Designation: D 1125 – 95 (Reapproved 1999)

Standard Test Methods for

Electrical Conductivity and Resistivity of Water1
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. A number 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 tivity of a Flowing High Purity Water Sample2

1.1 These test methods cover the determination of the E 1 Specification for ASTM Thermometers4
electrical conductivity and resistivity of water. The following
3. Terminology
test methods are included:
Range Sections
3.1 Definitions:
Test Method A—Field and Routine Laboratory 10 to 200 000 12 to 18 3.1.1 electrical conductivity—the reciprocal of the a-c re-
Measurement of Static (Non-Flowing) µS/cm sistance in ohms measured between opposite faces of a
Samples
Test Method B—Continuous In-Line Measure 5 to 200 000 19 to 23
centimetre cube of an aqueous solution at a specified tempera-
ment µ S/cm ture.
1.2 These test methods have been tested in reagent water. It NOTE 1—The unit of electrical conductivity is siemens per centimetre.
is the user’s responsibility to ensure the validity of these test (The previously used units of mhos/cm are numerically equivalent to
methods for waters of untested matrices. S/cm.) The actual resistance of the cell, Rx, is measured in ohms. The
conductance, 1/Rx, is directly proportional to the cross-sectional area, A
1.3 For measurements below the range of these test meth- (in cm 2), and inversely proportional to the length of the path, L (in cm):
ods, refer to Test Method D 5391.
1.4 This standard does not purport to address all of the 1/Rx 5 K·A/L
safety concerns, if any, associated with its use. It is the The conductance measured between opposite faces of a
responsibility of the user of this standard to establish appro- centimetre cube, K, is called conductivity. Conductivity values
priate safety and health practices and determine the applica- are usually expressed in microsiemens/centimetre or in
bility of regulatory limitations prior to use. siemens/centimetre at a specified temperature, normally 25°C.
3.1.2 electrical resistivity—the a-c resistance in ohms mea-
2. Referenced Documents sured between opposite faces of a centimetre cube of an
2.1 ASTM Standards: aqueous solution at a specified temperature.
D 1066 Practice for Sampling Steam2 NOTE 2—The unit of electrical resistivity is ohm-centimetre. The actual
D 1129 Terminology Relating to Water2 resistance of the cell, Rx, is measured in ohms, and is directly proportional
D 1192 Specification for Equipment for Sampling Water to the length of the path, L (in cm), and inversely proportional to the
and Steam in Closed Conduits3 cross-sectional area, A (in cm 2):
D 1193 Specification for Reagent Water2 Rx 5 R·L/A
D 2186 Test Method for Deposit-Forming Impurities in
The resistance measured between opposite faces of a centi-
Steam3
metre cube, R, is called resistivity. Resistivity values are
D 2777 Practice for Determination of Precision and Bias of
usually expressed in ohm·centimetre, or in megohm · centime-
Applicable Methods of Committee D-19 on Water2
tre, at a specified temperature, normally 25°C.
D 3370 Practices for Sampling Water from Closed Con-
3.1.3 For definitions of other terms used in these methods,
duits2
refer to Terminology D 1129.
D 4519 Test Method for On-Line Determination of Anions
3.2 Symbols:Symbols:
and Carbon Dioxide in High Purity Water by Cation
3.2.1 Symbols used in the equations in Sections 14 and 16
Exchange and Degassed Cation Conductivity2
are defined as follows:
D 5391 Test Method for Electrical Conductivity and Resis-
J 5 cell constant, cm −1,
K 5 conductivity at 25°C, µS/cm,
1
These test methods are under the jurisdiction of Committee D–19 on Water and Kx 5 measured conductance, S,
are the direct responsibility of Subcommittee D19.11 on Standards for Water for K1 5 conductivity of the KCl in the reference solution at the
Power Generation and Processes.
Current edition approved Oct. 10, 1995. Published December 1995. Originally
temperature of measurement (Table 1), µS/cm,
published as D 1125 – 50 T. Last previous edition D 1125 – 91.
2
Annual Book of ASTM Standards, Vol 11.01.
3 4
Annual Book of ASTM Standards, Vol 11.02. Annual Book of ASTM Standards, Vol 14.03.

Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.

