1、Designation: D5462 13Standard 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 revi
2、sion. 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
3、 (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 regar
4、ded 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 determin
5、e 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 B
6、ias 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
7、 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 t
8、hroughthe 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 measuringinstrumen
9、ts 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 b
10、y 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 me
11、asured 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
12、 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 Dif
13、fusion-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 t
14、he 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
15、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.Co
16、pyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1that 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 silv
17、er 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 Fatt (2).4.4 Equilibrium-type
18、 probes rely on oxygen diffusionthrough the membrane only until equilibrium between theinside and outside is achieved. Oxygen is reduced at the noblemetal cathode, as with diffusion-type probes. However, themeasuring circuit forces electrical current to flow through thenoble metal anode equal and op
19、posite to that at the cathode,and the resulting oxidation reaction produces oxygen. This isthe exact reverse of the reaction at the cathode, so there is nonet consumption of oxygen by the probe. It reaches equilibriumin constant DO samples, and no net oxygen diffuses throughthe membrane. Accuracy is
20、 not dependent on membranesurface condition or sample flowrate.5. Significance and Use5.1 DO may be either a corrosive or passivating agent inboiler/steam cycles and is therefore controlled to specificconcentrations that are low relative to environmental andwastewater treatment samples. Out-of-speci
21、fication DO con-centrations may cause corrosion in boiler systems, which leadsto corrosion fatigue and corrosion productsall detrimental tothe life and efficient operation of a steam generator. Theefficiency of DO removal from boiler feedwater by mechanicalor chemical means, or both, may be monitore
22、d by continuouslymeasuring the DO concentration before and after the removalprocess with on-line instrumentation. DO measurement is alsoa check for air leakage into the boiler water cycle.5.2 Guidelines for feedwater to high-pressure boilers withall volatile treatment generally require a feedwater D
23、O con-centration below 5 g/L (3).5.3 Boiler feedwater with oxygenated treatment is main-tained in a range of 50 to 300 g/L DO (4).5.4 In microelectronics production, DO can be detrimentalin some manufacturing processes, for example, causing unde-sirable oxidation on silicon wafers.6. Interferences6.
24、1 The leakage of atmospheric air into samples is some-times difficult to avoid and detect.Although sample line fittingsand connections to flow chambers may be water tight, it is stillpossible for air to diffuse through the water film of a joint tocontaminate a low-g/L sample. Sample flow through fit
25、tings,valves and rotometers can create a venturi effect, which drawambient air into the sample. Section 9 provides further detailson this non-obvious interference.6.2 Diffusion-type probes consume oxygen and will depleteit from the sample in immediate contact with the membranesurface unless an adequ
26、ate, turbulent sample flow is main-tained. The manufacturers minimum flowrate recommenda-tions must be met or exceeded in order to prevent erroneouslylow readings.6.3 Diffusion-type probes are subject to negative errorsfrom the buildup of coatings such as iron oxides, which impedethe diffusion rate
27、of oxygen. (Equilibrium-type probes are notsubject to errors from flowrate or coating.)6.4 Calibration must be corrected for barometric pressureaccording to the manufacturers recommendations at atmo-spheric conditions that deviate from a nominal range of 745 to775 mmHg. See Table 1 for altitude corr
28、ections. Calibrationunder low-pressure conditions without compensation wouldresult in positive measurement errors.6.5 The growth of bacteria in sample lines and flow cham-bers and on probe membranes can consume oxygen and causenegative errors. Chemical sterilization with hydrochloric acid(1 + 44) or
29、 sodium hypochlorite solution (10 mg/L) should beperformed if errors from bacteria growth are suspected.(WarningDo not mix hydrochloric acid and sodium hy-pochlorite since hazardous chlorine gas would be releasedrapidly.)6.6 The passage of high-temperature samples containingboth DO and an oxygen sca
30、venger through hot sample linescan allow continued reaction of the two. With long samplelines, the DO measured at the probe may be significantly belowthat at the sample point. Short sample lines and cooling nearthe source are recommended.6.7 Volatile oxygen scavengers or suppressants, such ashydrazi
31、ne, amines, and hydrogen, that pass through the probemembrane may cause unwanted reactions at the electrodes andnegative errors. The magnitude of errors depends on therelative concentrations of DO and the oxygen scavenger or3The boldface numbers in parentheses refer to the list of references at the
32、end ofthis test method.TABLE 1 Solubility of Oxygen (mg/L) at Various Temperaturesand Elevations (Based on Sea Level Barometric Pressure of760 mmHg) (5)Temperature,CElevation, ft above Sea Level0 1000 2000 3000 4000 5000 60000 14.6 14.1 13.6 13.2 12.7 12.3 11.82 13.8 13.3 12.9 12.4 12.0 11.6 11.24 1
33、3.1 12.7 12.2 11.9 11.4 11.0 10.66 12.4 12.0 11.6 11.2 10.8 10.4 10.18 11.8 11.4 11.0 10.6 10.3 9.9 9.610 11.3 10.9 10.5 10.2 9.8 9.5 9.212 10.8 10.4 10.1 9.7 9.4 9.1 8.814 10.3 9.9 9.6 9.3 9.0 8.7 8.316 9.9 9.7 9.2 8.9 8.6 8.3 8.018 9.5 9.2 8.7 8.6 8.3 8.0 7.720 9.1 8.8 8.5 8.2 7.9 7.7 7.422 8.7 8.
