wheres ‘Aco m ttrant for Tap A, sm ttant for Tap B, ‘N= normality of NajS,0s, and T= ozonation time (min). 1 Ozone demand: where (C= mL tant for Tap C. Report both the sample’s ozone demand and the blank’s ozone demand, as well as the ozone dose, ozonation time, sample tem= perature, sample pH, sample volume, and anal 2510 A. Introduation Because the ozone transfer rate is highly dependent on experi- ‘mental conditions, also report vessel volume, vessel type, gas flow rate, and sample volume. ¢. Ozone requirement: The ozone requirement in the semibatch testis the ozone dose (mg/min) required to obtain the target ozone ‘residual after the desired ozonation time. See paragraph a above to calculate the dose. When reporting ozone requirement, also include the target oxidant residual and other experimental charac- teristics listed in paragraph b above. 6, Precision and Bias See 2350B.6. Bibliography See Sections 4500-05 B.7 and 8, Conpuctivity Appcoved by Standard Methods Conmite, 197. Earl revises, 2021, oint Tk Group: Robert M. Bagtigan ci, Stephen W. Johnson, Willan F Kec, Rosell W Lane, Misha Pam, A. IntRoDUCTION Conductivity, f, is a measure ofthe ability of an aqueous solu- tion to carry an electric current, This ability depends on the pres- fence of ions; on their total concentration, mobility, and valence; and on the temperature of measurement. Solutions of most inor- ganic compounds are relatively good conductors, Conversely, ‘molecules of organic compounds that do not dissociate in aque ‘ous Solution conduct a current very poorly if at al 1, Terminology and Units of Expression Conductance, G, is defined asthe reciprocal of resistance, R: ‘where the unit of R is ohm and G is ohm" (sometimes writ- ten mho). Conductance of a solution is measured between 0 spatially fixed and chemically inert electrodes. To avoid polai ization at the electrode surfaces the conductance measurement is made with an alternating current signal.' The conductance of a solution, G, is directly proportional to the electrode sur- face area, A (cm), and inversely proportional to the distance between the electrodes, L (ct). The constant of proportionality, , such that: 4g) is conductivity (prefered to specific conductance). 1s a ehar- Acerstic property ofthe solution between the electrodes. The units of kare Vohm-om oF mho per centimeter. Conductivity is customarily reported in micrsiemens pee centimeter (Sem) or rmirombos per centimeter (imhoem) In the Interatonal System of Units (SI) the reciprocal ofthe chm is the siemens (S) and conductivity is reported as mil siemens per meter (mn | mSim = [0 ymholem and 1 Siem 1 mom. To repr result in ST units of mSim divide umbosfm ty 10, “To compare conductivities, values off are reported relative to electrodes with A= | mand =I em. Absolute condectances, Gry of standacd potassium chloride solutions between electrodes of precise goometry have been measured the comesporling stn dard conductivities, are shown in Table 2510: 1 “The equivalent conductivity, A, ofa solution isthe condutv- ity per nit of concentration, As the concentration is decreased toward zero, A approaches a constant, designated as A°. With k Jn units of microsiemens per centimeter ts necessary to conver, concentration to units of equivalents per eubie centimeter; there fore Part 2000 +1312510 PHYSICAL AND AGGREGATE PROPERTIES OF WATER AND WASTEWATER: Conductivity A= 0001k/concentration where the units of A, k, and concentration are mho-enlequiva- lent, s$/em, and equivalenvL, respectively, Equivalent conductiv- ity, A, values for several concentrations of KCI are listed in Table 2510:1. In practice, solutions of KCI more dilute than 0.001 M do ‘not maintain stable conductivities because of absorption of atmo- spheric C3, Protect these dilute Solutions from the atmosphere. 