ASTM D1125-95(2005)
(Test Method)Standard Test Methods for Electrical Conductivity and Resistivity of Water
Standard Test Methods for Electrical Conductivity and Resistivity of Water
SIGNIFICANCE AND USE
These test methods are applicable for such purposes as impurity detection and, in some cases, the quantitative measurement of ionic constituents dissolved in waters. These include dissolved electrolytes in natural and treated waters, such as boiler water, boiler feedwater, cooling water, and saline and brackish water.
4.1.1 Their concentration may range from trace levels in pure waters (1)4 to significant levels in condensed steam (see Test Methods D 2186 and D 4519, and Ref (2)), or pure salt solutions.
4.1.2 Where the principal interest in the use of conductivity methods is to determine steam purity, see Ref (3). These test methods may also be used for checking the correctness of water analyses (4).
SCOPE
1.1 These test methods cover the determination of the electrical conductivity and resistivity of water. The following test methods are included:RangeSectionsTest Method A-Field and Routine Laboratory10 to 200 000 12 to 18Measurement of Static (Non-Flowing) Samplesμ S/cmTest Method B-Continuous In-Line Measure 5 to 200 00019 to 23mentμ S/cm
1.2 These test methods have been tested in reagent water. It is the user's responsibility to ensure the validity of these test methods for waters of untested matrices.
1.3 For measurements below the range of these test methods, refer to Test Method D 5391.
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.
1.4 This test method is applicable to field and routine laboratory measurements of the electrical conductivity of water using static samples.
1.5 This test method is applicable to the continuous, in-line measurement of the electrical conductivity of water.
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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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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 1125–95 (Reapproved 2005)
Standard Test Methods for
Electrical Conductivity and Resistivity of Water
This standard is issued under the fixed designation D 1125; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope D4519 Test Method for On-Line Determination of Anions
and Carbon Dioxide in High Purity Water by Cation
1.1 These test methods cover the determination of the
Exchange and Degassed Cation Conductivity
electrical conductivity and resistivity of water. The following
D5391 Test Method for Electrical Conductivity and Resis-
test methods are included:
tivity of a Flowing High Purity Water Sample
Range Sections
E1 Specification forASTM Liquid-in-GlassThermometers
Test Method A—Field and Routine Laboratory 10 to 200 000 12 to 18
Measurement of Static (Non-Flowing) µS/cm
Samples
3. Terminology
Test Method B—Continuous In-Line Measure 5 to 200 000 19 to 23
3.1 Definitions:
ment µ S/cm
3.1.1 electrical conductivity—the reciprocal of the a-c re-
1.2 These test methods have been tested in reagent water. It
sistance in ohms measured between opposite faces of a
is the user’s responsibility to ensure the validity of these test
centimetre cube of an aqueous solution at a specified tempera-
methods for waters of untested matrices.
ture.
1.3 For measurements below the range of these test meth-
ods, refer to Test Method D5391. NOTE 1—The unit of electrical conductivity is siemens per centimetre.
(The previously used units of mhos/cm are numerically equivalent to
1.4 This standard does not purport to address all of the
S/cm.) The actual resistance of the cell, R , is measured in ohms. The
x
safety concerns, if any, associated with its use. It is the
conductance, 1/R , is directly proportional to the cross-sectional area, A
x
responsibility of the user of this standard to establish appro-
(in cm ), and inversely proportional to the length of the path, L (in cm):
priate safety and health practices and determine the applica-
1/R 5 K·A/L
x
bility of regulatory limitations prior to use.
The conductance measured between opposite faces of a
2. Referenced Documents
centimetre cube, K, is called conductivity. Conductivity values
are usually expressed in microsiemens/centimetre or in
2.1 ASTM Standards:
D1066 Practice for Sampling Steam siemens/centimetre at a specified temperature, normally 25°C.
