ASTM D5464-16

Standard Test Method for pH Measurement of Water of Low Conductivity

SIGNIFICANCE AND USE
6.1 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.  
6.2 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.  
6.3 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.  
6.4 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.  
6.5 When the preferred Test Method D5128, 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 D5128 obtains a real-time pH measurement from a flowing sample and this method obtains a time delayed pH measurement from a static grab sample.  
6.6 pH measurements of low conductivity water are always subject to interferences (7.1 – 7.5) and Test Method D5128 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 i...
SCOPE
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 pH range of 3 to 11 and is frequently used in power generation low conductivity samples. 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 Annex A2. 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 D5128 for on-line measurement is preferred over this method whenever possible. Test Method D5128 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 D6569.  
1.4 For laboratory measurements in water with conductivity of 100 μS/cm and higher, see Test Method D1293.  
1.5 The values stated in SI units are to be regarded as standard.  
1.6 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.

General Information

• Status: Published
• Publication Date: 31-May-2016
• ICS: 13.060.50 - Examination of water for chemical substances
• Technical Committee: D19 - Water
• Drafting Committee: D19.03 - Sampling Water and Water-Formed Deposits, Analysis of Water for Power Generation and Process Use, On-Line Water Analysis, and Surveillance of Water

Relations

• Refers: ASTM D1129-13(2020)e2 - Standard Terminology Relating to Water
• Effective Date: 01-May-2020
• Refers: ASTM D4453-17 - Standard Practice for Handling of High Purity Water Samples
• Effective Date: 01-Feb-2017
• Refers: ASTM D4453-16 - Standard Practice for Handling of High Purity Water Samples
• Effective Date: 15-Feb-2016
• Refers: ASTM D2777-12 - Standard Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
• Effective Date: 15-Jun-2012
• Refers: ASTM D1293-12 - Standard Test Methods for pH of Water
• Effective Date: 01-Jan-2012
• Refers: ASTM D4453-11 - Standard Practice for Handling of High Purity Water Samples
• Effective Date: 01-Feb-2011
• Refers: ASTM D3370-10 - Standard Practices for Sampling Water from Closed Conduits
• Effective Date: 01-Dec-2010
• Refers: ASTM D1129-10 - Standard Terminology Relating to Water
• Effective Date: 01-Mar-2010
• Refers: ASTM D5128-09 - Standard Test Method for On-Line pH Measurement of Water of Low Conductivity
• Effective Date: 01-Oct-2009
• Refers: ASTM D6569-05(2009) - Standard Test Method for On-Line Measurement of pH¹
• Effective Date: 01-May-2009
• Refers: ASTM D3370-08 - Standard Practices for Sampling Water from Closed Conduits
• Effective Date: 01-Oct-2008
• Refers: ASTM D2777-08 - Standard Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
• Effective Date: 15-Jan-2008
• Refers: ASTM D3370-07 - Standard Practices for Sampling Water from Closed Conduits
• Effective Date: 01-Dec-2007
• Refers: ASTM D1129-06ae1 - Standard Terminology Relating to Water
• Effective Date: 01-Sep-2006
• Refers: ASTM D1129-06a - Standard Terminology Relating to Water
• Effective Date: 01-Sep-2006

Overview

ASTM D5464-16: Standard Test Method for pH Measurement of Water of Low Conductivity establishes the procedures for accurately measuring the pH of water samples with low electrical conductivity (2 to 100 μS/cm). This test method is vital in industries with high purity water systems-especially power generation-where precise pH control is essential to prevent corrosion and scaling. ASTM D5464-16 uses a static grab-sample technique, designed to minimize sample contamination and ensure accurate pH results when real-time on-line pH monitoring is impractical.

Key Topics

• Applicability and Scope: This test method applies to the determination of pH in water samples with conductivity between 2 and 100 μS/cm over a pH range of 3 to 11. It is primarily used for low conductivity samples, such as those found in power plants and pure water systems.
• Sample Sensitivity: High purity water is extremely sensitive to contamination; even slight exposure to atmospheric gases (especially CO₂) or improper handling can significantly alter pH readings.
• Grab-Sample Technique: The method specifies handling and measurement procedures to minimize atmospheric exposure and volatile component loss, ensuring representative and reliable results.
• Apparatus Requirements: Special types of pH electrodes and reference electrodes (such as double junction designs with low leakage rates) are recommended for low ionic strength samples. Equipment must be dedicated exclusively to high purity water testing to avoid cross-contamination.
• Temperature Compensation: High purity water has a notable temperature coefficient, making temperature measurement and correction critical for accurate pH determination.
• Interferences: The method recognizes multiple sources of error, including contamination, temperature fluctuations, and junction potentials, emphasizing strict procedure adherence.
• Alternative Test Methods: While D5464-16 addresses grab-sample testing, ASTM D5128 (on-line, real-time pH measurement) is preferred when possible due to its increased resistance to interference and higher accuracy.

