ASTM_D_5462_-_13.pdf

Designation:D546213Standard Test Method forOn-Line Measurement of Low-Level Dissolved Oxygen inWater1This standard is issued under the fixed designation D5462;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,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 test method covers the on-line determination ofdissolved oxygen(DO)in water samples primarily in rangesfrom 0 to 500 g/L(ppb),although higher ranges may be usedfor calibration.On-line instrumentation is used for continuousmeasurements of DO in samples that are brought throughsample lines and conditioned from high-temperature and high-pressure sources when necessary.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 of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.For specific hazardsstatements,see 6.5.2.Referenced Documents2.1 ASTM Standards:2D1066 Practice for Sampling SteamD1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD3864 Guide for On-Line Monitoring Systems for WaterAnalysis3.Terminology3.1 DefinitionsFor definitions of terms used in this testmethod,refer to Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 diffusion-type probes,ngalvanic or polarographicsensors that depend on the continuous influx of oxygen throughthe membrane to develop the electrical signal.3.2.2 equilibrium-type probes,nmodified polarographicsensing probes that have a negligible influx of oxygen throughthe membrane except during changes of sample DO concen-tration.3.2.2.1 DiscussionOxygen consumption and regenerationbalance each other within the probes under stable conditions,and the net flux through the membrane is insignificant.3.2.3 galvanic systems,nsensing probes and measuringinstruments that develop an electrical current from two elec-trodes inside the probe from which the final measurement isderived.3.2.4 partial pressure(of oxygen),nthe volume fraction ofoxygen multiplied by the total pressure.3.2.4.1 DiscussionThe partial pressure of oxygen is theactual parameter detected by DO probes,whether in air ordissolved in water.3.2.5 polarographic systems,nsensing probes and mea-suring instruments that include circuitry to control the operat-ing voltage of the system,usually using a third(reference)electrode in the probe.4.Summary of Test Method4.1 Dissolved oxygen is measured by means of an electro-chemical cell separated from the sample by a gas-permeablemembrane.Behind the membrane and inside the probe,elec-trodes immersed in an electrolyte develop an electrical currentproportional to the oxygen partial pressure of the sample.4.2 The partial pressure signal is temperature compensatedautomatically to account for variations with temperature of thefollowing:oxygen solubility in water;electrochemical celloutput;and,when necessary,diffusion rate of oxygen throughthe membrane.This yields a direct readout in concentration ofg/L(ppb)or mg/L(ppm).4.3 Diffusion-type probes rely on a continuous diffusion ofoxygen through the membrane.Immediately inside themembrane,oxygen is reduced at the noble metal cathode,usually platinum or gold.An electrical current is developed1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.03 on Sampling Water andWater-Formed Deposits,Analysis of Water for Power Generation and Process Use,On-Line Water Analysis,and Surveillance of Water.Current edition approved June 15,2013.Published July 2013.Originallyapproved in 1993.Last previous edition approved in 2008 as D5462 08.DOI:10.1520/D5462-13.2For 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 Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 that is directly proportional to the arrival rate of oxygenmolecules at the cathode,which is in turn dependent on thediffusion rate through the membrane.The less noble anode,usually silver or lead,completes the circuit and is oxidized inproportion to the current flow.At steady state,the resultingcurrent signal is then proportional to the oxygen partialpressure of the sample.Thorough descriptions of diffusion-typeprobes are given by Hitchman(1)3and