1、Designation: D7785 12Standard Test Method forWater in Lint Cotton by Oven Evaporation Combined withVolumetric Karl Fischer Titration1This standard is issued under the fixed designation D7785; the number immediately following the designation indicates the year oforiginal adoption or, in the case of r
2、evision, 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 test method covers the determination of the totalamount of water (free and bound) in raw and
3、 lint cotton atmoisture equilibrium from conditioning in the standard atmo-sphere for testing textiles.NOTE 1For other methods of determination of moisture in lint cottonthat do not specify conditioning to moisture equilibrium, refer to TestMethods D2495 and D1348.1.2 This test method requires the u
4、se of oven evaporation toremove all of the water in the fiber matrix, volumetric KarlFischer (KF) titration to determine water content and waterregain, and control current potentiometry to detect the endpoint.1.3 This test method is not intended for use with potentio-metric (zero current) and coulom
5、etric Karl Fischer titrators (seeTest Methods D1533, D4377 and E1064), nor is this testmethod intended to be used with methanol extracts of cotton(See Test Methods D1348).1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 T
6、his 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. For specificprecaut
7、ionary warnings see 9.1.2. Referenced Documents2.1 ASTM Standards:2D123 Terminology Relating to TextilesD1193 Specification for Reagent WaterD1348 Test Methods for Moisture in CelluloseD1441 Practice for Sampling Cotton Fibers for TestingD1533 Test Method for Water in Insulating Liquids byCoulometri
8、c Karl Fischer TitrationD1776 Practice for Conditioning and Testing TextilesD2495 Test Method for Moisture in Cotton by Oven-DryingD4377 Test Method for Water in Crude Oils by Potentio-metric Karl Fischer TitrationD7139 Terminology for Cotton FibersE177 Practice for Use of the Terms Precision and Bi
9、as inASTM Test MethodsE203 Test Method for Water Using Volumetric Karl FischerTitrationE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE1064 Test Method for Water in Organic Liquids by Cou-lometric Karl Fischer Titration3. Terminology3.1 Definitions:3.
10、2 For all terminology relating to D13.11, Cotton Fibers,refer to Terminology D7139.3.3 The following terms are relevant to this standard: boundwater, free water, test specimen, water content, water regain.3.4 For definitions of all other textile terms see TerminologyD123.4. Summary of Test Method4.1
11、 A0.1 g test specimen is sealed in a glass vial, positionedon the sample turntable and lowered into the single sampleoven where dry nitrogen transports the water vapor that israpidly evaporated from the fibers into a titration cell. Theamount of water is determined by volumetric titration withKarl F
12、ischer reagent with the end point determined by elec-trodes that measure a sharp change in potential when the iodinein the reagent is reduced by sulfur dioxide in the presence ofwater. The volume of reagent required to titrate the wet gasstream is converted into the amount of water in the testspecim
13、en. For the reaction mechanism and the chemicalsinvolved with this test method, see Appendix X1.1This test method is under the jurisdiction of ASTM Committee D13 on Textilesand is the direct responsibility of Subcommittee D13.11 on Cotton Fibers.Current edition approved Feb. 1, 2012. Published March
14、 2012. DOI: 10.1520/D7785-12.2For 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.1Copyright ASTM International, 1
15、00 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5. Significance and Use5.1 The water content of raw or lint cotton determined bythis test method, calculated from the required volume ofreagent, may be greater, equal to or less than the moisturecontent measured by st
16、andard oven drying methods. Thesedifferences may be of significance in commercial transactions(1-3)3(see also Appendix X2). Water content by this method isnot to be considered the same attribute as moisture content.5.2 Standard test methods using volumetric and coulometricKarl Fischer reagent are tw
17、o of the most widely used proce-dures for the determination of water.5.3 The volumetric method is typically used for the routinedetermination of water in the mass percent range of concen-trations. If samples contain very low levels of water, thecoulometric technique should be considered (see Test Me
18、thodsD1533, E1064).5.4 This test method for testing the water content of cottoncan be used for acceptance testing of commercial shipments oflint cotton, manufacturing control and calibration of fast,indirect sensors to measure water.5.5 Information on the water content of cotton is desirablesince th