Applications

ASTM D5464-16 is a key standard in:

• Power Generation: Monitoring the pH of condensate, feedwater, and steam samples, supporting corrosion and scaling control strategies.
• Pure Water Treatment: Verifying pH levels between stages of high purity water systems, such as reverse osmosis and deionization, to optimize membrane and resin performance.
• Calibration of On-Line pH Monitors: Where direct on-line sampling is not feasible, grab-sample measurements can calibrate and check station sensors, ensuring plant instrumentation accuracy.
• Industrial and Laboratory Settings: Used whenever testing of water with low ionic strength is necessary and the potential for sample contamination or volatility must be minimized.

Related Standards

• ASTM D5128: Test Method for On-Line pH Measurement of Water of Low Conductivity (preferred for real-time measurements)
• ASTM D6569: Test Method for On-Line Measurement of pH in water with conductivity above 100 μS/cm
• ASTM D1293: Test Methods for pH of Water (laboratory measurements for higher conductivity samples)
• ASTM D4453: Practice for Handling of High Purity Water Samples
• ASTM D3370: Practices for Sampling Water from Closed Conduits
• ASTM D1193: Specification for Reagent Water

Practical Value

Utilizing ASTM D5464-16 ensures reliable, reproducible pH measurements in high purity or low conductivity water applications where contamination risk is high. Its procedures help safeguard the integrity of critical water chemistry controls in power plants and other process industries. Adherence to this standard supports regulatory compliance, optimizes plant operation, and reduces maintenance costs related to corrosion and scaling.