1
 D 1125
TABLE 1 Electrical Conductivity Values Assigned to the Potassium Chloride in the Reference Solution A
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
D 0.001 Dilute 100 mL of Solution C to 1 L at 20°C 0 77.69B
18 127.54B
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).

K2 5 conductivity of the water used to prepare the reference 5.3 If an unshielded cell is used to measure the resistivity/
solution, at the same temperature of measurement, µS/cm, conductivity of high resistivity water there is a possibility of
Q 5 temperature correction factor (see Section 11), electrical pickup causing erroneous reading. For this reason it
R 5 resistivity at 25°C, ohm · cm, is recommended that conductivity cells for this application be
Rx 5 measured resistance, ohm. of coaxial shielded type or equivalent, and that the cables and
instrument also be shielded.
4. Significance and Use
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
such as boiler water, boiler feedwater, cooling water, and saline
conductivity cell with alternating current and, together with the
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)5 to significant levels in condensed steam (see
Test Methods D 2186 and D 4519, and Ref (2)), or pure salt 6.1.1 In highly conductive solutions—Uncompensated elec-
solutions. trode polarization due to excessive current density at the
4.1.2 Where the principal interest in the use of conductivity electrode surfaces can cause negative conductivity errors.
methods is to determine steam purity, see Ref (3). These test Insufficient series capacitance at the electrode/solution inter-
methods may also be used for checking the correctness of face can allow charging effects to distort the a-c measurement
water analyses (4). and cause errors if not compensated. Leadwire resistance can
add significantly to the measured resistance.
5. Interferences 6.1.2 In low conductivity solutions—Excessive parallel ca-
5.1 Exposure of a sample to the atmosphere may cause pacitance in the cell and extension leadwire can shunt the
changes in conductivity/resistivity, due to loss or gain of measurement and cause positive conductivity errors. Tempera-
dissolved gases. This is extremely important in the case of very ture compensation errors can be significant below 5 µS/cm if
pure waters with low concentrations of dissolved ionized variable coefficient algorithms are not employed as described
materials. The carbon dioxide, normally present in the air, can in Test Method D 5391.
drastically increase the conductivity of pure waters by approxi- 6.1.3 These sources of error are minimized by an appropri-
mately 1 µS/cm. Contact with air should be avoided by using ate combination of a-c drive voltage, wave shape, frequency,
flow-through or in-line cell where feasible. Chemically pure phase correction, wave sampling technique and temperature
inert gases, such as nitrogen or helium, may be used to blanket compensation designed in by the instrument manufacturer. The
the surface of samples. instrument manufacturer’s recommendations shall be followed
5.2 Undissolved or slowly precipitating materials in the in selecting the proper cell constant, leadwire size, and length
sample can form a coating on the electrodes of the conductivity and maintenance of the electrode surface condition for the
cell that may cause erroneous readings. For example, biofoul- range of measurement. Calibration may be in either conduc-
ing of the cell or a build-up of filming amines may cause poor tivity or resistivity units.
cell response. In most cases these problems can be eliminated 6.1.4 When an output signal is required from an on-line
by washing the cells with appropriate solvents. instrument, it shall be electrically isolated from the cell drive
circuit to prevent interaction between a solution ground at the
5
The boldface numbers in parentheses refer to the list of references at the end of
cell and an external circuit ground.
these test methods. 6.2 Cells:

2
 D 1125
6.2.1 Flow-through or in-line cells shall be used for mea- rate to 0.1°C is acceptable for this application, when the
suring conductivities lower than 10 µS/cm (resistivities higher instrument is not provided with manual or automatic tempera-
than 100 000 ohm · cm), to avoid contamination from the ture compensation. (See Section 11).
