electrodes
This standard is issued under the fixed designation D4127; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope
2
1.1 This terminology covers those terms recommended by the International Union of Pure and Applied Chemistry (IUPAC),
and is intended to provide guidance in the use of ion-selective electrodes for analytical measurement of species in water,
wastewater, and brines.
2. Referenced Documents
3
2.1 ASTM Standards:
D1129 Terminology Relating to Water
3. Terminology
3.1 Definitions—For other definitions used in this terminology, refer to Terminology D1129.
3.2 Definitions of Terms Relevant to Ion-Selective Electrode Technology:
acid error—error, n—in very acid solutions, the activity of water is reduced (less than unity) causing a non-Nernstian response
in glass electrodes. A positive error in the pH reading results.
1
This terminology is under the jurisdiction of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents in Water.
Current edition approved Dec. 15, 2006Aug. 1, 2012. Published January 2007. Originally approved in 1982. Last previous edition approved in 20022006 as
D4127 – 02.D4127 – 06. DOI: 10.1520/D4127-06.10.1520/D4127-12.
2
Recommendations for Nomenclature of Ion-Selective Electrodes, IUPAC Commission on Analytical Nomenclature, Pergamon Press, Oxford, 1976.
3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
DISCUSSION—
A positive error in the pH reading results.
activity—activity, n—the thermodynamically effective concentration of a free ion in solution. In dilute solutions, ionic activity,
and concentration are practically identical, but in solutions of high ionic strength, or in the presence of complexing agents,
activity may differ significantly from concentration. Ionic activity, not concentration, determines both the rate and the extent of
chemical reactions.
DISCUSSION—
In dilute solutions, ionic activity, and concentration are practically identical, but in solutions of high ionic strength, or in the presence of complexing
agents, activity may differ significantly from concentration. Ionic activity, not concentration, determines both the rate and the extent of chemical
reactions.
activity coefficient—coefficient, n—a factor,γ, that relates activity, A, to the concentration, C of a species in solution:
A 5γC
The activity coefficient is dependent on the ionic strength of the solution. Ions of similar size and charge have similar activ-
ity coefficients.
DISCUSSION—
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D4127 − 12
The activity coefficient is dependent on the ionic strength of the solution. Ions of similar size and charge have similar activity coefficients.
alkaline error—error, n—in alkaline solutions, where hydrogen ion activity becomes very small, some glass electrodes respond
to other cations, such as sodium. A negative error in the pH reading results. By changing the composition of the glass, the affinity
of the glass for sodium ion can be reduced. Such electrodes are known as lithium glass, high-pH, or full-range electrodes.
DISCUSSION—
A negative error in the pH reading results. By changing the composition of the glass, the affinity of the glass for sodium ion can be reduced. Such
electrodes are known as lithium glass, high-pH, or full-range electrodes.
analate, n—the sample being analyzed; used in the terms “analate addition” and “analate subtraction”.
DISCUSSION—
This term differs from the term “analyte,” which describes the chemical species of interest in an analytical test.
asymmetry potential—potential, n—the potential across a glass pH electrode membrane when the inside and outside of the
membrane are in contact with solutions of identical pH. This term has also been used to define the observed potential differences
between identical elec
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