1、Designation: E1511 93 (Reapproved 2017)Standard Practice forTesting Conductivity Detectors Used in Liquid and IonChromatography1This standard is issued under the fixed designation E1511; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisi
2、on, the year 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.1. Scope1.1 This practice covers the testing of the performance ofconductivity detectors used as the detection com
3、ponent of aliquid or ion chromatography system.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility
4、 of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization esta
5、blished in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E1151 Practice for Ion Chromatography Terms and Rela-tionships
6、3. Terminology3.1 See Practice E1151.3.2 Definitions:3.2.1 cell constantthe cell constant (K) of a conductivitycell is equal to 1/A,so = GK.3.2.1.1 DiscussionIf the cell constant of the flow-throughcell used is equal to one, then the conductivity equals theconductance. Although the cell constant is
7、often specified forconductivity detectors, there is little practical value in knowingthe constant as long as the detector is properly calibrated forconductivity.3.2.2 conductancethe conductance (G) of a solution is theinverse of the resistance measured between two electrodes in acell, expressed in u
8、nits of siemens (S), equal to inverse ohms.3.2.2.1 DiscussionThe term resistance refers specificallyto the dc resistance to ionic current, independent of thecapacitive reactance at the interfaces between the electrodesand the solution.3.2.3 conductivitysince the conductance is dependent onboth the c
9、onductive properties of the solution and on thedimensions of the electrodes and the cell, the conductivity ()of the solution is defined to be independent of electrode andcell dimensions. Specifically, 5 G1A(1)where:1 = the distance between two planer disk electrodes, andA = the electrodes surface ar
10、ea.3.2.3.1 DiscussionIn liquid and ion chromatography, celldimensions are commonly measured in centimetres, so theunits of are S/cm. (Alternatively, the SI units of S/m may beused. S/m = 100 S cm.)3.2.4 driftthe average slope of the noise envelope ex-pressed in nano siemens per centimetre per hour a
11、s measuredover a period of 1 h.3.2.5 equivalent conductivityof an ionic solute, the con-tribution of the solute to the total conductivity of the solution,measured in microsiemens per centimetre, divided by itsconcentration in milliequivalents/litre.3.2.6 flow dependence ratethe change in measured co
12、n-ductivity as a function of flow rate.3.2.7 limiting equivalent conductivityof an ionic solute, itsequivalent conductivity extrapolated to infinite dilution.3.2.8 linear rangeof a conductivity detector for a givensolute in a specific solvent, the concentration range of solutefor which the detector
13、response factor is within 5 % of the1This practice is under the jurisdiction of ASTM Committee E13 on MolecularSpectroscopy and Separation Science and is the direct responsibility of Subcom-mittee E13.19 on Separation Science.Current edition approved Oct. 1, 2017. Published October 2017. Originallya
14、pproved in 1993. Last previous edition approved in 2010 as E1511 - 93(2010).DOI: 10.1520/E1511-93R17.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards D
15、ocument Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision o
16、n Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1response factor in the middle of the range as determined fromthe linearity plot specified in Section 11.3.2.8.1 DiscussionThe low
17、er limit may be limited bynoise, and the upper limit by deviation from linearity. (Theupper limit may instead be limited by the maximum full-scaledeflection on the detectors least sensitive output range.)3.2.9 long-term noisethe maximum amplitude in nanosiemens per centimetre for all random variatio
18、ns of the detectoroutput of frequencies between 2 and 60 cycles per hour.3.2.9.1 DiscussionLong-term noise represents noise thatcan be mistaken for eluting peaks.3.2.10 minimum detectabilityof a conductivity detector,that concentration of solute in a specific solvent that corre-sponds to twice the s
19、hort-term noise.3.2.10.1 DiscussionBecause of the difficulty of pumpingsolvents through the chromatographic system without anycontamination of the solvents from the system, this quantitycan only be measured with solutes retained by a column. Sinceminimum detectability is dependent on the chromatogra