34、4 8.1 7.8 7.7 7.3 7.124 8.4 8.1 7.8 7.6 7.3 7.1 6.826 8.1 7.8 7.6 7.3 7.0 6.8 6.628 7.8 7.5 7.3 7.0 6.8 6.6 6.330 7.5 7.2 7.0 6.8 6.5 6.3 6.132 7.3 7.1 6.8 6.6 6.4 6.1 5.934 7.1 6.9 6.6 6.4 6.2 6.0 5.836 6.8 6.6 6.3 6.1 5.9 5.7 5.538 6.6 6.4 6.2 5.9 5.7 5.6 5.440 6.4 6.2 6.0 5.8 5.6 5.4 5.2D5462 132
35、suppressant as well as the type of electrochemical cell used.The probe manufacturers cautions and limitations should beconsidered.6.8 New sample lines require conditioning to achieve equi-librium conditions. See Practices D3370 to avoid samplinginterferences.6.9 Iron oxides and other deposits accumu
36、late in slow-flowing horizontal sample lines and can developchromatograph-like retention of dissolved species, resulting invery long delay times. Precautions are described in Section 9.6.10 The response time can be slow for large decreases inDO. This is especially true of measurements below 10 g/Lfo
37、llowing air calibration, which corresponds to a concentrationdecrease of 3 to 4 orders of magnitude. Hours may be requiredfor all traces of oxygen to diffuse out of the probe and toachieve accurate measurements at low g/L levels.7. Apparatus7.1 Measuring Instrument:7.1.1 The instrument should have b
38、oth g/L (ppb) and mg/L(ppm) range capability. It must have a span calibration adjust-ment to match the readout to the sensitivity of a particularprobe.7.1.2 The direct readout of DO concentration requirestemperature compensation for effects of the following: (1)oxygen solubility in water; (2) electr
39、ochemical cell output; and(3) when necessary, diffusion rate of oxygen through themembrane. During air calibration, the instrument must disablethe oxygen solubility portion of the compensation to respondonly to partial pressure.7.1.3 If included, electrical output signal(s) from the instru-ment must
40、 be isolated from the probe measuring circuit andfrom earth ground in order to prevent ground loop problemswhen the instrument is connected to grounded external devices.7.2 Probe:7.2.1 Diffusion-type probes use galvanic or polarographicsystems, with a noble metal cathode and oxidizable anodeimmersed
41、 in an electrolyte and separated from the sample witha polyethylene or fluorocarbon gas-permeable membrane.7.2.2 Equilibrium-type probes are similar to polarographicprobes, except that both the anode and cathode are platinumand the anode is not oxidized.7.2.3 A sealed flow-through probe configuratio
42、n must beused to prevent contamination from the atmosphere, as de-scribed in 6.1. The flowrate must be maintained within themanufacturers recommendations. The probe must be capableof withstanding the flowrate, temperature, and pressure condi-tions of the installation. The probe must incorporate an i
43、ntegralprecision temperature sensor to ensure that it senses the sampletemperature at which the DO is being detected in order toensure accurate temperature compensation with fast response.7.2.4 Diffusion-type probes must have their electrodes,electrolyte, and membrane serviced or replaced according
44、tothe manufacturers recommendations. Equilibrium-type probesdo not require internal maintenance.7.2.5 Probe membranes must be cleaned in accordance withthe manufacturers recommendations. The cleaning frequencyis determined by experience with the particular sample andmust be sufficient to maintain ac
45、ceptable accuracy withdiffusion-type probes (see 6.3). The cleaning of equilibrium-type probes is not necessary unless a heavy coating increasesresponse time or becomes biologically active (see 6.5).8. Reagents8.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise
46、indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Society,where such specifications are available.4Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity t
47、o permit its use without lessening theaccuracy of the determination.8.2 Purity of WaterReferences to water shall be under-stood to mean water that meets or exceeds the quantitativespecifications for type III reagent water conforming to Speci-fication D1193, Section 1.1.8.3 Hydrochloric Acid (1 + 44)
48、Add 1 volume of concen-trated HCl (sp gr 1.19) to 44 volumes of water and mix.8.4 Sodium Hypochlorite (10 mg/L)Add approximately0.05 mL (1 drop) of 5 % NaOCl solution (commercial bleachis satisfactory for this purpose) to 250 mL of water.8.5 Cobalt Chloride Solution, SaturatedDissolve 4.5 g ofcobalt
49、 chloride (CoCl2) in 10 mL of water.8.6 Sodium Sulfite Zero Solution (10 g/200 mL)Dissolve10 g of sodium sulfite (Na2SO3) in 200 mL of water.NOTE 1To attain zero DO more rapidly, add two drops of saturatedcobalt chloride solution to the sodium sulfite zero solution.9. Sampling9.1 Design and operate the sample lines to maintain sampleintegrity and fast response. Follow the applicable samplingprecautions in Practices D1066, D3370, and D3864.9.2 The preferred permanent material for sample lines is316SS. Higher alloys in sample coolers may be required for
