Designation: D5391 − 14
Standard Test Method for
Electrical Conductivity and Resistivity of a Flowing High Purity Water Sample1 This standard is issued under the fixed designation D5391; the number immediately following the designation indicates the year of original adoption or, in the case of revis original revision, ion, the year of last revision. revision. A number in paren parenthese thesess indicates the year of last reappr reapproval. oval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Sco Scope pe
D2186 Test Met D2186 Method hodss for Dep Deposi osit-F t-Form orming ing Imp Impuri urities ties in Steam D2777 Practice D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water D3370 Practices D3370 Practices for Sampling Water from Closed Conduits D3864 Guide for On-Li D3864 On-Line ne Monit Monitoring oring Systems for Water Analysis D4519 Test Method for On-Line Determination of Anions D4519 and an d Ca Carb rbon on Di Diox oxid idee in Hi High gh Pu Purit rity y Wat ater er by Cat Catio ion n Exchange and Degassed Cation Conductivity
1.1 This test method covers the determination determination of electrical conductivity and resistivity of high purity water samples below 10 µS µS/cm /cm (a (abo bove ve 0. 0.1 1 Mo Mohm hm-c -cm) m).. It is ap appl plic icab able le to bo both th contin con tinuou uouss and per period iodic ic mea measur suremen ements ts but in all case cases, s, the water wa ter mu must st be flo flowi wing ng in or orde derr to pr prov ovid idee re repr pres esen entat tativ ivee sampling. samplin g. Static grab sampling cannot be used for such high purity water. Continuous measurements are made directly in puree wat pur water er pro proces cesss lin lines, es, or in sid sidee str stream eam sample sample lin lines es to enable ena ble mea measur suremen ements ts on hig high h tem temper peratu ature re or hig high h pre pressu ssure re samples, or both.
3. Terminology
1.2 1. 2 Th Thee va valu lues es sta stated ted in SI un units its are to be re rega gard rded ed as standard. No other units of measurement are included in this standard.
3.1 Definitions—For definitions of other terms used in these test methods, refer to Terminology D1129 D1129.. 3.1.1 electrical conductivity— refer to Test Methods D1125 Methods D1125..
1.3 This standar standard d doe doess not purport purport to add addre ress ss all of the safet sa fetyy co conc ncer erns ns,, if an anyy, as asso socia ciate ted d wi with th its us use. e. It is th thee responsibility of the user of this standard to establish appro priate safety and health practices and determine the applicability of regulatory limitations prior to use.
3.1.2 electrical resistivity— refer to Test Methods D1125 Methods D1125.. 3.2 Definitions of Terms Specific to This Standard: 3.2.1 cell constant, n— the the ratio of the length of the path, L (cm), (cm ), and the cro crossss-sec section tional al are areaa of the sol solutio ution, n, A (cm2), between the electrodes of a conductivity/resistivity cell, with units of cm−1.
2. Referenc Referenced ed Documents Documents 2.1 ASTM Standards:2 D1066 Practice D1066 Practice for Sampling Steam D1125 Test D1125 Test Methods for Electrical Conductivity and Resistivity of Water D1129 Terminology D1129 Terminology Relating to Water D1192 Guide D1192 Guide for Equipment for Sampling Water and Steam in Closed Conduits (Withdrawn Conduits (Withdrawn 2003)3 D1193 Specification for Reagent Water D1193
3.2.1.1 Discussion— In In high purity water measurements, the cell ce ll co cons nstan tantt is no norm rmal ally ly be betw twee een n 0. 0.00 001 1 an and d 0. 0.1 1 cm−1 to prevent preve nt electrical interference. interference. This is lower than the 1 cm −1 of the standard centimetre cube and is taken into account by direct reading instrument ranges that are matched with specific cell constants. 4. Summ Summary ary of Test Test Method 4.1 Condu Conductivity ctivity or resistivity resistivity is measur measured ed with a cell and temperature sensor or compensator in a flowing, closed system to prevent trace contamination from wetted surfaces and from the atmosp atmosphere. here. Specia Specialized lized temper temperature ature compen compensation sation corrects re cts th thee mea measu sure remen mentt to 25 25°C, °C, ta taki king ng in into to acc accou ount nt th thee temp te mper erat atur uree ef effe fect ctss on th thee io ioni niza zati tion on of wa wate terr, th thee contaminants, and interactions between the two. In the absence of speciali specialized zed temper temperature ature compensation, compensation, the sample temperature is controlled to 25 6 0.2°C.
1
This test method is under the juris jurisdictio diction n of ASTM Committee Committee D19 on Water and is the direct responsibility of Subcommittee D19.03 on Sampling Water and Water-Formed Deposits, Analysis of Water for Power Generation and Process Use, On-Line Water Analysis, and Surveillance of Water. Current Curre nt editio edition n appro approved ved Feb. 1, 2014. Published Published Febru February ary 2014. Origin Originally ally approved approv ed in 1993. Last previous edition edition approved in 2009 as D5391 – 99 (2009). DOI: 10.1520/D5391-14. 2 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at
[email protected]. For Annual Book of ASTM Standards volume information, refer to the standard’s Document Summary page on the ASTM website. 3 The last app approve roved d vers version ion of this historica historicall sta standa ndard rd is refe referenc renced ed on
4.2 To determine the cell constant of a high purity conducconductivity cell with an instru instrument ment capable of accura accurate te measur measurement ement
www.astm.org.