2. Measurement 4, Instrumental measurements: Inthe laboratory, conductance, G,, (or resistance) of a standard KCI solution is measured and from the corresponding conductivity, k,, (Table 2510:1) a cell constant, C (em), is calculated: 3 Most conductivity meters do not display the actual solution ‘conductance, G, or resistance, R; rather, they generally have a dial that permits the user to adjust the internal cell constant to match the conductivity, k, of a standard, Once the cell constant has been determined, or se, the conductivity of an unknown solution, is displayed by the meter. Distilled water produced in a laboratory generally has a con: ductivity in the range 0.5 t0 3 wSiem. The conductivity increases shortly after exposure to both air andthe water container. ‘The conductivity of potable waters inthe United States eanges generally from 50 to 1500 Siem. The conductivity of domestic wastewaters may be near that ofthe local water supply, although some industrial wastes have conductivities above 10 000 jS/e Conductivity instruments ate used in pipelines, channels, lowing. streams, and lakes and can be incorporated in multiple-parameter ‘monitoring stations using recorder. Most problems in obtaining good data with conductivity mon- itoring equipment are related (o electrode fouling and the inad- equate sample circulation. Conductivities greater than 10000 o 50000 uS/em or less than about 10 jSfem may be difficult {o measure with usual measurement electronics and cell eapac- itance. Consult the instrument manufacturer's manual ot pub- lished references." aboratory conductivity measurements are used to: tablish the degree of mineralization to asses the effect of the total concentration of ions on physical states (eg, chemical equilibria, rate of conosion, physiology of plants or animals). Assess the degree of mineralization of distilled and deion- ied water. Evaluate vatiations in dissolved mineral concentration of raw water or wastewater. Minor seasonal variations found in reservoir waters contrast sharply with the daily fluctua- ‘ions in some polluted river waters. Wastewater containing significant trade wastes also may show a considerable daily variation, Estimate sample sizes to be used for common chemical ‘deferminations and to check results of chemical analyses. *+ Determine the amount of an ionic reagent needed in certain precipitation and neutralization reactions, the endpoint being denoted by a change in slope ofthe curve resulting fom plot- ting conductivity against buret readings, Estimate total dissolved solids (mg/L) in a sample by multi- plying conductivity (in mS/em) by an empirical factor. This factor may vary from 0.55 to 0.9, depending on the soluble ‘components of the water and on the temperature of mea- surement. Relatively high factors may be required for saline of boiler waters, whereas lower factors may apply where considerable hydroxide or free acd is present, Even though sample evaporation results in the change of bicarbonate to carbonate, the empirical factor is derived fora comparatively ‘constant water supply by dividing dissolved solids by con ductivity ‘Table 2510:1, Equivalent Conductivity, A, and Conductivity, fof Potassium Chloride at 25.0 °C KQ Concentration Equivalent Condutiviy, A Conductviy, (Mor equivalent.) (imho-mYequivaln’) (Siem) 0 149.9) 0.0001 148.9) 5 49 0.0005 uar7 no ‘.001 1469 1469 ‘0.005 3.6 nts oot wiz 1412 0.02 1382 2765 00s 1333 6.667 04 i289 12390 02 1240 24 800 05 73 58670 L m9 111.900 “Based onthe bolt ob, he 1968 temperature standard hed volume andar! Veloce re asa to 401% oO pSlem, whichever is prower Referees 1. WaYC, Koch WE Hamer W, Koy RL Review of elect conductance standards J Suton Chem. 1987;16(2):988-97, 2 Jasper WS Secondary standard potassium chloride conduct solos at 25°C lew Springs (OH) Corporate Metrology Laboratory SE: 1988 3 Organization internationale de Méoege Lgoe Standard solions reproducing he condo elects, Intratonl Recommenaton N36, Ie Jane 1880. avis (France) Bureau of Ivational de MérlogieLégle; 198 482 + Part 2000‘Table 2510:2. Sample Analysis Mustang Calculation of Conductivity, ego for Natural Waters 2510 A. Introduction ‘Table 251033, Equivalent Conductance, A and 2, (mho-em’? equivalent for Ions in Water at 25.0°C Tons ell malt erg mM c 35 138 1642 352 Mg 2 049 520 1.96 Na 8 122 ou in K 32. 