ASTM D5391-99
(Test Method)Standard Test Method for Electrical Conductivity and Resistivity of a Flowing High Purity Water Sample
Standard Test Method for Electrical Conductivity and Resistivity of a Flowing High Purity Water Sample
SCOPE
1.1 This test method covers the determination of electrical conductivity and resistivity of high purity water samples below 10 [mu]S/cm (above 0.1 Mohm-cm). It is applicable to both continuous and periodic measurements but in all cases, the water must be flowing in order to provide representative sampling. Static grab sampling cannot be used for such high purity water. Continuous measurements are made directly in pure water process lines, or in side stream sample lines to enable measurements on high temperature or high pressure samples, or both.
1.2 The values stated in SI units are to be regarded as the standard.
1.3 This standard does not purport to address all of the safety problems, 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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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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.
An American National Standard
Designation:D 5391–99
Standard Test Method for
Electrical Conductivity and Resistivity of a Flowing High
Purity Water Sample
This standard is issued under the fixed designation D 5391; 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.
1. Scope D 3864 Guide for Continual On-Line Monitoring Systems
for Water Analysis
1.1 This test method covers the determination of electrical
D 4519 Test Method for On-Line Determination of Anions
conductivityandresistivityofhighpuritywatersamplesbelow
and Carbon Dioxide in High Purity Water by Cation
10 µS/cm (above 0.1 Mohm-cm). It is applicable to both
Exchange and Degassed Cation Conductivity
continuous and periodic measurements but in all cases, the
water must be flowing in order to provide representative
3. Terminology
sampling. Static grab sampling cannot be used for such high
3.1 Definitions:
purity water. Continuous measurements are made directly in
3.1.1 electricalconductivity—refertoTestMethodsD1125.
pure water process lines, or in side stream sample lines to
3.1.2 electrical resistivity—refer to Test Methods D1125.
enable measurements on high temperature or high pressure
3.1.3 For definitions of other terms used in these test
samples, or both.
methods, refer to Terminology D1129.
1.2 The values stated in SI units are to be regarded as the
3.2 Definitions of Terms Specific to This Standard:
standard.
3.2.1 cell constant—the ratio of the length of the path, L
1.3 This standard does not purport to address all of the
(cm) and the cross-sectional area of the solution, A (cm ),
safety concerns, if any, associated with its use. It is the
between the electrodes of a conductivity/resistivity cell, with
responsibility of the user of this standard to establish appro-
−1
units of cm . In high purity water measurements, the cell
priate safety and health practices and determine the applica-
−1
constant is normally between 0.001 and 0.1 cm to prevent
bility of regulatory limitations prior to use.
−1
electrical interference. This is lower than the 1 cm of the
2. Referenced Documents standard centimetre cube and is taken into account by direct
reading instrument ranges that are matched with specific cell
2.1 ASTM Standards:
2 constants.
D 1066 Practice for Sampling Steam
D 1125 Test Methods for Electrical Conductivity and Re-
4. Summary of Test Method
sistivity of Water
2 4.1 Conductivity or resistivity is measured with a cell and
D 1129 Terminology Relating to Water
temperaturesensororcompensatorinaflowing,closedsystem
D 1192 Specification for Equipment for Sampling Water
2 to prevent trace contamination from wetted surfaces and from
and Steam in Closed Conduits
2 the atmosphere. Specialized temperature compensation cor-
D 1193 Specification for Reagent Water
rects the measurement to 25°C, taking into account the
D 2186 Test Methods for Deposit-Forming Impurities in
3 temperature effects on the ionization of water, the contami-
Steam
nants, and interactions between the two. In the absence of
D 2777 Practice for Determination of Precision and Bias of
specialized temperature compensation, the sample temperature
Applicable Methods of Committee D-19 on Water
is controlled to 25 6 0.2°C.
D 3370 Practices for Sampling Water from Closed Con-
4.2 To determine the cell constant of a high purity conduc-
duits
tivity cell with an instrument capable of accurate measurement
over the range of pure water to 150 µS/cm with a single cell
constant, Test Methods D1125 are used directly. Manufactur-
This test method is under the jurisdiction ofASTM Committee D-19 on Water
ers’certificationofcellconstanttraceabilitybythismeansisan
and is the direct responsibility of Subcommittee D19.03 on Sampling of Water and
Water-Formed Deposits, Surveillance of Water, and Flow Measurement of Water.
acceptable alternative.
Current edition approved June 10, 1999. Published September 1999. Originally
4.3 To determine the cell constant of a high purity conduc-
published as D 5391–93. Last previous edition D 5391–93.
tivity cell with an instrument which does not accurately cover
Annual Book of ASTM Standards, Vol 11.01.
