Karl Fischer testing

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. 

The Karl Fischer test determines how much water is present due to inefficient drying, the hygroscopic nature of the molecule, and/or is chemically bound as a hydrate, but does not distinguish between these types... 

Chemical tests such as Karl Fischer testing and pH are also important and conducted routinely. 

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... 

Table 4 Milligrams of Water Absorbed by Sucrose After Lyophilization Compared to Moisture Load in 20 mm Lyo Closure (per Karl Fischer testing)... 

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. 

Anhydrous ammonia is normally analy2ed for moisture, oil, and residue. The ammonia is first evaporated from the sample and the residue tested (86). In most instances, the amount of oil and sediment ia the samples are insignificant and the entire residue may be assumed to be water. For more accurate moisture determinations, the ammonia can be dissociated into nitrogen and hydrogen and the dewpoint of the dissociated gas obtained. This procedure works well where the concentration of water is in the ppm range. Where the amount of water is in the range of a few hundredths of a percent, acetic acid and methanol can be added to the residue and a Karl Fischer titration performed to an electrometricaHy detected end point (89—92). 

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). 

Tests for purity include the Karl Fischer titration for water this can be applied directly. Acetic acid and methylamine can be detected polarographically. 

Small amounts of pyridine have been purified by vapour-phase chromatography, using a 180-cm column of polyethyleneglycol-4(X) (Shell 5%) on Embacel (May and Baker) at 100°, with argon as carrier gas. The Karl Fischer titration can be used for determining water content. A colour test for pyrrole as a contaminant is described by Biddiscombe et al. [J Ghent Soc 1957 1 954]. 

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. 

Karl Fischer Titrators These titrators measure moisture (water) in a variety of samples. The titrant s concentration is usually expressed as titer, or grams of water consumed per milliliter of titrant. Standardization involves a certified primary standard (a material containing a known amount of water). This standard is purchased in ampules and is accompanied by a test certificate indicating traceability to a reference material. In addition, the titrator should be calibrated for the titrant volume measurement. The moisture can be measued by weight loss upon drying and checked against the Karl Fischer results. 

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. 

Alkalinity as NasC03 Moisture by Karl Fischer KI Test at 82.2°C... 

All enthalpy of solution measurements were carried out with an LKB 8700-1 precision calorimetry system. The experimental procedure and tests of the calorimeter have been reported previously (3, 4, 5). The purification of the solvent DMF (Baker Analyzed Reagent) and of all solutes used has been described in the same papers. The solvent mixtures were prepared by weighing and the mole fraction of water in the DMF-water mixtures was corrected for the original water content of the amide as measured by Karl Fischer titration. 

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). 

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. 

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