atmosphere. However, samples with conductivity greater than
10 µS/cm may also be measured. In all other cases, pipet-type 7. Reagents
or dip cells can also be used. Pipet or dip cells may be used to 7.1 Purity of Reagents—Reagent grade chemicals shall be
measure samples in the range of 1 to 10 µS/cm if the sample is used in all tests. Unless otherwise indicated, it is intended that
protected by an inert gaseous layer of nitrogen or helium. all reagents shall conform to the specifications of the Commit-
6.2.2 A cell constant shall be chosen which will give a tee on Analytical Reagents of the American Chemical Society,
moderate cell resistance, matching the instrument manufactur- where such specifications are available.6 Other grades may be
er’s requirements for the range of measurement. For laboratory used, provided it is first ascertained that the reagent is of
bridges, Table 2 provides conservative guidelines. sufficiently high purity to permit its use without lessening the
6.2.3 Flow-through and in-line cells shall be mounted so accuracy of the determination.
that continuous flow of the sample through or past it is 7.2 Purity of Water—Unless otherwise indicated, references
possible. Flow rate should be maintained at a constant rate to water shall be understood to mean reagent water conforming
consistent with the manufacturer’s recommendations for the to Specification D 1193, Type I. In making up the potassium
cell being used, particularly at conductivities below 10 µS/cm. chloride solutions for cell constant determinations, use water of
The cell shall retain calibration under conditions of pressure, conductivity not greater than 1.5 µS/cm. If necessary, stabilize
flow, and temperature change, and shall exclude the atmo- to the laboratory atmosphere by aspirating air through the
sphere and be constructed of corrosion resistant, chemically water from a fritted glass or stainless steel gas dispersion tube.
inert materials. The chamber or cell shall be equipped with The equilibrium point is reached when the conductivity re-
means for accurate measurement of the temperature. mains constant but not greater than 1.5µ S/cm. The equilibrium
6.2.4 Platinized cells shall not be used for measurement of conductivity must be added to Table 1.
conductivities below 10 µS/cm, except that a trace or flash of 7.3 Alcohol—95 % ethyl alcohol. Alternatively, use isopro-
platinum black may be used on cells for measurements in the pyl alcohol or methyl alcohol.
range of 0.1 to 10 µS/cm (see 9.4). Because of the cost and 7.4 Aqua Regia (3 + 1)—Mix 3 volumes of concentrated
fragility of platinum cells, it is common practice to use hydrochloric acid (HCl, sp gr 1.19) with 1 volume of concen-
titanium, monel, and graphite electrodes for measurements trated nitric acid (HNO3, sp gr 1.42). This reagent should be
with accuracies on the order of 1 %. Note that these electrodes used immediately after its preparation.
may require special surface preparation. Titanium and monel 7.5 Ethyl Ether.
electrodes are especially suitable for high resistance solutions 7.6 Hydrochloric Acid (sp gr 1.19)—Concentrated HCl.
such as ultrapure water, but may introduce a small surface 7.7 Hydrochloric Acid (1 + 1)—Mix 1 volume of concen-
resistance which limits their accuracy when the measured trated HCl (sp gr 1.19) with 1 volume of water.
resistance is less than a few thousand ohms (1). 7.8 Platinizing Solution—Dissolve 1.5 g of chloroplatinic
6.2.5 It is recommended that cells intended for the measure- acid (H2PtCl6· 6H2O) in 50 mL of water containing 0.0125 g of
ment of conductivities below 10 µS/cm be reserved exclusively lead acetate (Pb(C2H3O2)2).
for such applications. 7.9 Potassium Chloride (KCl)—The assay of the potassium
6.3 Temperature Probes: chloride must be 100.06 0.1 %. This standardization grade of
6.3.1 For Temperature Control—The measurement of tem- KCl is available from NIST and from commercial sources. Dry
perature is necessary for control of a temperature bath, manual at 150°C for 2 h or until weight loss is less than 0.02 %; store
temperature compensation, or automatic temperature compen- in desiccator.
sation, or all of these. Thermometers, thermistors, and resis- 7.10 Potassium Chloride Reference Solution A—Dissolve
tance temperature detectors with accuracies of 60.1°C or 74.2460 g of KCl (weighed in air) in water and dilute to 1 L at
better are acceptable for this application. An ASTM precision 20 6 2°C in a Class A volumetric flask.
thermometer, Number 63C, as defined in Specification E 1, is 7.11 Potassium Chloride Reference Solution B—Dissolve
recommended. The calibration of temperature probes should be 7.4365 g of KCl (weighed in air) in water and dilute to 1 L at
checked periodically by comparison to a reference temperature 20 6 2°C in a Class A volumetric flask.
probe whose calibration is traceable to the U.S. National 7.12 Potassium Chloride Reference Solution C—Dissolve
Institute of Science and Technology (formerly NBS) or equiva- 0.7440 g of KCl (weighed in air) in water and to dilute 1 L at
lent. 20 6 2°C in a Class A volumetric flask.
