Karl Fischer test method

The Karl Fischer test method (ASTM D-1364, ASTM D-6304) covers the direct determination of water in petroleum. In the test, the sample injection in the titration vessel can be performed on a volumetric or gravimetric basis. Viscous samples can be analyzed with a water vaporizer accessory that heats the sample in the evaporation chamber, and the vaporized water is carried into the Karl Fischer titration cell by a dry, inert carrier gas. 

These residual moisture results are illustrative of an excellently freeze-dried product with relatively low vial-to-vial residual moisture variability as determined by the Karl Fischer test method. 

Note 2—Deviations shown reflect use of the Karl Fischer test method described in 0 4928 for water. 

The preferred method of determining water in glycerol is by the Karl Fischer volumetric method (18). Water can also be determined by a special quantitative distillation in which the distilled water is absorbed by anhydrous magnesium perchlorate (19). Other tests such as ash, alkalinity or acidity, sodium chloride, and total organic residue are included in AOCS methods (13,16,18). 

Assay and test results are determined on the basis of comparison of the test sample with the reference standard that has been freed from or corrected for volatile residues or water content as instructed on the reference standard label. If a reference standard is required to be dried before use, transfer a sufficient amount to a clean, dry vessel. Do not use the original container as the drying vessel, and do not dry a reference standard repeatedly at temperatures above 25°. Where the titrimetric determination of water is required at the time a reference standard is to be used, proceed as directed in the Karl Fischer Titrimetric Method under Water Determination, Appendix IIB. 

Water and Loss on Drying In general, for compounds containing water of crystallization or adsorbed water, a limit test, to be determined by the Karl Fischer Titrimetric Method, is provided under the heading Water. For compounds in which the loss on drying may not necessarily be attributable to water, a limit test, to be determined by other methods, is provided under the heading Loss on Drying. 

This procedure is used to determine the amount of volatile matter expelled under the conditions specified in the monograph. Because the volatile matter may include material other than adsorbed moisture, this test is designed for compounds in which the loss on drying may not definitely be attributable to water alone. For substances appearing to contain water as the only volatile constituent, the Direct (Karl Fischer) Titration Method, provided under Water, Appendix IIB, is usually appropriate. 

Free water in jet fuels can be detected by the use of the Karl Fischer titration method (ASTM D-1744) or by observing color changes when chemicals go into aqueous solution (ASTM D-3240). The standard water reaction test for jet fuel (ASTM D-1094, IP 289) is the same as for aviation gasoline, but the interface and separation ratings are more critically defined. Test assessment is by subjective visual observation and, although quite precise when made by an experienced operator, the test can cause rating difficulties under borderline conditions. As a consequence, a more objective test, known as the water separometer test, is now included in many specifications (ASTM D-2550). 

Kerosene, because of its higher density and viscosity, tends to retain fine particulate matter and water droplets in suspension for a much longer time than gasoline. Free water in kerosene can be detected by the use of a Dean and Stark adaptor (ASTM D-4006, IP 358) (Fig. 7.3), by the Karl Fischer titration method (ASTM D-1744, ASTM D-6304), by the distillation method (ASTM D-95, IP 74), or by a series of alternate tests (ASTM D-4176, ASTM D-4860). The standard water reaction test method (ASTM D-1094, IP 289) can also be used. 

In addition to the air-oven methods for moisture measurement, there is also a Karl Fischer titration method. In this method, moisture is considered to be the moisture that is extracted by methyl alcohol in a sealed container with ground soybeans for a specified time period (Paulsen, 1991). This water-alcohol extract is placed in a reaction chamber where the water reacts with iodine. The amount of iodine used in titration is a measure of the amount of water in the soybeans. Soybean samples tested with the Karl Fischer method usually show about 0.2 percentage points lower moisture than those tested with the USDA air-oven method (Paulsen, 1991). The standard deviations of differences from duplicate samples were lower (0.07 percentage points) for the USDA air-oven method than for the Karl Fischer method (0.11 percentage points) (Paulsen, 1991). 

Water Content (a) Karl Fischer test Mitsubishi Moisture Meter (MCI-Model CA-02) indirect method sample size 3-10 mg temperature 125°C typical heating time 2-10 minutes (b) DuPont... 

A number of substances and classes of compounds associated with condensation or oxidation-reduction reactions interfere in the determination of water by Karl Fischer. In crude oils, the most common interferences are mercaptans and sulfides. At levels of less than 500 pg/g (ppm) (as sulfiir) the interference firom these compounds is insignificant For more information on substances that interfere in the determination of water by Karl Fischer titration method see Test Method E 203. 

Chemical tests for particular types of impurities, e.g. for peroxides in aliphatic ethers (with acidified KI), or for water in solvents (quantitatively by the Karl Fischer method, see Fieser and Fieser, Reagents for Organic Synthesis J. Wiley Sons, NY, Vol 1 pp. 353, 528, 1967, Library of Congress Catalog Card No 66-27894). 

The method is clearly confined to those cases where the test substance does not react with either of the components of the reagent, nor with the hydrogen iodide which is formed during the reaction with water the following compounds interfere in the Karl Fischer titration. 