0.08 39 08, cos 170 279 142 279 804 n 80 1280 320, a 2 056 428 056 screams miss3) Reference emit CE. Menlo wate ASTM Special echnical publication #24, the Philadelphia Soto for Ttng a ata 197 ‘+ Approximate the milliequivalents per lter of either cations of anions in some waters by multiplying conductivity in units ‘of micromhos per centimeter by 0.01 4, Caleulation of conductivity: Fr naturally occuring waters that contain mostly Ca", Mg”, Na’, K', HCOs’, SO," and CI and with TDS less than about 2500 mg/L, the following proce- dare can be used to calculate conductivity from measured ionic concentrations The abbreviated water analysis in Table 2510:2 illustrates the calculation procedure. AL infinite dition, the contribution to conductivity by diferent kinds of ions is additive, In general, the relative contribution of each ‘ation and anioniscalculaed by multiplying equivalentconductances, 2and 42, mho-ens/equivalent, by concentration in equivalents per titer and conectng units. Table 2510:3 contains a short ist of equiva- ent conductance values for ions commonly found in natural water.* ‘Trace concentrations of fons generally make negligible contribution to the overall conductivity. A temperature coefficient of O.03/deg is applicable tall ions, except” (0.0139/deg) and OH” (0.018/des) At finite concentrations, as opposed to infinite dilution, con- ‘ductivity per equivalem decreases with increasing concentration (Gee Table 2510:1). For solutions composed of one anion type and ‘one cation type (eg, KCI as in Table 2510:1), the decrease in ‘conductivity per equivalent with concentration can be calculated, 40.1%, using an joni strength-based theory of Onsager® When ‘mixed salts are presen, as is nearly always the ease with natural and wastpwaters, the theory is quite complicated,’ The following semi-empirical procedure can be used to calculate conductivity for naturally occurring waters: First, calculate infinite dilution conductivity (Tuble 2510:2, ‘Column 4): a Hel(4,}mm) +E al( ome where lg = absolute value ofthe charge ofthe th fon, ‘Mf, = milimolar concentration ofthe ih ion, and 1,02) equivalent conductance ofthe ih ion If mM is used to express concentration, the produet, (3 (mM) oF (2)(mM;), corrects the units from liters to em? In this ease k° is 578.2 uS/em (Table 2510:2, Columa 4). Cation is Anion aM ry 350 or 1986 wee 95 HCO," 445 Me" 33 coy" n Ne sou 480," 800 x BS or 164 NEG! Bs ac 409 BR s F 54 Are 68 Nos na HPO¢ 3 YsHPOY 3 Reference ean JA. Lange's handbook of chess. 3th New York Ne Maw Hit Book Co. 1985. Next, calculate ionic strength, 1S in molar units i (mt,)/2000, ‘The ionic strength is 15.33/2000 = 0.00767 M (Table 2510%2, Column 5). Calculate the monovalent ion activity coefficient, y, using the Davies equation for IS < 0.5 M and for temperatures from 20 to 30°C yor @ss"415")-095] In the present example /S = 0.00767 M and y = 0.91. Finally, obtain the calculated value of conductivity, Kegte from: Fete = 9? In the example being considered, Keats = 578.2 x 0.91? 478.8 Sem versus the reported value as measured by the USGS of 477 Siem, For 39 analyses of naturally occurring waters," conductivi- ties calculated in this manner agreed with the measured values |, Willard HH, Merit LL, Dean JA. Instrumental methods of analy ‘th ed, New York (NY): D. Van Nostrand Company; 1974 2. ASTM D1125-82. Standard west methods for eletical conductivity and resisivity of water; West Conshohocken (PA): ASTM Intern tional; 2014 3. Schoemaker DS, Garland CW, Nibler JW. Expects in physical chemistry. 5th ed New York (NY): McGraw-Hill Book Co. 1989. 4, Hamilton CE. Manual on wate; ASTM Special technical publication 442A, Ath ed, Philadelphia (PA): American Society for Testing and ‘Materials; 1978. 5, Dean JA. Lange’ handbook of chemist. 13th ed. New York (NY) ‘McGraw-Hill Book Co. 198. Part 2000+ 133,£2510 PHYSICAL AND AGGREGATE PROPERTIES OF WATER AND WASTEWATER: Conductivity 6, Robinson RA, Stokes RH, Flectrolyte solutions. nd ed. New York (NY): Academie Press; 1959, 7. Hamed HS, Owen BB. The physical chemistry of electrolytic solu- tions. rd ed, New York (NY): Reinhold Publishing Comp; 1958, 8, Davies CW. lon association, Amsterdam, The Netherlands: Elsoviee rest 1982 9. Tehobanoglous G, Schroeder ED. Water quality, Vol 1, Reading (MA): Addison-Wesley Publishing Company; 1985, 2510) B. Lasoratory MetHoD 1. General Discussion See 2510.4. The QC practices considered to be an integral part of each ‘method are summarized in Table 2020:1 and Table 2020:2. 