1、Designation: D6869 17Standard 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 indicates the ye
2、ar 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 method uses the reaction of Iodine (I2) with wat
3、er(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 that
4、 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.NOTE 1This standard is equivalent to ISO
5、 15512 Method B.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, health, and environmental practices and deter-mine the applicability of regulatory limitati
6、ons prior to use.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization Tec
7、hnicalBarriers to Trade (TBT) Committee.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 solutio
8、n within the titration cell is determinedusing 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 C
9、oulombs (C) of generatingcurrent corresponding 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 process ability of some plastics.High moisture content ca
10、uses surface imperfections (that is,splay or 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
11、in the determination of moisture content using thismethod.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), nor
12、mally a glass sample boat or boatmanufactured of a suitable 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 s
13、olutionstirring capability. This apparatus has the capability to generate1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.70 on Analytical Methods.Current edition approved Dec. 1, 2017. Published January 2018. Originall
14、yapproved in 2003. Last previous edition approved in 2011 as D6869 - 03(2011).DOI:10.1520/D6869-17.2See Appendix X1, History of Reagents Associated With the Karl FischerReaction, for an explanation of coulometric and volumetric techniques as well as anexplanation of the Karl Fischer Reaction and Kar
15、l Fischer Reagents.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 1
16、9428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Tec
17、hnical Barriers to Trade (TBT) Committee.1or 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.The percent moisture in the sample is then calculated based onthe sample
18、 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), used to measure aknown amount of water, typically 2 mg (2000 g).7. Reagents and Materials7.1 Anode (Generator) Solution, per manufa
19、cturers recom-mendation.7.2 Cathode Solution, per manufacturers recommendation.NOTE 2Hydranal 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 t
20、ube of titration assembly (if applicable).7.4 Special Grease, as supplied by manufacturer for groundglass joints.7.5 Molecular Sieve, or suitable desiccant (for drying thenitrogen carrier gas stream).7.6 Nitrogen Gas (N2), containing less than 5 g/g of water.7.7 Neutralization Solution, or check sol
21、ution (per manu-facturers recommendation).8. Hazards8.1 Due to the low quantities of water measured, maximumcare shall be exercised at all times to avoid contaminating thesample with water from the sample container, the atmosphereor transfer equipment. Hygroscopic resin samples shall beprotected fro
22、m the atmosphere.8.2 Due to the high temperatures and the chemicals in-volved in this test method, safe lab practices must be followedat all times.9. Sampling, Test Specimens, and Test Units9.1 Unless otherwise agreed upon by interested parties ordescribed in a specification, the material shall be s
23、ampledstatistically or the sample shall come from a process that is instatistical control.9.2 Samples that will determine the moisture of a larger lotof material must be taken in such a manner that the moisturecontent will not change from the original material. Samplecontainers must be adequately dr
24、ied and the environment inwhich sampling is performed must not add additional moistureto the sample. Most normal plant or lab operating conditionsare adequate for sampling. The sample container shall beproperly sealed to prevent moisture pick-up before testing.9.3 Samples in many forms, such as mold
25、ed powder,molded shapes, or re-grind are permitted. It is recommendedthat molded specimens be cut into smaller parts prior to testing(recommended maximum size 4 by 4 by 3 mm)9.4 Transfer samples quickly from sealed container tobalance to instrument to prevent moisture pick-up.10. Preparation of Appa
26、ratus10.1 Assemble the apparatus according to the manufactur-ers instructions. Molecular sieve or suitable desiccant must beused in the drying tubes for the nitrogen carrier gas.10.2 Pour approximately 200 mL(or an amount specified bythe manufacturer) of generator (anode) solution into thetitration
27、cell.10.3 Add 10 mL of cathode solution to the cathode cell.NOTE 3The condition of both anode and cathode solutions aredetermined by the appearance of the fluids. The solutions must be lightamber in color. As solutions age, viscosity will increase and solution colorwill turn dark. The instrument wil
28、l indicate solution integrity by the“background” value titration rate. Do not analyze samples containing lowmoisture content if the “background” value is greater than 0.10 g/s.10.4 Turn the cell power switch on. If the cell potentialshows a negative value, indicating that the anode solutioncontains
29、excess iodine, add approximately 50 to 200 L ofneutralization solution or check solution.10.5 Disconnect the tube connecting the vaporizer unit tothe titration cell. Set nitrogen flow rate to achieve steadybubbling of nitrogen to the titration cell. (A flow rate of 200 to300 mL/min is recommended.)1
30、0.6 Lift the titration cell and agitate the solution by gentlyswirling the cell to remove any residual water from the walls.Stir the solution for a minute in the Titration Mode to dry andstabilize the inner atmosphere.10.7 Reconnect the tube from the vaporizer unit to thetitration cell. Keep the car
