ASTM D6869-2003(2011) 4375 Standard Test Method for Coulometric and Volumetric Determination of Moisture in Plastics Using the Karl Fischer Reaction (the Reaction of Iodine with Wa.pdf

1、Designation: D6869 03 (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 designatio

2、n 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 method uses the reaction of Iod

3、ine (I2) with 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 releasin

4、g components that 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

5、technically equivalent 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 regulat

6、ory limitations prior 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 th

7、e 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 Coulombs (C)

8、 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 processability of some plastics.High moisture content causes surface

9、 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 in the deter

10、mination 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), normally a glas

11、s 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 solutionstirr

12、ing capability. This apparatus has the capability 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.The percent moisture in the sample is then calculated

13、 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).1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.70 on Analytical M

14、ethods.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 explanation of coulometric and volume

15、tric 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Consh

16、ohocken, PA 19428-2959, United States.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 manufacturers recom-mendation.7.2 Cathode Solution, per manufacturers recommendation.NOTE 2Hydranal o

17、r 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 manufacturer for g

18、roundglass 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 solution (per manu-facturers recommendation).8. Hazards8.1 Due to the low quantities of water meas

19、ured, 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 from the atmosphere.8.2 Due to the high temperatures and the chemicals in-volved in this test meth

20、od, 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 sampledstatistically or the sample shall come from a process that is instatistical control.9.2 S

21、amples 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 dried and the environment inwhich sampling is performed must not add additional moistureto the sa

22、mple. 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 molded powder,molded shapes, or re-grind are permitted. It is recommendedthat molded specimens be c

23、ut 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 Apparatus10.1 Assemble the apparatus according to the manufactur-ers instructions. Molecular sieve

24、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 cell.10.3 Add 10 mL of cathode solution to the cathode cell.NOTE 3The condition of both anode a

25、nd 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 will indicate solution integrity by the“background” value titration rate. Do not analyze samples c

26、ontaining 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 excess iodine, add approximately 50 to 200 L ofneutralization solution or check solution.10.5 D

27、isconnect 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.)10.6 Lift the titration cell and agitate the solution by gentlyswirling the cell to remove any r

28、esidual 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 carrier gas flow on during the wholetitration. The instrument is now ready for sample analysis.10.

29、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 eliminating the generation of water fromthermal degradation of the sample. Selection of OptimumHeating Te

30、mperature 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 a curve as shown in Fig. 1.10.9.1.1 In the range from 1 to 2, the water in the sample isnot vap

31、orized 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 heatingtemperature range for determining moisture content.10.9.1.3 Water content appears to incr

32、ease between 3 and 4.This is probably caused by the generation of water due tothermal decomposition or solid phase polymerization of thesample.FIG. 1 Optimum Heating Temperature Selection for MaterialD6869 03 (2011)210.9.1.4 Measurement time is also a consideration in selec-tion of the optimum heati

33、ng 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 hydratesample that will release moisture upon heating. Two methodsof checking the instrument are listed here, a micro-capillarymethod

34、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 midpointwith a pair of tweezers and di

35、pping 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 Citrate Method:11.3.1 This metho

36、d 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.NOTE 4Another permissible meth

37、od, 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 boat to elimi-nate any moisture

38、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 expected in the sample. The followi

39、ngtable 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 the sample boat into the oven and

40、begin 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 sample will provide more accurate re

41、sults.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 test portion (expressed as aperce

42、ntage by mass) as follows:% moisture 5micrograms of watergrams of water3 1024% moisture 5grams of watergrams of sample3 10014. Report14.1 Report the sample type, oven temperature, sampleweight, and % moisture.15. Precision and Bias15.1 The precision of this test method is not known becauseinter-labo

43、ratory 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)FirstAnalysisSecondAnalysis1 1 190 0.2323 0

44、.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; plasticsD6869 03 (2011)3APPEN

45、DIX(Nonmandatory Information)X1.X1.1 History of Reagents Associated with the KarlFischer ReactionX1.1.1 The Karl Fischer chemical reaction is:I21 2H2O 1 SO22HI 1 H2SO4X1.1.2 This reaction takes place in the presence of a baseand a solvent. Karl Fischers original combination of reagents,which contain

46、ed 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 takeplace until the early 1980s when reagents were offered wherepyridine was replaced with methanol. This eliminated the odorproblem associat

47、ed 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

48、reagents that use the Karl Fischer reaction arebeing offered that are based on long-chain ethers or ethanol/salts combinations.X1.1.5 Reagents using the Karl Fischer chemical reactioninclude those sold under the trade names of Hydranal, Water-mark, Hydra-Point, Aquastar, and Aqualine from Riedel deH

49、aen, GFS Chemicals, Mallinckrodt, EM Science, and FischerScientific, respectively.X1.2 Coulometric TitrationX1.2.1 Coulometric titration instruments determine theamount of water present by measuring the amount of currentgenerated during the titration. Faradays law is used to calcu-late the moisture present, with 10.71 C (Coulombs) of gener-ating current corresponding to 1 mg of water (2I- I2+2e-).X1.3 Volumetric TitrationX1.3.1 Volumetric titration instruments measure the volumeof iodine-containing reagent needed to react with the moisturein a sample. Their