2. Apparatus 4a, Self-contained conductivity instruments: Use an instrument capable of measuring conductivity with an error not exceeding, 1% or | Siem, whichever is greater: +, Thermometer, capable of being read to the nearest 0.1 °C and. covering the range 23 to 27 °C, Many conductivity meters are equipped to read an automatic temperature sensor. ‘Conductivity cell 1) Platinum-electrode type—Conductivity cells containing platinized electrodes are available in cither pipet or immersion form. Cell choice depends on expected range of conductivity Experimentally check instrument by comparing. instrumental results with rue conductivities of the KCI solutions listed in Table 2510:1. Clean new cells, not already coated and ready for use, ‘with a chromic acid cleaning mixture (see Section 2580 B.362) and platinize the electrodes before use. Subsequently, clean and replatinize them whenever the readings become erratic, when a surp endpoint caunot be obtained, or when Inspection shows that any platinum black has flaked off. To platinize, prepare a solu- tion of 1 g chloroplatinic acid, HPtCls - 6H;0, and 12 mg lead acetate in 100 mL reagent water. A more concentrated solution reduces the time required to platinize electrodes ankd may be used. when time is a factor (eg, when the cell constant is 1,0/em or ‘more). Immerse electrodes in this solution and eonnect both 10 the negative terminal ofa 1,5-V dy cell battery. Connect the pos- itive side ofa battery toa piece of platinum wire and dip the wiee into the solution. Use a current such that only a small quantity of ‘28s is evolved. Continue electrolysis until both cell electrodes are ‘coated with platinum black. Save platinizing solution for subse {quent use. Rinse the electrodes thoroughly and when notin use ‘Keep immersed in reagent water. 2) Nonplatinum-electrode type—Use conductivity cells con- twining electrodes constructed from durable common metals (stainless steel among others) for continuous monitoring and field studies, Calibrate such cells by comparing sample conductivity, ‘with results obtained with a laboratory instrument, Use a properly {designed and mated cell and instrument wo minimize errors im cell constant. Very long meter leads ean affect the performance of a conductivity meter. Under such cireumstances, consult the mant= factures’s manual for appropriate correction factors if necessary. 3, Reagents 4. Conductivity water: Any of several methods ean be used to prepare reagent-grade water, The methods discussed in Section 184 Part 2000 1080 are recommended. The conductivity should be small com- pared to the value being measured. Standard potassium chloride solution (KC), 0.0100 M: Dis- solve 745.6 mg anhydrous KCl in conductivity water and dilute to 1000 min aclass A volumetric flask at 25 °C and store ina CO,- frce atmosphere. This isthe standard reference solution, which at 25°C has a conductivity of 1412 uS/em. tis satisfactory for most samples when the cell has a constant between 1 and 2 cns!, For ‘other cell constants, use stronger or weaker KCI solutions listed in Table 2510:1. Care must be taken when using KC! solutions less than 0.001 M, which can be unstable because ofthe influence ‘of carbon dioxide on pure water. For low conductivity standards, Standard Reference Material 3190, with a certified conductivity ‘of 25.0 pSiem + 0.3 uS/em may be obtained from NIST. Store in a glass-stoppered borosilicate glass ote, 4, Procedure 4, Determination of cell constant: Rinse conductivity ell with atleast 3 portions of0.01 M KCI solution. Adjust the temperature ofa fourth portion 0 25.0:+ 0.1 °C. Ifa conductivity meter ise plays resistance, R (ohms), measure the resistance ofthis portion and note the temperature. Compute the cell constant, C: Cem"! = 001412} Ryepl+0.01910—25) measured resistance (ohms) and observed temperature, °C