19、e physical properties of cotton are significantly affectedby its water content. Variations in the amount of water present,or its regain, affect the mass and hence the market value of a lotof material.5.6 The observed volume of Karl Fischer reagent used inthis test method to analyze a specimen repres
20、ents the water inthe absence of side reactions in an oven supplied with air (3).NOTE 2Side reactions in cotton that confound the actual weight lossdue to water have been demonstrated in two laboratory ovens and athermogravimetric analysis oven supplied with air (3). This results in anapproximation r
21、egarding the actual amount of water in cotton based onmass loss by drying. If the moisture content by oven drying agrees withthe water content measured by Karl Fischer titration, the one-to-onecorrespondence may be coincidental due to the presence of both negativeand positive biases in moisture cont
22、ent values.6. Interferences6.1 Compounds such as aldehydes, ketones, free halogens,most acids, and oxidizing agents may interfere in this titrimet-ric method. A detailed discussion of interfering substances canbe found in the treatise on aquametry (4). Detailed investiga-tions of sources of bias in
23、industrial samples analyzed by anautomatic oven evaporator combined with the coulometric KarlFischer method demonstrate the need to validate the proce-dures (5,6).6.2 To establish that the compounds listed in 6.1 do notcause a significant change in water results in this test method,information was o
24、btained by a series of observations during theperformance of these tests.6.2.1 A drifting endpoint, an indicator of interferences incotton, was not observed with the reagents used in this testmethod (see Test Method D1533).6.2.2 The recovery of spiked additions of water to thesample matrix was not s
25、ignificantly different from 100 % (seeTest Method E203).6.2.3 The slope of the plot of water content of cotton versusoven module temperature in the range of 150 to 160C was notsignificantly different from zero (7). A nonzero slope isindicative of biases due to interferences.6.2.4 Studies have shown
26、that the selectivity of this testmethod for water in cotton, relative to the interferences incotton, is not significantly influenced by these interferingsubstances (2,8).6.2.4.1 In practice, the first step in the selectivity determi-nation is to set up a low temperature laboratory oven at 50Cto pre-
27、dry the test specimen. The sealed Karl Fischer samplevial containing 0.1 g cotton (see 10.2.1) is placed in this ovenand the vial is purged overnight with dry nitrogen at 60mL/min to separate water from the test specimen. The lowtemperature distillation technique evaporates off the moisturewithout r
28、emoving interfering substances.6.2.4.2 Confirmation of complete water removal from eachtest specimen is checked or confirmed by recording a nearinfrared reflectance spectrum taken in vitro.NOTE 3Near infrared reflectance spectra taken through the bottom ofthe sealed glass specimen vial by an externa
29、l probe immediately after KarlFischer analysis will show the absence of the strong water band in cottonat 1400 nm (1,3).6.2.4.3 The recommended Karl Fischer titration procedure(see Section 14) is carried out on two different treatments ofspecimens of the same cotton in sealed vials: (a) the anhydrou
30、scotton and (b) the fibers before drying.6.2.4.4 The volumes of reagent consumed are reported as:(a) the equivalent water content of the interferences (%) in thepre-dried cotton and (b) the water content (%) of the cotton.6.2.4.5 The selectivity of this test method for water in cottonis computed fro
31、m the two water measures in 6.2.4.4.7. Apparatus7.1 Volumetric Karl Fischer Titratorwith dual platinumelectrodes with the following accessories:7.1.1 Titration VesselConsists of a sealed vessel contain-ing the platinum electrodes, several tubes in the cell withdifferent applications and a vent in th
32、e top of the cell. The ventis connected to a drying tube.7.1.2 Titration Vessel TubesThe four required tubes in thistest method extend below the liquid level in the cell. In onetube flows the wet nitrogen stream. Another tube is connectedto the mechanical burette that automatically dispenses theiodi
33、ne reagent. The two remaining tubes are used for pumpingin fresh solvent and pumping out spent solvent.7.1.3 Outlet Gas Pressure Line, with Flow ControllerThegas transfer line between the oven block and titration vesselshall be heated to prevent water condensation in the line. Thegas flow is selecte
34、d to ensure the water vapor is absorbed bythe solvent.7.1.4 Magnetic StirrerThe glass or PTFE covered mag-netic stirring bar should spin at a sufficient rate to create asolution vortex in the titration vessel that helps to capture thecarrier gas stream and allow for absorption of water by thesolvent
