1、Designation: D 6238 98 (Reapproved 2003)Standard Test Method forTotal Oxygen Demand in Water1This standard is issued under the fixed designation D 6238; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A n
2、umber in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of totaloxygen demand in the range from 100 to 100 000 mg/L, inwater and wastewater including
3、 brackish waters and brines (see6.5). Larger concentrations, or samples with high suspendedsolids, or both, may be determined by suitable dilution of thesample.1.1.1 Since the analysis is based on the change in oxygenreading of the carrier gas compared to that when a sample isintroduced (see 4.1), t
4、he measurement range is a function of theamount of oxygen in the carrier gas. The higher the desiredconcentration range, the more oxygen required in the carriergas. Under recommended conditions, the carrier gas concen-tration should be between two to four times the maximumdesired oxygen demand.1.1.2
5、 The lower measurement range is limited by thestability of the baseline oxygen detector output. This signal isa function of the permeation system temperature, carrier gasflow rate, oxygen detector temperature, and reference sensorvoltage. Combined, these variables limit the minimum recom-mended rang
6、e to 2 to 100 mg/L.1.1.3 The upper measurement range is limited by themaximum oxygen concentration in the carrier gas (100 %).With the recommended conditions of carrier gas concentrationbeing two to four times the maximum oxygen demand, thislimits the maximum possible oxygen demand to between250 000
7、 to 500 000 mg/L. However, as a practical applicationto water analysis, this test method will consider a maximumrange of 100 000 mg/L.1.2 This test method is applicable to all oxygen-demandingsubstances under the conditions of the test contained in thesample that can be injected into the reaction zo
8、ne. The injectoropening limits the maximum size of particles that can beinjected. If oxygen-demanding substances that are water-insoluble liquids or solids are present, a preliminary treatmentmay be desired. These pretreatment methods are described inAnnex A2.1.3 This test method is particularly use
9、ful for measuringoxygen demand in certain industrial effluents and processstreams. Its application for monitoring secondary sewageeffluents is not established. Its use for the monitoring of naturalwaters is greatly limited by the interferences defined in Section6.1.4 In addition to laboratory analys
10、is, this test method isapplicable to on-stream monitoring. Sample conditioning tech-niques for solids pretreatment applications are noted in AnnexA2.1.5 The values stated in SI units are to be regarded as thestandard.1.6 This standard does not purport to address all of thesafety concerns, if any, as
11、sociated 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.2. Referenced Documents2.1 ASTM Standards:2D 888 Test Methods for Dissolved Oxygen in WaterD 1129
12、Terminology Relating to WaterD 1192 Specification for Equipment for Sampling Waterand Steam in Closed Conduits3D 1193 Specification for Reagent WaterD 2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD 3370 Practices for Sampling Water from Clo
13、sed ConduitsD 3856 Guide for Good Laboratory Practices in Laborato-ries Engaged in Sampling and Analysis of WaterD 5789 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Organic Constituents3D 5847 Practice for Writing Quality Control Specificationsfor Standard Test Me
14、thods for Water Analysis3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this test method, referto Terminology D 1129.3.2 Definitions of Terms Specific to This Standard:1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of S
15、ubcommittee D19.06 on Methods forAnalysis forOrganic Substances in Water.Current edition approved March 10, 1998. Published March 1999.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume inf
16、ormation, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.1 total oxygen demand (TOD)the amount of oxygenrequired to convert the elements in compounds to
17、their moststable oxidized forms.4. Summary of Test Method4.1 The total oxygen demand (TOD) measurement isachieved by continuous analysis of the concentration of oxygenin a combustion process gas effluent. The decrease in oxygenresulting from introduction of the sample into the combustionzone is a me
18、asure of oxygen demand.4.2 The oxidizable components in a liquid sample intro-duced into a carrier gas stream containing a fixed amount ofoxygen flowing through a 900C combustion tube are con-verted to their stable oxides. The momentary reduction in theoxygen concentration in the carrier gas is dete