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Keywords: low conductivity water, high purity water, pH measurement, ASTM D5464-16, grab sample, water quality, power plant, corrosion prevention, scale control, sample handling, temperature compensation, ASTM standards, static grab-sample, pH electrode.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D5464 − 16
Standard Test Method for
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.Anumber 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
pHrangeof3to11andisfrequentlyusedinpowergeneration
2.1 ASTM Standards:
low conductivity samples. pH measurements of water of low
D1129Terminology Relating to Water
conductivity are problematic. Specifically, this test method
D1193Specification for Reagent Water
avoids contamination of the sample with atmospheric gases
D1293Test Methods for pH of Water
andpreventsvolatilecomponentsofthesamplefromescaping.
D2777Practice for Determination of Precision and Bias of
This test method provides for pH electrodes and apparatus that
Applicable Test Methods of Committee D19 on Water
address additional considerations discussed in AnnexA2. This
D3370Practices for Sampling Water from Closed Conduits
test method also minimizes problems associated with the
D4453Practice for Handling of High Purity Water Samples
sample’s pH temperature coefficient when the operator uses
D5128Test Method for On-Line pH Measurement of Water
thistestmethodtocalibrateanon-linepHmonitororcontroller
of Low Conductivity
(see Appendix X1).
D6569Test Method for On-Line Measurement of pH
1.2 ThistestmethodcoversthemeasurementofpHinwater
3. Terminology
of low conductivity with a lower limit of 2.0 µS/cm, utilizing
a static grab-sample procedure where it is not practicable to
3.1 Definitions of Terms—For definitions of terms used in
take a real-time flowing sample.
this test method, refer to Terminology D1129.
NOTE1—TestMethodD5128foron-linemeasurementispreferredover
3.2 Definitions:
this method whenever possible. Test Method D5128 is not subject to the
limited conductivity range, temperature interferences, potential KCl
3.3 Definitions of Terms Specific to This Standard:
contamination, and time limitations found with this method.
3.3.1 liquid-junction potential, n—a dc potential that ap-
1.3 For on-line measurements in water with conductivity of pears at the point of contact between the reference electrode’s
salt bridge (also known as reference junction or diaphragm)
100 µS/cm and higher, see Test Method D6569.
and the sample solution.
1.4 Forlaboratorymeasurementsinwaterwithconductivity
3.3.1.1 Discussion—Ideally,thispotentialisnearzeroandis
of 100 µS/cm and higher, see Test Method D1293.
stable. However, in low-conductivity water this potential may
1.5 The values stated in SI units are to be regarded as
change from its value in buffer solution by an unknown
standard.
amount, and is a zero offset (1).
1.6 This standard does not purport to address all of the
4. Reagents
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- 4.1 Purity of Reagents—Reagent grade chemicals shall be
used in all tests. Unless otherwise indicated, it is intended that
These test methods are under the jurisdiction of ASTM Committee D19 on
WaterandarethedirectresponsibilityofSubcommitteeD19.03onSamplingWater 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 [e-mail]. 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 June 1, 2016. Published June 2016. Originally the ASTM website.
approved in 1993. Last previous edition approved in 2011 as D5464–11. DOI: Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
10.1520/D5464-16. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5464 − 16
all reagents conform to the specifications of the Committee on 6. Significance and Use
Analytical Reagents of theAmerican Chemical Society where
6.1 pHmeasurementoflowconductivitywaterisfrequently
such specifications are available. Other grades may be used,
applied to power plant water and condensed steam samples for
provided it is first ascertained that the reagent is of sufficiently
corrosion and scale prevention. It is sometimes used in pure
high purity to permit its use without lessening the accuracy of
water treatment systems between multiple pass membranes to
the determination.
optimize performance.
4.2 Purity of Water—References to water that is used for
6.2 High purity water is highly unbuffered and small
reagent preparation, rinsing or dilution shall be understood to
amounts of contamination can change the pH significantly.
mean water that conforms to the quantitative specifications of
Specifically, high purity water rapidly absorbs CO gas from
Type II reagent water of Specification D1193.
the atmosphere, which lowers the pH of the sample. The
4.3 Commercial Buffer Solutions —Commercially available
sample container and accompanying pH measurement tech-
prepared buffers traceable to NIST standards should be ad-
niqueminimizeexposureofthehighpuritywatersampletothe
equate to perform the calibration procedures in 10.1 – 10.4.
atmosphere.
The exact pH of the buffer will change with temperature and
6.3 The high purity water sample may contain volatile trace
this pH versus temperature data will be provided by the
components that will dissipate from the sample if exposed to
purveyor of the specific buffer. Refer to Test Methods D1293
the atmosphere. The sample container used in this test method
for the preparation of reference buffer solutions if desired.
will prevent these losses.
4.4 Buffer A—Commercially available 7.0 pH buffer.
6.4 High purity water has a significant solution temperature
4.5 Buffer B—Commercially available 4.0 pH buffer.
coefficient. For greatest accuracy the sample to be measured
4.6 BufferC—Commerciallyavailable9.0or10.0pHbuffer.
should be close to the temperature of the sample stream and
appropriate compensation should be applied.
5. Summary of Test Method
6.5 When the preferredTest Method D5128, which requires
5.1 The pH meter and associated electrodes are first stan-
a real-time, flowing sample, cannot be utilized for practical
dardized with two calibration pH buffer solutions.
reasons such as physical plant layout, unacceptable loss of
water, location of on-line equipment sample points, or avail-
5.2 Agrabsampleofhighpuritywateristakenbymeansof
ability of dedicated test equipment, this method offers a viable
rinsing and filling two narrow mouth bottles at the sample
