Karl-Fischer method

By this method the weighed dry product is dissolved in methanol and titrated with the Karl Fischer solution until the color changes from brown to yellow. The visual observation can be replaced by an ammeter, which shows an steep increase in current, when the titration is terminated (dead-stop-titration). The samples can be two to four times smaller than for the gravimetric method. To avoid the visual observation completely, iodine can be produced by electrolyzation and the water content is calculated by Coulomb s law. Such an apparatus (e. g. Fig. 1.97.1 and 1.97.2) is available commercially. The smallest amount of water to be detected by such instruments is 10 pg. Wekx and De Kleijn [1.84) showed, how the Karl Fischer method can be used directly in the vial with the dried product. The Karl 

Fischer titration cannot be used if the product reacts with iodine in the Karl Fischer reagent, or does not dissolve in methanol, or the moisture cannot be extracted by the methanol. 

---

Water (content) NFT 60-154 ISO/DIS 6296 ASTM D 1744 Karl Fischer Method (electrometric, alter addition of KF reagent)... 

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). 

A selection of coulometric titrations of different types is collected in Table 14.2. It may be noted that the Karl Fischer method for determining water was first developed as an amperometric titration procedure (Section 16.35), but modern instrumentation treats it as a coulometric procedure with electrolytic generation of I2. The reagents referred to in the table are generated at a platinum cathode unless otherwise indicated in the Notes. 

The quantitative analysis procedure involves benz extr of TNT, water extr of AN, and taking of the A1 content as insol residue. Moisture content is detd by the Karl Fischer method described in ASTM Method E203-62, except that 8 to lOg samples are added to methanol. Specific gravity is detd by water displacement, and workmanship by visual examination... 

Ibid, E170 (Electrolytic Hygrometer Method) Ibid, E171-L to E172-L (Moisture Determination in Propellants and Explosives by Distillation Method) Ibid, E172-L to E173-L (Moisture Determination in Propellants and Explosives by the Karl Fischer Method)... 

A1 from 100%, 9.0 0.5% (6) moisture content by the Karl Fischer method, 0.5% max (7) compressive strength, by pressing to 30000psi with subsequent measurement of pellet diam and height to 0.001 inch, lOOOOpsi min (8) density, by wt and vol measurement, 1.8l4g/cc min ... 

NaOH soln and w washing, 5.0 0.5% (3) HMX (MlL-H-45444A al by subtracting the binder percent from 100%, 95.0 0.5% (4) moisture content by the Karl Fischer method, 0.1 S% max (5) granulation, both Type I and II compns, gravimetrically after w/aerosol OT washing —... 

Karl Fischer Method. See below under Specifications... 

ISO 4317 1991, Surface active agents and detergents Determination of water content—Karl Fischer method. 

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. 

Natural gas - Determination of water by the Karl Fischer method. Also BS 3156 (10053) Environmental management systems - Specification with guidance for use. Superseded BS 7750 1994 which remains current... 

In almost all theoretical studies of AGf , it is postulated or tacitly understood that when an ion is transferred across the 0/W interface, it strips off solvated molecules completely, and hence the crystal ionic radius is usually employed for the calculation of AGfr°. Although Abraham and Liszi [17], in considering the transfer between mutually saturated solvents, were aware of the effects of hydration of ions in organic solvents in which water is quite soluble (e.g., 1-octanol, 1-pentanol, and methylisobutyl ketone), they concluded that in solvents such as NB andl,2-DCE, the solubility of water is rather small and most ions in the water-saturated solvent exist as unhydrated entities. However, even a water-immiscible organic solvent such as NB dissolves a considerable amount of water (e.g., ca. 170mM H2O in NB). In such a medium, hydrophilic ions such as Li, Na, Ca, Ba, CH, and Br are selectively solvated by water. This phenomenon has become apparent since at least 1968 by solvent extraction studies with the Karl-Fischer method [35 5]. Rais et al. [35] and Iwachido and coworkers [36-39] determined hydration numbers, i.e., the number of coextracted water molecules, for alkali and alkaline earth metal... 

Instrumental methods for the determination of water in polymeric materials often rely on heat release of water from the polymer matrix. However, in some cases (e.g. PET) the polymer is hydrolysed and a simple Karl Fischer method is then preferred. Small quantities of water (10 pg-15mg) of water in polymers (e.g. PBT, PA6, PA4.6, PC) can be determined rapidly and accurately by means of a coulometric titration after heating at 50 to 240 °C with a detection limit in the order of 20 ppm. 

After prolonged degassing of a large batch of PPG, analyses showed that its hydroxyl, unsaturation, and water contents were 0.97 meq/g, 0.033 meq/g, and 0.0035%, respectively. The hydroxyl content was determined by an acetylation method, carried out with acetic anhydride (10). The amounts of unsaturation and water were determined by the mecuric acetate and Karl Fischer methods (10), respectively. The obtained analytical results indicate that the number-average molecular weight of the dihydroxy material is 2062, provided its molecular weight is arbitrarily assumed to be twice that of the monohydroxy material, and that the mole fraction of the monohydroxy poly (propylene oxide) is 0.066. This value corresponds to a number-average functionality of 1.93 for the PPG. 

The Karl Fischer method is a titration to determine the water content in liquid and solid materials. The method utilizes a rather complex reaction in which the water in a sample is reacted with a solution of iodine, methanol, sulfur dioxide, and an organic base ... 

Why is an anode-cathode assembly as well as a dual-pin platinum electrode needed in the coulometric Karl Fischer method ... 

Applications of Karl Fischer Method for Determination of Water in Pharmaceutical Analysis... 

APPLICATIONS OF KARL FISCHER METHOD FOR DETERMINATION OF WATER IN PHARMACEUTICAL ANALYSIS... 

The Karl Fischer method for the determination of water is used for prednisolone sodium phosphate as described below. 

A number of other official pharmaceutical substances may be assayed for their water content by the Karl Fischer method as summarized in the following Table 14.1. 

Table 14.1 Cognate Assays of Pharmaceutical Substances by Karl Fischer Method...

A determination of the surface hydroxyl groups was made by Noll et al. (183). The total water content was determined by heating to 1100°. The content ofmolecular water was titrated by the Karl Fischer method. Silanol groups react with this reagent only very slowly. Good agreement was observed with silanol contents determined independently by other methods. With silica gel, 5.2 silanol groups were found per 100 A. ... 

Borer et al. developed a NIR method to determine moisture in a highly hygroscopic product. Because the sample absorbed water very rapidly (0.02%/min), use of the Karl Fischer method as reference was very complicated. This led them to the choice of NIR spectroscopy, where the sample can be kept inside a sealed vial instead. Analyses were completed within a few seconds and the samples not exposed to ambient air at any time, which prevented moisture absorption and the ensuing determination errors. 

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. 

Total water may be determined by the Karl Fischer method, using pretitrated methanol as the vessel solvent [8], The level of water is typically... 

Karl Fischer Method for Determination of Moisture. See under Dynamites in Vol 5, p D1622-L and under Ethanol in Vol 6, p E158-R... 

III. Moisture Determination in Propellants and Explosives by Karl Fischer Method 101,5, Prescribed by MIL-STD-286B (1 Dec 1967). Detailed description of Fischer method as applied to various substances is given in the following works ... 

Water Content — 0.20% by wt. This limit insures that the material is miscible without turbidity with 19 volumes of 99% heptane at 20°. Determination is conducted by Karl Fischer Method, as described in ASTM D1364 and here as Spec MIL-E-463B, Procedure 4.3 7 uoder ETHANOL, Analytical Procedures... 

---