35、 in the cell.7.2 Turntable Oven Assemblywith oven module thatheats one specimen at a time with the following accessory:3The boldface numbers in parentheses refer to a list of references at the end ofthis standard.D7785 1227.2.1 Needle Guide Double Wall NeedleThe needleguide moves the double wall nee
36、dle to penetrate the septum ofa sealed vial on the turntable, moves the vial with penetrationneedle inside the vial in and out of the oven block, and removesthe needle from the vial. The double wall needle shall be longenough to penetrate the septum but not penetrate the samplematrix.7.3 Glass Vials
37、 and Canning Jarswith crimp type PTFEseptum caps to seal the specimen vials and wide-mouth typejars with lids and rings to seal the jars used to store specimenvials before Karl Fischer analysis.8. Reagents and Materials8.1 Purity of ReagentsUnless otherwise stated, all re-agents shall conform to the
38、 specifications of the Committee onAnalytical Reagents of the American Chemical Society, wheresuch specifications are available.48.2 Purity of WatersUnless otherwise indicated, refer-ences to water shall mean reagent water as defined by Type IIand III of Specifications D1193.8.3 Volumetric Karl Fisc
39、her ReagentsSolvent and titra-tion reagents are available commercially.8.3.1 Solvent ReagentThe working medium or solution inthe titration vessel. Consists of a mixture of organic chemicals.8.3.2 Titration ReagentConsists of a mixture of iodine(the key ingredient) and other organic chemicals.8.4 Wat
40、er StandardsSolutions are available commerciallyto calibrate the combination of the oven and volumetric titrator.Consist of water (units are mg water/mL water standard) and amixture of organic chemicals. The response of the volumetrictitrator itself, without the oven, shall be checked with purewater
41、 (see 8.2).8.5 Dry NitrogenReferences to dry nitrogen shall meancompressed nitrogen gas containing 1 ppm water (volume/volume) and used without further purification.9. Hazards9.1 Commercially available Karl Fischer solvent and titra-tion reagents used in this test method may contain potentiallyhazar
42、dous chemicals, such as iodine, sulfur dioxide, chloro-form, imidazole and substituted imidazole, hydriodic acid,diethylene glycol monoethyl ether, or other organic materials.Commercially available water standards used in this testmethod may contain propylene carbonate, xylene, or otherorganic mater
43、ials. Wear chemically resistant gloves whenhandling the materials. Care must be exercised to avoidunnecessary inhalation of organic vapors or direct contact withthe skin or eyes.NOTE 4Carefully read and follow manufacturers instructions andMaterial Safety Data Sheets when using commercially availabl
44、e reagentsand water standards.10. Sampling, Test Specimens, and Test Units10.1 The preferred method for sampling cotton fibers fortesting is Practice D1441.10.2 Test SpecimensThree test specimens shall be taken atrandom from each laboratory sample.10.2.1 Test Specimen SizeThe test specimen size is 0
45、.1 60.0003 g.11. Preparation of Apparatus11.1 Thoroughly clean and dry the titration vessel andreassemble according to the manufacturers recommendations.11.2 Turn the oven and volumetric titrator on and allowsoftware and hardware initializations to be completed. Checkthat the oven temperature is set
46、 at 150C.11.3 Fill reagent reservoirs with appropriate reagents ac-cording to the manufacturers instructions.11.4 Open the cylinder of compressed dry nitrogen.12. Calibration and Standardization12.1 All successive steps must be done in the generallaboratory area of the Karl Fischer instrumentation.N
47、OTE 5The cotton fiber atmospheric conditioning requirements donot apply to the oven evaporator and Karl Fischer titrator because it isbeneficial to operate the system at lower humidity.12.2 Tightly crimp five of the PTFE septum caps onto theempty glass sample vials. Place one of the empty vials in t
48、he“conditioning position” of the sample rack on the oventurntable. Place the remaining four vials into the first foursample positions of the oven rack. The first position is toinitialize the system (initializing blank) and remove anyextraneous water. The following three are the blank vials forthe ti
49、tration of atmospheric water in the vials.12.3 Follow the manufacturers software instructions tocondition or purge the complete tubing system with drynitrogen flowing through the conditioning vial, which ismaintained on the rack at room temperature.12.3.1 With the conditioning vial on the rack, the titrationvessel is conditioned with the volumetric Karl Fischer titratoruntil the reaction mixture in the titration vessel is dry.12.4 Each of the three blank vials, in turn, with programmedconditioning of the reaction medium in between, is moved intothe ove