D1129 Terminology Relating to Water 3.1.2 electrical resistivity—the a-c resistance in ohms mea-
D1192 Specification for Equipment for Sampling Water sured between opposite faces of a centimetre cube of an
and Steam in Closed Conduits aqueous solution at a specified temperature.
D1193 Specification for Reagent Water
NOTE 2—Theunitofelectricalresistivityisohm-centimetre.Theactual
D2186 Test Method for Deposit-Forming Impurities in
resistanceofthecell, R ,ismeasuredinohms,andisdirectlyproportional
x
Steam
to the length of the path, L (in cm), and inversely proportional to the
D2777 Practice for Determination of Precision and Bias of
cross-sectional area, A (in cm ):
Applicable Methods of Committee D19 on Water
R 5 R·L/A
x
D3370 PracticesforSamplingWaterfromClosedConduits
The resistance measured between opposite faces of a centi-
metre cube, R, is called resistivity. Resistivity values are
usually expressed in ohm·centimetre, or in megohm · centime-
These test methods are under the jurisdiction of Committee D19 on Water and tre, at a specified temperature, normally 25°C.
are the direct responsibility of Subcommittee D19.03 on Sampling of Water and
3.1.3 For definitions of other terms used in these methods,
Water-Formed Deposits, Surveillance of Water, and Flow Measurement of Water.
refer to Terminology D1129.
Current edition approved April 1, 2005. Published April 2005. Originally
3.2 Symbols:Symbols:
approved in 1950. Last previous edition approved in 1999 as D1125–95 (1999).
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.2.1 Symbols used in the equations in Sections 14 and 16
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
are defined as follows:
Standards volume information, refer to the standard’s Document Summary page on
−1
J =cell constant, cm ,
the ASTM website.
Withdrawn. K =conductivity at 25°C, µS/cm,
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 1125–95 (2005)
A
TABLE 1 Electrical Conductivity Values Assigned to the Potassium Chloride in the Reference Solution
Approximate Electrical
Reference Tempera-
Normality of Method of Preparation Conductivity,
Solution ture, °C
Solution µS/cm
A 1 74.2460 g of KCl weighed in air per 1 L of 0 65 176
solution at 20°C 18 97 838
25 111 342
B 0.1 7.4365 g of KCl weighed in air per 1 L of 0 7 138
solution at 20°C 18 11 167
25 12 856
C 0.01 0.7440 g of KCl weighed in air per 1 L of 0 773.6
solution at 20°C 18 1 220.5
25 1 408.8
B
D 0.001 Dilute 100 mL of Solution C to 1 L at 20°C 0 77.69
B
18 127.54
25 146.93
A
Excluding the conductivity of the water used to prepare the solutions. (See 7.2 and Section 14.) These tabulated conductivity values are in international units. When
using measuring instruments calibrated in absolute units, multiply the tabular values by 0.999505.
B
From Glasstone (13).
K =measured conductance, S, cell that may cause erroneous readings. For example, biofoul-
x
K =conductivity of the KCl in the reference solution at the ing of the cell or a build-up of filming amines may cause poor
temperature of measurement (Table 1), µS/cm, cell response. In most cases these problems can be eliminated
K =conductivity of the water used to prepare the reference by washing the cells with appropriate solvents.
solution, at the same temperature of measurement, µS/cm, 5.3 If an unshielded cell is used to measure the resistivity/
Q =temperature correction factor (see Section 11), conductivity of high resistivity water there is a possibility of
R =resistivity at 25°C, ohm · cm, electrical pickup causing erroneous reading. For this reason it
R =measured resistance, ohm. is recommended that conductivity cells for this application be
x
of coaxial shielded type or equivalent, and that the cables and
4. Significance and Use
instrument also be shielded.
