1、Designation: D 1125 95 (Reapproved 2009)Standard Test Methods forElectrical Conductivity and Resistivity of Water1This standard is issued under the fixed designation D 1125; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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. Scope1.1 These test methods cover the deter
3、mination of theelectrical conductivity and resistivity of water. The followingtest methods are included:Range SectionsTest Method AField and Routine Laboratory 10 to 200 000 12 to 18Measurement of Static (Non-Flowing)SamplesS/cmTest Method BContinuous In-Line Measure 5 to 200 000 19 to 23ment S/cm1.
4、2 These test methods have been tested in reagent water. Itis the users responsibility to ensure the validity of these testmethods for waters of untested matrices.1.3 For measurements below the range of these test meth-ods, refer to Test Method D 5391.1.4 The values stated in SI units are to be regar
5、ded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determin
6、e the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 1066 Practice for Sampling SteamD 1129 Terminology Relating to WaterD 1192 Guide for Equipment for Sampling Water andSteam in Closed Conduits3D 1193 Specification for Reagent WaterD 2186 Test Met
7、hods for Deposit-Forming Impurities inSteamD 2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD 3370 Practices for Sampling Water from Closed ConduitsD 4519 Test Method for On-Line Determination of Anionsand Carbon Dioxide in High Purity Water
8、by CationExchange and Degassed Cation ConductivityD 5391 Test Method for Electrical Conductivity and Resis-tivity of a Flowing High Purity Water SampleE1 Specification for ASTM Liquid-in-Glass Thermometers3. Terminology3.1 Definitions:3.1.1 electrical conductivitythe reciprocal of the a-c re-sistanc
9、e in ohms measured between opposite faces of acentimetre cube of an aqueous solution at a specified tempera-ture.NOTE 1The unit of electrical conductivity is siemens per centimetre.(The previously used units of mhos/cm are numerically equivalent toS/cm.) The actual resistance of the cell, Rx, is mea
10、sured in ohms. Theconductance, 1/Rx, is directly proportional to the cross-sectional area, A(in cm2), and inversely proportional to the length of the path, L (in cm):1/Rx5 KA/LThe conductance measured between opposite faces of acentimetre cube, K, is called conductivity. Conductivity valuesare usual
11、ly expressed in microsiemens/centimetre or insiemens/centimetre at a specified temperature, normally 25C.3.1.2 electrical resistivitythe a-c resistance in ohms mea-sured between opposite faces of a centimetre cube of anaqueous solution at a specified temperature.NOTE 2The unit of electrical resistiv
12、ity is ohm-centimetre. The actualresistance of the cell, Rx, is measured in ohms, and is directly proportionalto the length of the path, L (in cm), and inversely proportional to thecross-sectional area, A (in cm2):Rx5 RL/AThe resistance measured between opposite faces of a centi-metre cube, R, is ca
13、lled resistivity. Resistivity values areusually expressed in ohmcentimetre, or in megohm centime-tre, at a specified temperature, normally 25C.1These test methods are under the jurisdiction of Committee D19 on Water andare the direct responsibility of Subcommittee D19.03 on Sampling Water andWater-F
14、ormed Deposits, Analysis of Water for Power Generation and Process Use,On-Line Water Analysis, and Surveillance of Water.Current edition approved May 1, 2009. Published June 2009. Originallyapproved in 1950. Last previous edition approved in 2005 as D 1125 95 (2005).2For referenced ASTM standards, v
15、isit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.org
16、.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.3 For definitions of other terms used in these methods,refer to Terminology D 1129.3.2 Symbols:3.2.1 Symbols used in the equations in Sections 14 and 16are defined as follows:J = c
17、ell constant, cm1,K = conductivity at 25C, S/cm,Kx= measured conductance, S,K1= conductivity of the KCl in the reference solution at thetemperature of measurement (Table 1), S/cm,K2= conductivity of the water used to prepare the referencesolution, at the same temperature of measurement, S/cm,Q = tem
18、perature correction factor (see Section 11),R = resistivity at 25C, ohm cm,Rx= measured resistance, ohm.4. Significance and Use4.1 These test methods are applicable for such purposes asimpurity detection and, in some cases, the quantitative mea-surement of ionic constituents dissolved in waters. The