over the range of pure water to 150 µS/cm with a single cell
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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constant, Test Methods D1125 are used directly. Manufacturers’ certification of cell constant traceability by this means is an acceptable alternative.
tivity due to formation of carbonic acid. Closed flow-through or sealed in-line cell installation is required for this reason. 6.2 Power plant installations installations utilizing utilizing long sample lines can experience significant sampling problems. New sample lines normally norma lly requir requiree longte longterm rm condit conditioning ioning.. Iron oxides and other deposits accumulate in slow flowing horizontal sample lines and can develop chromatograph-like retention of ionic species, resulting in very long delay times. Precautions are described in Section 9. Section
4.3 To determine the cell constant of a high purity purity conductivity cell with an instrument which does not accurately cover the range from pure water to 150 µS/cm with a single cell constant, a secondary standard cell is used that has an intermediate cell constant with precise value determined by Test Methods D1125 Methods D1125.. That secondary standard cell is then used in low co low cond nduc ucti tivi vity ty wa water ter (n (not ot a sta stand ndar ard) d) an and d re read adin ings gs ar aree compared with those of the low constant cell under test. In this manner, the cell constant of the latter is determined. Manufacturers’ certification of cell constant traceability by this means is an accepta acceptable ble altern alternative. ative.
6.3 Cell and flow chamber surfaces surfaces will slowly leach trace ionic contaminants, evidenced by increasing conductivity readings with very low or zero flowrate. There must be sufficient flow to keep these contaminants from accumulating to the point thatt the tha they y af affec fectt the mea measur sureme ement. nt. The hig high h and con convol volute uted d surfac sur facee are areaa of plat platini inized zed cel cells ls pre preclud cludes es the their ir use for high purity measurements for this reason.
5. Sign Significan ificance ce and Use 5.1 Condu Conducti ctivit vity y mea measur sureme ements nts are typ typica ically lly mad madee on samples of moderate to high ionic strength where contamination of open samples in routine laboratory handling is negligible. Under those conditions, standard temperature compensation sati on usi using ng coe coeffficie icients nts of 1 to 3 % of rea readin ding g per degree degree Celsius Cels ius ove overr wid widee con concen centra tration tion ran ranges ges is app approp ropria riate. te. In contra con trast, st, this test met method hod req requir uires es spe special cial con consid sidera eration tionss to reduce trace contamination contamination and accommodates accommodates the high and
6.4 Cap Capacit acitanc ancee of the cel celll and extension extension leadwire, leadwire, especially in high purity ranges can add significant positive error to conductance readings (negative error to resistance readings). The measuring instrument must be designed to accommodate cell ce ll an and d lea leadw dwir iree ch char arac acter terist istics ics in hi high gh pu puri rity ty wa wate terr as described in 7.1.1 7.1.1 and and Annex Annex A1. A1. In addition, the instrument manufa man ufactu cturer rers’ s’ rec recomm ommend endatio ations ns on cel celll lead leadwir wiree mus mustt be carefully followed.
variable temper variable temperature ature coefficients coefficients of pure water sample sampless that can range as high as 7 % of reading per degree Celsius. In addition, additio n, measur measuring ing instru instrument ment desig design n perfo performance rmance must be proven under high purity conditions.
6.5 Con Conduc ductiv tivity ity and res resisti istivit vity y meas measure uremen ments ts are ref refer er-enced to 25°C. Either samples must be controlled to 25.0 6 0.2°C or specialized temperature compensation must be employed that accounts for the characteristics of high purity water with specific contaminants, as described in 7.1.2 7.1.2..
5.2 This 5.2 This tes testt me metho thod d is ap appl plica icabl blee fo forr de detec tectin ting g tr trace ace amounts of ionic contaminants in water. It is the primary means of monitoring the performance of demineralization and other high purity water treatment operations. It is also used to detect ionic contamination contamination in boiler waters, microelectronics microelectronics rinse water wa ters, s, ph phar arma mace ceut utica icall pr proc ocess ess wa water ters, s, et etc., c., as we well ll as to monitor and control the level of boiler and power plant cycle chemistry treatment chemicals. This test method supplements the basic measurement requirements for Test Methods D1125 Methods D1125,, D2186,, and D2186 and D4519 D4519..
6.6 Samples containing dissolved gases must have sufficient sufficient flow through through the cell tha thatt bub bubble bless can cannot not accumulate accumulate and occupy occup y sample volume within the cell, causing low condu conductivctivity (h (hig igh h re resi sisti stivi vity ty)) re read adin ings gs.. Th This is pr prob oble lem m is ty typi pical cal in makeup water treatment systems where water warms up, drops in pre pressu ssure, re, and is aci acidifi dified ed by cati cation on exc exchan hange ge ope operat ration ions. s. This releases dissolved air and converts carbonates to carbon
5.3 5. 3 At very ve ry low lo w levels lev els of alk alkali aline cont co ntami amina natio tion, n, can forr fo exampl example, e, 0–1 µg/L NaOH, conductivit conductivity yne is supp suppressed ressed, , and actually be slightly below the theoretical value for pure water. (1 and 2) 2)4 Alkaline materials suppress the highly conductive hydrogen ion concentration while replacing it with less conductive sodium and hydroxide ions. This phenomenon is not an interference with conductivity or resistivity measurement itself but could give misleading indications of inferred water purity in this range if it is not recognized.
