ASTM D5464-07
(Test Method)Standard Test Method for pH Measurement of Water of Low Conductivity
Standard Test Method for pH Measurement of Water of Low Conductivity
SIGNIFICANCE AND USE
pH measurement of low conductivity water is frequently applied to power plant water and condensed steam samples for corrosion and scale prevention. It is sometimes used in pure water treatment systems between multiple pass membranes to optimize performance.
High purity water is highly unbuffered and small amounts of contamination can change the pH significantly. Specifically, high purity water rapidly absorbs CO2 gas from the atmosphere, which lowers the pH of the sample. The sample container and accompanying pH measurement technique minimize exposure of the high purity water sample to the atmosphere.
The high purity water sample may contain volatile trace components that will dissipate from the sample if exposed to the atmosphere. The sample container used in this test method will prevent these losses.
High purity water has a significant solution temperature coefficient. For greatest accuracy the sample to be measured should be close to the temperature of the sample stream and appropriate compensation should be applied.
When the preferred Test Method D 5128, which requires a real-time, flowing sample, cannot be utilized for practical reasons such as physical plant layout, unacceptable loss of water, location of on-line equipment sample points, or availability of dedicated test equipment, this method offers a viable alternative. The most significant difference between the two test methods is that Test Method D 5128 obtains a real-time pH measurement from a flowing sample and this method obtains a time delayed pH measurement from a static grab sample.
pH measurements of low conductivity water are always subject to interferences (7.1-7.5) and Test Method D 5128 is more effective in eliminating these interferences especially with regard to contamination. This static grab sample method is more prone to contamination and temperature-induced errors because of the time lag between the sampling in the plant and sample pH reading which is taken in the laboratory.
SCOPE
1.1 This test method is applicable to determine the pH of water samples with a conductivity of 2 to 100 µ S/cm over the pH range of 3 to 11. pH measurements of water of low conductivity are problematic. Specifically, this test method avoids contamination of the sample with atmospheric gases and prevents volatile components of the sample from escaping. This test method provides for pH electrodes and apparatus that address additional considerations discussed in . This test method also minimizes problems associated with the sample's pH temperature coefficient when the operator uses this test method to calibrate an on-line pH monitor or controller (see Appendix X1).
1.2 This test method covers the measurement of pH in water of low conductivity with a lower limit of 2.0 µS/cm, utilizing a static grab-sample procedure where it is not practicable to take a real-time flowing sample.Note 1
Test Method D 5128 for on-line measurement is preferred over this method whenever possible. Test Method D 5128 is not subject to the limited conductivity range, temperature interferences, potential KCl contamination, and time limitations found with this method.
1.3 For on-line measurements in water with conductivity of 100 µS/cm and higher, see Test Method D 6569.
1.4 For laboratory measurements in water with conductivity of 100 µS/cm and higher, see Test Method D 1193.
1.5 The values stated in SI units are to be regarded as standard.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D5464–07
Standard Test Method for
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pH Measurement of Water of Low Conductivity
This standard is issued under the fixed designation D5464; 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.
1. Scope priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
1.1 This test method is applicable to determine the pH of
water samples with a conductivity of 2 to 100 µS/cm over the
2. Referenced Documents
pH range of 3 to 11. pH measurements of water of low
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2.1 ASTM Standards:
conductivity are problematic. Specifically, this test method
D1129 Terminology Relating to Water
avoids contamination of the sample with atmospheric gases
D1193 Specification for Reagent Water
and prevents volatile components of the sample from escaping.
D1293 Test Methods for pH of Water
This test method provides for pH electrodes and apparatus that
D2777 Practice for Determination of Precision and Bias of
address additional considerations discussed inAnnexA2. This
Applicable Test Methods of Committee D19 on Water
test method also minimizes problems associated with the
D4453 Practice for Handling of High Purity Water Samples
sample’s pH temperature coefficient when the operator uses
D5128 Test Method for On-Line pH Measurement of Water
thistestmethodtocalibrateanon-linepHmonitororcontroller
of Low Conductivity
(see Appendix X1).
D6569 Test Method for On-Line Measurement of pH
1.2 ThistestmethodcoversthemeasurementofpHinwater
of low conductivity with a lower limit of 2.0 µS/cm, utilizing
3. Terminology
a static grab-sample procedure where it is not practicable to
3.1 Definitions—For definitions of terms used in these test
take a real-time flowing sample.
methods, refer to Terminology D1129.
NOTE 1—Test Method D5128 for on-line measurement is preferred
3.2 Definitions of Terms Specific to This Standard:
over this method whenever possible. Test Method D5128 is not subject to
3.2.1 liquid junction potential—a dc potential which ap-
the limited conductivity range, temperature interferences, potential KCl
pears at the point of contact between the reference electrode’s
contamination, and time limitations found with this method.
salt bridge (also known as reference junction or diaphragm)
1.3 For on-line measurements in water with conductivity of
and the sample solution. Ideally this potential is near zero, and
100 µS/cm and higher, see Test Method D6569.
is stable. However, in low conductivity water it may change
1.4 For laboratory measurements in water with conductivity
from its value in buffer solution by an unknown amount, and is
of 100 µS/cm and higher, see Test Method D1193. 3
a zero offset (1).
1.5 The values stated in SI units are to be regarded as
standard. 4. Reagents
1.6 This standard does not purport to address all of the
4.1 Purity of Reagents—Reagent grade chemicals shall be
safety concerns, if any, associated with its use. It is the
used in all tests. Unless otherwise indicated, it is intended that
responsibility of the user of this standard to establish appro-
all reagents conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society where
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These test methods are under the jurisdiction of ASTM Committee D19 on
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Water and are the direct responsibility of Subcommittee D19.03 on Sampling Water For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and Water-Formed Deposits, Analysis of Water for Power Generation and Process contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Use, On-Line Water Analysis, and Surveillance of Water Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Aug. 1, 2007. Published August 2007. Originally the ASTM website.
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approved in 1993. Last previous edition approved in 2001 as D5464 – 93 (2001). The boldface numbers in parentheses refer to the list of references at the end of
DOI: 10.1520/D5464-07. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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D5464–07
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such specifications are available. Other grades may be used, 6.2 High purity water is highly unbuffered and small
provided it is first ascertained that the reagent is of sufficiently amounts of contamination can change the pH significantly.
high purity to permit its use without lessening the accuracy of Specifically, high purity water rapidly absorbs CO gas from
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the determination. the atmosphere, which lowers the pH of the s
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