Karl Fischer titration method

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. 

Water addition method (4) was suggested for calibrating die Karl-Fischer titration method for pyrolysis oils. 

Karl Fischer Titration Method. In this method the moisture content is measured by titration, using the Karl Fischer reagent, which consists of a solution of pyridine (C5H5N), sulfur dioxide, and iodine in methanol (MeOH). This solution reacts with water as follows ... 

As the drying methods commonly used for the determination of the water content of powders do not selectively measure the water content, but rather the mass lost under specific drying conditions, the Karl Fischer titration method was used... 

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). 

The presence of any appreciable amount of moisture in solvents used in a two-component polyurethane system can react with isocyanate crosslinkers and thus impair crosslinking efficiency. Therefore, moisture content is one of the important properties of solvents such as ketones and esters, which are used in two-component polyurethane coatings. Moisture content is normally determined by the Karl-Fischer titration method. 

METHOD 2 - DETERMINATION OF WATER IN POLYALKENES. SEMI-AUTOMATED KARL FISCHER TITRATION METHOD. 

Determination of water in polyalkenes. Semi-automated Karl Fischer titration method... 

Hydrogen reduction is carried out by Fischer et al. (52) by determining the water formed by the Karl Fischer titration method, a procedure which is nowadays again being used more widely (76)(79). 

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. 

As the sample RTIL in this study, we used N, N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium tetrafluoroborate, [DEME][Bp4] (Fig. 2) (Kanto Chemical Co., Tokyo, Japan), which is a hydrophilic RTIL (Sato et al., 2004). The as-received sample contains a small amount of water (126 ppm). Generally, RTILs are easily contaminated by vacuum drying to reduce H2O, so we used the sample without further purification. Mixtures were prepared by dissolving RTILs in a dry box, under a flow of He gas to exclude atmospheric H2O. The amoxmt of water was estimated on the basis of the Karl-Fischer titration method. Special care was taken not to contaminate chemicals further with atmosphere. For H2O mixtures, distilled water (Wako Pure Chemical Co. Japan), was used, while D2O (99.9%) (Cambridge Isotope Laboratories, Inc.) was used for D2O mixtures. H2O concentrations, x, ranged from 0.0 to 98.5 mol% H2O. H2O-D2O mixtures are represented as (l-y)H20 yD20. Sample solutions were prepared simply by dissolving the required amormts of water in [DEME] [BFJ in the dry box fUled with He gas. 

Kaibutilate [4849-32-5] Kail-Fischer method Karl Fischer titration Karl Fischer titrations Karmex... 

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 water content should be and is increasingly determined during RM preparation by Karl Fischer titration. The principle of this method is that it quantifies water selectively by measuring the consumption of iodine. During the titration, iodine oxidizes methylsulfite, formed from methanol and sulfur dioxide in a first step, to methylsulfate under stoichiometric involvement of water. Complete reac-... 

Applications The coulometric Karl Fischer titration is a widely used moisture determination method (from ppm to 100%). In the presence of water, iodine reacts with sulfur dioxide through a redox process, as follows ... 

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. 

One of the most important applications of the dead-stop end-point method is the Karl Fischer titration of water the titrant usually consists of I2 amd S02 with pyridine in methanol, which reacts with H20 as follows ... 

Interpretation of measurements of methods X-ray fluorescence spectrometry (Janssen and van Espen [1986] Arnold et al. [1994]), X-ray diffraction spectra (Adler et al. [1993]), NMR spectra (HIPS, Wehrens et al. [1993a]), HPLC retention indices (RIPS, Wehrens [1994]), Karl Fischer titration (HELGA, Wunsch and Gansen [1989]). 

The near-IR technique has been used very successfully for moisture determination, whole tablet assay, and blending validation [23]. These methods are typically easy to develop and validate, and far easier to run than more traditional assay methods. Using the overtone and combination bands of water, it was possible to develop near-IR methods whose accuracy was equivalent to that obtained using Karl-Fischer titration. The distinction among tablets of differing potencies could be performed very easily and, unlike HPLC methods, did not require destruction of the analyte materials to obtain a result. 

Thermogravimetry (TG) is a measure of the thermally induced weight loss of a material as a function of the applied temperature [39], Thermogravimetric analysis is restricted to studies involving either a mass gain or loss, and it is most commonly used to study desolvation processes and compound decomposition. Thermogravimetric analysis is a very useful method for the quantitative determination of the total volatile content of a solid, and it can be used as an adjunct to Karl Fischer titrations for the determination of moisture. 

The amount of water present is fundamental to the stability of confectionery products. Unsurprisingly, therefore, measuring water content is an important exercise. Various methods are used. Some oven drying moisture content determinations are still carried out. This sort of work is difficult since the moisture contents are normally low and the samples can only be dried with difficulty. In particular, there are problems in drying the product in a reasonable time without charring it. Various other methods of water content determination are in use. One such is the Karl Fischer titration. 

The Karl Fischer titration is a generally accepted method for the determination of moisture in a sample [2],... 

Explain the bipotentiometric method for detecting the end point in a Karl Fischer titration. Why is it called a bipotentiometric method ... 

Distinguish between the volumetric and coulometric methods for the Karl Fischer titration. 

End-point Detection The end-point of the Karl Fischer titration may be determined quite easily by adopting the electrometric technique employing the dead-stop end-point method. When a small quantum of e.m.f. is applied across two platinum electrodes immersed in the reaction mixture, a current shall tend to flow till free iodine exists, to remove hydrogen and ultimately depolarize the cathode. A situation will soon arise when practically all the traces of iodine have reacted completely thereby setting the current to almost zero or veiy close to zero or attain the end-point. 

An important source of error in nonaqueous conductance measurements is the presence of water in the system. As little as 1 X 10 "4 M water (2mg/l) may cause errors in many solvents. The difficulties faced in maintaining anhydrous conditions are formidable. Closed cell systems for handling solvents and salts have been described earlier. The most widely used method for measuring the water content of a solvent at low levels is still the Karl Fischer titration. 

Ordinarily water content may be determined by a Karl Fischer titration, but for the low concentrations in aliphatic hydrocarbons this method is filled with difficulties. To obtain even modest accuracy such as 5 ppm at HtO levels about or below 30 ppm as specified by the German Standard DIN S1777 relatively large eluent volumes (>2001 ) are required. On the other hand, the absolute and relative retentions are sensitive to 1 to 2 ppm of water consequently, two different batches of eluent with identical water content according to the above mentioned Karl Fischer titration can yield different retention values. Therefore, it is impossible to use titration as the sole method for eluent standardization. The reproducibility of adsorption chromatography, however, can be increased by continuously recycling a sufficiently lapge volume in a closed system to maintain equilibrium. 

The absolute methods (meaning no independent calibration is necessary) for determining H20t include manometry (Newman et al., 1986), Karl-Fischer titration (Behrens et al., 1996), and nuclear reaction analyses (NRA). NRA is a bulk method for H20t and requires a density estimate to convert data to weight percent. Secondary ion mass spectrometry (SIMS) can measure H20t, but it requires... 

In their Progress Report No 20-310 (Ref 20) are given descriptions and evaluations of the following methods of moisture detn a)Abder-halden Drying Procedure (by loss of wt) b)New Procedure for Determination of Moisture by Loss of Weight c)Oven-Drying at 130° d)Modified Karl Fischer Titration Apparatus for Use with AN Coated with ZnO e)Q-Metry Method (attempts to use this method were unsuccessful)... 

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