METHOD 410.4 THE DETERMINATION OF …

1 DETERMINATION OF CHEMICAL OXYGEN DEMANDBY SEMI-AUTOMATED COLORIMETRYE dited by James W. O'DellInorganic Chemistry BranchChemistry Research DivisionRevision 1993 ENVIRONMENTAL MONITORING SYSTEMS LABORATORYOFFICE OF RESEARCH AND ENVIRONMENTAL PROTECTION AGENCYCINCINNATI, OHIO 45268 METHOD DETERMINATION OF CHEMICAL OXYGEN DEMANDBY SEMI-AUTOMATED AND METHOD covers the DETERMINATION of chemical oxygen demand (COD) inground and surface waters, domestic and industrial applicable range is 3-900 OF , blanks, and standards in sealed tubes are heated in an oven or blockdigestor in the presence of dichromate at 150 C. After two hours, the tubesare removed from the oven or digester, cooled, and measuredspectrophotometrically at 600 nm.

2 The colorimetric DETERMINATION may also beperformed volume versions of this METHOD that use the same reagents and molarratios are acceptable provided they meet the quality control and performancerequirements stated in the performance-based METHOD modifications may be acceptable providedthey are fully documented and meet or exceed requirements expressed inSection , Quality Blank (CB) -- A volume of reagent water fortified with the samematrix as the calibration standards, but without the analytes, internalstandards, or surrogate Standard (CAL) -- A solution prepared from the primary dilutionstandard solution or stock standard solutions and the internal standards andsurrogate analytes. The CAL solutions are used to calibrate the instrumentresponse with respect to analyte Performance Check Solution (IPC) -- A solution of one or moremethod analytes, surrogates, internal standards, or other test substances usedto evaluate the performance of the instrument system with respect to a definedset of Fortified Blank (LFB) -- An aliquot of reagent water or other blankmatrices to which known quantities of the METHOD analytes are added in thelaboratory.

3 The LFB is analyzed exactly like a sample, and its purpose is todetermine whether the methodology is in control, and whether the laboratoryis capable of making accurate and precise Fortified Sample Matrix (LFM) -- An aliquot of an environmentalsample to which known quantities of the METHOD analytes are added in thelaboratory. The LFM is analyzed exactly like a sample, and its purpose is todetermine whether the sample matrix contributes bias to the analytical results. The background concentrations of the analytes in the sample matrix must bedetermined in a separate aliquot and the measured values in the LFMcorrected for background Reagent Blank (LRB) -- An aliquot of reagent water or other blankmatrices that are treated exactly as a sample including exposure to allglassware, equipment, solvents, reagents, internal standards, and surrogatesthat are used with other samples .

4 The LRB is used to determine if methodanalytes or other interferences are present in the laboratory environment, thereagents, or the Calibration Range (LCR) -- The concentration range over which theinstrument response is Safety Data Sheet (MSDS) -- Written information provided byvendors concerning a chemical's toxicity, health hazards, physical properties,fire, and reactivity data including storage, spill, and handling Detection Limit (MDL) -- The minimum concentration of an analytethat can be identified, measured and reported with 99% confidence that theanalyte concentration is greater than Control Sample (QCS) -- A solution of METHOD analytes of knownconcentrations that is used to fortify an aliquot of LRB or sample matrix.

5 TheQCS is obtained from a source external to the laboratory and different fromthe source of calibration standards. It is used to check laboratory performancewith externally prepared test Standard Solution (SSS) -- A concentrated solution containing one ormore METHOD analytes prepared in the laboratory using assayed referencematerials or purchased from a reputable commercial are quantitatively oxidized by dichromate and represent a positiveinterference. Mercuric sulfate is added to the digestion tubes to complex interferences may be caused by contaminants in the reagent water,reagents, glassware, and other sample processing apparatus that bias toxicity or carcinogenicity of each reagent used in this METHOD has notbeen fully established.

