ASTM_D_7781_-_14.pdf

Designation:D778114Standard Test Method forNitrite-Nitrate in Water by Nitrate Reductase1This standard is issued under the fixed designation D7781;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 is applicable to the determination ofnitrate plus nitrite(as nitrogen)in drinking water,surface,saline,wastewater,and ground waters.The applicable range ofthis test method is from 0.05 to 5 mg/L of nitrogen.The rangemay be extended upward by dilution of an appropriate aliquot.The 40 CFR Part 136 Method Detection Limit(MDL)is 0.02mg/L.1.2 It is the users responsibility to ensure the validity of thistest method for waters of untested matrices.The quality controlcriteria in Section 17 for method blanks,laboratory controlsamples,matrix spikes and matrix duplicates must be met.1.3 The values stated in SI units are regarded as standard.No other units of measurement are included in this standard.1.4 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.2.Referenced Documents2.1 ASTM Standards:2D992D1129 Terminology Relating to WaterD1141 Practice for the Preparation of Substitute OceanWaterD1193 Specification for Reagent WaterD1254 Method of Test for Nitrite Ion in Water(Withdrawn1980)3D3867 Test Methods for Nitrite-Nitrate in WaterD5810 Guide for Spiking into Aqueous SamplesD6146 Guide for Monitoring Aqueous Nutrients in Water-sheds3.Terminology3.1 DefinitionsFor definitions of terms used in these testmethods,refer to Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 bispecific NaR,nnitrate reductase that can use eitherNADH or NADPH as its electron donor(cofactor).3.2.2 discrete analyzer,na programmable,computer-controlled instrument that automates wet-chemical analysis byusing one or more robotic arms interfaced to high-precisionvolumetric dispensers to aspirate and dispense samples,standards,diluents,and reagents.3.2.3 Greiss reaction,nchemical formation of an azo dyeby diazotization of nitrite ion with sulfanilamide and subse-quent coupling with N-(1-naphthyl)ethylenediamine hydro-chloride.3.2.4 NADH,nnicotinamide adenine dinucleotide,re-duced form is a coenzyme found in all living cells.3.2.5 NADPH,nnicotinamide adenine dinucleotidephosphate,reduced form is a coenzyme found in all livingcells;NADP+is the oxidizing form and NADPH is thereducing form.3.2.6 nitrate reductase(NaR),nNADH:NaR(EC1.7.1.1and CAS 9013-03-0)or bispecific NaR(EC 1.7.1.2 and CAS9029-27-0)with 1 unit of enzyme activity defined as 1micromol nitrite produced per minute at 30C,at pH 7 withNADH(refer to 3.2.4 and 10.2)as an electron donor.4.Summary of Test Method4.1 Nitrite-Nitrate NitrogenThe sample is mixed with abuffered solution containing NAD(P)H:nitrate reductase(EC1.7.1-3)and NADH or NADPH to reduce nitrate ion to nitriteion.The combined nitrite-nitrate(expressed as mg/LNO3+NO2-N)is determined by diazotizing the total nitrite ionwith sulfanilamide and coupling with N-(1-naphthyl)ethylene-diamine dihydrochloride to form a highly colored azo dye thatis measured spectrophotometrically at about 540 nm.4.2 Nitrite NitrogenThe nitrite ion(expressed as mg/LNO2-N)originally present in the sample can be determinedseparately by carrying out the procedure and omitting thereduction step.1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.05 on Inorganic Constituentsin Water.Current edition approved April 1,2014.Published May 2014.DOI:10.1520/D7781-14.2For 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.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 4.3 Nitrate NitrogenThe nitrate ion as nitrogen can becalculated as the difference between the combined nitrate plusnitrite(NO3+NO2-N)and the nitrite(NO2-N):mgLNO32 N 5 mgLNO31 NO22 N!2 mgLNO22 N!(1)5.Significance and Use5.1 This test method replaces Test Methods D1254(Nitrite)and D992(Nitrate).The nitrite test method(Test MethodD1254)used a reagent that is considered to be a potentialcarcinogen.The nitrate test method(Test Method D992)hasbeen shown to have relatively large errors when used inwastewaters and also has greater manipulative difficulties thanthe test method described herein.5.2 This test metho