Determination of water

Molecular organic compounds, including the lower aliphatic alcohols, can also be separated by I EC. The lack of a sensitive detector is a drawback. 

A very important analysis is the determination of small quantities of water in chemicals, pharmaceuticals and a host of other samples. The Karl Fischer method is widely used for this purpose, but it has some limitations. 

If an alcohol such as methanol can be separated by ion-exclusion chromatography using water as the eluent, why not do the reverse and separate water using a methanol eluent Stevens et al. [23] did just this. They added a small amotmt of sulfuric acid to the eluent and detected the chromatographic water peak by a decrease in conductivity. The main drawback with this method was a non-Unear calibration curve with very poor detection sensitivity in some concentration regions. 

Fortier and Fritz [24] separated water by lEC and devised a unique equiUbrium system for in-Hne spectrophotometric detection. This method has been refined and its capabilities expanded by continuing research by Chen and Fritz [25-27]. Water is separated chromatographicaUy from the other sample components on a short column packed with cation-exchange resin in the form using dry methanol as the eluent Detection of the water peak is made possible by addition of a low concentration of ciimamaldehyde to the methanol eluent In the presence of an acid catalyst, such as an H -cation exchanget cinnamaldehyde reacts with methanol to form the dimethylacetal. 

CgHsCH = CHCHO-I-2 CH3OH CgHsCH = CHCH(OCH3)2-1-H2O (8.9) 

Whilst it is not an additive, for completeness, the determination of water in polymers is briefly discussed here. 

Jeffs [1] has developed a versatile gas chromatographic unit (GC), described next, for the determination of water and other volatiles in vinyl, acrylic and polyolefin polymer powders. 

Maltese and co-workers [2] describe a GC procedure for determining moisture in polypropylene in which water was removed from the polymer in vacuo (molten sample), or in a stream of dry nitrogen at a pressure of 400 Pa (granular sample), and was then determined by Karl Fischer titration. 

A2 and Aj = Edwards VPC pressure controller Bj, B2 and B3 = Pressure gauges 0 to 0.2 MPa Cj, C2 and C3 = Rotameter-type flow gauges 

D = Clear plasticised PVC tubing (1.5 m x 6.4 mm bore), packed with copper sulfate crystals, CUSO4.5H2O, 44 mesh E = Katharometer F = Pneumatic sample valve G = Internal loop 

The UV spectra of cinnamaldehyde and its reaction product (an acetal) are quite different, as shown by Fig. 8.5. The necessity of an acid catalyst must be emphasized. Cinnamaldehyde dissolved in methanol will retain its own spectrum (A in Fig. 8.5) for 

TTie detector signal (Ajet), which is the change in absorbance when water passes through the detector cell is given by the following equation  

Typically, a sharp water peak is obtained in approximately 2 min. The water peak is always well separated from an earlier injection peak that is due to the sample matrix. Under favorable conditions a very short column (length 2.5 cm) can be used and a water peak obtained in as little as 20 s [17]. 

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Another important example of a redox titration for inorganic analytes, which is important in industrial labs, is the determination of water in nonaqueous solvents. The titrant for this analysis is known as the Karl Fischer reagent and consists of a mixture of iodine, sulfur dioxide, pyridine, and methanol. The concentration of pyridine is sufficiently large so that b and SO2 are complexed with the pyridine (py) as py b and py SO2. When added to a sample containing water, b is reduced to U, and SO2 is oxidized to SO3. 

Determination of Water in DMAC. DMAC is hygroscopic and precautions must be taken to minimize exposure to the atmosphere. Trace amounts of water can be deterrnined by the Kad-Fischer method. 

The quaHtative determination of water-soluble perchlorates by precipitation using methylene blue yields a violet precipitate (105). Using potassium, mbidium, or cesium salts for precipitation from ethanol—water solutions can serve as a quaHtative determination of perchlorates (106). 

Obtaining of data concerning the chemical composition of water is critical significance for monitoring water reservoirs and forecasting the quality of drinking water from different water supply sources. A dry residue is commonly used with the methods AAS, ICP-AES, ICP-MS (analysis of liquid) widely applied for determination of water composition. So it is vital to create a standard sample of the composition of dry residue of ultra-fresh Lake Baikal water, its development launched since 1992 at the Institute of Geochemistry SB RAS. 

Determination of water of different materials is one of the important tasks of the analytical chemistry. For water determination in organic solvents physical-chemical methods use side by side with the classic titration method by Karl Fisher. In particular, gas chromatography (GC), distinguished its universality and selectivity, is used. However, GC usually used for determination of relatively large quantity of water. 

Suggested method characterized by relative standard deviation of 0.02-0.1 allows determination of water in organic solvents until 0.008 mass.%. Concentrations under mentioned above can not be detected by direct GC due to residual humidity of sorbent and parts of chromatographic equipment. 

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

Another important reaction (between H2O, I2 and SO2) forms the basis of the quantitative determination of water when present in small amounts. The reaction, originally investigated by R. Bunsen in 1835, was introduced in 1935 as an analytical reagent by Karl Fischer who believed, incorrectly, that each mole of I2 was equivalent to 2 moles of H2O ... 