dioxide gas. dioxide 6.7 High High pur purity ity con conduc ductiv tivity ity meas measure uremen mentt mus mustt not be made ma de on a sa samp mple le do down wnst stre ream am of pH sen senso sors rs sin since ce th they ey invaria inv ariably bly con contami taminat natee the sam sample ple with tra traces ces of ref refere erence nce electr ele ctrol olyt ytee sa salts lts.. Us Usee a de dedi dicat cated ed sam sampl plee lin linee or pl place ace th thee conductivity cell upstream from the pH sensors. 6.8 Condu Conductivity ctivity cells mounted downstream downstream from ion exchangers are vulnerable to catching resin particles between the cell electrodes. Resin particles are sufficiently conductive to short sho rt the cell and cause hig high h of off-s f-scale cale conductiv conductivity ity or extrem tr emely ely lo low w re resis sisti tivi vity ty re read adin ings gs.. Res Resin in re reta tain iner erss mu must st be effective and cells must be accessible for cleaning. Cell designs with electrode spacing greater than 1.5 mm have been found to be less likely to trap such particles.
6. Interfere Interferences nces 6.1 Exp Exposu osure re of the sample sample to the atmosphe atmosphere re may cause change chan gess in co cond nduc uctiv tivit ity/ y/re resis sistiv tivity ity du duee to lo loss ss or ga gain in of dissolved ionizable gases. Carbon dioxide, normally present in the air air,, can rea reach ch an equ equilib ilibriu rium m con concen centra tratio tion n in wate waterr of about 1 mg/L and add approximately 1 µS/cm to the conduc-
6.9 Condu Conductivity ctivity cells, if subjected to demineralizer demineralizer regeneration reagents, would require excessive rinse time to obtain satisfactory results. Therefore, locate cells where they will be isolated isolate d durin during g regene regeneration ration cycles.
4 The boldface numbers in parentheses refer to a list of references at the end of this standard.
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7. Appar Apparatus atus 7.1 Measuring Instrument: 7.1.1 The instrument instrument shall be continuously continuously reading in either conduc con ductiv tivity ity or res resisti istivit vity y uni units. ts. It sha shall ll be spe specifi cificall cally y designe sig ned d to me meas asur uree in hi high gh pu puri rity ty ra rang nges, es, mea measu surin ring g wi with th alternating current (ac) of appropriate voltage, frequency, wave shape, sha pe, pha phase se cor correc rectio tion, n, and wav wavee sam samplin pling g tech techniq nique ue to minimize errors due to parallel and series capacitance of cell and lead leadwir wiree as well as min minimiz imizing ing elec electro trode de pol polari arizati zation on errors and effects errors effects of small direct curre current nt (dc) poten potentials. tials. A cell simulation technique to verify the performance of an unproven measu mea surin ring g cir circu cuit it de desig sign n un unde derr hi high gh pu purit rity y co cond nditi ition onss is provided in Annex in Annex A1. A1. 7.1.2 The measurement measurement shall include algorithms algorithms to temperatemperature compensate conductivity or resistivity values to 25.0°C. The algorithm shall compensate for changes in water ionization as well as for solute ion mobility for neutral salt contaminants. The conductivity of pure water has been documented with high accuracy (3-5 accuracy 3-5)). 7.1. 7. 1.3 3 In th thee cas casee of sa samp mples les co cont ntain ainin ing g aci acidi dicc or ba basi sicc solute sol utess (su (such ch as po power wer pla plant nt tre treatm atment ent usi using ng amm ammon onia, ia, morpho mor pholine line,, etc. etc.,, or acid acidic ic cation cond conductivity uctivity samples samples or microel micr oelectr ectroni onics cs acid etch rin rinse se mon monito itorin ring), g), spe special cial alg algoorithms shall be employed that account for the interaction of acids and bases with the ionization of water ( (6-8 6-8)). The user is caution cau tioned ed tha thatt accu accurac racy y of temp temperat erature ure com compen pensat sation ion alg algoorithms for these solutes may vary significantly. The user must deter de termi mine ne th thee ap appl plic icab abili ility ty an and d ac accu cura racy cy fo forr a pa part rtic icul ular ar sample in the anticipated temperature range. Fig. 1 illustrates the variation in temperature effects on conductivity representative of neutral salts, ammonia, morpholine, and acids. Where specialized high purity temperature compensation algorithms are not prov provided ided to accura accurately tely compensate for these ef effects, fects, sample temperature shall be controlled to 25.0 6 0.2°C. (Note that cond conductivity uctivity temperature temperature coefficients coefficients exceed 7 % of reading per degree Celsius in the temperature range of 0 to 10°C.) 7.1.4 7.1 .4 Out Output put sig signal( nal(s) s) fro from m the ins instru trumen ment, t, if pro provid vided, ed, shall be electrically isolated from the cell and from the earth ground to prevent ground loop problems when the instrument
NOTE 1—Curves represent concentrations of impurities given in Table 1. FIG. 1 Te Temperat mperature ure Effects on the Conductivity Conductivity of High Purity Water TABLE 1 Concentrations of Trace Contaminants Plotted in Fig. 1
is connected to grounded external devices. 7.2 Cell: 7.2.1 Flow-t Flow-throu hrough gh or in-lin in-linee condu conductivity ctivity/resist /resistivity ivity cells shall be used to prevent contamination from the atmosphere and wetted surfaces as described in 6.1 in 6.1 and and 6.3 6.3.. Flowrates shall be mainta maintained ined within the manuf manufacture acturer’s r’s recomm recommendati endations. ons. The cell shall retain its constant calibration under the conditions of flowra flowrate, te, temperature, and pressure of the installation. installation. The cell sha shall ll inc incorp orpora orate te an int integr egral al pre precisi cision on temp tempera eratur turee sensor to ensure that it accurately senses the sample temperaturee whe tur where re the con conduc ductiv tivity/ ity/res resisti istivity vity is bein being g det detecte ected d to ensure accurate temperature compensation. 7.2.2 The cell for high purity water measurements measurements shall not 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 measurements in high purity ranges. ranges. A high purity cell in a demineralizer system shall not be located where it can be exposed expos ed to regene regeneration ration reagents.