Annual Book of ASTM Standards, Vol 11.02. the range from pure water to 150 µS/cm with a single cell
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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.
D 5391–99
constant, a secondary standard cell is used that has an inter- andcandevelopchromatograph-likeretentionofionicspecies,
mediate cell constant with precise value determined by Test resultinginverylongdelaytimes.Precautionsaredescribedin
Methods D1125. That secondary standard cell is then used in Section 9.
low conductivity water (not a standard) and readings are 6.3 Cell and flow chamber surfaces will slowly leach trace
comparedwiththoseofthelowconstantcellundertest.Inthis ioniccontaminants,evidencedbyincreasingconductivityread-
manner, the cell constant of the latter is determined. Manufac- ings with very low or zero flowrate. There must be sufficient
turers’certificationofcellconstanttraceabilitybythismeansis flowtokeepthesecontaminantsfromaccumulatingtothepoint
an acceptable alternative. that they affect the measurement. The high and convoluted
surface area of platinized cells precludes their use for high
5. Significance and Use
purity measurements for this reason.
6.4 Capacitance of the cell and extension leadwire, espe-
5.1 Conductivity measurements are typically made on
ciallyinhighpurityrangescanaddsignificantpositiveerrorto
samples of moderate to high ionic strength where contamina-
conductance readings (negative error to resistance readings).
tion of open samples in routine laboratory handling is negli-
The measuring instrument must be designed to accommodate
gible. Under those conditions, standard temperature compen-
cell and leadwire characteristics in high purity water as
sation using coefficients of 1 to 3% of reading per degree
described in 7.1.1 and Annex A1. In addition, the instrument
Celsius over wide concentration ranges is appropriate. In
manufacturers’ recommendations on cell leadwire must be
contrast, this test method requires special considerations to
carefully followed.
reduce trace contamination and accommodates the high and
6.5 Conductivity and resistivity measurements are refer-
variable temperature coefficients of pure water samples that
enced to 25°C. Either samples must be controlled to 25.0 6
can range as high as 7% of reading per degree Celsius. In
0.2°C or specialized temperature compensation must be em-
addition, measuring instrument design performance must be
ployedthataccountsforthecharacteristicsofhighpuritywater
proven under high purity conditions.
with specific contaminants, as described in 7.1.2.
5.2 This test method is applicable for detecting trace
6.6 Samplescontainingdissolvedgasesmusthavesufficient
amountsofioniccontaminantsinwater.Itistheprimarymeans
flow through the cell that bubbles cannot accumulate and
of monitoring the performance of demineralization and other
occupy sample volume within the cell, causing low conductiv-
high purity water treatment operations. It is also used to detect
ity (high resistivity) readings. This problem is typical in
ionic contamination in boiler waters, microelectronics rinse
makeupwatertreatmentsystemswherewaterwarmsup,drops
waters, pharmaceutical process waters, etc., as well as to
in pressure, and is acidified by cation exchange operations.
monitor and control the level of boiler and power plant cycle
This releases dissolved air and converts carbonates to carbon
chemistry treatment chemicals. This test method supplements
dioxide gas.
the basic measurement requirements forTest Methods D1125,
6.7 High purity conductivity measurement must not be
D2186, and D4519.
made on a sample downstream of pH sensors since they
5.3 At very low levels of alkaline contamination, for ex-
invariably contaminate the sample with traces of reference
ample, 0–1 µg/L NaOH, conductivity is suppressed, and can
electrolyte salts. Use a dedicated sample line or place the
actually be slightly below the theoretical value for pure water.
conductivity cell upstream from the pH sensors.
(13,14) Alkaline materials suppress the highly conductive
6.8 Conductivity cells mounted downstream from ion ex-
hydrogen ion concentration while replacing it with less con-
changers are vulnerable to catching resin particles between the
ductivesodiumandhydroxideions.Thisphenomenonisnotan
cell electrodes. Resin particles are sufficiently conductive to
interferencewithconductivityorresistivitymeasurementitself
short the cell and cause high off-scale conductivity or ex-
but could give misleading indications of inferred water purity
tremely low resistivity readings. Resin retainers must be
in this range if it is not recognized.
effectiveandcellsmustbeaccessibleforcleaning.Celldesigns
with electrode spacing greater than 0.06 in. (1.5 mm) have
6. Interferences
been found to be less likely to trap such particles.