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

K. Johansen and P. O. Edlund, Determination of water-soluble vitamins in blood and plasma by coupled-column liquid clrromatography , 7. Chromatogr. 506 471-479 (1990). 

Determination of water phase salinity. By entering the graph in Figure 4-110 with total soluble salts, Ib/bbl of mud, at the correct volume percent of water line, the water phase salinity can be read from the left-hand scale. 

DETERMINATION OF WATER WITH THE KARL FISCHER REAGENT 16.35... 

The Karl Fischer procedure was applied to the determination of water present in hydrated salts or adsorbed on the surface of solids. The procedure, where applicable, was more rapid and direct than the commonly used drying process. A sample of the finely powdered solid, containing 5-10 millimoles (90-180 mg) of water, was dissolved or suspended in 25 mL of dry methanol in a 250-mL glass-stoppered graduated flask. The mixture was titrated with standard Karl Fischer reagent to the usual electrometric end point. A blank titration was also carried out on a 25 mL sample of the methanol used to determine what correction (if any) needed to be applied to the titre obtained with the salt. 

MAKOWER—DETERMINATION OF WATER IN SOME DEHYDRATED FOODS... 

Determination of water removal rate. This technique is usually applied to the continuous following of esterification kinetics. 

Kuvada, Determination of Water in Hydrazine by Gas Chromatography , JetPropulsionLabora-tory TR 32-362 (1962) 30) M. Roth, Pro-... 

Universal Titrimetric Micromethod for Determination of Water by Fischer Reagent . Inst-OrgKhimimZelinskogo 12, 2761-64 (1967)... 

Methods of EGA using selective sorption, condensation of effluent gases, infrared absorption and thermoparticulate analysis have been reviewed by Lodding [144]. The use of simple gas burette systems should not be forgotten and an Orsat gas analysis apparatus can provide useful measurements in studies of the decomposition of formates [169]. Problems have been encountered in the determination of water released Kiss et al. [170—172] have measured the formation of this compound from infrared analyses of the acetylene evolved following reaction of water with calcium carbide. Kinetic data may be obtained by wet methods ammonia, determined by titration after absorption in an aqueous solution, has been used to measure a—time values for the decomposition of ammonium salts in a fluidized bed [173],... 

The complete analysis of alcohol sulfates is described in the Standard Methods of the International Organization of Standards (ISO) [200] and of the American Society for Testing and Materials (ASTM) [201]. These methods describe the analysis of inorganic sulfate content, chloride content, unsulfated matter, and water as well as other analytical values. Other ISO standards describe the analysis of sodium secondary alkyl sulfates [202], determination of pH [203], determination of water content [204,205], chlorides [206], total active matter in sul fated ethoxylated alcohols and alkylphenols [207], mean relative molecular mass in sulfated ethoxylated alcohols and alkylphenols [208], sulfate content... 

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

ISO 4318 1989, Surface active agents and soaps Determination of water content—Azeotropic distillation method. 

A weighed amount of sample is dissolved in a mixture of propanone and ethanoic acid and titrated potentiometrically with standard lead nitrate solution, using glass and platinum electrodes in combination with a ferro-ferricyanide redox indicator system consisting of 1 mg lead ferrocyanide and 0.5 ml 10% potassium ferricyanide solution. The endpoint of the titration is located by graphical extrapolation of two branches of the titration plot. A standard solution of sodium sulfate is titrated in the same way and the sodium sulfate content is calculated from the amounts of titrant used for sample and standard. (d) Water. Two methods are currently available for the determination of water. 

Nodes, E.E., Mazur, P., Watson, P.F., Kleinhans, F.W., Critser, J.K. (1993). Determination of water permeability coefficient for human spermatozoa and its activation energy. Biol, of Reprod. 48,... 

Vol. 5. Aquametry A TVeatise on Methods for the Determination of Water. Second Edition (in three parts). By John Mitchell, Jr. and Donald Milton Smith... 

Otson R, Williams DT. 1982. Headspace chromatographic determination of water pollutants. AnalChem 54 942-946. 

Avdeef, A., Comer, J. E. A., Thomson, S. J. pH-metric log P. 3. Glass eledrode calibration in methanol-water, applied to pK determination of water-insoluble substances. Anal. Chem. 1993, 65, 42-49. 

Takacs-Novak, K., Box, K. J., Avdeef, A. Potentiometric pKa determination of water-insoluble compounds. Validation smdy in methanol/water mixmres. Int. J. Pharm. 1997, 151, 235-248. 

Avdeef, A., Box, K. J., Comer,). E. A., Gilges, M., Hadley, M., Hibbert, C Patterson, W Tam, K. Y. pH-metric log P. 11. pfCa determination of water-insoluble drugs in organic solvent-water mixtures. 

Summation of the results of the determinations of water, organic solvents, mineral impurities and the organic components amounts to loo %. The results of methods employed to analyze the substance other than these given above are not used for the calibration of the assigned value but are reported to support the results obtained by the defining methods. For most reference substances intended as assay standards the assigned content is normally expressed as is so that it is essential (when establishing the CRS) to determine the content of water and residual solvents for a non-specific assay and also, for a selective assay, to determine the content of impurities. 

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