Conductivity µS/cm at 25°C
NaCl
Concentration (µg/L) HCl NH3
5.00 2.00 1.00 0.500 0.250 0.100 0.055
2295 903 439 207 91 21.0 0.0
430 172 86 42.6 20.7 6.5 0.0
638 177 76 34.4 16.1 5.4 0.0
Morpholine 13 755 2632 837 298 117 34.6 0.0
7.2.3 Electro Electrodes des of the cell shall not be platin platinized ized for pure water measurements since the microscopically rough, porous surface would retain ionic contaminants and produce excessive downscale response times. Only a trace or flash of platinum blac bl ack k is pe perm rmiss issib ible le on el elect ectro rode de su surf rfac aces. es. El Elect ectro rode dess of titanium, nickel, monel, stainless steel, or platinum are suitable for hig high h pur purity ity mea measur suremen ement. t. How Howeve ever, r, ext extra ra care mus mustt be taken tak en us usin ing g pl plati atinu num m ce cells lls no nott to ex excee ceed d ma manu nufa factu cture rers rs’’ 3
D5391 − 14
recommended flowrate and not to permit rough handling that could bend the electrodes and change the cell constant. 7.2.4 7.2 .4 If the cell constan constantt as checked checked doe doess 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 oth er sol solids ids and film filmss can dev develo elop. p. Ins Insula ulatin ting g coa coating tingss ove overr electro elec trode de sur surface facess can cau cause se neg negativ ativee con conduc ductivi tivity ty err errors ors.. Conductive accumulations between electrodes can short them
9.2.2 The sample line shall not have pH electrodes electrodes upstream upstream of the conductivity cell as noted in 6.7 6.7.. 9.2.3 In power plant plant installations where iron oxide oxide and other solids sol ids occur in pur puree wate waterr sam sample ples, s, flow flowrat rates es mus mustt be con con-trolled to minimize accumulation of deposits that could greatly delay transport of ionic materials. A sample flow velocity of 2 m/ss in ho m/ hori rizo zont ntal al sam sampl plee lin lines es ha hass be been en fo foun und d op optim timum um.. Additional sample line design criteria have been documented (9-11 9-11)).
and cause cau sewith positiv pos itive e err errors ors. . Mec Mechan hanical ical clea cleanin g mus must t not the be attempted platinum electrodes since thisning would change cell con constan stant. t. Clea Cleanin ning g mus mustt eith either er fol follow low man manufa ufactu cturer rer’s ’s recommendations or that given in Test Methods D1125 D1125.. Ultrasonic cleaners have also been found effective in some cases.
be continuously continu ously flow ing flo9.2.4 flowr wrat atee The to sample enab en able le shall samp sa mple le linee we lin wette tted d flowing surf su rfac aces esattoa stable reac re ach h equilibrium equilib rium with sample conditions. conditions. Do not make measur measureements following changes to the sample flowrate for the period of tim timee re requ quir ired ed to re reco cove verr fr from om tr tran ansi sien entt ef effe fect ctss on th thee particular particu lar samplin sampling g system. 9.2.5 Contro Controll the sample temperature temperature within the capabilities capabilities of the temperature compensation algorithms used in the measuring instrument. The sample temperature shall be sufficiently stable to maintain reasonable equilibrium with the sample line wetted surfaces. 9.2.6 9.2 .6 Do not locate the cell where where it would be exposed exposed to demineralizer reagents as noted in 6.9 6.9.. 9.2.7 Additi Additional onal sampling precaution precautionss are prov provided ided in Practices D1066 tices D1066and and D3370 D3370 and and Guides D1192 Guides D1192 and and D3864 D3864..
7.3 Extens 7.3 Extensio ion n le lead adwi wire re ty type pe,, siz size, e, an and d len lengt gth h sh shal alll be according accord ing to manuf manufacture acturers’ rs’ recom recommendat mendations, ions, primar primarily ily to preven pre ventt par paralle allell lead leadwir wiree cap capacit acitanc ancee err errors ors wit with h this hig high h resistance ac measurement. In particular, the length shall not exceed the measur measuring ing instrument’s instrument’s ability to minimize capacitance error errors. s. 8. Reag Reagents ents 8.1 Purity of Reagents— Reagent Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the Commit-5 tee on Analyt Analytical ical Reagents of the America American n Chemical Society. Society. Other grades may be used, provided it is first ascertained that thee re th reag agen entt is of su sufffici icien ently tly hi high gh pu puri rity ty to pe perm rmit it its us usee without lessening the accuracy of the determination.
