1、Designation: D 6869 03Standard 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 D 6869; the number immediately following the designation indicates the
2、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 method uses the reaction of Iodine (I2) with w
3、ater(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 th
4、at 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 technically equ
5、ivalent 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
6、 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 the titration cel
7、l 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) of generatingc
8、urrent 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 imperfections
9、(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 determination of moi
10、sture 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 glass sample boat o
11、r 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 solutionstirring capability.
12、 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 based onthe sa
13、mple weight used and is given as a direct digital readout.1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.70.01 on Physical Methods.Current edition approved July 10, 2003. Published August 2003.2See Appendix X1, Histor
14、y 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 Karl Fischer Reagents.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 100
15、36.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.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.
16、Reagents and Materials7.1 Anode (Generator) Solution, per manufacturers 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
17、 Silica Gel, granules, approximately 2 mm, desiccant fordrying tube 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 le
18、ss 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 measured, maximumcare shall be exercised at all times to avoid contaminating thesample with water from the sample container, the atmosphereor tra
19、nsfer equipment. Hygroscopic resin samples shall beprotected from 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
20、 parties ordescribed in a specification, the material shall be sampledstatistically 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 fr
21、om the original material. Samplecontainers must be adequately dried 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 moistur
22、e 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 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 t
23、o instrument to prevent moisture pick-up.10. Preparation of Apparatus10.1 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 byt
24、he 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 and cathode solutions aredetermined by the appearance of the fluids. The solutions must be lightamber in color. As solutions age, viscosity w
25、ill increase and solution colorwill turn dark. The instrument will 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 potentialsh
26、ows a negative value, indicating that the anode solutioncontains 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 t
27、itration 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 residual water from the walls.Stir the solution for a minute in the Titration Mode to dry andstabilize the inner atmosphere.10.7 Reconnect th
28、e 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.10.8 Set the oven and furnace tube temperature as requiredto obtain accurate results for the plastic to be tested. Thetemperature is set so tha
29、t the analysis is completed in a shorttime period, yet eliminating 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 teste
30、d 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 vaporized sufficiently so that the water content indicatedincreases in proportion to the temperature.10.9.1.2 Between 2 and 3, the water conten
31、t measuredappears nearly constant and is considered the optimum heatingtemperature range for determining moisture content.FIG. 1 Optimum Heating Temperature Selection for MaterialD686903210.9.1.3 Water content appears to increase between 3 and 4.This is probably caused by the generation of water due
32、 tothermal decomposition or solid phase polymerization of thesample.10.9.1.4 Measurement time is also a consideration in selec-tion 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
33、 or analysis of a hydratesample that will release moisture upon heating. Two methodsof checking the instrument are listed 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
34、 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 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 cap
35、illary 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 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 thenea
36、rest 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 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 performanc
37、e.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 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
38、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 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$
39、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 andbegin analysis.12.4 At completion of the sample analysis, the instrumentwill automatically report the result or display g of moisturetitrated.12.5 R
40、emove the sample boat and empty the contents, thenprepare the sample boat for next analysis. Removal of theprevious sample will provide more accurate results.13. Calculation or Interpretation of Results13.1 Most commercial coulometric instruments will per-form calculations automatically based on the
41、 micrograms ofwater detected.13.2 If the moisture is not calculated automatically, calcu-late the water content in the test portion (expressed as apercentage by mass) as follows:% moisture 5micrograms of watergrams of water3 1024% moisture 5grams of watergrams of sample3 10014. Report14.1 Report the
42、 sample type, oven temperature, sampleweight, and % moisture.15. Precision and Bias15.1 The precision of this test method is 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 “r
43、uggedness” test was run at three labs using nylon6,6 with the following results:LabNumberDayAnalysisTemp. (C)FirstAnalysisSecondAnalysis1 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
44、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; plasticsD6869033APPENDIX(Nonmandatory Information)X1.X1.1 History of Reagents Associated with the KarlFischer ReactionX1.1.1 The Karl Fischer chemical reaction is:I21 2H2O 1 SO2
45、 2HI 1 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
46、not takeplace 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 la
47、rge 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 ethanol/salts combinations.X1.1.5 Reagents using the Ka
48、rl Fischer chemical reactioninclude those sold under the trade names of Hydranal, Water-mark, Hydra-Point, Aquastar, and Aqualine from Riedel deHaen, GFS Chemicals, Mallinckrodt, EM Science, and FischerScientific, respectively.X1.2 Coulometric TitrationX1.2.1 Coulometric titration instruments determ
49、ine 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 electrode detects the current generatedduring the titration. A volumetric burette adds iodine-containing reagent to the titration cell until no more current i
