Solvent 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. 

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... 

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... 

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. 

Study of the effect of small amounts of water in the liquid, organic phase on the polymerization of bisphenol-A and HFB in several solvents.[14] Solvents were rigorously dried and assayed for water content by potentiometric Karl Fischer titration. A series of polymerizations catalyzed and uncatalyzed in each solvent were carried out in which the water content was increased incrementally. Polymer yields and inherent viscosities were determined as a function of water content in each solvent. The optimal water content expressed as the mole ratio of water to catalyst shows that the necessary water level varies substantially with solvent (see Table V and Figure 1-3). 

IL. Dilute solution viscosity measurements were done at 30 with the appropriate Ostwald-Fenske capillary viscometers. The water content of all organic solvents, used as the liquid phase in solid-liquid PTC runs was analyzed by potentiometric Karl Fischer titration using a Metrohm AG CH 9100 model automatic titrator. 

Determination of the Effect of Water on Poljnnerization. To a solution of 4.76 mmole of HFB and 4.76 mmole of Bis-A in 20 ml of the appropriate solvent of known water content was added 20.6 mmole of K2CO3 and 1.32 mmole of 18-crown-6 ether. The crown ether, when necessary was dried by complexation with acetonitrile. Water content of solvent and catalyst was determined in all runs by Karl Fischer titration. Known microliter quantites of water in increments of lOyl were then added to the reaction mixture. The magnetically stirred, heterogeneous mixture was heated in an oil bath and maintained under N2. Upon cooling to room temperature, the reaction mixture was slowly poured into ca. 300 ml of a nonsolvent vigorously stirred in a blender. The filtered solids were washed three times with 300-ml portions of distilled water. 

Attention to catalyst preparation and reaction conditions is of crucial importance for the success of an Ir-catalyzed allylic substitution, because many ligands are altered by C—H activation at aryl (see above) or CH3 groups. For most reactions, tetrahydrofuran (THF) is the preferred solvent it is important that dry THF (<35gg H20mr THF, Karl Fischer titration) is used for catalyst preparation because this step is very sensitive to water. The following procedures have been appHed. 

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. 

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 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. 

The Karl Fischer titration requires 20 to 45 min (depending on sample being tested) to complete calibration, blank determination, sample equilibration (extraction in Karl Fischer solvent), and final testing. 

Propargyl alcohol (2-propyn-l-ol, boiling point 114°C) is a colorless volatile liquid with an unpleasant odor that is the only commercially available acetylenic primary alcohol. It is miscible with water and with many organic solvents. The commercial material is specified as 97% minimum purity, determined by gas chromatography or acetylation. Moisture is specified at 0.05% maximum (Karl-Fischer titration). Formaldehyde content is determined by bisulfite titration. 

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... 

Some of the traditional methods used for the characterization of bar soaps are moisture, free acid or free alkalinity, total soap, and chloride (salt). Moisture determinations are typically run by Karl Fischer titration. However, under certain circumstances, moisture can be measured gravimetric ally. The measure of free fatty acid or free alkalinity is typically done via a simple pH titration using phenophtha-lein or potentiometric end point. Total soap is generally done using an extraction/ gravimetric procedure the soap sample is acidified in an ethanol-water mixture, the fatty acids are extracted into a hydrocarbon solvent, and the amount of extracted... 

The main conclusions of the Round Robin were Karl-Fischer titration is recommended for analysing water in pyrolysis oils. Solids content as ethanol insolubles is accurate for white wood oils but a more powerful solvent, like a mixture of methanol and methylene chloride (1 1) is needed for extractive-rich oils. For the elemental analysis at least triplicates are recommended. Kinematic viscosity is an accurate method for pyrolysis oils. Stability index needs more clarification and testing,- Results of chemical characterisation were not very consistent. It may be necessary to prepare standard solutions with known aniounts of conqiounds for... 

Karl Fischer titration Chemical titration that is water-specific. Material can be either added directly to a solvent or heated in an oven, with the headspace purged and bubbled through solvent. Specific to water only and very precise. Units can be purchased with an autosampler. Measurement takes only a few minutes. Equipment is e3q>ensive and requires solvents. Minimal calibration required. Sample size is small, which may pose a problem for heterogeneous mixtures. 

Pyridine combines with both products. A Karl Fischer titration unit is available (A.H. Thomas Co.) for detection of the end point by means of platinum electrodes and a pH meter. A.H. Thomas Co. supplies two solutions which are to be mixed (I2 in CH3OH and SO2 in pyridine) as well as a stabilized single solution (also available from Fisher and MCB). Methyl Cellosolve has been suggested as solvent in place of methanol, A similar reagent utilizing a solution of bromine and sulfur dioxide in chloroform has been described. ... 

Maintenance of suitable levels of H2O.This can be important for running a reaction, crystallizing an intermediate, and other steps. Starting materials, reagents, and solvents may be checked before being charged to a reactor. The most convenient quantitation is usually a Karl Fischer titration. 

When the samples have been withdrawn from the vessels, suitable analytical separations must be available to analyze the reaction. This would include starting materials, products, impurities, and solvents, as appropriate. Quantitations may need to be developed for key components. Karl Fischer titrations may be needed... 

When one performs a volumetric Karl Fischer titration, there are two basic classes of reagents one-component reagents and two-component reagents. The one-component reagents contain all of the reactants (iodine, sulfur dioxide, and base) in an alcohol solvent. These reagents have a large water capacity, and they are economical and easy to use. The sample is dissolved in an alcohol, but co-solvents can be used to improve sample solubility. 

Hydrates and solvates can be prepared by crystallization in water or an organic solvent or by conversion of the anhydrous material through moisture or solvent adsorption. In quality control testing, hydrates or solvates are identified by the assay of water of crystallization or solvent found in the crystal. Water determination is achieved by Karl Fischer titration or a coulometric method or loss-on-drying by the USP method. In the preformulation study, the hot stage microscope is a useful simple technique. TGA can also be an informative tool, as shown in Figure 15. 

Purification. N. S. Moe [Chem. Scand., 21 1389 (1967)] obtained highly pure solvent for polarographic use by first drying with molecular sieves (Linde 4A) and then treatment with active alumina (Woelm, activity grade one). The final water content was shown to be about 100 p.p.m. by Karl Fischer titration. 

Many manufactured products, as well as solvents and raw materials are analyzed for their water content (percent humidity). Of all the available methods, the Karl Fischer titration is perhaps the most widely used, accounting more than 500 000 determinations performed daily world-wide. 

A special titration vessel with a side opening through which powdered solids are introduced with a weighing spoon Is used for Karl Fischer titrations. These have a distinct feature In that the solvent must be titrated before the sample Itself as It also contains water. To avoid dosing the solvent with every new sample, the vessel Is furnished with a stopcock which allows draining of the solution to make room for the next sample and for the Karl Fischer reagent to be added. 

---