ASTM D5128-90(2005)
(Test Method)Standard Test Method for On-Line pH Measurement of Water of Low Conductivity
Standard Test Method for On-Line pH Measurement of Water of Low Conductivity
SIGNIFICANCE AND USE
pH measurements are typically made in solutions that contain relatively large amounts of acid, base, or dissolved salts. Under these conditions, pH determinations may be made quickly and precisely. Continuous on-line pH measurements in water samples of low conductivity are more difficult (4, 5). These low ionic strength solutions are susceptible to contamination from the atmosphere, sample stream hardware, and the pH electrodes. Variations in the constituent concentration of low conductivity waters cause liquid junction potential shifts (see 3.1.1) resulting in pH measurement errors. The aggressive nature and the high electrical resistance of pure and ultra-pure, low conductivity waters may degrade the pH measurement electrodes resulting in unstable and drifting pH output signals.
It is essential to make on-line pH measurements of low conductivity water as accurately as possible to determine the proper control of pH adjustment chemicals, the effectiveness of demineralizer equipment, the event and nature of impurity contamination of the water, and information pertaining to the overall status of the pure water system.
SCOPE
1.1 This test method covers the precise on-line determination of pH in water samples of conductivity lower than 100 [mu]S/cm (see Tables 1 and 2) over the pH range of 3 to 11 (see Fig. 1), under field operating conditions, utilizing a sealed, non-refillable, reference electrode. pH measurements of water of low conductivity are problematical for conventional pH electrodes, methods, and related measurement apparatus.
1.2 This test method includes the procedures and equipment required for the continuous pH measurement of low conductivity water sample streams including the requirements for the control of sample stream pressure, flow rate, and temperature.
1.3 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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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D 5128 – 90 (Reapproved 2005)
Standard Test Method for
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On-Line pH Measurement of Water of Low Conductivity
This standard is issued under the fixed designation D5128; 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 (e) indicates an editorial change since the last revision or reapproval.
TABLE 1 Calculated Conductivity and pH Values at 25°C of Low
1. Scope
A
Concentrations of NaOH in Pure Water
1.1 This test method covers the precise on-line determina-
NOTE 1—This table tabulates the theoretical conductivity and pH
tion of pH in water samples of conductivity lower than 100
values of low levels of NaOH in pure water as calculated from available
µS/cm (see Table 1 and Table 2) over the pH range of 3 to 11
thermodynamic data.
(seeFig.1),underfieldoperatingconditions,utilizingasealed,
NOTE 2—ToillustratethehighsensitivityofthesamplepHattheselow
non-refillable, reference electrode. pH measurements of water
concentrations to contaminants, the last column lists errors that would
of low conductivity are problematical for conventional pH
result if the sample were contaminated with an additional 1 mg/Lthrough
electrodes, methods, and related measurement apparatus.
sample or equipment handling errors.
1.2 Thistestmethodincludestheproceduresandequipment
Sample Sample D pH Error from Addi-
Sample
Concentration, Conductivity, tional 1 mg/L NaOH
required for the continuous pH measurement of low conduc-
pH
mg/L µS/cm Contaminate
tivity water sample streams including the requirements for the
0.001 0.055 7.05 D 2.35
control of sample stream pressure, flow rate, and temperature.
0.010 0.082 7.45 D 1.95
1.3 This standard does not purport to address all of the
0.100 0.625 8.40 D 1.03
safety concerns, if any, associated with its use. It is the
1.0 6.229 9.40 D 0.30
8.0 49.830 10.30 D 0.05
responsibility of the user of this standard to establish appro-
A
Data courtesy of Ref (13). This data developed from algorithms originally
priate safety and health practices and determine the applica-
published in Ref (14).
bility of regulatory limitations prior to use.
2. Referenced Documents
3. Terminology
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2.1 ASTM Standards: 3.1 Definitions of Terms Specific to This Standard:
D1129 Terminology Relating to Water
3.1.1 liquid junction potential—a dc potential that appears
D1193 Specification for Reagent Water at the point of contact between the reference electrode’s salt
D1293 Test Methods for pH of Water
bridge and the sample solution. Ideally this potential is near
D2777 Practice for Determination of Precision and Bias of
Applicable Methods of Committee D19 on Water
TABLE 2 Calculated Conductivity and pH Values at 25°C of Low
A
D3864 Guide for Continual On-Line Monitoring Systems Concentrations of HCl in Pure Water
for Water Analysis
NOTE 1—This table tabulates the theoretical conductivity and pH
D4453 Practice for Handling of Ultra-Pure Water Samples
values of low levels of HCl in pure water as calculated from available
2.2 ASTM Proposal: thermodynamic data
NOTE 2—ToillustratethehighsensitivityofthesamplepHattheselow
P228 ProposedTestMethodsforpHMeasurementofWater
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concentrations to contaminants, the last column lists errors that would
of Low Conductivity
result if the sample were contaminated with an additional 1 mg/Lthrough
sample or equipment handling errors.
Sample Sample D pH Error from Addi-
1
This test method is under the jurisdiction ofASTM Committee D19 on Water Sample
Concentration, Conductivity, tional 1 mg/L HCl Con-
pH
and is the direct responsibility of Subcommittee D19.03 on Sampling of Water and
mg/L µS/cm taminate
Water-Formed Deposits,Analysis of Water for Power Generation and Process Use,
0.001 0.060 6.94 D2.38
On-Line Water Analysis, and Surveillance of Water.
0.010 0.134 6.51 D 1.95
Current edition approved Jan. 1, 2005. Published January 2005.
2
0.100 1.166 5.56 D 1.03
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
1.0 11.645 4.56 D 0.30
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
8.0 93.163 3.66 D 0.05
Standards volume information, refer to the standard’s Document Summary page on
A
the ASTM website. Data courtesy of Ref (13). This data developed from algorithms originally
3
Withdrawn. published in Ref (14).
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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D 5128 – 90 (2005)
diffusion contact to the sample, resists significant dilution for
periods up to several months on continuous operation.
4.2 Thistestmethoddescribestheapparatusandprocedures
to be used for the continuous on-line pH measureme
...
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