6.1 Exposure of the sample to the atmosphere may cause
6.9 Conductivity cells, if subjected to demineralizer regen-
changes in conductivity/resistivity due to loss or gain of
eration reagents, would require excessive rinse time to obtain
dissolved ionizable gases. Carbon dioxide, normally present in
satisfactory results. Therefore, locate cells where they will be
the air, can reach an equilibrium concentration in water of
isolated during regeneration cycles.
about 1 mg/L and add approximately 1 µS/cm to the conduc-
tivity due to formation of carbonic acid. Closed flow-through
7. Apparatus
or sealed in-line cell installation is required for this reason.
7.1 Measuring Instrument:
6.2 Power plant installations utilizing long sample lines can
7.1.1 The instrument shall be continuously reading in either
experience significant sampling problems. New sample lines
conductivity or resistivity units. It shall be specifically de-
normally require longterm conditioning. Iron oxides and other
signed to measure in high purity ranges, measuring with ac of
deposits accumulate in slow flowing horizontal sample lines
appropriate voltage, frequency, wave shape, phase correction,
andwavesamplingtechniquetominimizeerrorsduetoparallel
and series capacitance of cell and leadwire as well as minimiz-
ing electrode polarization errors and effects of small direct
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this test method. current(dc)potentials.Acellsimulationtechniquetoverifythe
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.
D 5391–99
performance of an unproven measuring circuit design under to accurately compensate for these effects, sample temperature
high purity conditions is provided in Annex A1. shall be controlled to 25.06 0.2°C. (Note that conductivity
7.1.2 Themeasurementshallincludealgorithmstotempera- temperature coefficients exceed 7% of reading per degree
ture compensate conductivity or resistivity values to 25.0°C. Celsius in the temperature range of 0 to 10°C.)
Thealgorithmshallcompensateforchangesinwaterionization
7.1.4 Output signal(s) from the instrument, if provided,
as well as for solute ion mobility for neutral salt contaminants. shall be electrically isolated from the cell and from the earth
Theconductivityofpurewaterhasbeendocumentedwithhigh
ground to prevent ground loop problems when the instrument
accuracy (15,1). is connected to grounded external devices.
7.1.3 In the case of samples containing acidic or basic
7.2 Cell:
solutes (such as power plant treatment using ammonia, mor-
7.2.1 Flow-through or in-line conductivity/resistivity cells
pholine, etc., or acidic cation conductivity samples or micro-
shall be used to prevent contamination from the atmosphere
electronicsacidetchrinsemonitoring),specialalgorithmsshall
andwettedsurfacesasdescribedin6.1and6.3.Flowratesshall
beemployedthataccountfortheinteractionofacidsandbases
be maintained within the manufacturer’s recommendations.
withtheionizationofwater(2,3,4).Theuseriscautionedthat
The cell shall retain its constant calibration under the condi-
accuracy of temperature compensation algorithms for these
tions of flowrate, temperature, and pressure of the installation.
solutes may vary significantly. The user must determine the
The cell shall incorporate an integral precision temperature
applicability and accuracy for a particular sample in the
sensor to ensure that it accurately senses the sample tempera-
anticipatedtemperaturerange.Fig.1illustratesthevariationin
ture where the conductivity/resistivity is being detected to
temperature effects on conductivity representative of neutral
ensure accurate temperature compensation.
salts,ammonia,morpholine,andacids.Wherespecializedhigh
7.2.2 The cell for high purity water measurements shall not
purity temperature compensation algorithms are not provided
be used for measuring higher ionic content samples (greater
than 20 µS/cm, less than 0.05 Mohm-cm) since it would retain
ionic contaminants and require excessive rinse-down time for
valid measurements in high purity ranges.Ahigh purity cell in
a demineralizer system shall not be located where it can be
exposed to regeneration reagents.
7.2.3 Electrodes of the cell shall not be platinized for pure
water measurements since the microscopically rough, porous
surfacewouldretainioniccontaminantsandproduceexcessive
downscale response times. Only a trace or flash of platinum
black is permissible on electrode surfaces. Electrodes of
titanium,nickel,monel,stainlesssteel,orplatinumaresuitable
for high purity measurement. However, extra care must be
taken using platinum cells not to exceed manufacturers’
recommended flowrate and not to permit rough handling that
could bend the electrodes and change the cell constant.
7.2.4 If the cell constant as checked does not fall within
acceptable limits of its nominal value, it is necessary to clean
or replace the cell. Even in pure water samples, coatings such
as iron oxide crud in power plant installations, resin fines, and
other solids and films can develop. Insulating coatings over
electrode surfaces can cause negative conductivity errors.
Conductive accumulations between electrodes can short them
and cause positive errors. Mechanical
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