6 Each chemical should be regarded as a potential healthhazard and exposure should be as low as reasonably achievable. Cautions areincluded for known extremely hazardous materials or laboratory is responsible for maintaining a current awareness file ofOSHA regulations regarding the safe handling of the chemicals specified inthis METHOD . A reference file of Material Safety Data Sheets (MSDS) should bemade available to all personnel involved in the chemical analysis. Thepreparation of a formal safety plan is also following chemicals have the potential to be highly toxic or hazardous,consult sulfate (Section ) dichromate (Section ) acid (Sections , , and ) AND -- Analytical, capable of accurately weighing to the nearest -- Class A volumetric flasks and pipets as digestor or drying oven capable of maintaining 150 furnace capable of 500 tube with Teflon-lined screw cap, 16 x 100 mm or 25 x 150 continuous flow analysis equipment designed to deliver and reactsample and reagents in the required order and device (sampler) unit or recording AND water: Distilled or deionized water, free of the analyte of interest.

7 ASTM Type II or equivalent. solution: Add g potassium dichromate K Cr O (CASRN2277778-50-9), 84 mL conc. sulfuric acid H SO (CASRN 8014-95-7) and g24mercuric sulfate HgSO (CASRN 7783-35-9) to 250 mL of reagent water, cool4and dilute to 500 mL. CAUTION: CAN BE VERY HOT! solution: Add 22 g silver sulfate Ag SO (CASRN 10294-26-5) to kg bottle of conc. H SO . Stir until wash solution: Add 250 mL of conc. H SO to 250 mL of reagent24water. CAUTION: PREPARE CAREFULLY, HIGH HEAT GENERATION! potassium hydrogen phthalate standard: Dissolve g KHP (CASRN877-24-7) in 400 mL of reagent water and dilute to 500 mL. 1 mL = 1 COLLECTION, PRESERVATION AND should be collected in plastic or glass bottles.

8 All bottles must bethoroughly cleansed and rinsed with reagent water. Volume collected shouldbe sufficient to insure a representative sample, allow for replicate analysis (ifrequired), and minimize waste must be preserved with H SO to a pH <2 and cooled to 4 C at the24time of should be analyzed as soon as possible after collection. If storage isrequired, preserved samples maintained at 4 C may be held for up to 28 laboratory using this METHOD is required to operate a formal qualitycontrol (QC) program. The minimum requirements of this program consist ofan initial demonstration of laboratory capability, and the periodic analysis oflaboratory reagent blanks, fortified blanks, and other laboratory solutions as acontinuing check on performance.

9 The laboratory is required to maintainperformance records that define the quality of the data that are DEMONSTRATION OF PERFORMANCE initial demonstration of performance is used to characterizeinstrument performance ( DETERMINATION of linear calibration ranges andanalysis of QCS) and laboratory performance ( DETERMINATION of MDLs)prior to performing analyses by this Calibration Range (LCR) -- The LCR must be determinedinitially and verified every six months or whenever a significant changein instrument response is observed or expected. The initialdemonstration of linearity must use sufficient standards to insure thatthe resulting curve is linear. The verification of linearity must use aminimum of a blank and three standards.

10 If any verification dataexceeds the initial values by 10%, linearity must be reestablished. Ifany portion of the range is shown to be nonlinear, sufficient standardsmust be used to clearly define the nonlinear portion. Control Sample (QCS) -- When beginning the use of thismethod, on a quarterly basis or as required to meet data-quality needs,verify the calibration standards and acceptable instrument performancewith the preparation and analyses of a QCS. If the determinedconcentrations are not within 10% of the stated values, performance ofthe determinative step of the METHOD is unacceptable. The source ofthe problem must be identified and corrected before either proceedingwith the initial DETERMINATION of MDLs or continuing with Detection Limit (MDL) -- MDLs must be established for allanalytes, using reagent water (blank) fortified at a concentration of twoto three times the estimated instrument detection limit.