4.1 These test methods are applicable for such purposes as
6. Apparatus
impurity detection and, in some cases, the quantitative mea-
6.1 Measuring Circuit—The instrument may be a manually
surement of ionic constituents dissolved in waters. These
operated wheatstone bridge or the equivalent, or a direct
include dissolved electrolytes in natural and treated waters,
reading analog or digital meter. Instruments shall energize the
suchasboilerwater,boilerfeedwater,coolingwater,andsaline
conductivitycellwithalternatingcurrentand,togetherwiththe
and brackish water.
cell and any extension leadwire, shall be designed to reduce
4.1.1 Their concentration may range from trace levels in
errors from the following sources:
pure waters (1) to significant levels in condensed steam (see
6.1.1 In highly conductive solutions—Uncompensated elec-
Test Methods D2186 and D4519, and Ref (2)), or pure salt
trode polarization due to excessive current density at the
solutions.
electrode surfaces can cause negative conductivity errors.
4.1.2 Where the principal interest in the use of conductivity
Insufficient series capacitance at the electrode/solution inter-
methods is to determine steam purity, see Ref (3). These test
face can allow charging effects to distort the a-c measurement
methods may also be used for checking the correctness of
and cause errors if not compensated. Leadwire resistance can
water analyses (4).
add significantly to the measured resistance.
5. Interferences
6.1.2 In low conductivity solutions—Excessive parallel ca-
pacitance in the cell and extension leadwire can shunt the
5.1 Exposure of a sample to the atmosphere may cause
measurement and cause positive conductivity errors.Tempera-
changes in conductivity/resistivity, due to loss or gain of
ture compensation errors can be significant below 5 µS/cm if
dissolvedgases.Thisisextremelyimportantinthecaseofvery
variable coefficient algorithms are not employed as described
pure waters with low concentrations of dissolved ionized
in Test Method D5391.
materials. The carbon dioxide, normally present in the air, can
6.1.3 These sources of error are minimized by an appropri-
drasticallyincreasetheconductivityofpurewatersbyapproxi-
ate combination of a-c drive voltage, wave shape, frequency,
mately 1 µS/cm. Contact with air should be avoided by using
phase correction, wave sampling technique and temperature
flow-through or in-line cell where feasible. Chemically pure
compensationdesignedinbytheinstrumentmanufacturer.The
inert gases, such as nitrogen or helium, may be used to blanket
instrument manufacturer’s recommendations shall be followed
the surface of samples.
in selecting the proper cell constant, leadwire size, and length
5.2 Undissolved or slowly precipitating materials in the
and maintenance of the electrode surface condition for the
samplecanformacoatingontheelectrodesoftheconductivity
range of measurement. Calibration may be in either conduc-
tivity or resistivity units.
6.1.4 When an output signal is required from an on-line
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
these test methods. instrument, it shall be electrically isolated from the cell drive
D 1125–95 (2005)
TABLE 2 Recommended Cell Constants for Various Conductivity
probe whose calibration is traceable to the U.S. National
Ranges
InstituteofScienceandTechnology(formerlyNBS)orequiva-
−1
Range of Conductivity, µS/cm Cell Constant, cm
lent.
0.05 to 10 0.01 to 0.1
6.3.2 For Temperature Correction—A thermometer accu-
10 to 200 0.1 to 1
rate to 0.1°C is acceptable for this application, when the
200 to 5000 1 to 10
instrument is not provided with manual or automatic tempera-
5000 to 1 000 000 10 to 100
ture compensation. (See Section 11).
7. Reagents
circuit to prevent interaction between a solution ground at the
7.1 Purity of Reagents—Reagent grade chemicals shall be
cell and an external circuit ground.
used in all tests. Unless otherwise indicated, it is intended that
6.2 Cells:
all reagents shall conform to the specifications of the Commit-
6.2.1 Flow-through or in-line cells shall be used for mea-
tee onAnalytical Reagents of theAmerican Chemical Society,
suring conductivities lower than 10 µS/cm (resistivities higher
where such specifications are available. Other grades may be
than 100000 ohm · cm), to avoid contamination from the
used, provided it is first ascertained that the reagent is of
atmosphere. However, samples with conductivity greater than
sufficiently high purity to permit its use without lessening the
10 µS/cm may also be measured. In all other cases, pipet-type
accuracy of the determination.