6.3.2 For Temperature Correction—A thermometer accu- 7.13 Potassium Chloride Reference Solution D—Dilute 100
mL of reference solution C to 1 L with water at 20 6 2°C in
TABLE 2 Recommended Cell Constants for Various Conductivity
Ranges
Range of Conductivity, µS/cm Cell Constant, cm −1 6
Reagent Chemicals, American Chemical Society Specifications, American
0.05 to 10 0.01 to 0.1 Chemical Society, Washington, DC. For suggestions on the testing of reagents not
10 to 200 0.1 to 1 listed by the American Chemical Society, see Analar Standards for Laboratory
200 to 5000 1 to 10 Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
5000 to 1 000 000 10 to 100 and National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,
MD.

3
 D 1125
a Class A volumetric flask shortly before using. Store the using from 1.5 to 3 coulombs/cm2 of electrode area. For
solution in a glass-stoppered bottle of chemically resistant example, for an electrode having a total area (both sides) of 10
glass which has only been used for storage of this solution. cm2, the plating time at a current of 20 mA would be from 121⁄2
to 25 min. The current density may be from 1 to 4 mA/cm2 of
NOTE 3—The electrical conductivity of each of the referenced solutions
is given in Table 1. The values for electrical conductivities for the electrode area. Plate the electrodes one at a time with the aid of
solutions are those of G. Jones and B. C. Bradshaw (5), confirmed in 1987 an extra electrode. During the plating, agitate the solution
(6) and 1989 (7) by the National Institute of Standards and Technology gently, or use ultrasonic bath. When not in use, platinized cells
(NIST). The data of T. Shedlovsky (8) are used for Solution D. Solutions should be filled with water to prevent the drying out of
A, B, and C were prepared by Jones and Bradshaw using the molal or electrodes while in storage.
demal basis by dissolving 71.1352, 7.4191, and 0.7453 g, respectively, of 9.4 For measurement of conductivities in the range of 0.1 to
KCl (in vacuum) per 1000 g of solution (in vacuum). The method of
preparation given in Table 1 includes the corrections to weights of KCl (in
10µ S/cm, a trace or flash coating of platinum black may be
air against brass weights) per litre of solutions at 20°C and assumes the used. For a flash coating, the cell is left in the platinic chloride
density of KCl 5 1.98, density of brass 5 8.4, and the density of solution for only 2 or 3 s at a current of about 20 mA. A flash
air 5 0.00118. The densities of 1.0 N, 0.10 N, and 0.010 N KCl at 20°C, coating will leave the electrodes with their metallic appear-
1.04420, 1.00280, and 0.99871 g/mL, respectively, were interpolated from ance, but with a faint blackish tint.
the data in the International Critical Tables (9).
10. Calibration
8. Sampling 10.1 Measuring Instrument—A calibrating resistor to be
8.1 Samples shall be collected in accordance with Practice used in place of the conductivity cell may be furnished by the
D 1066, Specification D 1192, and Practices D 3370, as appli- manufacturer, together with information as to the correct scale
cable. reading the instrument shall assume when this resistor is
8.2 Avoid exposure of the sample to atmospheres containing connected in place of the conductivity cell. Follow the manu-
ammonia or acidic gases. Protect the sample to avoid gain or facturer’s instructions and periodically check the instrument.
loss of dissolved gases, particularly if there is some delay Alternatively, standard resistors with certified accuracy of
before the conductivity measurements are made. Preferably, 60.05 % may be used with appropriate calculations adapted to
use a flow-type cell for sampling and measuring condensed the instrument scale. Some instruments may be factory cali-
steam or water having a conductivity of less than 10 µS/cm. brated, taking into account the resistance of the cable wire
For waters in the range of 5 to 10 µS/cm, a dip-type cell may attached to the conductivity cell; this may be indicated by a
be used if a layer of chemically pure nitrogen or helium is warning to avoid cutting or extending the cable length. When
maintained over the surface. lead wires between the instrument and the cell are long, check
the installation at least once by connecting the calibrating
9. Preparation of Electrodes resistor at the far end of the lead wire and noting the difference,
9.1 If the cell constant as checked does not fall within if any, in reading with the long lead wire in the circuit. Check
reasonable limits of its nominal value, it is necessary to clean portable or manually operated instruments in a similar manner
or replatinize the electrodes or replace the cell. In general, no with one or several calibrating resistors. Note errors of signifi-
mechanical cleaning should be attempted. In high purity water cant magnitude and correct subsequent conductivity readings.
