ASTM_D_6174_-_01.pdf

Designation:D 6174 01Standard Test Method forInorganic Sulfate in Surfactants by Potentiometric LeadTitration1This standard is issued under the fixed designation D 6174;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(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method describes a potentiometric titrationprocedure for determining the inorganic sulfate content ofsurfactants.It is intended for the analysis of a-olefin sul-fonates,alkane sulfonates,alcohol sulfates,alcohol ethersulfates,alkylbenzenesulfonates,and the like.1.2 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:D 1193 Specification for Reagent Water23.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 inorganic sulfate,nsulfate species present as sulfu-ric acid,ionic salts of this acid,or mixtures of these.4.Summary of Test Method4.1 A surfactant sample containing inorganic sulfate istitrated in ethanolic medium with a standard lead solution.Lead sulfate precipitate is formed during the titration.Ethanoland sodium perchlorate are present to decrease the solubility oflead sulfate,thus sharpening the endpoint.Acetic acid is addedto remove possible interference from carbonate.The endpointis signaled by an increase in lead ion activity,as measured bya lead-selective electrode.5.Significance and Use5.1 Anionic surfactants,such as those listed in 1.1,com-monly are used in detergent formulations.Their acceptabilityfor use depends on their purity.Sulfate content,as measured bythis test method,can be used to estimate the purity of ananionic surfactant under test.6.Apparatus6.1 Potentiometric Titration Assembly,consisting of anautomatic titrator fitted with a lead ion-selective electrode,adouble-junction reference electrode,and a 10-mL buret.Thereference electrode should be filled with the standard inner andouter filling solutions supplied with it.A TFE-fluorocarbon-coated magnetic stirring bar should be used for mixing duringtitration,with a separate magnetic stirring motor if the autoti-trator is not so equipped.NOTE1Proper care of the lead-selective electrode is essential forobtaining high-quality titration curves.Follow manufacturers instruc-tions.7.Reagents7.1 Glacial Acetic Acid.7.2 Lead Nitrate,reagent grade.7.3 Sodium Sulfate,anhydrous,reagent grade.7.4 Sodium Perchlorate,reagent grade.7.5 Ethanol,denatured,formula 3A.7.6 Water,Type III reagent water conforming to Specifica-tion D 1193.38.Preparation of Standard Solutions8.1 10%Acetic AcidDilute glacial acetic acid 1/10 withwater.8.2 Lead Titrant,0.05 MDissolve 16.6 g lead nitrate in300 mL water.Pour into a 1-L bottle and fill with 3A ethanol.Mix well.Standardize according to 9.1.8.3 Sulfate Standard,0.05 MDry 5 g anhydrous sodiumsulfate at 110C for 1 h.Accurately weigh about 3.5 g into a500-mL volumetric flask,dilute to volume with water,and mixto dissolve.Calculate the exact concentration as follows:G142.02!0.500!5 Molarity(1)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 of Soaps and Synthetic Detergents.Current edition approved Aug.10,2001.Published October 2001.Originallypublished as D 6174-97.Last previous edition D 6174-97.2Annual Book of ASTM Standards,Vol 11.01.3Reagent 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.1Copyright ASTM,100 Barr Harbor Drive,West Conshohocken,PA 19428-2959,United States.where:G=weight in grams of Na2SO4dissolved in the 500 mLand 142.02 is its gram molecular weight.8.4 Ethanolic Sodium Perchlorate,0.05 MDissolve ap-proximately 7 g sodium perchlorate in 300 mL water.Pour intoa 1-L bottle,fill with 3A ethanol,and mix well.9.Standardization9.1 The exact concentration of the lead titrant shall bedetermined experimentally by titration of the sulfate standardof 8.3.Pipet 5.00 mL sulfate standard solution into a 50-mLbeaker.Add approximately 20 mL ethanolic sodium perchlor-ate solution and approximately 1 mL 10%acetic acid.Preparethe autotitrator for operation,immerse the electrodes in thetitration solution,and titrate to the potentiometric endpointw