alternative. The most significant difference between the two
point. Once each container is filled to the top with a represen-
test methods is thatTest MethodD5128 obtains a real-time pH
tative sample excluding any air, the containers are capped and
measurement from a flowing sample and this method obtains a
thesamplesaretransportedquicklytoalaboratoryforanalysis.
time delayed pH measurement from a static grab sample.
5.3 pHmeasurementofthesampleismadewithhighpurity
water pH calibration apparatus comprised of pH and reference 6.6 pH measurements of low conductivity water are always
electrodes, and automatic temperature compensator (if used). subject to interferences (7.1 – 7.5) and Test Method D5128 is
The first container is used to rinse the sensors and begin more effective in eliminating these interferences especially
temperature equilibration and the second container is used for with regard to contamination. This static grab sample method
measurement. ismorepronetocontaminationandtemperature-inducederrors
because of the time lag between the sampling in the plant and
5.4 A trace amount of KCl electrolyte enters calibration
sample pH reading which is taken in the laboratory.
buffer solutions and samples via the controlled leakage rate of
the reference electrode liquid junction (diaphragm) to stabilize
7. Interferences
the liquid junction potential. Excessive KCl introduction from
the electrode liquid junction into low ionic strength samples
7.1 High purity, low conductivity samples are especially
will increase solution conductivity, and may alter solution pH,
sensitive to contamination from atmospheric gases, from
and should be avoided.
sample containers, from sample handling techniques and from
excessiveelectrolyte(KCl)contaminationfromreferenceelec-
5.5 Temperature must be measured and both Solution Tem-
trode or sample preparation such as a KCl “dosing” technique.
perature Coefficient (STC) and Nernst electrode effects
RefertoPracticeD4453and ASTM STP823 (2)fordiscussions
compensated, either manually to the measured value or auto-
of sample handling and avoidance of sample contamination.
matically by the pH meter. See Appendix X1 for a discussion
of temperature effects.
7.2 High purity water will rapidly absorb CO from the
atmosphere and this will lower the pH of the sample at a rate
depending on the buffer capacity of the sample, the surface
areaofthesampleexposedtoair,movementofthesample,and
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For Suggestions on the testing of reagents not
the concentration of CO at the surface of the sample which
listed by the American Chemical Society, see Annual Standards for Laboratory
may increase if the operator exhales over the container during
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
sampling or measurement. See Appendix X3, Table X3.1, and
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
MD. Fig. X3.1.
D5464 − 16
7.3 Thetemperaturestabilityofthesampleandhowclosely fit into the sample container to measure the temperature of the
the sample’s temperature matches the sample stream’s tem- water within the container.
perature will have a direct effect on accuracy of the pH
8.7 Temperature Indicator—Adirect temperature indicating
determination since temperature compensation is not perfect.
device must be used to measure sample water temperature
7.4 If pH is to be referenced to 25°C as required by most within the sample container if an automatic temperature
specifications,temperaturecompensationmustbeprovidedfor compensator is not used.
both the Nernst response of the electrode output (provided in
8.8 Equipment for this test method should be dedicated for
most pH meters) and solution ionization effects (provided only
high purity water use only.
with some on-line pH meters or by calculation with lab
meters). For a discussion of temperature effects on pH mea-
9. Sampling and Sample Handling
surements of high purity water see Appendix X1.
9.1 The sample containers should be rinsed three times
7.5 The reference junction potential can vary with ionic
before use, with sample or reagent water.
strength of the sample and provide an undetectable zero offset
between the high ionic strength of the buffer solution and the 9.2 Static grab samples are taken via clean tubing attached
to the sample take-off point. The other end of the tubing is
low ionic strength of the sample.Aflowing junction reference
electrode(onewhichrequiresperiodicrefillingwithelectrolyte inserted to the bottom of the sample container. The sample
flows through the tube, into the bottom of the container, and
solution or that has internal electrolyte pressurization or both)
minimizes this effect. thenoverthetoptotroughorsinkdrain.Aftera5-minflushof
thecontainerwiththesamplewater,thetubingisremovedand
the cap immediately installed, excluding any air.This seals the
8. Apparatus
container and isolates the sample from the atmosphere. The
8.1 pH Meter, capable of reading to 0.01 pH. The meter
second container is filled and capped in the same way. In the
should preferably have automatic temperature compensation
lab, the first container is used to rinse the electrodes and
for the Nernst response of pH electrodes which provides the
temperature device and the second container is used for
conversion of the electrode millivolt signal to the pH value at
measurement.
the measured temperature. Some on-line meters also provide
an input for a solution temperature coefficient for ionization
10. Calibration
effects of the particular sample. This allows direct readout of
10.1 Turn on the pH meter and allow it to warm up
pH referenced to 25°C. Otherwise a calculation is required.
according to the manufacturer’s instructions. If an on-line
8.2 Sample Containers—Two clean, narrow-mouth 250 to
meterisusedthathasasolutiontemperaturecoefficientsetting,
500 mL bottles with cap are required. The mouth diameter
be sure it is turned off or is set to 0 pH/°C for calibration in
should be the minimum necessary to allow insertion of the
buffer solutions. Conventional Nernst temperature compensa-
electrode(s), and temperature compensator or thermometer. A
tion should be active at all times and requires no setting.
3-hole stopper may be used to hold these sensors. The
10.2 Remove the electrode(s) and temperature compensator
container and cap minimize exposure to atmospheric gases.