or dip cells can also be used. Pipet or dip cells may be used to
7.2 Purity of Water—Unlessotherwiseindicated,references
measure samples in the range of 1 to 10 µS/cm if the sample is
towatershallbeunderstoodtomeanreagentwaterconforming
protected by an inert gaseous layer of nitrogen or helium.
to Specification D1193, Type I. In making up the potassium
6.2.2 A cell constant shall be chosen which will give a
chloridesolutionsforcellconstantdeterminations,usewaterof
moderate cell resistance, matching the instrument manufactur-
conductivity not greater than 1.5 µS/cm. If necessary, stabilize
er’srequirementsfortherangeofmeasurement.Forlaboratory
to the laboratory atmosphere by aspirating air through the
bridges, Table 2 provides conservative guidelines.
water from a fritted glass or stainless steel gas dispersion tube.
6.2.3 Flow-through and in-line cells shall be mounted so
The equilibrium point is reached when the conductivity re-
that continuous flow of the sample through or past it is
mainsconstantbutnotgreaterthan1.5µS/cm.Theequilibrium
possible. Flow rate should be maintained at a constant rate
conductivity must be added to Table 1.
consistent with the manufacturer’s recommendations for the
7.3 Alcohol—95% ethyl alcohol.Alternatively, use isopro-
cell being used, particularly at conductivities below 10 µS/cm.
pyl alcohol or methyl alcohol.
The cell shall retain calibration under conditions of pressure,
7.4 Aqua Regia (3 + 1)—Mix 3 volumes of concentrated
flow, and temperature change, and shall exclude the atmo-
hydrochloric acid (HCl, sp gr 1.19) with 1 volume of concen-
sphere and be constructed of corrosion resistant, chemically
trated nitric acid (HNO , sp gr 1.42). This reagent should be
inert materials. The chamber or cell shall be equipped with
used immediately after its preparation.
means for accurate measurement of the temperature.
7.5 Ethyl Ether.
6.2.4 Platinized cells shall not be used for measurement of
7.6 Hydrochloric Acid (sp gr 1.19)—Concentrated HCl.
conductivities below 10 µS/cm, except that a trace or flash of
7.7 Hydrochloric Acid (1 + 1)—Mix 1 volume of concen-
platinum black may be used on cells for measurements in the
trated HCl (sp gr 1.19) with 1 volume of water.
range of 0.1 to 10 µS/cm (see 9.4). Because of the cost and
7.8 Platinizing Solution—Dissolve 1.5 g of chloroplatinic
fragility of platinum cells, it is common practice to use
acid(H PtCl·6H O)in50mLofwatercontaining0.0125gof
2 6 2
titanium, monel, and graphite electrodes for measurements
lead acetate (Pb(C H O ) ).
2 3 2 2
with accuracies on the order of 1%. Note that these electrodes
7.9 Potassium Chloride (KCl)—The assay of the potassium
may require special surface preparation. Titanium and monel
chloride must be 100.06 0.1%. This standardization grade of
electrodes are especially suitable for high resistance solutions
KClisavailablefromNISTandfromcommercialsources.Dry
such as ultrapure water, but may introduce a small surface
at 150°C for 2 h or until weight loss is less than 0.02%; store
resistance which limits their accuracy when the measured
in desiccator.
resistance is less than a few thousand ohms (1).
7.10 Potassium Chloride Reference Solution A—Dissolve
6.2.5 Itisrecommendedthatcellsintendedforthemeasure-
74.2460 g of KCl (weighed in air) in water and dilute to 1 Lat
mentofconductivitiesbelow10µS/cmbereservedexclusively
20 6 2°C in a Class A volumetric flask.
for such applications.
7.11 Potassium Chloride Reference Solution B—Dissolve
6.3 Temperature Probes:
7.4365 g of KCl (weig
...
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