ASTM_D_3598_-_89_2009.pdf

Designation:D359889(Reapproved 2009)Standard Test Method forCitrate in Synthetic Detergents1This standard is issued under the fixed designation D3598;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 enzymatic determination ofcitrate in both liquid and solid synthetic detergents.The testmethod is applicable to most detergents containing citrate at aminimum concentration of approximately 5%(1-8).21.2 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.Material SafetyData Sheets are available for reagents and materials.Reviewthem for hazards prior to usage.2.Referenced Documents2.1 ASTM Standards:3D501 Test Methods of Sampling and Chemical Analysis ofAlkaline DetergentsD1193 Specification for Reagent Water3.Summary of Test Method3.1 This test method employs an enzyme system that isbased upon the selective cleavage of citrate by citrate lyase(citrate oxaloacetate-lyase;EC 4.1.3.6)(1).One of theproducts,oxaloacetate,is reduced to malate by malic dehydro-genase(L-malate:NAD oxidoreductase;EC 1.1.1.37)with thesimultaneous oxidation of reduced b-nicotinamide adeninedinucleotide to b-nicotinamide adenine dinucleotide,oxidizedform.The course of the reaction is measured spectrophoto-metrically.The decrease in absorbance at 340 nm caused by theformation of b-nicotinamide adenine dinucleotide,oxidizedform,is directly proportional to the concentration of citrate.4.Interferences4.1 The test method is highly specific for citrate.Otherorganic acids,for example,cisand trans-aconitic,d,l-isocitric,a-ketoglutaric,oxalic,succinic,or tartaric acids,do not inter-fere.4.2 Although low levels of zinc or magnesium,or both,arerequired as an activator for the enzyme citrate lyase,exces-sively high levels of divalent metallic ions including zinc andmagnesium will cause inactivation of the enzyme and poten-tially interfere with the test method(7).4.3 The test method is not applicable to those detergentscontaining components with excessive absorptivity at 340 nmsuch that ultraviolet measurements are inappropriate at 340 nmunder test conditions.5.Apparatus5.1 Interval Timer.5.2 Micropipet,suitable Eppendorf pipets for dispensing 10and 100-L volumes and with disposable tips.5.3 Spectrophotometer,suitable for measuring ultravioletabsorbance at 340 nm and equipped with 1-cm matched quartzcells with tapered TFE-fluorocarbon stoppers and a minimumvolume of 4 mL.6.Reagents6.1 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 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 to permit its use without lessening theaccuracy of the determination.1This test method is under the jurisdiction of ASTM Committee D12 on Soapsand Other Detergents and is the direct responsibility of Subcommittee D12.12 onAnalysis and Specifications of Soaps,Synthetics,Detergents and their Components.Current edition approved Oct.1,2009.Published December 2009.Originallyapproved in 1977 as D3598 77 T.Last previous edition approved in 2003 asD3598 89(2003).DOI:10.1520/D3598-89R09.2The boldface numbers in parentheses refer to the references at the end of thistest method.3For 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.4Reagent 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 Pharmacopeiaand National Formulary,U.S.Pharmacopeial Convention,Inc.(USPC),Rockville,MD.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 6.2 Purity of WaterUnless otherwise indicated,referencesto water shall be understood to mean Type II reagent waterconforming to Specification D1193.6.3 Citrate Lyase Solution(40 units/mL)Add sufficientcold water to a vial of citrate lyase containing a premeasuredweight of enzyme protein such that the resulting solution