20、phicsystem used, it is not measured in this practice. However, if theminimum detectability of a solute is measured on one systemwith one detector, the minimum detectability can be predictedwhen other detectors are tested on the same system bycomparing the measured values of short-term noise.3.2.11 r
21、esponse factorof a conductivity detector, the mea-sured conductivity response of a solute divided by the soluteconcentration.3.2.12 response time of the detectorthe time required forthe output of the detector to change from 10 to 90 % of the newequilibrium value when the composition of the eluent is
22、changed in a stepwise manner, within the linear range of thedetector.3.2.12.1 DiscussionA slow response time has the effect oflimiting resolution for efficient peaks such as early elutingpeaks and those from highly efficient columns or microborecolumns. Response time is generally dependent on threef
23、actors: (a) cell volume, (b) volume of heat transfer tubingleading to the cell, and (c) electronic filtering of the output.3.2.13 sensitivitythe detector response divided byconcentration, which is also the response factor (11.1.1).3.2.13.1 DiscussionSensitivity is therefore by definitionthe same for
24、 all properly calibrated conductivity detectors.(Sensitivity is often confused with minimum detectability,which is dependent on both sensitivity and noise.) Therefore,the calibration of the detector should be measured, and ifnecessary, adjusted. Follow the manufacturers procedure forcalibrating the
25、detector. The procedure in Section 9 is used bymany manufacturers and is useful for the tests in this practice.3.2.14 short-term noisethe maximum amplitude in nanosiemens per centimetre for all random variations of the detectoroutput of a frequency greater than one cycle per minute.3.2.14.1 Discussi
26、onShort-term noise determines thesmallest signal detectable by a conductivity detector, limits theprecision available for the determination of trace samples, andmay set the lower limit of linearity.4. Summary of Practice4.1 Four different tests are performed to characterize adetector.4.1.1 Noise and
27、 drift are measured while a solution isflowing through the detector cell. The test is performed usingtwo different solutions: deionized water (DI) and 1 mMpotassium chloride (KCl).4.1.2 Linear range is determined by preparing a plot ofresponse factor versus the log of solute concentration usingstand
28、ard solutions of KCl and hydrochloric acid (HCl) assolutes.4.1.3 Dependence of response on flow rate is measured bypumping 1 mM KCl through the conductivity cell at severalflow rates and measuring the detector output.4.1.4 Response time is measured by measuring the timerequired for the detector outp
29、ut to change from that measuredwith DI water to that measured with 1 mM KCl.5. Significance and Use5.1 This practice is intended to describe the performance ofa conductivity detector independent of the chromatographicsystem in terms that the analyst can use to predict overallsystem performance when
30、the detector is coupled to thecolumn and other chromatography system components.5.2 Although it is possible to observe each of the severalcharacteristics of a detector under different and uniqueconditions, it is the intent of this practice that a complete set ofdetector specifications should be obta
31、ined at the same operat-ing conditions, including the setup used for testing, flow rates,and temperatures. It should be noted that to specify a detectorscapability completely, its performance should be measured atseveral sets of conditions within the useful range of thedetector. The terms and tests
32、described in this practice aresufficiently general so that they may be used at whateverconditions may be chosen for other reasons.6. Reagents6.1 Reagent chemicals are reagent grade or better.6.1.1 Deionized Water, (DI water), 18 M-ohm.6.1.2 Potassium Chloride, (KCl) dry powder.6.1.3 Hydrochloric Aci
33、d, (HCl) standard 0.1000 N solution.7. Preparation of Standards7.1 Potassium Chloride Standards:7.1.1 Prepare a 10-mM KCl standard stock solution. Weighout 0.7455 g KCl (desiccated) and dissolve it in 18 M-ohm DIwater in a 1-L plastic volumetric flask. Fill the flask to 1 L withDI water.7.1.2 Prepar
34、e KCl standards from the 10-mM KCl standardstock solution. Using accurate Class A pipettes, pipette thevolumes of the 10-mM standard stock solution listed belowinto 100-mL plastic volumetric flasks. For the 1-mM KClstandard, fill a 100-mLplastic volumetric flask with the 10-mMKCl solution and transf
35、er to a 1-L plastic volumetric flask. Fillto the line with DI water.E1511 93 (2017)2KCl Concentration,mmVolume in 100 mL DI Water,mL0.05 0.50.1 10.2 20.5 51 100 mL in 1 L2205510 mM No dilution7.2 Hydrochloric Acid Standards:7.2.1 Prepare a 2.00-mM HCl standard stock solution bydiluting 20.0 mL of st