10. Cali Calibrat bration ion 10.1 Measuring Measuring Instru Instrument— ment— Evaluat Evaluatee instru instrumentati mentation on of unproven performance in high purity samples using the procedure in Annex A1. A1. Thereafter Thereafter,, use calibr calibrating ating resisto resistors rs with 60.1 % tolerance in place of the measuring cell and temperature compensator. The conductivity check resistance in ohms equals the cell constant (cm −1) divided by the conductivity to be indicated (S/cm). Resistivity check resistance equals the cell constant (cm −1) times the resistivity to be indica indicated ted (ohm-cm). (ohm-cm). The temp tempera eratur turee com compen pensato satorr res resista istance nce as defi defined ned by the manufacturer must simulate a sample temperature of 25.0°C, the reference temperature, that eliminates any compensation in order to follow the relationships given above.
8.2 Purity of Water— Unless Unless otherwise indicated, references to water shall be understood to mean reagent water conforming to Type I of Specification D1193 Specification D1193.. In making up the potassium chloride chlori de compar comparison ison solution for cell const constant ant determ determination inations, s, usee wa us wate terr of co cond nduc ucti tivi vity ty no nott gr grea eate terr th than an 1 µS µS/c /cm. m. If necessary necessa ry,, stabili stabilize ze to the labor laboratory atory atmosphere atmosphere by aspirating air through the water from a fritted glass or stainless steel gas disper dis persio sion n tub tube. e. The equ equilib ilibriu rium m poi point nt is rea reache ched d whe when n the conductivity remains constant but not greater than 1.5 µS/cm.
NOTE 1—It should be understood that the use of a precision resistor in
8.3 Conductivity Conductivity Stand Standard ard Refer Reference ence Solut Solutions— ions— See Test Methods D1125 Methods D1125..
place of thewhereas cell checks of the instrument toinclude measure a pure resistance, theonly cell the andability leadwire characteristics parallel and series capacitance. The manufacturer’s circuit design must have the capability capabi lity to measu measure re with installed cell and leadwire charac characterist teristics, ics, verified by the test in Annex in Annex A1. A1.
9. Samp Sampling ling 9.1 Direct measuremen measurements ts in the proce process ss shall have the cell located in an active flowing part of the piping. Stagnant areas or dead legs must be avoided to ensure a representative sample and prevent any bubbles from adhering to cell surfaces.
10.2 Leadwire Effects— When When leadwire length between the instrument and cell is greater than 7 m, check calibration of the instrument a second time by connecting the calibrating resistors at the far end of the leadwire and noting the difference, if any, in readings with the long leadwire in the circuit. Check both temp temperat erature ure and con conduct ductivity ivity/res /resisti istivity vity read reading ings. s. Leadwir Lead wire-i e-indu nduced ced err errors ors in hig high h pur purity ity mea measur sureme ements nts are typically caused by parallel capacitance of the cell leads and resista res istance nce of the temp tempera eratur turee com compen pensato satorr lead leads. s. Lea Leadwi dwire re capacitance is minimized on some instruments by isolating one cell lead within a driven shield. With other instruments, the use of fluorocarbon insulated or shortened leadwire, or both, may be necessary. (Fluorocarbon provides the best available dielectric properties and can reduce capacitance to about half that of cable using other insulating material.) Do not use long shielded
9.2 Desig Design n and operate side stream stream sample lines to maintain maintain sample integrity. 9.2.1 Do not expose the sample to the atmosphere atmosphere to prevent absorption or loss of gases, particularly carbon dioxide, that affect conductivity. 5
American an Reagent Chemicals, American Chemical Society Specifications, Americ
Chemical Society, Washington, DC. For Suggestions on the testing of reagents not listed by the American American Chemi Chemical cal Society, Society, see Annual Standa Standards rds for Labor Laboratory atory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
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leadwire unless the instrument is specifically designed for it since the shield can increa increase se capacit capacitance ance and associa associated ted errors with conventional measuring circuits. Follow manufacturer’s wiring recommendations closely.
sample initially to preve prevent nt an accumu accumulation lation of contam contaminants inants in the cell. If using a sample line, establish a flowrate through the cell of 200 cc/min or according to manufacturer’s recommendation dat ionss and allow several several hou hours rs of rin rinse se time if usi using ng new sample components, flow chamber, or cell to ensure complete removal of air and trace contaminants.
10.3 Temperature Measurement Circuit— Some Some temperature measurement circui measurement circuits ts requi require re precis precisee tempera temperature ture calibr calibration ation afterr ins afte install tallatio ation n to com compen pensat satee for lead leadwir wiree res resista istance nce and ensure accurate temperature compensation. Where necessary, perform perfo rm this accord according ing to manuf manufacture acturer’s r’s recomm recommendati endations. ons.
11.2 If spe 11.2 special cialized ized temp temperat erature ure com compen pensati sation on is not available, verify that the sample temperature is stabilized at 25.0 6 0.2°C. 11.3 11 .3 Read the condu conductivity ctivity or resistivity. resistivity.