19、seinclude dissolved electrolytes in natural and treated waters,such as boiler water, boiler feedwater, cooling water, and salineand brackish water.4.1.1 Their concentration may range from trace levels inpure waters (1)4to significant levels in condensed steam (seeTest Methods D 2186 and D 4519, and
20、Ref (2), or pure saltsolutions.4.1.2 Where the principal interest in the use of conductivitymethods is to determine steam purity, see Ref (3). These testmethods may also be used for checking the correctness ofwater analyses (4).5. Interferences5.1 Exposure of a sample to the atmosphere may causechan
21、ges in conductivity/resistivity, due to loss or gain ofdissolved gases. This is extremely important in the case of verypure waters with low concentrations of dissolved ionizedmaterials. The carbon dioxide, normally present in the air, candrastically increase the conductivity of pure waters by approx
22、i-mately 1 S/cm. Contact with air should be avoided by usingflow-through or in-line cell where feasible. Chemically pureinert gases, such as nitrogen or helium, may be used to blanketthe surface of samples.5.2 Undissolved or slowly precipitating materials in thesample can form a coating on the elect
23、rodes of the conductivitycell that may cause erroneous readings. For example, biofoul-ing of the cell or a build-up of filming amines may cause poorcell response. In most cases these problems can be eliminatedby washing the cells with appropriate solvents.5.3 If an unshielded cell is used to measure
24、 the resistivity/conductivity of high resistivity water there is a possibility ofelectrical pickup causing erroneous reading. For this reason itis recommended that conductivity cells for this application beof coaxial shielded type or equivalent, and that the cables andinstrument also be shielded.6.
25、Apparatus6.1 Measuring CircuitThe instrument may be a manuallyoperated wheatstone bridge or the equivalent, or a directreading analog or digital meter. Instruments shall energize theconductivity cell with alternating current and, together with thecell and any extension leadwire, shall be designed to
26、 reduceerrors from the following sources:6.1.1 In highly conductive solutionsUncompensated elec-trode polarization due to excessive current density at theelectrode surfaces can cause negative conductivity errors.Insufficient series capacitance at the electrode/solution inter-face can allow charging
27、effects to distort the a-c measurementand cause errors if not compensated. Leadwire resistance canadd significantly to the measured resistance.6.1.2 In low conductivity solutionsExcessive parallel ca-pacitance in the cell and extension leadwire can shunt themeasurement and cause positive conductivit
28、y errors. Tempera-ture compensation errors can be significant below 5 S/cm ifvariable coefficient algorithms are not employed as describedin Test Method D 5391.6.1.3 These sources of error are minimized by an appropri-ate combination of a-c drive voltage, wave shape, frequency,phase correction, wave
29、 sampling technique and temperaturecompensation designed in by the instrument manufacturer. Theinstrument manufacturers recommendations shall be followed4The boldface numbers in parentheses refer to a list of references at the end ofthis standard.TABLE 1 Electrical Conductivity Values Assigned to th
30、e Potassium Chloride in the Reference SolutionAReferenceSolutionApproximateNormality ofSolutionMethod of PreparationTempera-ture, CElectricalConductivity,S/cmA 1 74.2460 g of KCl weighed in air per 1 L of 0 65 176solution at 20C 18 97 83825 111 342B 0.1 7.4365 g of KCl weighed in air per 1 L of 0 7
31、138solution at 20C 18 11 16725 12 856C 0.01 0.7440 g of KCl weighed in air per 1 L of 0 773.6solution at 20C 18 1 220.525 1 408.8D 0.001 Dilute 100 mL of Solution C to 1 L at 20C 0 77.69B18 127.54B25 146.93AExcluding the conductivity of the water used to prepare the solutions. (See 7.2 and Section 1
32、4.) These tabulated conductivity values are in international units. Whenusing measuring instruments calibrated in absolute units, multiply the tabular values by 0.999505.BFrom Glasstone (13).D 1125 95 (2009)2in selecting the proper cell constant, leadwire size, and lengthand maintenance of the elect
33、rode surface condition for therange of measurement. Calibration may be in either conduc-tivity or resistivity units.6.1.4 When an output signal is required from an on-lineinstrument, it shall be electrically isolated from the cell drivecircuit to prevent interaction between a solution ground at thec