Conductivity meters often indicate conductivity directly, Com- ‘mercial probes commonly contain a temperature sensor. With such instruments, rinse the probe 3 times with 0.0100 M KCl, as above. Adjust the temperature compensation dial to 0.0191 C-' With the probe ina standard KCI solution, adjust the mete to read 1412 uSfem. This procedure automatically adjusts cell constant internal tothe meter. b. Conductivity measurement: Thoroughly rinse the cell with ‘one of more portions of sample. Adjust the temperature of a final Portion to about 25 °C. Measure the sample resistance or conduc- Livty and note temperature to 0.1 °C, 5. Calculation ‘The temperature coefficient of most waters is only approx: imately the same as that of standard KCI solution; the more the temperature of measurement deviates from 25.0 °C, the {greater the uncertainty in applying the temperature correction, Report temperature-compensated conductivities as “uS/em @ 250°C" 4, When sample resistance is measured, conductivity at 25 °C is:(1000000)(¢) 10000)(C) Balt 00191(1-25) where: = conductivity (uS/em), ll constant (cm), measured resistance of sample (ohms), and a temperature of measurement. >, When sample conductivity is measured without internal tem perature compensation conductivity at 25 °C is fypSiem = ——(ta)__—_ TFO0181(/=25) £2520 A. Introduction eq = measured conductivity in units of uSlem at ¢ (°C), and other units are defined as above For instruments with automatic temperature compensation and. readout directly in S/em or similar units, the readout automati- cally is corrected to 25.0 °C. Report the displayed conductivity in, the designated units 6. Precision and Bias ‘The precision of commercial conductivity meters is commonly ‘between 0.1% and 1.0%. Reproducibility of 1% to 2% is expected after an instrument has been calibrated with such data as is shown in Table 2510:1 ‘Sauinity ‘Approved by Standard Methods Commie, 2070, Earl eins, 202. (20) A. intpooucion 1. General Discussion Salinity is an important unitless property of industrial and nat- ural waters. It was originally conceived as @ measure of the mass ‘of dissolved sults in a given mass of solution, The experimental ‘determination ofthe salt content by drying and weighing presents some difficulties due to the loss of some components, The only reliable way to determine the true or absolute salinity of a natu ral water is to make a complete chemical analysis. However, this ‘method is time consuming and cannot yield the precision neces- sary for accurate work. Thus, o determine salinity, one normally ‘uses indirect methods involving the measurement of a physical property such as conductivity, density, sound speed, or refractive index. From an empirical relationship of salinity and the physi cal property detemined for a standard solution, itis possible to calculate salinity. The resultant salinity is no more accurate than the empirical relationship. The precision of the measurement of a physical property determines the precision in salinity. Following, are the precisions of various physical measurements and the resu- tant salinity presently attainable with commercial instruments Precision of Salinity 010002 Precision of Measurement +4000 Sem Property Conductivity Density Sound speed 33x 10* glen +0008 4002 m/s 001 Although conductivity has the greatest precision, it responds only to ionic solutes. Density, although less precise, responds 10 all dissolved solutes. 2, Selection of Method In the past, the salinity of seawater was determined by hydro- rmettic and argentometsie methods, both of which were included in previous editions of Standard Methods (see Sections 210 B and. C, 16th Edition). In recent years the conductivity (2520 B) and density (2520 C) methods have been used because of their high sensitivity and precision. These two methods are recommended for precise field and laboratory work, 8. Quality Assurance Calibrate the salinometer or densimeter against standards of KCI or standard seawater. Expected precision is better than +40.01 salinity units with careful analysis and use of bracketing standards, Pat 2000+ 195