10.4 Conductivity Conductivity Cells— The cell con consta stant nt cali calibra bratio tion n of conductivity/resistivity cells is ultimately referenced to standard solutions of potass potassium ium chloride of know known n condu conductivity ctivity from Test Methods D1125 Methods D1125 or NIST standards standards (12 12)). However, due to the hig high h unc uncert ertain ainties ties of atm atmosp ospher heric ic and container container surfac sur facee con contami taminat nation ion,, dir direct ect cell cali calibra bration tion with stan standar dard d solutio sol utions ns bel below ow 100 µS/ µS/cm cm is not rec recomm ommend ended. ed. Although Although these solutions are available, their successful use for calibration is beyond the scope of this test method. See Note 2 2 and Note 3. 3. 10.4 10 .4.1 .1 To de deter termin minee th thee ce cell ll co cons nstan tantt of a hi high gh pu puri rity ty cond co nduc uctiv tivity ity ce cell ll wi with th an in inst stru rume ment nt ca capa pabl blee of ac accu cura rate te measurement over the range of pure water to 150 µS/cm with a single cell constant, use Test Methods D1125, D1125, Solution D, 146.93 146 .93 µS/ µS/cm cm or NIS NIST T Sta Standa ndard rd Ref Refere erence nce Mat Materi erial al 319 3191, 1, nomi no mina nall va valu luee 10 100 0 µS µS/c /cm m di dire rectl ctly y. Th This is cal calib ibra ratio tion n wi with th documented certification can be provided by some cell manufacturers. 10.4 10 .4.2 .2 To de deter termin minee th thee ce cell ll co cons nstan tantt of a hi high gh pu puri rity ty conductivity cell with an instrument which does not accurately cover the range from pure water to 150 µS/cm with a single cell constant, accomplish calibration using an intermediate higher constant cell as a secondary standard. Calibrate in a higher conduc con ductiv tivity ity stan standar dard d sol soluti ution on fro from m Test Met Method hodss D1125, D1125, Reference Solution C, 1408.8 µS/cm, or Reference Solution D, 146.93 146.9 3 µS/cm or NIST Standard Standard Referen Reference ce Materia Materials ls 3192 3192,, nominal nom inal val value ue 500 500.0 .0 µS/ µS/cm cm or 319 3193, 3, nom nomina inall val value ue 100 1000.0 0.0 µS/cm ( µS/cm (12 12)). This cell then becomes the secondary standard for compar com pariso ison n wit with h low con consta stant nt cell cellss in low lower er con conduc ductiv tivity ity solu so lutio tions ns th that at ne need ed no nott be st stan anda dard rdss (13 and 14). Th This is calibration with documented certification can be provided by cell man manufa ufactu cturer rers. s. Ref Refer er to Annex Annex A2 for for de detai tails ls of ce cell ll constant calibration.
12. Pre Precisi cision on and Bias 12.1 Neithe Neitherr precision nor bias data can be obtained obtained for this test method from a collabo collaborative rative study designed in accord accordance ance with the requirements of Practice D2777 Practice D2777 since since this test method is a continuous determination. This inability of Practice D2777 Practice D2777 proced pro cedure uress to obt obtain ain pre precisi cision on and bia biass dat dataa for con contin tinuou uouss determinations is recognized and stated in the scope of Practice D2777.. (Some experience approximating single-operator preD2777 cision on high purity specific and cation conductivity measurements in power plants has been reported as a part of EPRI project RP2712-3 RP2712-3 (16 16)).) 13. Quali Quality ty Control Control 13.1 Follow Follow sens sensor or manu manufactu facturer rer reco recommen mmendati dations ons for storage, preparation, use and periodic cleaning of the sensor. 13.2 Verify that the conductivity temperature compensation in the instrument provides a close match to the temperature characteristics of the sample in accordance with 7.1.2 with 7.1.2.. 13.3 13 .3 De Depe pend ndin ing g on ac accu cura racy cy re requ quir irem emen ents ts of th thee measureme measur ement, nt, ver verify ify tha thatt con conduc ductivi tivity ty rea readin dings gs are wit within hin acceptable accepta ble toleran tolerance ce perio periodically dically,, using a standa standard rd refere reference nce soluti sol ution on or com compar paring ing wit with h a sta standa ndard rd ref referen erence ce mea measur suring ing system. 13.3.1 13.3. 1 When a reference solution solution is used, it should have a conduc con ductiv tivity ity val value ue hig high h eno enough ugh that it will hav havee neg neglig ligible ible influence from variable exposure to the carbon dioxide in air, in accordance with 6.1 with 6.1.. Follow the standard solution manufacturer’s instructions regarding air exposure and other precautions carefully. The reference solution value must also be within the accurate measuring range of the sensor/instrument combination. 13.3.2 13.3. 2 When a standard reference reference measuring measuring system is used on the flowing high purity water sample for comparison, take precautions to keep the sample enclosed without exposure to air, in accordance with 6.1 6.1,, all the way through the flow path.
NOTE 2—Direct cell calibration in a low conductivity standard near 15 µS/cm has been proposed under highly controlled conditions. However, determination of the contribution of the background water conductivity, which represents about 7 % of the total measurement if performed in open (15 15)). air, was not addressed ( NOTE 3—The lowest conductivity NIST Standard Reference Material has a nominal conductivity of 5 µS/cm at 25.0°C. However, the typical uncertainty is greater than that expected by other methods.
13.4 Becaus Becausee measurement is performed performed continuously continuously on a pure water sample, normal quality control (QC) batch testing of blanks, matrix spikes, and control standards are not applicable.
11. Procedur Proceduree 11.1 Set up the flow type conductivity/resi 11.1 conductivity/resistivity stivity cell, leadwire and instrument with calibration verified as in Section 10 10..