measurements, where the presence of finely divided platinum Calibration checks should be made at values as close as
is undesirable due to its long retention of impurities, platini- possible to the conductivity values expected in samples. This is
zation of electrodes should be omitted, especially for testing of especially important if the measurement is made at the extreme
water having a conductivity below 10 µS/cm (see 9.4). On the high or low end of an instrument’s range. Instruments sub-
other hand, clean and well-platinized electrodes are increas- jected to field use may require more frequent checks of
ingly important in testing water of higher conductivities, calibration. For direct reading instruments, the conductivity
particularly above 1000 µS/cm. check resistance in ohms equals the cell constant (cm −1)
9.2 The cell manufacturer’s instructions may be followed divided by the conductivity desired (S/cm) while the resistivity
for cleaning the electrodes as well as other parts of the cell. A check resistance equals cell constant (cm −1) times the resis-
suitable cleaning solution consists of a mixture of 1 part by tivity desired (ohm · cm).
volume of isopropyl alcohol, 1 part of ethyl ether, (with 10.2 Conductivity Cells—For field and routine laboratory
polymer cells, check compatibility) and 1 part of HCl (1 + 1). testing, the calibration of conductivity cells may be checked by
After cleaning, thoroughly flush the cell with water. If the old comparing instrument readings taken with the cell in question
platinum black coating is to be removed, judicious application against readings on the same sample or series of samples taken
of aqua regia to the electrodes, or electrolysis in HCl (sp gr with a conductivity cell of known or certified cell constant.
1.19) is frequently successful. Exercise care to ensure that both working and reference cells
9.3 Platinize the electrodes of the cell with H2PtCl6 solu- are at the same temperature or, alternatively, at different but
tion. A suitable plating apparatus consists of a 6 volt a-c supply, known temperatures so that a correction as later described can
a variable resistor, milliammeter, and an electrode. The deposit be applied. Resistivity-reading instruments will indicate in
should present a black, velvety appearance and should adhere direct proportion to the cell constant, while conductivity
well to the electrode surface. The procedure for platinizing is reading instruments will indicate in inverse proportion to cell
not critical. Follow the manufacturer’s instructions or the constant. Conductivity cells may be calibrated with reference
following guidelines. Good platinized coatings are obtained solutions in accordance with Section 14.

4
 D 1125
11. Temperature Coefficient of Conductivity/Resistivity temperature T, and this ratio or correction factor, Q, taken from
11.1 The conductivity/resistivity of water and aqueous so- the smoothed curve.
lutions depends strongly upon the temperature. (See Table 3.) NOTE 4—Depending on the type of compensation used, uncompensated
The normal practice is to report conductivity and resistivity readings may be obtained by setting temperature to 25°C, by putting the
values referenced to 25.0°C. The coefficient varies depending temperature probe in a 25°C bath, or by substituting an electrical
upon the nature and composition of the dissolved electrolytes, resistance equivalent to 25°C.
and upon the concentration. The dissociation of water contrib- 11.5 When using an instrument provided with a manual or
utes significantly to conductivities at 5 µS/cm or less and automatic temperature compensator, follow the manufacturer’s
increases the temperature coefficient from near 2 % per °C at instructions to calibrate the compensator or check its accuracy
above 5 µS/cm to near 5 % per °C at 0.055 µS/cm. To avoid and applicability to the sample being tested.