(ifused)fromstorage.Checkthereferenceelectrodeforproper
8.3 Combination pH Electrode—A probe incorporating the
electrolyte level as recommended by the manufacturer.
measuring, reference and temperature compensator functions
10.3 Calibrate the electrode(s) and pH meter at two points
in a single unit is recommended for its ease of insertion into a
accordingtomanufacturer’sinstructions.Also,refertoSection
very narrow mouth sample container. Each function should
12 of Test Methods D1293 for guidelines on the calibration of
conform to the characteristics in 8.4 – 8.6. Where this is not
a pH meter and electrode assembly. Use a quiescent sample of
available, individual electrodes and compensator (8.4 – 8.6)
BufferAand Buffer B if the sample point of interest is below
may be used with a 3-hole stopper to hold them and seal the
container during measurement. 7.0pH.UseaquiescentsampleofBufferAandBufferCifthe
sample point of interest is above 7.0 pH. Use laboratory
8.4 pH Glass Electrode—The pH response of the glass
glassware dedicated for this service only.Thoroughly rinse the
electrode shall conform to the requirements set forth in 12.1
electrode(s) and glassware with reagent water three times
through12.5ofTestMethodsD1293.Newglasselectrodesand
between immersion in each buffer solution.
those that have been stored dry shall be conditioned and
10.4 Obtain calibration precision of the pH electrode(s) and
maintained as recommended by the manufacturer.
the pH meter by repeating the two-point calibration described
8.5 Reference Electrode—Double junction design, having a
in 10.3, making any necessary readjustments to the pH meter.
refillable flowing junction with a positive electrolyte leakage
If the electrode slope (efficiency) is less than 94% or greater
rate not to exceed 10 µL/h. A sealed reference electrode is
than 101%, refer to manufacturer’s instructions for repair or
suitable only if it is internally pressurized to force an electro-
replacement of electrode(s).
lyteflowoutward.Prepareandmaintainthereferenceelectrode
according to the manufacturer’s instructions. NOTE 2—The pH electrodes in use may pass the above calibration
procedures (10.1 – 10.4), but caution should be taken. pH electrodes that
8.6 Temperature Compensator—See paragraph 10.4 in Test
are not specifically designed for use in high purity water may develop
MethodsD1293.Theautomatictemperaturecompensatormust problems with liquid junction potential during actual test measurements.
D5464 − 16
10.5 Determine the frequency of the two-point calibration 11.9 Report the pH value with 0.01 pH resolution and the
of the electrode(s) and the pH meter based on experience. temperature with 0.1°C resolution.
Perform calibration at least daily when pure water sample
11.10 If the pH must be referenced to 25°C and the sample
testing is performed daily. For less frequent pure water sample
is not already at 25.0 6 0.5°C, determine the applicable
testing, perform calibration procedures just prior to a consecu-
solutiontemperaturecoefficientandcalculatethepHat25.0°C
tive series of sample tests.
in accordance with Appendix X1 and report it with resolution
10.6 Thoroughly rinse the electrode(s) and the temperature of 0.01 pH.
compensator or temperature reading device and the sample
11.11 TousethispHmeasurementtocalibrateanon-linepH
container three times with sample or reagent water after
sensor, call the value from 11.9 or 11.10 R and refer to the
calibration and before measurement.
procedure addendum in Appendix X2.
NOTE 4—If no further samples are to be taken, the calibrated pH
11. Procedure
electrode(s)maybekeptstoredinthesamplecontainercontainingthelast
pure water sample until the next calibration or sample requirement. For
11.1 Before starting the procedure, make certain the two
long term storage of the pH electrode(s), replace them in their respective
sample containers are clean and empty. See Section 9.
soaker bottles and appropriate storage solutions (see manufacturer’s
instructions).
NOTE 3—If on-line pH sensors are to be calibrated by this test method
(refer to Test Method D5128), steps should be taken to prevent the
12. Quality Control
disturbance of the on-line pressure and flow rate while the grab sample is
being taken. Appropriate pressure and flow regulation equipment should
12.1 Two-point instrument calibration must be performed
be installed at the grab sample point upstream of the on-line sensor. See
according to the manufacturer’s instructions within 12 h of
D3370. Appendix Appendix X2 provides guidance on grab sample
making measurements.
calibration of on-line instrumentation.
11.2 Open the sample valve and pull sample without inter- 12.2 With power plant samples containing predominately
rupting the sample flow-rate or pressure of the on-line pH ammonia and negligible carbon dioxide, an accurate correla-
sensor assembly if used (see on-line pH sensor manufacturer’s tion with specific conductivity can be made. See Fig. X3.1.
instructions for its optimum flowrate). The grab sample flow- Under these conditions, periodically verify pH readings cor-
rate should be at least 200 mL/min. rected to 25°C by solution temperature compensation with the
conductivity also referenced to 25°C. Some two-channel con-
11.3 With the sample flowing, rinse the outside surfaces of
ductivityinstrumentationincludesanoptionforthecalculation
thesampletubingforatleast15secondsbyholdingitwiththe
of pH based on specific and cation conductivity and will make
open discharge end upward like a fountain, allowing the
a correction for the presence of minor amounts of carbon
sample to flow over the outside tubing surfaces for more than
dioxideandothercontaminants.Ifavailable,usethiscalculated
the length that will be later immersed in the sample container,
value to verify the measured pH readings under normal plant
allowing the flow to drain into the sampling trough or sink.
operating conditions.
11.4 Run the end of the sample tubing to the bottom of the
sample container letting the sample overflow into the sink. 13. Precision and Bias
11.5 Thoroughly flush the sample container with sample 13.1 Neitherprecisionnorbiasdatacanbeobtainedforthis
water for at least 5 min at a flow rate of at least 200 mL/min. test method from a collaborative study designed in accordance
withtherequirementsofPracticeD2777sincethistestmethod
11.6 Remove the sample tubing and immedia
...