19、cted by anoxygen sensor and indicated on a digital display or recorded.4.3 The TOD for the sample is obtained by comparing thepeak height to a calibration curve of peak heights for TODstandard solutions. The TOD for the standard solution is basedon experimentally observed reactions in which carbon i
20、sconverted to carbon dioxide, hydrogen to water, combinednitrogen including ammonia to nitric oxide, and elemental ororganic sulfur to sulfur dioxide. Sample injection is achievedby means of an automatic valve, that provides unattendedmultiple sampling in the laboratory or on-stream monitoring.4.4 F
21、or monitoring applications, pretreatment of the samplemay be required. However, no single instruction can be writtensince pretreatment steps will be a function of the specificcharacteristics of the sample stream.5. Significance and Use5.1 The measurement of oxygen demand parameters iscritical to the
22、 control of process wastewaters. Biochemicaloxygen demand (BOD) and chemical oxygen demand (COD)analyzers have long time cycles and in the case of CODanalyzers use corrosive reagents with the inherent problem ofdisposal. Total oxygen demand analysis is faster, approxi-mately 3 min, and uses no liqui
23、d reagents in its analysis.5.2 TOD can be correlated to both COD and BOD, provid-ing effective on-line control.5.3 TOD offers several features which make it a moreattractive measurement than carbon monitoring using TotalCarbon (TC) or Total Organic Carbon (TOC) analyzers. TODis unaffected by the pre
24、sence of inorganic carbon. TODanalysis will also indicate noncarbonaceous materials thatconsume or contribute oxygen. For example, the oxygendemand of ammonia, sulfite and sulfides will be reflected in theTOD measurement. Also, since the actual measurement isoxygen consumption, TOD reflects the oxid
25、ation state of thechemical compound (that is, urea and formic acid have thesame number of carbon atoms, yet urea has five times theoxygen demand of formic acid).6. Interferences6.1 The dissolved oxygen concentrations will contribute amaximum error of 8 ppm. This error is only significant onranges be
26、low 0 to 100 ppm when samples have no dissolvedoxygen (DO) content. When operating in this range andsamples contain low DO concentrations then compensationmay be necessary. Measure the dissolved oxygen (DO) in bothsolutions in accordance with Test Method D 888. Adjust theTOD result as follows: If DO
27、 of the sample is less than in thestandard, subtract DO variation. If DO of the sample is greaterthan in the standard, add DO variation to the TOD result.6.2 Sulfuric acid will normally decompose under samplecombustion conditions as follows:H2SO4900CCatalystH2O 1 SO2112O2(1)The oxygen release will r
28、esult in a reduction in the TODreading. However, alkali metal sulfates (that is, sodium andpotassium salts) do not decompose under the combustionconditions. If sulfates are present in the samples, adjust to pH11 with NaOH prior to analysis.6.3 Nitrate salts decompose under sample combustion con-diti
29、ons as follows:2 NaNO3900CCatalystNa2O 1 2NO1 112O2(2)The resulting generation of oxygen reduces the oxygendemand.6.4 Heavy metal ions have been reported to accumulate inthe system resulting in a significant loss of sensitivity. Thehistory of the combustion column appears to be a major factorcontrib
30、uting to interferences of this nature. Similarly, highconcentrations of dissolved inorganic salts will tend to build upand coat the catalyst as indicated by a loss of sensitivity. Tocorrect the problem, replace the combustion tube and refrac-tory packing material and clean the catalyst in accordance
31、 withthe manufacturers recommendations. The effects of theseproblems can be minimized by dilution of the sample.6.5 Some brackish waters and natural brines may exhibitbase line drift. In such cases, continue to inject samples until astable response is observed.7. Apparatus7.1 Total Oxygen Demand Ins
32、trument(See Fig. 1), includ-ing a pure nitrogen source, an oxygen permeation system,sample injection valve, catalyst-combustion zone, gas flowcontrols, oxygen sensor and display or recorder, as detailed inAnnex A2.47.2 Homogenizing ApparatusA high speed blender, or amechanical or ultrasonic homogeni
33、zer is satisfactory for ho-mogenizing immiscible liquid samples and suspended solids(see Annex A1).8. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the
34、Commit-tee on Analytical Reagents of the American Chemical Society,4The sole source of supply of the apparatus known to the committee at this timeis Ionics, Inc., P.O. Box 9131, 65 Grove Street, Watertown, MA 02272. If you areaware of alternative suppliers, please provide this information to ASTM He