14. Keyw Keywords ords
Wher Wh eree se seve vere re fo foul ulin ing g is an antic ticip ipate ated d at st star artu tup, p, di dive vert rt th thee
resistivity; resisti vity; specifi specificc condu conductance; ctance; specifi specificc resista resistance nce
14.1 cation cation;; condu conductivity ctivity;; high purity water measurements; measurements;
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D5391 − 14 ANNEXES (Mandatory Information) A1. EV EVALUA ALUATION TION OF INSTRUMENT HIGH PURITY MEASUREMENT MEASUREMENT CAPABILITY CAPABILITY TABLE A1.1 Conductivity Cell Model Component Nominal Values
A1.1 The performance performance of a condu conductivity ctivity/resisti /resistivity vity measuring instrument design is evaluated using an electrical circuit model. This is necessary because measurement of a conduc-
Simulated Conditions 0.055 µS/cm, 18.2 MΩ-cm 0.01 cm −1 cell 2 m cable 0.055 µS/cm, 18.2 MΩ-cm 0.01 cm −1 cell 50 m cable 0.055 µS/cm, 18.2 MΩ-cm 0.1 cm −1 cell 2 m cable 0.055 µS/cm, 18.2 MΩ-cm 0.1 cm −1 cell 50 m cable 0.1 µS/cm, 10 MΩ-cm 0.01 cm −1 cell 2 m cable 0.1 µS/cm, 10 MΩ-cm 0.01 cm −1 cell 50 m cable 0.1 µS/cm, 10 MΩ-cm 0.1 cm −1 cell 2 m cable 0.1 µS/cm, 10 MΩ-cm
tivity cellresistance. in high purity is more complex measuring a simple Notwater all instrument designsthan are capable of accurat accu ratee meas measure uremen ments ts und under er the these se con condit dition ions. s. Fig. Fig. A1. A1.1 1 shows sho ws the sch schemat ematic ic of a simp simple le netw network ork that elec electric trically ally simulates a conductivity cell immersed in high purity water. The instrument must be able to measure the solution resistance, R , accurately in this network. c
A1.1.1 Evaluation A1.1.1 Evaluation of the con conduc ductivi tivity ty meas measuri uring ng circ circuit uit performance is not required when using a sensor with integral measuri meas uring ng circ circuit uit and dig digital ital out output put sig signal nal as thes thesee sen sensor sorss have no significant leadwire capacitance affecting the measurement. A1.2 From Table From Table A1.1 A1.1 select measurement conditions closest to those in which the equipment will be installed and find
C (pF) w
C (µF) e
R (ohms) c
330
1
182 k
8200
1
182 k
330
0.47
1.82 M
8200
0.47
1.82 M
330
5
100 k
8200
5
100 k
330
0.1
1M
8200
0.1
1M
−1
the appropriate circuit component values. A1.3 A1. 3 Con Connec nectt the network network to the cell inp input ut of the ins instru tru-ment. Connect a resistor to the temperature compensator input of the instrumen instrumentt with value to sim simula ulate te 25. 25.0 0 6 0.1°C, 0.1°C, as specified specifie d by the instru instrument ment manuf manufacture acturerr. Altern Alternatively atively,, read uncompensated conductivity, if available on the instrument.
0.1 cm cell 50 m cable
A1.4 Remove any trims, trims, cell calibrations, calibrations, etc., from instrument memory that would prevent it from indicating absolute, uncorrected conductivity or resistivity. A1.5 Tak A1.5 akee re read adin ings gs wi with th th thee in instr strum umen entt me meas asur urin ing g th thee network and again measuring only the resistor. The difference betwee bet ween n the these se rea readin dings gs rep repres resent entss an app approx roximat imation ion of the error that can be anticip anticipated ated in actual cell measur measurements ements due to instrument signal handling limitations. (This does not include errors from temperature compensation or cell constant uncertainties.) This test will identify most signal handling deficiencies but is not intended to quantify errors. Also, note that more comple com plex x mod models els are nee needed ded to rep repres resent ent hig higher her ranges of conductivity measurement. This model is appropriate only for the ranges given.
FIG. A1.1 Circui Circuitt Model of Conductivity Conductivity Cell in High Purity Water
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D5391 − 14
A2. HIGH PURITY CONDUCTIVITY CONDUCTIVITY CELL CONSTANT CONSTANT CALIBRATION CALIBRATION WITH LIMITED-RANGE INSTRUMENTS INSTRUMENTS
A2.1 The con A2.1 conduc ductiv tivity ity cell constant constant is the gre greates atestt unc uncerertainty in the measurement once the requirements for temperature compensation, measuring instrument capability, leadwire, sampling, etc., are satisfied. Therefore, it must be determined with wit h pr preci ecisio sion, n, wh wheth ether er in th thee lab labor orato atory ry or by th thee ce cell ll manufacturer.
A2.3 Rinse the secondary secondary standard cell and the high purity cell to be tested for at least an hour with flowing Type I water prior to measurement to fully wet electrode surfaces and to wash away any residual contaminants accumulated in storage. A2.4 Immer Immerse se the two cells in stirred Type Type I water to which dilu di lute te KC KCll so solu lutio tion n ha hass be been en ad adde ded d dr drop opwi wise se to ra raise ise th thee conductivity to 5 to 10 µS/cm. Allow time for the cells and solution to reach temperature equilibrium and tap the cells to remove any bubbles adhering to the cell surfaces. Using the same type of instrument as in A2.2 in A2.2,, measure the conductivity/ resistivity of each cell as quickly as possible.