making a correction, it is necessary to hold the temperature of
the sample to 25 6 0.1°C. If this cannot be done, the TEST METHOD A—FIELD AND ROUTINE
temperature coefficient must be determined and a correction LABORATORY MEASUREMENT OF STATIC (NON-
applied. This requires a series of conductivity and temperature FLOWING) SAMPLES
measurements on the sample over the required temperature
range. Where automatic temperature compensation is used, the 12. Scope
temperature compensation algorithm should be chosen that 12.1 This test method is applicable to field and routine
best simulates the composition of the samples to be tested. In laboratory measurements of the electrical conductivity of water
high purity water, 5µ S/cm or less, the variable coefficient shall using static samples.
be automatically determined and applied across the range of
measurement for both the dissociation of water and its inter- 13. Summary of Test Method
action with salt or other contaminations. (See Test Method 13.1 This test method utilizes dip-type or pipet-type con-
D 5391 and Refs (10), (11), and (12) for more information.) ductivity cells for testing static samples having conductivities
11.2 In static systems, exercise care to avoid change of greater than 10µ S/cm. Temperature control and correction
composition caused by loss of volatile constituents or by methods are also provided.
pick-up of contaminants from the air to the containing vessel
during the series of measurements. 14. Determination of Cell Constant
11.3 In flowing systems, provide means for variable heating 14.1 For the purposes of this test method, the cell constant
or cooling so that the desired range of temperature will be of the conductivity cell used shall be known within 61 %. The
covered. Regulate the rate of flow through each cell so as to manufacturer’s certification of the cell constant within this
keep the cell adequately flushed. accuracy is generally considered satisfactory but the user is
11.4 From the data obtained, plot conductivity against advised that damage could occur in shipment and it is best to
temperature. Make sure that the conductivity readings are recheck the cell constant when received. If the conductivity
uncompensated. From the curve a table of temperature correc- cell has been in service for a period subsequent to this
tion factors may be prepared, or the ratio of conductivity at certification, it shall be rechecked by the manufacturer, or in
temperature T to conductivity at 25°C may be plotted against the laboratory.
14.2 Rinse the conductivity cell several times with water,
TABLE 3 Conductivity Values of Pure Water and Increases Due
then at least twice with the KCl reference solution that has a
to Sodium Chloride A conductivity nearest to that of the sample under test (Table 1).
Conductivity of Pure Water, Conductivity Increase Due to 1
Control the solution temperature to 25 6 0.1°C. Measure the
Temperature, °C resistance of the cell. Repeat the measurement on additional
µ S/cm mg/L NaCl, µS/cm
0 0.011649 1.1463 portions of the KCl reference solution until the value obtained
5 0.016607 1.3311 remains constant to within the limits of precision in accordance
10 0.02310 1.5261 with Section 18.
15 0.03143 1.7297
20 0.04194 1.9435 14.3 For instruments reading measured resistance in ohms,
25 0.05501 2.1642 calculate the cell constant:
30 0.07101 2.3935
35 0.09037 2.6296 J 5 10 26 · Rx ~K1 1 K2!
40 0.11351 2.8760
45 0.14081 3.1257 14.4 For instruments reading measured conductance in Si-
50 0.17268 3.3841 emens, calculate the cell constant:
55 0.2095 3.6476
60 0.2514 3.9179 J 5 10 26 · ~K1 1 K2!/Kx
65 0.2987 4.1882
70 0.3516 4.4773 NOTE 5—Since the conductivities of a mixture of two solutions are not
75 0.4102 4.7648 exactly additive, the use of K1 + K2 is only an approximation and requires
80 0.4744 5.0556 that K2 be much smaller than K1.
85 0.5444 5.3550
90 0.6205 5.6527 15. Procedure
95 0.7030 5.9264
100 0.7930 6.1933 15.1 Precision Method Using Temperature Control—Use a
A
From Thornton (1). dip-type or pipet-type cell. Rinse the cell, container, and

5
 D 1125
thermometer thoroughly several times with water and then two 18. Precision and Bias 7
or more times with the sample. Adjust the temperature to 25 6 18.1 This test method was tested by nine laboratories, at
0.1°C as indicated by a thermometer as described in 6.3.1. four concentration levels, with each operator analyzing each
Allow sufficient time for equalization of temperatures. Read sample on three different days. These collaborative test data
the conductance or resistance. Calculate conductivity or resis- were obtained on reagent water. For other matrices, these data
tivity according to Section 16 using Q 5 1, since no tempera- may not apply. These data were developed using the routine
ture correction is required. method (temperature correction) described in 15.2. The actual
15.2 Routine Method Using Temperature Correction—Use temperature of samples tested by the participants ranged from
a dip-type or pipet-type cell. Rinse the conductivity cell 18.5 to 26.0°C.