31、rier gas flow on during the wholetitration. The instrument is now ready for sample analysis.10.8 Set the oven and furnace tube temperature as requiredto obtain accurate results for the plastic to be tested. Thetemperature is set so that the analysis is completed in a shorttime period, yet eliminatin
32、g the generation of water fromthermal degradation of the sample. Selection of OptimumHeating Temperature is discussed below.10.9 Selection of Optimum Heating Temperature:10.9.1 Select optimum heating temperature for material tobe tested by carrying out tests in several different temperaturesto make
33、a curve as shown in Fig. 1.10.9.1.1 In the range from 1 to 2, the water in the sample isnot vaporized sufficiently so that the water content indicatedincreases in proportion to the temperature.10.9.1.2 Between 2 and 3, the water content measuredappears nearly constant and is considered the optimum h
34、eatingtemperature range for determining moisture content.10.9.1.3 Water content appears to increase between 3 and 4.This is probably caused by the generation of water due tothermal decomposition or solid phase polymerization of thesample.10.9.1.4 Measurement time is also a consideration in selec-tio
35、n of the optimum heating temperature.11. Calibration and Standardization11.1 The apparatus is verified for proper operation by eitheranalysis of a known quantity of water or analysis of a hydrateD6869 172sample that will release moisture upon heating. Two methodsof checking the instrument are listed
36、 here, a micro-capillarymethod and a sodium citrate method.11.2 Micro-capillary Method:11.2.1 A glass capillary (micropipette) is used to measure aknown amount of water, typically 2 mg (2000 g). Prepare theinstrument as detailed in Section 12.11.2.2 Fill the micropipette by holding it at its midpoin
37、twith a pair of tweezers and dipping the tip into distilled ordemineralized water. Take care not to get excess moisture onthe outside surface of the capillary.11.2.3 Place the capillary in the sample boat through thefurnace tube port. An oven temperature of 150C or greatershall be used.11.3 Sodium C
38、itrate Method:11.3.1 This method uses sodium citrate dihydrate(C6H5Na3O72H2O) with theoretical water content of 12.24 %.11.3.2 Weigh 0.0100 to 0.0200 g of sodium citrate to thenearest 0.0001 g. Record the sample weight.11.3.3 Analyze the moisture content using an oven tempera-ture of 225C or greater
39、.NOTE 4Another permissible method, which uses a micro syringe, isdescribed in section 4.5.3.1 of ISO 15512. It is permissible to use similarhydrates to check instrument performance.12. Procedure12.1 If the oven is at the selected operating temperaturebefore the analysis begins, pre-heat the sample b
40、oat to elimi-nate any moisture present. Heat the boat in the oven for 2 min,and then allow the boat to cool for 2 min prior to theintroduction of samples.12.2 Weigh the sample to be tested and record the weight tothe nearest 0.1 mg. Sample weight to be used is dependent onthe amount of moisture expe
41、cted in the sample. The followingtable lists recommended sample weights for various moistureranges:Expected Moisture Content (w) Sample Weight (m)w1% 0.2gm$ 0.1 g1%$ w0.5% 0.4gm$ 0.2 g0.5 % $ w0.1% 1gm$ 0.4 g0.1 % $ wm$ 1g12.3 Place the sample in the sample boat through thefurnace tube port. Move th
42、e sample boat into the oven andbegin analysis.12.4 At completion of the sample analysis, the instrumentwill automatically report the result or display g of moisturetitrated.12.5 Remove the sample boat and empty the contents, thenprepare the sample boat for next analysis. Removal of theprevious sampl
43、e will provide more accurate results.13. Calculation or Interpretation of Results13.1 Most commercial coulometric instruments will per-form calculations automatically based on the micrograms ofwater detected.13.2 If the moisture is not calculated automatically, calcu-late the water content in the te
44、st portion (expressed as apercentage by mass) as follows:% moisture 5micrograms of watergrams of water31024% moisture 5grams of watergrams of sample310014. Report14.1 Report the sample type, oven temperature, sampleweight, and % moisture.15. Precision and Bias15.1 The precision of this test method i
45、s not known becauseinter-laboratory data are not available. If and when inter-laboratory data are obtained, a precision statement will beadded at a subsequent revision.15.2 A “ruggedness” test was run at three labs using nylon6,6 with the following results:LabNumberDayAnalysisTemp. (C)FirstAnalysisS
46、econdAnalysis1 1 190 0.2323 0.22981 2 190 0.2047 0.23231 1 200 0.2491 0.22501 2 200 0.1842 0.19272 1 240 0.308 0.3162 2 240 0.314 0.3042 1 200 0.264 0.2632 2 200 0.285 0.2973 1 220 0.25 0.243 2 220 0.24 0.233 1 200 0.23 0.243 2 200 0.25 0.2416. Keywords16.1 moisture content; moisture determination;
47、plasticsFIG. 1 Optimum Heating Temperature Selection for MaterialD6869 173APPENDIX(Nonmandatory Information)X1. HISTORY OF REAGENTS ASSOCIATED WITH THE KARL FISCHER REACTIONX1.1 History of Reagents Associated with the Karl Fis-cher ReactionX1.1.1 The Karl Fischer chemical reaction is:I212H2O1SO22HI1
48、H2SO4X1.1.2 This reaction takes place in the presence of a baseand a solvent. Karl Fischers original combination of reagents,which contained pyridine, was first used in 1935. It was notwidely used because of the objectionable odor of pyridine.X1.1.3 Wider use of the Karl Fischer reaction did not tak
49、eplace until the early 1980s when reagents were offered wherepyridine was replaced with methanol. This eliminated the odorproblem associated with pyridine. Halogenated alcohols (espe-cially trifluoroethanol) were used in place of methanol in somecases to overcome side reactions caused by a large group ofsamples.X1.1.4 Because of the safety and environmental concernsassociated with methanol and halogenated compounds, newgenerations of reagents that use the Karl Fischer reaction arebeing offered that are based on long-chain ethers or ethano