A2.2 Using Test Test Methods D1125 Methods D1125 prepare prepare a Standard Referencee Sol enc Soluti ution on C, 140 1408.8 8.8 µS/ µS/cm, cm, or Ref Refere erence nce Sol Soluti ution on D, 146.93 µS/cm. Alternatively, obtain NIST Standard Reference Materia Mate riall 319 3191, 1, nom nomina inall val value ue 100 100.0 .0 µS/ µS/cm, cm, 319 3192, 2, nom nomina inall value 500.0 µS/cm or 3193,nominal value 1000.0 1µ S/cm, or from fro m a tra traceab ceable le sou source rce (12 12)). Us Usin ing g on onee of th thee st stan anda dard rd solu so lutio tions ns ab abov ove, e, de deter termi mine ne th thee pr prec ecise ise ce cell ll co cons nstan tantt of a nominal 0.5 to 5 cm −1 cell using Test Methods D1125 Methods D1125,, with the standard solution temperature controlled and cell equilibrated to 25.0 6 0.2°C. This cell is used as the secondary standard. The type of instrument used for this determination must meet the perfo performanc rmancee requi requirement rementss of Annex A1, A1, since the same instrument is used for the comparison in A2.4 A2.4..
A2.5 Calcula Calculate te the cell constant of the low constant constant cell as follows: cell constant 5 nomin nominal al test cell consta constant nt
3
(A2.1)
standard cell conductivity test cell conductivity
REFERENCES (1) Light, T.S., and Sawyer, P.B., “Resistivity of Very Pure Water and its Maximum Value,”Power Plant Instrumentation for Measurement of High-Purity Water Quality, ASTM STP 742, 1981, pp. 175–184. (2) Pate, K.T., “DI Water Water Resistivity Versus Trace Ion Levels,” Ultrapure Water , Vol 8, No. 1, January/February 1991, pp. 26–33. (3) Thornt Thornton, on, R.D R.D., ., Mor Morash ash,, K.R K.R., ., Lig Light, ht, T.S. .S.,, Sau Saunde nders, rs, C.H C.H., ., and Bevilacqua, Bevila cqua, A.C., A.C., “Meas “Measurem urement ent of the Resis Resistivity tivity of HighHigh-Purity Purity Water at Elevated Temperatures,” Ultrapure Water , Vol 11, No. 9, December 1994, pp. 18–24. (4) Light, Light, T. T.S., S., Licht, S., Bevilacqua, Bevilacqua, A.C., and Moras Morash, h, K.R. K.R.,, “The Fundamental Conductivity and Resistivity of Water,” Electrochemical and Solid-State Letters, Vol 8, No. 1, 2005, pp. E16–E19. (5) Light, T. T. S., and Licht, S. L., “Conductivity “Conductivity and Resistivity Resistivity of Water
Condensate and Feedwater Sampling Systems,” Ultrapure Water , Vol 6, No. 3, April 1989, pp. 18–27. (10) “Survey of Corrosion Product Generation, Transport, and Deposition in Light Water Water Reacto Reactors,” rs,” Electric Powe Powerr Resea Research rch Insti Institute tute Repor Reportt NP-522, March 1979. (11) Ea Eate ter, r, L. L.,, “M “Mak akee S ure ure Wat ater er-C -Che hem m is is try try S am am ple pless A re re Representative,” Power , July 1989, pp. 47–50. (12) Certificate of Analysis, Aqueous Electrolytic Conductance Standard Reference Materials 3190–3195, National Institute of Standards and Technology, U.S. Department of Commerce, Gaithersburg, MD. (13) Gray, D. M., “High Purity Conductivity Cell Standardization,” 1990 Interna Int erna tio tional nal Con Conferen feren ce on Meas urin g Waterbo rne Trace Substances Subst ances,, EPRI and NIST , Baltimore, Aug. 1990.
from the Melting to Critical Points,” Analytical Chemistry, Vol 59, No. 19, Oct. 1987, pp. 2327–2330. (6) Hunt, R. C., “Conduct “Conductivi ivity ty and pH Mea Measur sureme ements nts in Hig High h Pur Purity ity Water,” Ultrapure Water , Vol 3, No. 4, March/April 1986, pp. 39–46. (7) Hunt, R. C., “Combined Conductivity and pH Temperature CompenUltrapure Water , Vol 3, No sation sat ion in Hig High h Pur Purity ity Wate ater, r,”” Ultrapure No.. 2, July/August 1986, pp. 31–39. (8) Gray, D., and Tenney, A.,“Improved A.,“Improved Conductivity/Resistivity Temperature Compensation for High Purity Water,” Ultrapure Water , Vol 3, No. 2, July/August 1986, pp. 27–30. (9) Davis, Davis, J., and Bla Blair ir,, C., C.,“Gu “Guide ideline liness for Des Design ign and Ope Operat ration ion of
(14) Scheerer, C. C., Cluzel, J., and Lane, R. W.,“ W.,“ Monitoring Condensate Polisher Operation Using Conductivity (Specific, Cation, and Degassed Cation) and Sodium Analysis,” International Water Conference Proceedings, 1989, pp. 321–334. (15) Light, T. S., and Thornton, R. D., “Conductivity Cell Standard for Low Ionic Strength Solutions,” Ultrapure Water , Vol 8, No. 3, April 1991, pp. 59–66. (16) Rice, J. K., Sopocy, D. M., and Dooley, R. B.,“ Quantification of Continuous Contin uous Instru Instrument ment Error Error,” ,” 1990 Inter Internation national al Confe Conference rence on EPRI an and d NI NIST ST , Measuring Measu ring Waterbo aterborne rne Trac Tracee Subs Substances tances,, EPRI Baltimore, Aug. 1990.
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