thoroughly several times with water and then two or more 18.1.1 Precision—The precision of this test method within
times with the sample. Measure the resistance or the conduc- its designated range appears in Table 4.
tance, and the temperature (to the nearest 0.1°C), on successive 18.1.2 Bias—Recoveries of known amounts of conductivity
portions of the sample until a constant value is obtained. If the values in a series of prepared standards appears in Table 5.
measuring instrument is provided with a manual temperature 18.2 This test method meets requirements for precision and
compensator, adjust this to the sample temperature value bias specified in Practice D 2777 – 86.
before reading the instrument. If an automatic temperature
compensator is provided, no adjustment is necessary, but TEST METHOD B—CONTINUOUS, IN-LINE
sufficient time must be allowed to permit equalization of MEASUREMENT
temperature. If the instrument has no means of temperature
compensation, determine a temperature correction factor in 19. Scope
accordance with the instructions in Section 11 to convert 19.1 This test method is applicable to the continuous, in-line
readings to 25°C. If instrument temperature compensation is measurement of the electrical conductivity of water.
used, calculate conductivity or resistivity according to Section
16 using Q 5 1, otherwise use Q as determined in Section 11. 20. Summary of Test Method
20.1 This test method utilizes a flow-type conductivity cell
16. Calculation
to sample a continuous stream of the water under test.
16.1 For instruments reading measured resistance in ohms, Temperature control and correction methods are also provided.
calculate the conductivity of the sample:
K 5 10 6 · J/RxQ
21. Procedure
16.2 For instruments reading measured resistance in ohms, 21.1 Precision Method Using Temperature Control—Use a
calculate the resistivity of the sample: flow-type conductivity cell. Adjust the sample stream, known
to be free of corrosion products and other particulate contami-
R 5 RxQ/J nation, to a proper flow rate and bring the temperature to 25 6
16.3 For instruments reading measured conductance in Si- 0.1°C as indicated by a thermometer as described in 6.3. Allow
emens, calculate the conductivity of the sample: sufficient time to reach equalization of temperatures. Read the
K 5 10 6 · JKx/Q
conductance or resistance. Calculate the conductivity or resis-
tivity according to Section 16 using Q 5 1, since no tempera-
16.4 For instruments reading measured conductance in Si- ture correction is required.
emens, calculate the resistivity of the sample: 21.2 Routine Method Using Temperature Correction—Use
R 5 Q/JKx a flow-type conductivity cell. Adjust the sample stream, known
16.5 Automatic recorders and indicators provided with tem- to be free of corrosion products and other particulate contami-
perature compensators, when used with conductivity cells of nation, to a proper flow rate and bring the temperature to a
the required cell constant, usually read directly in terms of steady value as near 25°C as possible. Read the temperature to
siemens per centimetre orµ S/cm referred to 25°C. No calcu- the nearest 0.1°C. If the measuring instrument is provided with
lations are necessary if the compensator is corrected for the a manual temperature compensator, adjust this to the sample
solution in the cell. temperature value. If an automatic temperature compensator is
provided, no adjustment is necessary but sufficient time must
17. Report
17.1 Report the value of the conductivity at 25°C in terms of
microsiemens per centimetre to the nearest 1 % of the deter- 7
Supporting data are available from ASTM Headquarters. Request RR:D-19-
mined conductivity if measurements were made at 25 6 0.1°C, 1139.
otherwise report to the nearest 3 % of the determined conduc-
tivity. TABLE 4 Precision of Test Method A
17.2 Alternatively, report the value of the resistivity at 25°C Mean Concentration, Overall Precision, St, Single-Operator Precision
in terms of ohm-centimetres to the nearest 1 % of the deter- µS/cm µS/cm Pooled, So, µS/cm
mined resistivity if measurements were made at 25 6 0.1°C, 25.6 3.4 0.83
otherwise report to the nearest 3 % of the determined resistiv- 162.0 6.1 3.8
1378.8 60.9 14.1
ity. 108169 6600 2918

6
 D 1125
TABLE 5 Bias of Test Method A 22.2 Alternatively, report the value of the resistivity at 25°C
Amounts
Mean
Statistically
in terms of ohm-centimetres to the nearest 1 % of the deter-
Recovery,x, Bias % Bias
Added, µS/cm
µS/cm
Significant mined resistivity if measurements were made at 25 6 0.1°C,
otherwise report to the nearest 3 % of the determined resistiv-
27.8 25.6 −2.2 − 7.9 yes
167.6 162.0 −5.6 − 3.3 yes ity.
