ASTM_D_3868_-_15.pdf

Designation:D386815Standard Test Method forFluoride Ions in Brackish Water,Seawater,and Brines1This standard is issued under the fixed designation D3868;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.Scope*1.1 This test method2covers the determination of solublefluoride ions in brackish water,seawater and brines by use ofa fluoride selective electrode.1.2 Samples containing from 1.0 to 25 mg/L can be ana-lyzed by this test method.1.3 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.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:3D1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water Analysis3.Terminology3.1 DefinitionsFor definitions of terms used in this testmethod,refer to Terminology D1129.4.Summary of Test Method4.1 A fluoride selective electrode,reference electrode,andmillivoltmeter are used to determine fluoride in brine samplesby a standard addition method.4.2 The fluoride selective electrode consists of a lanthanumfluoride crystal that develops an electrode potential corre-sponding to the level of fluoride ion in solution.5.Significance and Use5.1 Identification of a brackish water,seawater,or brine isdetermined by comparison of the concentrations of theirdissolved constituents.The results are used to evaluate theorigin of the water,determine if it is a possible pollutant,or ifit is related to a potential source of a valuable mineral.Forexample,in geochemical studies some correlation data indicatethat fluoride is an indirect indicator of the presence of lithium.6.Interferences6.1 Metal ions such as aluminum and iron(III)interferewith the fluoride determination by forming complexes withfluoride ions.The buffer solution contains a complexing agentthat preferentially complexes these metal ions.This solutionalso contains a pH buffer to reduce electrode interference fromhydroxide ions and to prevent the formation of HF.Sodiumchloride is added as ionic strength adjustor.Increasing amountsof aluminum,iron(III),and borate ions were added to 1.5mg/L fluoride solutions and were found not to interfere up to 5,350,and 250 mg/L(as boron),respectively.7.Apparatus7.1 Millivoltmeter accurate to 60.1 mV),specific ion meter.NOTE1A specific ion meter that directly reads concentration may beused.7.2 Fluoride Selective Electrode,reference electrode.7.3 Microlitre Pipets.8.Reagents8.1 Purity of ReagentsReagent grade chemicals shall beused in all tests.Unless otherwise indicated,it is intended thatall reagents shall conform to the specification of the Committeeon Analytical Reagents of the American Chemical Society,1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of D19.05 on Inorganic Constituents in Water.Current edition approved March 15,2015.Published April 2015.Originallyapproved in 1979.Last previous edition approved in 2009 as D3868 09.DOI:10.1520/D3868-15.2Additional information is contained in the following references:Hoke,S.H.,Fletcher,G.E.,and Collins,A.G.,“Fluoride and Iodide Selective ElectrodesApplied to Oilfield Brine Analysis,”U.S.Department of Energy,Report ofInvestigations,BETC/RI-78/7.Rix,C.J.,Bond,A.M.,and Smith,J.D.,“DistrictDetermination of Fluoride in Sea Water with a Fluoride Selective Ion Electrode bya Method of Standard Additions,”Analytical Chemistry,Vol 48,1976,p.1236.3For 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 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.8.2 Purity of WaterUnless otherwise indicated,referenceto water shall be understood to mean reagent water conformingto Specification D1193,Type I.Other reagent water types maybe used provided it is first ascertaine