Karl Fischer Titration of

The Karl Fischer titration,30 which measures traces of water in transformer oil, solvents, foods, polymers, and other substances, is performed half a million times each day.31 The titration is usually performed by delivering titrant from an automated buret or by coulometric generation of titrant. The volumetric procedure tends to be appropriate for larger amounts of water (but can go as low as 1 mg H20) and the coulometric procedure tends to be appropriate for smaller amounts of water. 

Anode solution contains an alcohol, a base, S02, I-, and possibly another oiganic solvent. Methanol and diethylene glycol monomethyl ether (CH3OCH2CH2OCH2CH2OH) are typical alcohols. Typical bases are imidazole and diethanolamine. The organic solvent may contain chloroform, formamide, or other solvents. The trend is to avoid chlorinated solvents because of their environmental hazards. When analyzing nonpolar substances such as transformer oil, sufficient solvent, such as chloroform, should be used to make the reaction homogeneous. Otherwise, moisture trapped in oily emulsions is inaccessible. (An emulsion is a fine suspension of liquid-phase droplets in another liquid.) 

The net reaction is oxidation of S02 by I2, with formation of ROSO3. One mole of 12 is consumed for each mole of H20 when the solvent is methanol. In other solvents, the stoichiometry can be more complex.31 

It is routine to standardize Karl Fischer reagents, or even a coulometer, with a standard such as lincomycin hydrochloride monohydrate, which contains 3.91 wt% H20. The coulometer is run until the end point is reached, indicating that the Karl Fischer reagent is dry. A port is opened briefly to add solid lincomycin, which is then titrated to the same end point. Then an unknown is added and titrated in the same manner. Find the wt% HzO in the unknown. 

SOURCE Data from W. C. Schinzer, Pfizer Co., Michigan Pharmaceutical Sciences, Portage, MI. 

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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 ... 

The Karl Fischer titration of water uses a buret to deliver reagent or coulometry to generate reagent. In bipotentiometric endpoint detection, the voltage needed to maintain a constant current between two Pt electrodes is measured. The voltage changes abruptly at the equivalence point, when one member of a redox couple is either created or destroyed. 

Water the Aquatest I does a coulometric Karl Fischer titration of water dissolved in oils. 

Vapor Pressure Measurements. Total vapor pressures were measured at 30°C with a Texas Instruments quartz spiral gauge. The procedure used was similar to that given previously (5). The concentration of water after the experiment was checked by Karl Fischer titration, while that of ether was found by weighing the cell before and after the vapor pressure determination the loss of weight was that of ether. Since Sb( V) interferes with the Karl Fischer titration of water, the water concentration in the HSbClG solutions was also obtained from the loss of weight of the cell. 

Karl Fischer titration of a dry methanol solution (15 mL) of the resulting cerium(lll) chloride (731-817 mg) shows that it contains 0.71-0.94% of water and can be represented by a formula CeCl3(H20)o.io-0.i3- This result indicates that this procedure affords practically anhydrous cerium(lll) chloride, although Evans, et al. reported that gradual heating to 150°C at 0.03 mm over 3 hr, followed by further... 

Most titrations are carried out in aqueous solution, including all those described above. In some circumstances, however, it is advantageous to use other solvents, especially organic solvents. Such nonaqueous titrations are normally used for acid-base reactions, but redox reactions may also be applicable. The Karl-Fischer titration of water, in particular, is based upon redox reactions in a nonaqueous medium. 

A well-known use of pyridine as a cosolvent is in the Karl Fischer titration of water in organic solvents, described in Bassett et al. (1978). A solution of iodine and sulfur dioxide in pyridine/methanol or pyridine/cellosolve is fairly stable in the absence of water, but when it is added to a sample of a solvent containing water, reaction 7.7 occurs quantitatively. 

Scholz, E. Karl Fischer titrations of aldehydes and ketones. Anal. Chem. 57 2965-2980, 1985. 

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). 

For efficiency of desiccants in drying acetone see Burfield and Smithers [7 Org Chem 43 3966 1978]. The water content of acetone can be determined by a modified Karl Fischer titration [Koupparis and Malmstadt A/w/ Chem 54 1914 1982]. 