The Karl Fischer procedure has now been simplified and the accuracy improved by modification to a coulometric method (Chapter 14). In this procedure the sample under test is added to a pyridine-methanol solution containing sulphur dioxide and a soluble iodide. Upon electrolysis, iodine is liberated at the anode and reactions (a) and (b) then follow the end point is detected by a pair of electrodes which function as a biamperometric detection system and indicate the presence of free iodine. Since one mole of iodine reacts with one mole of water it follows that 1 mg of water is equivalent to 10.71 coulombs. 

Test Method 0D1A45-Karl Fischer , MIL-T-20326 (1951) 23) S.H. Liff, Fuze Sealants ,... 

MOISTURE.dat Section 4.4 At 10 selected locations inside a dryer samples of eight tablets each were drawn to determine water content by the Karl Fischer method using MULTI, the hypothesis Ho is tested that all 10 sample means and standard deviations are indistinguishable. 

The water (moisture) content can rapidly and accurately be determined in polymers such as PBT, PA6, PA4.6 and PC via coulometric titration, with detection limits of some 20 ppm. Water produced during heating of PET was determined by Karl Fischer titration [536]. The method can be used for determining very small quantities of water (10p,g-15mg). Certified water standards are available. Karl Fischer titrations are not universal. The method is not applicable in the presence of H2S, mercaptans, sulfides or appreciable amounts of hydroperoxides, and to any compound or mixture which partially reacts under the conditions of the test, to produce water [31]. Compounds that consume or release iodine under the analysis conditions interfere with the determination. 

Ammonium chloride is analyzed by treatment with formaldehyde (neutralized with NaOH) and the product HCl formed is analyzed by titration using an acid-base color indicator such as phenolphthalein. Alternatively, it may be mixed with caustic soda solution and distdled. The distillate may be analyzed for NH3 by titration with H2SO4 or by colorimetric Nesslerization or with an ammonia-selective electrode (APHA, AWWA, WEF. 1995. Standard Methods for the Examination of Water and Wastewater. 19th ed. Washington, DC, American Pubhc Health Association). The presence of ammonia or any other ammonium compound would interfere in the test. The moisture content in NH4CI may be determined by Karl—Fischer method. 

Refs l)K.Van Keuren, "A Procedure for Chemical Analysis of Composition A-3 , NAVORD Report 1781, US Naval Ordnance Laboratory, White Oak, Md. (1951) la)S.M. Kaye, PATR 1936 (1953) (Nonaqueous titration method for detn of RDX content in Comp A-3) 2)Anon, Military Explosives , TM 9-1910 (1955), 271 (Identification of Composition A-3) 3)Purchase Description X-PA-PD-940 (1956) (Karl Fischer moisture detn) 4)Federal Test Method Std No 141 (1958), Method 4082 (Karl Fischer moisture detn) 4a)C.C.Jamison, "Determination of Nitrogenous Coumpounds of Ordnance Interest by Chromous Chloride Reduction , PicArsn, FRL TechMemo ACS-3-60 (I960) 5)U.S. 

In Figure 1.68.2 the influence of shielding the product in vials from the walls and doors is summarized. For each run (a), (b) and (c) six groups of vials (168 vials each) filled with 2.8 cm3 (9 mm thickness) of human albumin product, containing 6% solids, were used. Rows 4, 5 and 6 were close to the door and 1, 2 and 3 close to the back wall the condenser connection was at the bottom of the chamber. The RM were determined by the Karl Fischer method. Figure 1.68.3 shows the program of the tests. 

Principle See the information in the section entitled Principle under Method la. In the residual titration, add excess Karl Fischer Reagent to the test specimen, allow sufficient time for the reaction to reach completion, and titrate the unconsumed Karl Fischer Reagent with a standard solution of water in a solvent such as methanol. The residual titration procedure is generally applicable and avoids the difficulties that may be encountered in the direct titration of substances from which the bound water is released slowly. 

Procedure Where the individual monograph specifies the water content is to be determined by Method lb, transfer 35 to 40 mL of methanol or other suitable solvent into the titration vessel, and titrate with the Karl Fischer Reagent to the electrometric or visual endpoint. Quickly add the Test Preparation, mix, and add an accurately measured excess of the Karl Fischer Reagent. Allow sufficient time for the reaction to reach completion, and titrate the unconsumed Karl Fischer Reagent with standardized Water Solution to the electrometric or visual endpoint. Calculate the water content of the specimen, in milligrams, with the formula... 

Note During the dehydration procedure described in Vol 3, p C399-L, it is required to determine ethanol and water in the cylindrical block removed from the press. In these detns a piece of block (cake) is dried in an oven at 100° to obtain "total volatile content , the water is detd by Karl Fischer Method and then ale is obtd by difference. Finally ether is added to make a colloiding mixture contg 2 parts of ether to 1 part alcohol by wt. The above tests are described in the items which follow... 

PROCEDURES which follow 4.3 TEST METHODS AND PROCEDURES 4.3.1 Determination of Moisture in EGDN by Karl Fischer. Weigh accurately a 5—lOg portion of the sample (sample size shall be in accordance with the strength of the Karl Fischer reagent) of the EGDN into a tared narrow-necked stoppered flask. Titrate directly until a brown tinge persists in the soln for 30 seconds (Poten-tiometric endpoint indicators may also be used in titration with Karl Fischer reagent). Calculate as follows ... 

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