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
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. 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
2.1 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
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.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Eriochrome is a registered trademark of Huntsman Petrochemical, LLC.
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.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8192 − 23
TABLE 1 Freedom of Reaction from Interferences
Maximum Concentration Maximum Concentration
Without Interference in Without Interference in the
Substance
the Total Hardness Test, Calcium Hardness Test,
mg/L mg/L
+++
Aluminum, Al 20 5
+ A
Ammonium, NH 2 000
–
Bicarbonate, HCO . 500
Bromine, Br . 2
++
Cadmium, Cd 20 .
– –
Carbonate, CO 1 000 50
–
Chloride, Cl 10 000 .
Chlorine, Cl . 2
– –
Chromate, CrO 500 500
++
Cobalt, Co 0.3 .
++
Copper, Cu 20 2
+++ B
Iron, ferric, Fe 10 20
++ B
Iron, ferrous, Fe 10 20
++
Lead, Pb 20 5
FIG. 1 Titration Curve
++ C C
Manganese, Mn 1 10
++ D
Nickel, Ni 0.5 .
–
Nitrate, NO 500 500
titrant added to achieve this equivalence point is then used to
–
Nitrite, NO 500 500
calculate the calcium and magnesium ions in water. – – –
Phosphate, PO 100 .
– –
Silicate, SiO 200 100
++ E E
5. Significance and Use
Strontium, Sr
– –
Sulfate, SO 10 000 10 000
5.1 Hardness salts in water, notably calcium and – –
Sulfite, SO 500 500
magnesium, are the primary cause of tube and pipe scaling, Tannin, Quebracho 200 50
++++
Tin, stannic, Sn 10 5
which frequently causes failures and loss of process efficiency
++
Tin, stannous, Sn 10 5
due to clogging or loss of heat transfer, or both. ++
Zinc, Zn 20 5
A
5.2 Hardness is caused by any polyvalent cations, but those No data are available.
B
+2 +2
Iron will not interfere in concentrations up to 200 mg/L. However, the red color of
other than Ca and Mg are seldom present in more than
the end point may return in about 30 s.
trace amounts. The term hardness was originally applied to C
Manganese will not interfere in concentrations up to 10 mg/L if a few crystals of
K Fe(CN) ·3H O are added to the buffer immediately before use.
water in which it was hard to wash; it referred to the
4 6 2
D
Accurate results can be obtained in the presence of 1 mg/L nickel, but the end
soap-wasting properties of water. With most normal alkaline
point is slow under these conditions.
E
water, these soap-wasting properties are directly related to the
If strontium is present, it will be titrated with calcium and magnesium.
calcium and magnesium content.
6. Interferences
6.1 The substances shown in Table 1 represent the highest
7.2 Analytical Balance capable of weighing at least to the
concentrations that have not been found to interfere with this
nearest 0.01 g.
determination.
8. Reagents
7. Apparatus
8.1 Purity of Reagents—Reagent grade chemicals shall be
7.1 Automatic Titrator:
used in all tests. Unless otherwise indicated, it is intended that
7.1.1 Automatic Titrator, consisting of a control unit, optical
all reagents shall conform to the specifications of the Commit-
sensing electrode, and stirrer. An automatic titrator must be
tee on Analytical Reagents of the American Chemical Society.
capable of adding fixed increments of titrant (monotonic) with
Other grades may be used, provided it is first ascertained that
endpoint seeking capabilities as prescribed in this test method.
the reagent is of sufficiently high purity to permit its use
Titrant increment additions of 0.1 mL are recommended for
without lessening the accuracy of the determination.
this test method. At the very least, the automatic titration
system shall meet the performance and specification require-
8.2 Purity of Water—Unless otherwise indicated, reference
ments as warranted by the manufacturer. to water shall be understood to mean reagent water conforming
7.1.1.1 The optical sensor must produce light between to Specification D1193, Type I. Other reagent water types may
500 nm to 700 nm wavelength to detect color change of be used provided it is first ascertained that the water is of
3, 4
Eriochrome Black T hardness indicator and hydroxyl naph- sufficiently high purity to permit its use without adversely
thol blue. It shall interface with the automatic titrator in such a affecting the precision and bias of the test method.
way that the optical signal received from the change in color in
the sample beaker is converted to millivolts and an end point
volume of EDTA to equivalence can be determined. This end
ACS Reagent Chemicals, Specifications and Procedures for Reagents and
Standard-Grade Reference Materials, American Chemical Society, Washington,
point volume shall be used to calculate hardness. Refer to the
DC. For suggestions on the testing of reagents not listed by the American Chemical
optical
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