36、andard 0.1000 N HCl into a 1-L plasticvolumetric flask and filling to the line with DI water. Ifstandard 0.1000 N HCl is not available, a 0.10-mM HClsolution can be prepared by diluting 8.3 mL of 12 N (37 %)concentration HCl into 1 L of DI water. (The concentration ofthis solution will be less accur
37、ate than that prepared from0.1000 N HCl standard.)7.2.2 Prepare the following HCl calibration standards fromthe 2.00-mM HCl standard stock solution. Use accurate ClassA pipettes and 100-mL plastic volumetric flasks.HCl Concentration,mMVolume in 100 mL DI Water,mL0.02 10.04 20.1 50.2 100.4 20152 No d
38、ilution8. Instrumentation Set-Up8.1 Set up the chromatographic system according to themanufacturers recommendation. Also, passivate the conduc-tivity cell using the manufacturers recommended procedure.Set the flow rate on the pump to 1.0 mL/min or to the flow ratenormally used in your application. F
39、ill the eluent bottle with 18M-ohm DI water. Connect the outlet of the pump to theinjection valve, and the outlet of the injection valve directly tothe conductivity cell using as short a length of tubing as ispractical. (Standard 0.25-mm (0.01-in.) internal diameterHPLC tubing may be used.) Do not i
40、nstall any columns orsuppressors. To ensure smooth operation of the pump, it isnecessary to supply more pressure than that normally providedby the detector cell and the standard tubing alone. This isaccomplished by installing a 1-m coil of 0.25-mm internaldiameter narrow bore tubing between the pump
41、 and theinjection valve. Increase the length or decrease the diameter ofthe tubing if the pressure is not high enough to produce smoothpump operation. Generally, 500 to 1000 psi will be sufficient.The waste line connected to the cell outlet should be ofsufficient length to provide enough backpressur
42、e on the cell toprevent the formation of bubbles inside the cell. Inserting20 cm of 0.25-mm internal diameter tubing between the celland waste line should provide sufficient backpressure.8.2 Install a sample injection loop of approximately 200 Lon the injection valve. This can be constructed from1mo
43、f0.5-mm (0.02-in.) internal diameter tubing. During the testsdescribed in Sections 6 and 7, observe the recorder trace andverify that a plateau is reached after injection of the standardsolutions. If no plateau is reached, then a larger sampleinjection loop is needed.8.3 If the conductivity detector
44、 has a setting for temperaturecompensation, set it to 2.0. If not, the DI water eluent and allof the test solutions should be thermostated as close as possibleto 25 C. Or, the detector cell may be thermostated at a highertemperature but be calibrated as if the cell were at 25 C. If thecell is thermo
45、stated, ensure that the cell temperature hasstabilized. Refer to the manufacturers procedure for celltemperature stabilization. Turn off any output filtering on thedetector. The output from the detector should be monitored ona strip-chart recorder, integrator, or computer. The calibrationand lineari
46、ty tests can be performed with a voltmeter monitor-ing the detector output or, on some detectors, the output ismonitored on the front panel readout.9. Calibration9.1 MethodThe detector is calibrated by adjusting thedetector output to 147.0 S/cm for a 1-mM solution ofpotassium chloride flowing throug
47、h the conductivity cell at 1mL/min.9.1.1 Set up the chromatographic system according to theinstructions in Section 8. Turn on the pump and ensure that thepump is pumping smoothly.9.1.2 Monitor the detector output. The conductivity shouldbe below 1S/cm. If it is higher, continue flushing out thesyste
48、m to remove leftover salts until the conductivity stabilizesbelow 1 S/cm. (A higher reading is an indication of either anincompletely cleaned flow system or of poor deionized waterquality and may compromise noise and linearity tests.) Fill thesample injection loop with DI water and inject. Note them
49、inimum conductivity reported during the elution of the DIwater through the detector cell. Either calibrate the detector tozero using the injected DI water or subtract the conductivity ofinjected DI water from all subsequent measurements.9.1.3 Fill the sample injection loop with the 1-mM KClstandard and inject the standard. Note the maximum conduc-tivity reported during the elution through the detector cell ofthe 1-mM KCl standard. It should be 147.0 S/cm. If it is not,follow the manufacturers procedure for calibrating the con-ductivity dete
