1、Designation: D7677 16Standard Test Method for theContinuous Measurement of Dissolved Ozone in LowConductivity Water1This standard is issued under the fixed designation D7677; 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.1. Scope1.1 This test method covers the on-line and in-line determi-nation of dissolved ozone (DO3) in low conductivity water
3、inthe range from 0.001 mg/L to 5.0 mg/L DO3and conductivity90, before pumps, the tops of horizontalpipes, vertical pipes that have liquid flowing downward,immediately after increases in pipe diameter, after a depres-surization or any turbulence creating point.11. Calibration11.1 Calibration of ZeroW
4、ith the sensor removed fromthe line and still reading DO3values, place it in a location inthe air known to be free of ozone gas. Dry the sensormembrane to remove all sample water which may containDO3.Allow the sensor to equilibrate with the air temperature to62C. If there is a large temperature diff
5、erence between the airand the process, for example, 5C; this may take over an hour.Perform a zero calibration according to the manufacturersinstructions. Equivalence of zero is considered to be 0.005D7677 163mg/L (ppm) in most commercial instruments. Some polaro-graphic sensors have an intrinsic zer
6、o and do not require a zerocalibration. Follow the sensor manufacturers recommenda-tions.11.2 Two methods are used for span calibration of polaro-graphic ozone sensors: in-line calibration using a colorimetricreference and air calibration.11.2.1 Colorimetric Calibration of SpanEither of thereagent s
7、ystems noted in 8.3 can be used as the reference forspan calibration. The IOA has approved the indigo method.3With the sensor inline and reading stable DO3values, collect asample of water representative of the water the sensor ismeasuring. This can be from a port near an inserted sensor oron the out
8、let of the sensor flow housing drain. In either case,the sample must flow gently, without spray or turbulence thatcould de-gas the sample. Sample the water using three aliquotsor ampoules, simultaneously noting the reading on the on-lineinstrument. Measure all three grab samples. Discard an outlieri
9、f it differs by 0.015 mg/L (0.02 mg/L for displays not readingto the third decimal place) from the mean of the other two. Ifno two of the three agree, redo all three. Calculate the averageand input the value as the on-line instrument span calibrationaccording to manufacturers instructions.11.2.2 Air
10、 Calibration of Span (suitable for instruments soequipped)Since oxygen and ozone are similar in their per-meation rates through the sensor membrane, the rate ofpermeation of a known oxygen quantity can be equated to anozone calibration value. Single point air calibration can be ameans to calibrate s
11、pan in a DO3instrument with this capabil-ity. Remove the sensor from the line and place it in a locationknown to be free of ozone gas. Be sure the outer surface of thesensor membrane is dry and free of sample water, which maycontain DO3. Allow the sensor to equilibrate with the airtemperature within
12、 62C. If there is a large temperaturedifference between the air and the sensor, for example, 5C,this may take over an hour. Enter the air calibration mode in theanalyzer electronics which temporarily changes the polariza-tion potential applied to the cathode and changes the responseto oxygen (O2) pa
13、rtial pressure. Determination of the O2partialpressure of air is determined from the barometric pressure andtemperature of the air. Allow at least 10 minutes for the sensorto stabilize and then perform the calibration function accordingto the manufacturers instructions. Return to the ozone mea-surem
14、ent mode of the instrument and allow the extendedperiod of time required for the sensor to repolarize and stabilizeon ozone measurement per manufacturers recommendations.11.3 Calibration VerificationSpan and zero verificationare normally required.11.3.1 Colorimetric Verification of SpanWith the sens
15、orinline and reading DO3values under stable conditions, collecta sample of water representative of the water the sensor ismeasuring, this can be from a spigot near an inserted sensor oron the outlet of the flow housing drain. The DO3value forverifying the span should be 70 % of the target processcon
16、trol limit DO3value. System DO3values for verificationmay be higher than the target control limit. Sample andmeasure the ozone concentration of the water the same as forcalibration in 11.1. Compare the average of the three values tothe reading of the instrument. If they differ by 0.015 mg/L(0.02 mg/
17、L if either the spectrophotometer or ozone instru-ment displays do not read to the third decimal place) then aspan calibration is required.11.3.2 Air Verification of Span (for instruments soequipped)With the sensor removed from the line and stillreading DO3values, place it in a location known to be
18、free ofozone gas. Dry the sensor membrane to remove sample waterwhich may contain DO3. Allow the sensor to equilibrate withthe air temperature within 62C. If there is a large temperaturedifference between the air and the process, for example, 5C,this may take over an hour. To check the air calibrati
19、on value,enter into the air calibration mode (which changes the cathodepolarization voltage to make it respond to O2). Allow at least10 minutes for equilibration and record the % last calibrationvalue. If % last calibration value is not available then record %ideal value or absolute air value. Compa
20、re to % ideal orabsolute air value when calibrated. If the two agree within thequality limits set (typically 65 to 15 %), the sensor span hasbeen verified. Restore the instrument to the ozone measure-ment mode and allow the manufacturers extended repolariza-tion time before ozone measurements are us