1408.8 1378.8 −30.0 − 2.1 yes
111342 108169 − 3173 − 2.8 yes
23. Precision and Bias
23.1 Since this test method involves continuous sampling, a
be allowed to permit equalization of temperatures. Read the general statement of precision and bias is not applicable.
conductance or resistance. If the instrument has no means of 23.2 Experience has shown that errors of 1 to 30 % may be
temperature compensation, determine a temperature correction encountered, depending on the equipment and techniques used.
factor in accordance with Section 11 to convert readings to Errors in temperature compensation are especially troublesome
25°C. If instrument temperature compensation is used, calcu- at conductivities below 10 µS/cm. Additional errors may be
late conductivity or resistivity according to Section 16 using Q encountered with low constant cells because of the difficulties
5 1, otherwise use Q as determined in Section 11. involved in verifying the cell constant at low conductivity
22. Report levels.
22.1 Report the value of the conductivity at 25°C in terms of
microsiemens per centimetre to the nearest 1 % of the deter- 24. Keywords
mined conductivity if measurements were made at 25 6 0.1°C, 24.1 cell constant; conductivity; resistivity; temperature co-
otherwise report to the nearest 3 % of the determined conduc- efficient
tivity.

REFERENCES

(1) Thornton, R. D., Light, T. S., “A New Approach to Accurate Resis- Specific Conductance of Primary Standard KCl Solutions,” Journal of
tivity Measurement of High Purity Water,” Ultrapure Water, Vol 6, No. Solution Chemistry, Vol 18, No. 6, 1989, pp. 515–528.
5, 1989, pp. 14–26. (8) Shedlovsky, T.,“ The Electrolytic Conductivity of Some Univalent
(2) Symposium on Power Plant Instrumentation for Measurement of Electrolytes in Water at 25°C,” Journal of American Chemical Society,
High-Purity Water Quality, ASTM STP 742, ASTM, 1981. Vol 54, 1932, p. 1411.
(3) “Methods for Determination of Quality and Purity of Steam,” ASME (9) International Critical Tables, Vol 3, 1928, p. 87.
Power Test Code, Supplement on Instruments and Apparatus, Part (10) Light, T. S., Licht, L. L. “Conductivity and Resistivity of Water from
19.11. the Melting to Critical Points,” Analytical Chemistry, Vol 59, 1987,
(4) Rossum, J. R., “Conductance Method for Checking Accuracy of Water pp. 2327–2330.
Analyses,” Analytical Chemistry, Vol 21, 1949, p. 631. (11) Harned, H. S., Owen, B. B., The Physical Chemistry of Electrolytic
(5) Jones, G., Bradshaw, B. C., “The Measurement of the Conductance of Solutions, Third Ed., Reinhold Publishing Corp., New York, 1958, p.
Electrolytes, V. A. Redetermination of the Conductance of Standard 234.
KCl Solutions in Absolute Units,” Journal of American Chemical (12) Gray, D. M., Tenney, A. S., “Improved Conductivity/Resistivity
Society, Vol 55, 1933, p. 1780. Temperature Compensation for High Purity Water,” Ultrapure Water,
(6) Wu, Y. C., Koch, W. F., Hamer, W. J., Kay, R. L.,“ Review of July/August, 1986.
Electrolytic Conductance Standards,” Journal of Solution Chemistry, (13) Glasstone, S., An Introduction to Electrochemistry, D. Van Nostrand,
Vol 16, No. 12, 1987, pp. 985–997. New York, 1942, pp. 50, 56, 61.
(7) Wu, Y. C., Pratt, K. W., Koch, K. F.,“ Determination of the Absolute

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