1、Designation: D7677 11Standard 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 to6 2C. If there is a large temperature dif
5、ference between the airand the process, e.g. 5C; this may take over an hour.Perform a zero calibration according to the manufacturersinstructions. Equivalence of zero is considered to be #0.005mg/L (ppm) in most commercial instruments. Some polaro-graphic sensors have an intrinsic zero and do not re
6、quire 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.D7677 11311.2.1 Colorimetric Calibration of SpanEither of thereagent systems
7、 noted in Section 8.3 can be used as thereference for span calibration. The IOA has approved theindigo method3. With the sensor inline and reading stable DO3values, collect a sample of water representative of the water thesensor is measuring. This can be from a port near an insertedsensor or on the
8、outlet of the sensor flow housing drain. Ineither case, the sample must flow gently, without spray orturbulence that could de-gas the sample. Sample the waterusing three aliquots or ampoules, simultaneously noting thereading on the on-line instrument. Measure all three grabsamples. Discard an outlie
9、r if it differs by $.015 mg/L (0.02mg/L for displays not reading to the third decimal place) fromthe mean of the other two. If no two of the three agree, redo allthree. Calculate the average and input the value as the on-lineinstrument span calibration according to manufacturers in-structions11.2.2
10、Air Calibration of SpanSpan(suitable for instru-ments so equipped) Since oxygen and ozone are similar in theirpermeation 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 cali
11、brate span 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
12、 within 6 2 C. If there is a large temperaturedifference between the air and the sensor, e.g. 5C, this maytake over an hour. Enter the air calibration mode in the analyzerelectronics which temporarily changes the polarization poten-tial applied to the cathode and changes the response to oxygen(O2) p
13、artial pressure. Determination of the O2partial pressureof air is determined from the barometric pressure and tempera-ture of the air. Allow at least 10 minutes for the sensor tostabilize and then perform the calibration function according tothe manufacturers instructions. Return to the ozone measur
14、e-ment mode of the instrument and allow the extended period oftime required for the sensor to repolarize and stabilize on ozonemeasurement per manufacturers recommendations.11.3 Calibration VerificationSpan and zero verificationare normally required.11.3.1 Colorimetric Verification of SpanWith the s
15、ensorinline 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 proces
16、scontrol 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 Section 11.1. Compare the average of the threevalues to the reading of the instrument. If they differ by#0.015mg
17、/L (#0.02 mg/L if either the spectrophotometer or ozoneinstrument displays do not read to the third decimal place) thena span 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 k
18、nown to be free ofozone gas. Dry the sensor membrane to remove sample waterwhich may contain DO3. Allow the sensor to equilibrate withthe air temperature within 6 2C. If there is a large tempera-ture difference between the air and the process, e.g. 5C, thismay take over an hour. To check the air cal
19、ibration value, enterinto 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.
20、 Compare to % ideal orabsolute air value when calibrated. If the two agree within thequality limits set (typically 6 5 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
21、are used.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 temperaturew
22、ithin 6 2C. If there is a large temperature differencebetween the air and the process, e.g. 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 operatio
23、n 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 verification shouldbe 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 (DO3 0.150 mg/L), 2) membranewear due to excessive flow rates, pressure fluctuations, orabrasive water action, and 3) electrolyte depletion. Verificationshould be performed at least every two months or according tomanufacturers recommendations.13.3 Calibration frequencyCalib
27、ration must be per-formed at least as frequently as the manufacturers scheduleand instructions and whenever a sensor is returned to service3International Ozone Association Revised guideline document, “ColorimetricMethod for Manual Determination of Ozone Concentration in Water,” OzoneScience sanitiza
28、tion; dissolved gas; high purity water;pharmaceutical waterAPPENDIX(Nonmandatory 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
29、 ringelectrode. The sensor also includes a temperature sensor forcompensation 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
30、 of molecular ozone to hydroxide ion and oxygen.The change in chemical species 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 pres
31、sure in the sample. The relationship betweenchemistry and electrical current 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
32、membrane is the limiting factor forhow much ozone from the liquid makes its way to the cathode. Variation inmembrane permeation rate results in the need for calibration. Once the mem-brane permeation rate is normalized by calibration, the partial pressure valuecan be converted to dissolved ozone con
33、centration. The measuring systemcompensates for the temperature dependence of the permeation rate and thesolubility of ozone in water.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standa
34、rd are expressly advised that determination of the validity of any such patent 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
35、 not revised, either reapproved or withdrawn. Your comments are invited either 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, whi
36、ch you may attend. If you feel that your comments have not received a fair 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,U
37、nited States. Individual reprints (single or multiple copies) of this standard 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 ASTM website (www.astm.org/COPYRIGHT/).4St. Germain, M., and Gray, D, “Ozone Measurement Technology in Pure WaterSystems,” Semiconductor Pure Water and Chemicals Conference, Santa Clara, CA2006, and related work.D7677 115
