ASTM D6569-23

Standard Test Method for On-Line Measurement of pH

SIGNIFICANCE AND USE
5.1 pH is a measure of the hydrogen ion activity in water. It is a major parameter affecting the corrosivity and scaling properties of water, biological life in water and many applications of chemical process control. It is therefore important in water purification, use and waste treatment before release to the environment.  
5.2 On-line pH measurement is preferred over laboratory measurement to obtain real time, continuous values for automatic control and monitoring purposes.
SCOPE
1.1 This test method covers the continuous determination of pH of water by electrometric measurement using the glass, the antimony or the ion-selective field-effect transistor (ISFET) electrode as the sensor.  
1.2 This test method does not cover measurement of samples with less than 100 μS/cm conductivity. Refer to Test Method D5128.  
1.3 This test method does not cover laboratory or grab sample measurement of pH. Refer to Test Method D1293.  
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.5 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.6 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.

General Information

• Status: Published
• Publication Date: 31-Mar-2023
• ICS: 71.040.50 - Physicochemical methods of analysis
• 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

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: D6569 − 23
Standard Test Method for
1
On-Line Measurement of pH
This standard is issued under the fixed designation D6569; 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 D3370 Practices for Sampling Water from Flowing Process
Streams
1.1 This test method covers the continuous determination of
D3864 Guide for On-Line Monitoring Systems for Water
pH of water by electrometric measurement using the glass, the
Analysis
antimony or the ion-selective field-effect transistor (ISFET)
D5128 Test Method for On-Line pH Measurement of Water
electrode as the sensor.
of Low Conductivity
1.2 This test method does not cover measurement of
samples with less than 100 μS/cm conductivity. Refer to Test
3. Terminology
Method D5128.
3.1 Definitions—For definitions of terms used in this test
1.3 This test method does not cover laboratory or grab
method, refer to Terminology D1129, Test Method D1293 and
sample measurement of pH. Refer to Test Method D1293.
Guide D3864.
1.4 The values stated in SI units are to be regarded as
3.2 Definitions of Terms Specific to This Standard:
standard. No other units of measurement are included in this
3.2.1 liquid junction potential, n—the dc potential which
standard.
appears at the point of contact between the reference elec-
1.5 This standard does not purport to address all of the
trode’s salt bridge and the sample solution.
safety concerns, if any, associated with its use. It is the
3.2.1.1 Discussion—Ideally this potential is near zero and is
responsibility of the user of this standard to establish appro-
stable. However, in samples with extreme pH it becomes larger
priate safety, health, and environmental practices and deter-
by an unknown amount and is a zero offset.
mine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accor-
4. Summary of Test Method
dance with internationally recognized principles on standard-
4.1 pH is measured as a voltage between measuring elec-
ization established in the Decision on Principles for the
trode and reference electrode elements. The sensor assembly
Development of International Standards, Guides and Recom-
typically includes a temperature compensator to compensate
mendations issued by the World Trade Organization Technical
for the varying output of the measuring electrode due to
Barriers to Trade (TBT) Committee.
temperature.
2. Referenced Documents
4.2 The sensor signals are processed with an industrial pH
2
2.1 ASTM Standards: analyzer/transmitter.
D1129 Terminology Relating to Water
4.3 The equipment is calibrated with standard pH buffer
D1193 Specification for Reagent Water
solutions encompassing or in close proximity to the anticipated
D1293 Test Methods for pH of Water
pH measurement range.
D2777 Practice for Determination of Precision and Bias of
Applicable Test Methods of Committee D19 on Water
5. Significance and Use
5.1 pH is a measure of the hydrogen ion activity in water. It
is a major parameter affecting the corrosivity and scaling
1
This test method is under the jurisdiction of ASTM Committee D19 on Water
properties of water, biological life in water and many applica-
and is the direct responsibility of Subcommittee D19.03 for Sampling of Water and
Water-Formed Deposits, Surveillance of Water, and Flow Measurement of Water.
tions of chemical process control. It is therefore important in
Current edition approved April 1, 2023. Published April 2023. Originally
water purification, use and waste treatment before release to
approved in 2000. Last previous edition approved in 2014 as D6569 – 14 which was
the environment.
withdrawn January 2023 and reinstated in April 2023. DOI: 10.1520/D6569-23.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
5.2 On-line pH measurement is preferred over laboratory
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
measurement to obtain real time, continuous values for auto-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. matic control and monitoring purposes.
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D6569 − 23
6. Interferences the samples being measured and make the correction on all
measurements. The pH to be reported is referenced to 25 °C
6.1 Pressur
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