1、Designation:D686903(Reapproved 2011)Standard Test Method forCoulometric and Volumetric Determination of Moisture inPlastics Using the Karl Fischer Reaction(the Reaction ofIodine with Water)1This standard is issued under the fixed designation D6869;the number immediately following the designation ind
2、icates 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 method uses the reaction of Iodine(I2)with
3、water(Karl Fischer Reaction)to determine the amount of moisture ina polymer sample.21.2 This test method is intended to be used for the determi-nation of moisture in most plastics.Plastics containing volatilecomponents such as residual monomers and plasticizers arecapable of releasing components tha
4、t will interfere with theI2/water reaction.1.3 This method is suitable for measuring moisture over therange of 0.005 to 100%.Sample size shall be adjusted toobtain an accurate moisture measurement.1.4 The values stated in SI units are regarded as thestandard.NOTE1This standard is technically equival
5、ent to ISO 15512 MethodB.1.5 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
6、to use.2.Referenced Documents2.1 ISO Document:ISO 15512 PlasticsDetermination of Water Content33.Summary of Test Method23.1 Samples are heated to vaporize water that is transportedby a nitrogen carrier gas to the titration cell.The moisturecollected in the solution within the titration cell is deter
7、minedusing the reaction of water with I2.3.2 Endpoint detection is made by instrumented methods.Determination of the moisture present is made using thereaction of I2with water.3.3 Coulometric instruments use Faradays law to measurethe moisture present with 10.71 Coulombs(C)of generatingcurrent corre
8、sponding to 1 mg of water(2I-I2+2e-).Volumetric instruments measure the volume of solution con-taining I2that is required to keep the current constant.4.Significance and Use4.1 Moisture will affect the processability of some plastics.High moisture content causes surface imperfections(that is,splay o
9、r bubbling)or degradation by hydrolysis.Low moisture(with high temperature)causes polymerization.4.2 The physical properties of some plastics are affected bythe moisture content.5.Interferences5.1 Some compounds,such as aldehydes and ketones,interfere in the determination of moisture content using t
10、hismethod.6.Apparatus6.1 Heating Unit,consisting of an oven capable of heatingthe sample to approximately 300C,a furnace tube,a tempera-ture control unit,a carrier gas flow meter,and desiccating tubesfor the carrier gas.6.2 Sample Pan(Boat),normally a glass sample boat or boatmanufactured of a suita
11、ble material to transfer the oven heat tothe sample.It is permitted to use aluminum foil as a disposableliner for the sample pan.6.3 Titration Unit,consisting of a control unit,titration cellwith a solution cathode,platinum electrode,and solutionstirring capability.This apparatus has the capability
12、to generateor deliver iodine to react stoiciometrically with the moisturepresent in the titration cell.The current or volume required togenerate the iodine converts to micrograms of water present.1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsib
13、ility of Subcommittee D20.70 on Analytical Methods.Current edition approved Sept.1,2011.Published October 2011.Originallyapproved in 2003.Last previous edition approved in 2003 as D6869-03.DOI:10.1520/D6869-03R11.2See Appendix X1,History of Reagents Associated With the Karl FischerReaction,for an ex
14、planation of coulometric and volumetric techniques as well as anexplanation of the Karl Fischer Reaction and Karl Fischer Reagents.3Available from American National Standards Institute(ANSI),25 W.43rd St.,4th Floor,New York,NY 10036,http:/www.ansi.org.Copyright ASTM International,100 Barr Harbor Dri
15、ve,PO Box C700,West Conshohocken,PA 19428-2959.United States1 The percent moisture in the sample is then calculated based onthe sample weight used and is given as a direct digital readout.6.4 Analytical Balance,capable of weighing 0.1 mg(fourdecimal place balance).6.5 Glass Capillary(Micropipette),u
16、sed to measure aknown amount of water,typically 2 mg(2000 g).7.Reagents and Materials7.1 Anode(Generator)Solution,per manufacturers recom-mendation.7.2 Cathode Solution,per manufacturers recommendation.NOTE2Hydranal or similar anode and cathode solutions are recom-mended.These reagents do not contain pyridine,are less toxic,and haveno offensive odor.7.3 Silica Gel,granules,approximately 2 mm,desiccant fordrying tube of titration assembly(if applicable).7.4 Special Grease,as supplied by manufactu