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: D5464 − 11 D5464 − 16
Standard Test Method for
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
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 pH range
of 3 to 11. 11 and is frequently used in power generation low conductivity samples. 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 Annex A2. 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 D5128 for on-line measurement is preferred over this method whenever possible. Test Method D5128 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 D6569.
1.4 For laboratory measurements in water with conductivity of 100 μS/cm and higher, see Test Method D1193D1293.
1.5 The values stated in SI units are to be regarded as standard.
1.6 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.
2. Referenced Documents
2.1 ASTM Standards:
D1129 Terminology Relating to Water
D1193 Specification for Reagent Water
D1293 Test Methods for pH of Water
D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
D3370 Practices for Sampling Water from Closed Conduits
D4453 Practice for Handling of High Purity Water Samples
D5128 Test Method for On-Line pH Measurement of Water of Low Conductivity
D6569 Test Method for On-Line Measurement of pH
3. Terminology
3.1 Definitions—Definitions of Terms—For definitions of terms used in thesethis test methods,method, refer to Terminology
D1129.
3.2 Definitions:
3.3 Definitions of Terms Specific to This Standard:
3.3.1 liquid-junction potential, n—a dc potential that appears at the point of contact between the reference electrode’s salt bridge
(also known as reference junction or diaphragm) and the sample solution.
These test methods are under the jurisdiction of ASTM Committee D19 on Water and are the direct responsibility of Subcommittee D19.03 on Sampling Water and
Water-Formed Deposits, Analysis of Water for Power Generation and Process Use, On-Line Water Analysis, and Surveillance of Water
Current edition approved May 1, 2011June 1, 2016. Published May 2011June 2016. Originally approved in 1993. Last previous edition approved in 20072011 as
D5464 – 07.D5464 – 11. DOI: 10.1520/D5464-11.10.1520/D5464-16.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5464 − 16
3.3.1.1 Discussion—
Ideally, this potential is near zero and is stable. However, in low-conductivity water this potential may change from its value in
buffer solution by an unknown amount, and is a zero offset (1).
4. Reagents
4.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where such
specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity
to permit its use without lessening the accuracy of the determination.
4.2 Purity of Water—References to water that is used for reagent preparation, rinsing or dilution shall be understood to mean
water that conforms to the quantitative specifications of Type II reagent water of Specification D1193.
4.3 Commercial Buffer Solutions —Commercially available prepared buffers traceable to NIST standards should be adequate to
perform the calibration procedures in 10.1 – 10.4. The exact pH of the buffer will change with temperature and this pH versus
temperature data will be provided by the purveyor of the specific buffer. Refer to Test Methods D1293 for the preparation of
reference buffer solutions if desired.
4.4 Buffer A—Commercially available 7.0 pH buffer.
4.5 Buffer B—Commercially available 4.0 pH buffer.
4.6 Buffer C—Commercially available 9.0 or 10.0 pH buffer.
5. Summary of Test Method
5.1 The pH meter and associated electrodes are first standardized with two calibration pH buffer solutions.
5.2 A grab sample of high purity water is taken by means of rinsing and filling two narrow mouth bottles at the sample point.
Once each container is filled to the top with a representative sample excluding any air, the container iscontainers are capped and
the samples are transported quickly to a laboratory for analysis.
5.3 pH measurement of the sample is made with high purity water pH calibration apparatus comprised of pH and reference
electrodes, and automatic temperature compensator (if used). The first container is used to rinse the sensors and begin temperature
equilibration and the second container is used for measurement.
5.4 A trace amount of KCl electrolyte enters calibration buffer solutions and samples via the controlled leakage rate of the
reference electrode liquid junction (diaphragm) to stabilize the liquid junction potential. Excessive KCl introduction from the
electrode liquid junction into low ionic strength samples will increase solution conductivity, and may alter solution pH, and should
be avoided.
5.5 Temperature must be measured and both Solution Temperature Coefficient (STC) and NernstianNernst electrode effects
compensated, either manually to the measured value or automatically by the pH meter. See Appendix X1 for a discussion of
temperature effects.
6. Significance and Use
6.1 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.
6.2 High purity water is highly unbuffered and small amounts of contamination can change the pH significantly. Specifically,
high purity water rapidly absorbs CO 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.
6.3 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.
6.4 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.
6.5 When the preferred Test Method D5128, 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
The boldface numbers in parentheses refer to the list of references at the end of this standard.
Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC. For Suggestions on the testing of reagents not listed by
the American Chemical Society, see Annual Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and National
Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
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test equipment, this method offers a viable alternative. The most significant difference between the two test methods is that Test
