Karl Fischer titration for water

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

The n-butanol (99.7 mole% stated purity) was from Malinckrodt, and n-butoxyethanol (99+ % stated purity) was from Aldrich. Each was analyzed by gas chromatography for impurities and by Karl Fischer titration for water, and used without further purification. The water was distilled. 

The analytical chemistry of redox reactions in nonaqueous solvents has received less attention than acid-base reactions in these solvents. It should be a fruitful subject for future study. Thus far the Karl Fischer titration for water has been the most... 

Utility-grade pH meters usually cost about 100-300. Most are battery operated, and thus portable generally they offer enough sensitivity to be used in many quality-control applications and out in the field. Their relative accuracy is about +0.1 pH unit, and they have taut-band meter movements. General-purpose pH meters are more often line operated, and cost about 300-700. For the extra cost, they usually offer better stability and accuracy ( 0.05 pH or 3 mV), larger taut-band scales, and extra features such as a recorder output, mV scales, and a constant-current jack for performing polarized electrode measurements or dead-stop titrations such as the Karl Fischer titration for water determination. 

O—H, and N—H. These bands enable the quantitative characterization of polymers, chemicals, foods, and agricultural products for analytes such as water, fatty acids, proteins, and the like. In many cases, the use of NIR reflectance spectroscopy has been able to replace time consuming, classical wet chemical analyses, such as the Kjeldahl method for protein nitrogen and the Karl Fischer titration for water content. The NIR region has been used for qualitative studies of hydrogen bonding, complexation in organometallic compounds, and solute-solvent interactions because the NIR absorptions are sensitive to intermolecular forces. 

The significance of the mercaptan and sulfide interference on the Karl Fischer titration for water levels in the 0.005 to 0.02 mass % range has not been determined experimentally. At these low water levels, however, the interference can be expected to be significant for mercaptan and sulfide levels of less than 500 pg/g (ppm) (as sulfur). 

The solubility of water in a water-immiscible solvent at water activity 1 can be determined by equilibrating the solvent with pure water, followed by water analysis, for example, by Karl Fischer titration. At water activities lower than 1, lower amounts of water dissolve in the solvents, as shown in Figure 1.3. It should be noted that the solubility of water in the solvent changes when solvent composition is changed, for example, by dissolving substrates (Figure 1.3). In a hydrophobic solvent the increase in solubility of water can be substantial when substrates are dissolved in it. 

The most common end-point detection method for the Karl Fischer titration for determining water (see Section 20C-5) is the amperometric method with dual polarized electrodes. Several manufacturers offer fully automated instruments for use in performing these titrations. A closely related end-point detection method for Karl Fischer titrations measures the potential difference between two identical electrodes through which a small constant current is passed. 

Figure 28B represents a titration situation which has extended use in laboratories as the Karl Fischer titration for the determination of water. This titration will be covered in detail later. In the meantime the example used wiU be that of the titration of As + by I2. This is a titration that can be carried in food analysis under the proper conditions. The arsenic reaction is... 

Feigner, A., Schlink, R., Kirchenbiihler, R, Faas, B., and Isengaid, H. D., Automated Karl Fischer titration for liquid samples—Water determination in edible oils. Food Chemistry, 106 1379-1384, 2008. 

The absolute determination of the moisture content of gases can be carried out by the absorption method (allowing gas to flow through a silica-gel bed or allowing it to be absorbed by methanol and then determining the water content by Karl-Fischer titration, for example). A detailed description of these and other special methods are given in Refs. [3,7]. 

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. 

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]. 

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]. 

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. 

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 submitters obtained N-Boc-4-hydroxyproline methyl ester from Synthetech, Inc. [Albany, OR, (503) 967-6575] or Bachem California [Torrance, CA, (310) 530-1571] and dried THF over 4A molecular sieves for two days prior to use (Karl-Fischer titration gave 145 pg/mL water). The checkers purchased N-Boc hydroxyproline methyl ester (97%) and fert-butyl acetate (99+%) from Aldrich Chemical Co. and obtained THF (HPLC grade) from Fisher Scientific. 

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. 

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 (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. 

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. 

Accessories are available for some instruments to enable photometric or voltammetric titrations (e.g. the Karl-Fischer determination of water) to be performed. Others allow the direct transfer of weighings from an electronic balance into RAM where they can be used in the computation of results. 

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