34、ell and an external circuit ground.6.2 Cells:6.2.1 Flow-through or in-line cells shall be used for mea-suring conductivities lower than 10 S/cm (resistivities higherthan 100 000 ohm cm), to avoid contamination from theatmosphere. However, samples with conductivity greater than10 S/cm may also be mea
35、sured. In all other cases, pipet-typeor dip cells can also be used. Pipet or dip cells may be used tomeasure samples in the range of 1 to 10 S/cm if the sample isprotected by an inert gaseous layer of nitrogen or helium.6.2.2 A cell constant shall be chosen which will give amoderate cell resistance,
36、 matching the instrument manufactur-ers requirements for the range of measurement. For laboratorybridges, Table 2 provides conservative guidelines.6.2.3 Flow-through and in-line cells shall be mounted sothat continuous flow of the sample through or past it ispossible. Flow rate should be maintained
37、at a constant rateconsistent with the manufacturers recommendations for thecell being used, particularly at conductivities below 10 S/cm.The cell shall retain calibration under conditions of pressure,flow, and temperature change, and shall exclude the atmo-sphere and be constructed of corrosion resi
38、stant, chemicallyinert materials. The chamber or cell shall be equipped withmeans for accurate measurement of the temperature.6.2.4 Platinized cells shall not be used for measurement ofconductivities below 10 S/cm, except that a trace or flash ofplatinum black may be used on cells for measurements i
39、n therange of 0.1 to 10 S/cm (see 9.4). Because of the cost andfragility of platinum cells, it is common practice to usetitanium, monel, and graphite electrodes for measurementswith accuracies on the order of 1 %. Note that these electrodesmay require special surface preparation. Titanium and monele
40、lectrodes are especially suitable for high resistance solutionssuch as ultrapure water, but may introduce a small surfaceresistance which limits their accuracy when the measuredresistance is less than a few thousand ohms (1).6.2.5 It is recommended that cells intended for the measure-ment of conduct
41、ivities below 10 S/cm be reserved exclusivelyfor such applications.6.3 Temperature Probes:6.3.1 For Temperature ControlThe measurement of tem-perature is necessary for control of a temperature bath, manualtemperature compensation, or automatic temperature compen-sation, or all of these. Thermometers
42、, thermistors, and resis-tance temperature detectors with accuracies of 60.1C orbetter are acceptable for this application. An ASTM precisionthermometer, Number 63C, as defined in Specification E1,isrecommended. The calibration of temperature probes should bechecked periodically by comparison to a r
43、eference temperatureprobe whose calibration is traceable to the U.S. NationalInstitute of Science and Technology (formerly NBS) or equiva-lent.6.3.2 For Temperature CorrectionA thermometer accu-rate to 0.1C is acceptable for this application, when theinstrument is not provided with manual or automat
44、ic tempera-ture compensation. (See Section 11).7. Reagents7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Society
45、,where such specifications are available.5Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.7.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understoo
46、d to mean reagent water conformingto Specification D 1193, Type I. In making up the potassiumchloride solutions for cell constant determinations, use water ofconductivity not greater than 1.5 S/cm. If necessary, stabilizeto the laboratory atmosphere by aspirating air through thewater from a fritted
47、glass or stainless steel gas dispersion tube.The equilibrium point is reached when the conductivity re-mains constant but not greater than 1.5 S/cm. The equilibriumconductivity must be added to Table 1.7.3 Alcohol95 % ethyl alcohol. Alternatively, use isopro-pyl alcohol or methyl alcohol.7.4 Aqua Re
48、gia (3 + 1)Mix 3 volumes of concentratedhydrochloric acid (HCl, sp gr 1.19) with 1 volume of concen-trated nitric acid (HNO3, sp gr 1.42). This reagent should beused immediately after its preparation.7.5 Ethyl Ether.7.6 Hydrochloric Acid (sp gr 1.19)Concentrated HCl.7.7 Hydrochloric Acid (1 + 1)Mix
49、1 volume of concen-trated HCl (sp gr 1.19) with 1 volume of water.7.8 Platinizing SolutionDissolve 1.5 g of chloroplatinicacid (H2PtCl66H2O) in 50 mLof water containing 0.0125 g oflead acetate (Pb(C2H3O2)2).7.9 Potassium Chloride (KCl)The assay of the potassiumchloride must be 100.06 0.1 %. This standardization grade ofKCl is available from NIST and from commercial sources. Dryat 150C for 2 h or until weight loss is less than 0.02 %; storein desiccator.5Reagent Chemicals, American Chemical Society Specifications , Amer