35、adquar-ters. Your comments will receive careful consideration at a meeting of theresponsible technical committee that you may attend.D 6238 98 (2003)2where such specifications are available.5Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to p
36、ermit its use without lessening theaccuracy of the determination.8.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water conformingto Specification D 1193, Type II except that distillation is notnecessary.8.3 Carrier Gas SupplyPrepurified nitrogen
37、containingoxidizable or reducible gases in concentrations of less than 10ppm is recommended. Other pure inert gases, such as helium orargon, are acceptable. The required oxygen is added to thecarrier gas by means of the permeation system in the apparatus.Alternatively, a bottled, fixed oxygen concen
38、tration carrier gasmay be used in place of a permeation system.8.4 Total Oxygen Demand Calibration Standard Solutions:8.4.1 Potassium Acid Phthalate (KHP) Solution Stock(10 000 mg/L TOD) Dissolve 8.509 g of potassium acidphthalate (KHP) in water in a volumetric flask and dilute 1L.This solution is s
39、table for several weeks at average roomtemperature but is eventually subject to bacteriological dete-rioration. Refrigeration extends the shelf-life.8.4.2 Acetic Acid Solution, Stock(111 900 mg/L TOD)For calibration standards above 10 000 mg/L, the use of aceticacid is recommended. Pipet 100 mL of g
40、lacial acetic acid to a1 L volumetric flask containing approximately 500 mL ofwater. Dilute to 1 L with water and mix thoroughly. Thissolution is stable for several weeks at average room tempera-ture but is eventually subject to bacteriological deterioration.Refrigeration extends the shelf-life.8.4.
41、3 Water solutions of other pure organic compounds maybe used as standards based on the compounds theoreticaloxygen demand.8.4.4 Calibration StandardsPrepare by appropriate dilu-tion of the above stock solutions.9. Sampling9.1 Collect the sample in accordance with SpecificationD 1192 and Practices D
42、3370.5Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharm
43、acopeiaand National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,MD.FIG. 1 Flow Diagram for TOD AnalyzerD 6238 98 (2003)39.2 Because of the possibility of oxidation or bacterialdecomposition of some components of aqueous samples, thetime lapse between collection of samples and a
44、nalysis must bekept to a minimum. After collection, keep the samples atapproximately 4C.9.3 Sample preservation may also be accomplished by theaddition of NaOH to a pH of 12 or higher, or HCl to a pH of2 or lower. Do not use sulfuric acid or nitric acid to preservethe sample (see Section 6).10. Prep
45、aration of Apparatus10.1 Provide required services and adjust variables (carriergas flow rate, permeation tube lengths etc.) according tomanufacturers specifications for the desired oxygen demandrange. Set the furnace temperature to the specified temperaturesetting. Allow approximately 1 h for the i
46、nstrument to ap-proach equilibrium.10.2 Monitor oxygen sensor output stability as an indicationof degree of equilibrium. Detector output must be stable beforeproceeding.10.3 It is recommended that the furnace and instrumentcontrols along with the carrier gas flow remain on continuouslyonce the analy
47、zer is activated (that is, do not shutdownovernight).10.4 Preliminary Operation:10.4.1 Place sample/standard inlet tubing into a full scalestandard solution container, and rinse water tubing into adeionized water container.10.4.2 Place instrument in calibrate, active operation mode.10.4.3 Operate in
48、strument for several analysis cycles (5 to10).10.4.4 Observe repeatability of analyses to ensure analyzeris repeating within 6 3 % of full scale.10.4.5 Proceed to calibration and sample analysis.11. Calibration11.1 Prepare a series of at least four samples of dilutedstandard solutions in the desired
49、 operating range of theinstrument. For example, if the desired full scale range is 5000mg/L, prepare dilutions containing 5000, 2500, 1000 and 200mg/L of TOD. Pipette 50, 25, 10 and 2.0 mL aliquots of the10 000 mg/L stock standard solution into separate 100 mLvolumetric flasks and dilute to volume with reagent water.11.2 In operation, standard (or sample) is drawn from thesample/standard inlet tubing to a sample injection valve whichdelivers a 20 to 100 L sample into the combustion chamber.Insert the sample/standard inlet tubing into the container ofstandard.NOTE 1N
