ASTM D8192-23

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: D8192 − 23
Standard Test Method for
1
Hardness in Colored and Colorless Water
This standard is issued under the fixed designation D8192; 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 D2777 Practice for Determination of Precision and Bias of
Applicable Test Methods of Committee D19 on Water
1.1 This test method covers the determination of hardness in
D3370 Practices for Sampling Water from Flowing Process
water by titration with potentiometric detection via optical
Streams
sensor. This test method is applicable to waters that are free of
D5847 Practice for Writing Quality Control Specifications
chemicals that will complex calcium or magnesium. The lower
for Standard Test Methods for Water Analysis
detection limit of this test method is approximately 2 mg ⁄L to
5 mg/L as CaCO ; the upper limit can be extended to all
3
3. Terminology
concentrations by sample dilution. It is possible to differentiate
3.1 Definitions—For definitions of terms used in this test
between hardness due to calcium ions and that due to magne-
method, refer to Terminology D1129.
sium ions by this test method.
3.2 Definitions of Terms Specific to This Standard:
1.2 This test method is applicable to both colorless and
3.2.1 equivalent parts per million (epm), n—unit chemical
colored water samples including groundwater, surface water,
equivalent weight of solute per million unit weights of solu-
wastewater, and drinking water.
tion.
1.3 The values stated in SI units are to be regarded as
3.2.2 laboratory control sample (LCS), n—solution with
standard. No other units of measurement are included in this
certified hardness.
standard.
3.2.3 optical sensor, n—potentiometric sensor for titration
1.4 This standard does not purport to address all of the
with photometric endpoint recognition.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
4. Summary of Test Method
priate safety, health, and environmental practices and deter-
4.1 Calcium and magnesium ions in water are sequestered
mine the applicability of regulatory limitations prior to use.
by the addition of disodium ethylenediamine tetraacetate
1.5 This international standard was developed in accor-
(EDTA). The equivalence point of the reaction is detected by
dance with internationally recognized principles on standard-
3, 4
means of Eriochrome Black T, which has a red color in the
ization established in the Decision on Principles for the
presence of calcium and magnesium and a blue color when
Development of International Standards, Guides and Recom-
they are sequestered. This can be determined by both manual
mendations issued by the World Trade Organization Technical
colorimetric titration with visual detection or by automatic
Barriers to Trade (TBT) Committee.
titration using an optical sensor. During a manual titration the
titrant is added by the operator and color change is determined
2. Referenced Documents
by visual inspection. This can lead to subjective and inaccurate
2
2.1 ASTM Standards:
results. This method describes the use of an automatic titrator
D1066 Practice for Sampling Steam
equipped with an optical sensor to accurately add known
D1129 Terminology Relating to Water
volumes of titrant and accurately determine the titration
D1193 Specification for Reagent Water
equivalence or end point. During an automatic titration, the
optical sensor measures absorbance at a particular wavelength
that is converted to a millivolt signal and plotted versus titrant
1
This test method is under the jurisdiction of ASTM Committee D19 on Water
volume. See Fig. 1. At the equivalence point, where the color
and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents
change from red to blue occurs, there will be a corresponding
in Water.
inflection or break point on the titration curve. The volume of
Current edition approved April 15, 2023. Published May 2023. DOI: 10.1520/
D8192-23.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Eriochrome is a registered trademark of Huntsman Petrochemical, LLC.
4
Standards volume information, refer to the standard’s Document Summary page on 3–Hydroxy–4–(1–hydroxy–2–napththyl) azo–7–nitro–1 naphthalenesulfonic
the ASTM website. acid, sodium salt, Color Index 14645.
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