21、ed.11.3.3 Air Verification of ZeroWith the sensor removedfrom the line and still reading DO3values, place it in a locationin the air known to be free of ozone gas. Dry the sensormembrane to remove all sample water, which may containDO3. Allow the sensor to equilibrate with the air temperaturewithin
22、62C. If there is a large temperature difference betweenthe air and the process, for example, 5C, this may take overan hour. The sensor must read zero or the equivalence of zero(0.005 mg/L, in most commercial instruments). Otherwise azero calibration is required.12. Procedure12.1 The normal operation
23、 of the analyzer is automatic afterconfiguration by the user and does not require user interventionfor routine analysis.12.2 Based on calibration verification results showing anincreasing drift rate, it is necessary to replace the electrolyte ormembrane or both. With some sensors a cleaning process
24、isalso required. If using manufacturer-recommended materialsfor sensor cleaning, observe all safety precautions whenhandling those materials.13. Quality Control13.1 Instrument and sensor verification and calibration mustbe performed according to the manufacturers instructions forboth the continuous
25、measuring equipment and the colorimetricstandard, if used.13.2 Verification FrequencyCalibration verificationshould be checked on a periodic basis. Verification frequency isdetermined based on risk of sensor drift or failure. Factors thatcontribute to sensor drift and failure are (1) continuous high
26、levels of ozone exposure (in accordance with manufacturer3International Ozone Association Revised guideline document, “ColorimetricMethod for Manual Determination of Ozone Concentration in Water,” OzoneScience and Engineering, Vol 20.6, 1998, p. 443.D7677 164specifications), (2) membrane wear due to
27、 excessive flow rates,pressure fluctuations, or abrasive water action, and (3) electro-lyte depletion. Verification should be performed at least everytwo months or according to manufacturers recommendations.13.3 Calibration FrequencyCalibration must be per-formed at least as frequently as the manufa
28、cturers scheduleand instructions and whenever a sensor is returned to serviceafter maintenance. Sensors must be allowed to fully polarizeand reach stability before calibration after maintenance.Minimally, calibration should be performed semi-annually.13.4 Where the verification and calibration of oz
29、one sensorsdepend on a colorimetric method as the standard, at least threecolorimetric samples and measurements must always be madeas outlined in 11.2.1 and 11.3.1.14. Precision and Bias14.1 Neither precision nor bias data can be obtained for thistest method from a collaborative study designed in ac
30、cordancewith the requirements of Practice D2777 since this test methodis a continuous determination. This inability to obtain precisionand bias data for continuous determinations is recognized andstated in the scope of Practice D2777.14.2 The ephemeral nature of ozone makes it impossible toprovide s
31、table ozone standards for comparisons.14.3 Accuracy of ozone measurements by this method areprimarily limited by the reference method to which they arecalibrated.14.3.1 Some colorimetric methods to measure ozone usinggood technique have been found to give repeatability on theorder of 60.02 mg/L in t
32、he range of 0.05 to 0.50 mg/L.414.3.2 Air span calibration, in instruments so equipped, hasbeen found to give repeatability of 65 %, that is, 0.0025 mg/Lat an ozone concentration of 0.05 mg/L.15. Keywords15.1 dissolved gas; high purity water; ozone; pharmaceuti-cal water; sanitizationAPPENDIX(Nonman
33、datory Information)X1. POLAROGRAPHIC OZONE SENSOR OPERATIONX1.1 The typical polarographic ozone sensor consists of atleast two electrodes. Minimally there is an anode and cathodeand sometimes a third electrode known as a guard ringelectrode. The sensor also includes a temperature sensor forcompensat
34、ion of the ozone measurement. The electrodes arecovered by a gas permeable membrane and submersed inelectrolyte typically containing a bromide salt dissolved inwater. The cathode is set to a potential suitable for thereduction of molecular ozone to hydroxide ion and oxygen.The change in chemical spe
35、cies results in an amperometricdraw at the cathode and this draw is directly related to thepartial pressure of ozone contacting the cathode. The partialpressure at the cathode is, in turn, proportional to the ozonepartial pressure in the sample. The relationship betweenchemistry and electrical curre
36、nt can be described by thefollowing pair of redox reactions.Cathode Reduction: H2O+O3+2e- O2+2OH-Anode Oxidation: Ag+2Br- 2 AgBr + 2 e-Overall Reaction: H2O+2Ag+2Br-+O3 2 AgBr + O2+2OH-The permeation rate of ozone through the membrane is thelimiting factor for how much ozone from the liquid makes it
37、sway to the cathode. Variation in membrane permeation rateresults in the need for calibration. Once the membrane perme-ation rate is normalized by calibration, the partial pressurevalue can be converted to dissolved ozone concentration. Themeasuring system compensates for the temperature depen-dence
38、 of the permeation rate and the solubility of ozone inwater.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such pa
39、tent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited ei
40、ther for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair
41、 hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this stan
42、dard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ Germain, M., and Gray, D, “Ozone Measurement Technology in Pure WaterSystems,” Semiconductor Pure Water and Chemicals Conference, Santa Clara, CA2006, and related work.D7677 165
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