Method D5128 obtains a real-time pH measurement from a flowing sample and this method obtains a time delayed pH
measurement from a static grab sample.
6.6 pH measurements of low conductivity water are always subject to interferences (7.1 – 7.5) and Test Method D5128 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.
7. Interferences
7.1 High purity, low conductivity samples are especially sensitive to contamination from atmospheric gases, from sample
containers, from sample handling techniques and from excessive electrolyte (KCl) contamination from reference electrode or
sample preparation such as a KCl “dosing” technique. Refer to Practice D4453 and ASTM STP 823(2) for discussions of sample
handling and avoidance of sample contamination.
7.2 High purity water will rapidly absorb CO from the atmosphere and this will lower the pH of the sample at a rate depending
on the buffer capacity of the sample, the surface area of the sample exposed to air, movement of the sample, and the concentration
of CO at the surface of the sample which may increase if the operator exhales over the container during sampling or measurement.
See Appendix X3, Table X3.1, and Fig. X3.1.
7.3 The temperature stability of the sample and how closely the sample’s temperature matches the sample stream’s temperature
will have a direct effect on accuracy of the pH determination since temperature compensation is not perfect.
7.4 If pH is to be referenced to 25°C as required by most specifications, temperature compensation must be provided for both
the NernstianNernst response of the electrode output (provided in most pH meters) and solution ionization effects (provided only
with some on-line pH meters or by calculation with lab meters). For a discussion of temperature effects on pH measurements of
high purity water see Appendix X1.
7.5 The reference junction potential can vary with ionic strength of the sample and provide an undetectable zero offset between
the high ionic strength of the buffer solution and the low ionic strength of the sample. A flowing junction reference electrode (one
which requires periodic refilling with electrolyte solution or that has internal electrolyte pressurization or both) minimizes this
effect.
8. Apparatus
8.1 pH Meter—Meter, See 10.1 in Test Methodscapable of reading to 0.01 D1293.pH. The meter should preferably have
automatic temperature compensation for the Nernst response of pH electrodes which provides the conversion of the electrode
millivolt signal to the pH value at the measured temperature. Some on-line meters also provide an input for a solution temperature
coefficient for ionization effects of the particular sample. This allows direct readout of pH referenced to 25°C. Otherwise a
calculation is required.
8.2 Sample Containers—Two clean, narrow-mouth 250 to 500 mL bottles with cap are required. The mouth diameter should be
the minimum necessary to allow insertion of the electrode(s), and temperature compensator or thermometer. A 3-hole stopper may
be used to hold these sensors. The container and cap minimize exposure to atmospheric gases.
8.3 Combination pH Electrode—A probe incorporating the measuring, reference and temperature compensator functions in a
single unit is recommended for its ease of insertion into a very narrow mouth sample container. Each function should conform to
the characteristics in 8.4 – 8.6. Where this is not available, individual electrodes and compensator (8.4 – 8.6) may be used with
a 3-hole stopper to hold them and seal the container during measurement.
8.4 pH Glass Electrode—The pH response of the glass electrode shall conform to the requirements set forth in 12.1 through 12.5
of Test Methods D1293. New glass electrodes and those that have been stored dry shall be conditioned and maintained as
recommended by the manufacturer.
8.5 Reference Electrode—Double junction design, having a refillable flowing junction with a positive electrolyte leakage rate
not to exceed 10 μL/h. A sealed reference electrode is suitable only if it is internally pressurized to force an electrolyte flow
outward. Prepare and maintain the reference electrode according to the manufacturer’s instructions.
8.6 Temperature Compensator—See paragraph 10.4 in Test Methods D1293. The automatic temperature compensator must
adapt for use with fit into the sample container to measure the temperature of the water within the container.
8.7 Temperature Indicator—A direct temperature indicating device must be used to measure sample water temperature within
the sample container if an automatic temperature compensator is not used.
8.8 Equipment for this test method should be dedicated for high purity water use only.
9. Sampling and Sample Handling
9.1 Equipment described in Section 8 should be dedicated for high purity water use only.
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9.1 The sample containers should be rinsed three times before use, with sample or reagent water. The electrode(s) and
temperature device should be rinsed three times, using the same procedure as with the sample containers after each calibration in
pH buffer solutions and before they are inserted into the first sample container.
9.2 Static grab samples are taken via vinylclean tubing attached to the sample take-off point. The other end of the tubing is
inserted to the bottom of the sample container. The sample flows through the vinyl tube, into the bottom of the container, and then
over the top to trough or sink drain. After a 5-min flush of the container with the sample water, the tubing is removed and the cap
immediately installed, excluding any air. This seals the container and isolates the sample from the atmosphere. The second
container is filled and capped in the same way. In the lab, the first container is used to rinse the electrodes and temperature device
and the second container is used for measurement.
10. Calibration
10.1 Turn on the pH meter and allow it to warm up according to the manufacturer’s instructions. If an on-line meter is used