A colourless, odourless, neutral liquid at room temperature with a high dielectric constant. The amount of water present can be determined directly by Karl Fischer titration GLC and NMR have been used to detect unreacted propionic acid. Commercial material of high quality is available, probably from the condensation of anhydrous methylamine with 50% excess of propionic acid. Rapid heating to 120-140° with stirring favours the reaction by removing water either directly or as the ternary xylene azeotrope. The quality of the distillate improves during the distn. 

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]. 

E. SCHOLZ, Karl Fischer Titration Determination of Water, Springer Verlag, Berlin, 1984, 150 pp. 

To remove water, commercial ionic liquids used for fundamental research purposes should be dried at 60 °C in vacuo overnight. The water content should be checked prior to use. This can be done qualitatively by infrared spectroscopy or cyclovoltametric measurements, or quantitatively by Karl-Fischer titration. If the ionic liquids cannot be dried to zero water content for any reason, the water content should always be mentioned in all descriptions and documentation of the experiments to allow proper interpretation of the results obtained. 

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. 

Toluene and THF were purchased from Fisher Scientific and dried over 4A molecular sieves overnight prior to use. The water content of the solvents was <50 pg/mL by Karl Fischer titration. 

Karl Fischer titration. This titration procedure determines the concentration of water present in AOS samples containing 40-70 wt % water. In Karl Fischer titrations, each equivalent of base interferes as 18 g of water. Since AOS samples are basic, water values obtained must be corrected for side reactions of reagent with alkaline material. Alkalinity must be determined to correct for this error. 

Add sufficient water (normally 1 % w/w) to transform anhydrides to avoid pH drift of pastes (check by Karl Fischer titration)... 

Fischer titration may not be reliable for water concentration determination in the presence of highly hygroscopic electrolytes, e.g., LiCl/DMAc [119]. This conclusion has been also verified for TBAF/DMSO, by adding known amounts of water to the solvent system, followed by determination of the water content by Karl-Fischer titration. Whereas the added water ranged from 0.23 to 1.19 mol H, that determined by titration ranged from 0.21 to... 

The availability of water, i.e. the water activity, in a material is of great importance for its biological and biochemical properties. It depends both on the water content, and significantly on the nature of the structural bond of water molecules, in other words, how strongly they are retained by the matrix. Thus, for similar water contents, when determined by Karl Fischer titration, quite different water activities may be obtained for different materials. This is of paramount importance for RM stability. 

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. 

Glacial acetic acid, pure or mixed with other solvents, is one of the most attractive solvents for the titration of amines. Commercial acetic acid containing not more than 1% of water (Karl Fischer titration check) can be used in normal practice for the highest accuracy, however, the water content must be lowered to about 0.01% by addition of acetic anhydride and standing for 24 h not more than the stoichiometric amount of acetic anhydride should be used in order to avoid possible reactions with active hydrogen-containing analyte components such as primary or secondary amines or alcohols. A similar procedure is followed in the preparation of perchloric acid titrant from the commercial... 

Although the DL 40 was capable of performing Karl Fischer water titrations and Mettler developed a separate microprocessor-controlled push-button operated DL 18 KF titrator, they also introduced as an all-purpose apparatus the improved DL 40 RC (see Fig. 5.11) with a dual titration head and with a modified software program to handle the new two-component titrants for Karl Fischer titration (see pp. 204-205). The instrument can also be expanded into an automatic series titrator by connecting the RT 40 sample transport for 16 samples and storage of 50 sample weights from a connected balance this series routine can be interrupted at any time after completion of the titration in progress. 

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 produced bio oil was analyzed by GC-MS and Karl Fischer titration. The surface area of the spent catalyst was also measured. Regeneration of the spent catalyst was performed at 450°C for 2h in a muffle oven in the presence of air. The regenerated catalysts were characterized in a similar fashion as the fresh ones. 

Pyrolysis of pine wood biomass was conducted at 400°C followed by catalytic deoxygenation at 450°C. The yield of the different product phases was gravimetrically determined. The gas yield was calculated by the difference. The water content of the bio oil was measured by Karl Fischer titration. The yield of the different product phases is given in Table 3, calculated from the pyrolyzed biomass. The non-catalytic experiment was carried out in the same way as the catalytic ones with the exception that the upper catalyst bed was empty. 

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. 

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