that has a solution temperature coefficient setting, be sure it is turned off or is set to 0 pH/°C for calibration in buffer solutions.
Conventional Nernst temperature compensation should be active at all times and requires no setting.
10.2 Remove the electrode(s) and temperature compensator (if used) from storage. Check the reference electrode for proper
electrolyte level as recommended by the manufacturer.
10.3 Calibrate the electrode(s) and pH meter at two points according to manufacturer’s instructions. Also, refer to Section 12
of Test Methods D1293 for guidelines on the calibration of a pH meter and electrode assembly. Use a quiescent sample of Buffer
A and Buffer B if the sample point of interest is below 7.0 pH. Use a quiescent sample of Buffer A and Buffer C if the sample
point of interest is above 7.0 pH. Use laboratory glassware dedicated for this service only. Thoroughly rinse the electrode(s) and
glassware with reagent water three times between immersion in each buffer solution.
10.4 Obtain calibration precision of the pH electrode(s) and the pH meter by repeating the two-point calibration described in
10.3, making any necessary readjustments to the pH meter. If the electrode slope (efficiency) is less than 94 % or greater than
101 %, refer to manufacturer’s instructions for repair or replacement of electrode(s).
NOTE 2—The pH electrodes in use may pass the above calibration procedures (10.1 – 10.4), but caution should be taken. pH electrodes that are not
specifically designed for use in high purity water may develop problems with liquid junction potential during actual test measurements.
10.5 Determine the frequency of the two-point calibration of the electrode(s) and the pH meter based on experience. Perform
calibration at least daily when pure water sample testing is performed daily. For less frequent pure water sample testing, perform
calibration procedures just prior to a consecutive series of sample tests.
10.6 Thoroughly rinse the electrode(s) and the temperature compensator or temperature reading device and the sample container
three times with sample or reagent water after calibration and before measurement.
11. Procedure
11.1 Before starting the procedure, make certain the two sample containers are clean and empty. See Section 9.
NOTE 3—If on-line pH sensors are to be calibrated by this test method (refer to Test Method D5128), steps mustshould be taken to prevent the
disturbance of the on-line pressure and flow rate while the grab sample is being taken. TheAppropriate pressure and flow controlregulation equipment
shown inshould be Fig. 1 will control and stabilize this on-line pressure and flow rate byinstalled at the grab sample point upstream of the on-line sensor.
See D3370means of rotameter. Appendix Appendix X2 Rprovides and secondary pressure regulatorguidance on grab sample PRcalibration even when
1 1
a sample is taken at grab sample point of on-line instrumentation.S (see Appendix X2).
11.2 Open the sample valve V and pull sample without interrupting the sample flow-rate or pressure of the on-line pH sensor
assembly if used (see on-line pH sensor manufacturer’s instructions for its optimum flowrate). The grab sample flowrate should
be at least 200 mL/min.
11.3 With the sample flowing, rinse the outside surfaces of the vinyl sample tubing for at least 15 seconds by holding it with
the open discharge end upward like a fountain, allowing the sample to flow over the outside tubing surfaces for more than the
length that will be later immersed in the sample container, allowing the flow to drain into the sampling trough or sink.
11.4 Run the end of the vinyl sample tubing to the bottom of the sample container letting the sample overflow into the sink.
11.5 Thoroughly flush the sample container with sample water for at least 5 min at a flow rate of at least 200 mL/min.
11.6 Remove the vinyl sample tubing and immediately cap the container. Repeat for the second container and close sample
valve valve.V .
11.7 Transport the sample containers to the laboratory without delay and immediately immerse the sensors (which have already
been calibrated and rinsed thoroughly) in the first container for 1 min to acclimate them to the sample composition and temperature.
11.8 Move the sensors to the second container. Take the pH measurement and temperature measurements within 3 min in order
to minimize KCl contamination from the reference electrode and change in the temperature of the grab sample.
11.9 Report the pH value with 0.01 pH resolution and the temperature with 0.1°C resolution.
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11.10 If the pH must be referenced to 25°C and the sample is not already at 25.0 6 0.5°C, determine the applicable solution
temperature coefficient and calculate the pH at 25.0°C in accordance with Appendix X1 and report it with resolution of 0.01 pH.
11.11 To use this pH measurement to calibrate an on-line pH sensor, call this reading the value from 11.9 or 11.10 R and refer
to the procedure addendum in Appendix X3X2.
NOTE 4—If no further samples are to be taken, the calibrated pH electrode(s) may be kept stored in the sample container containing the last pure water
sample until the next calibration or sample requirement. For long term storage of the pH electrode(s), replace them in their respective soaker bottles and
appropriate storage solutions (see manufacturer’s instructions).
12. Quality Control
12.1 Two-point instrument calibration must be performed according to the manufacturer’s instructions within 12 h of making
measurements.
12.2 With power plant samples containing predominately ammonia and negligible carbon dioxide, an accurate correlation with
specific conductivity can be made. See Fig. X3.1. Under these conditions, periodically verify pH readings corrected to 25°C by
solution temperature compensation with the conductivity also referenced to 25°C. Some two-channel conductivity instrumentation
includes an option for the c
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