Water determination, Karl Fischer

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

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. 

Specifications and Analytical Methods. Vinyl ethers are usually specified as 98% minimum purity, as determined by gas chromatography. The principal impurities are the parent alcohols, limited to 1.0% maximum for methyl vinyl ether and 0.5% maximum for ethyl vinyl ether. Water (by Karl-Fischer titration) ranges from 0.1% maximum for methyl vinyl ether to 0.5% maximum for ethyl vinyl ether. Acetaldehyde ranges from 0.1% maximum in ethyl vinyl ether to 0.5% maximum in butyl vinyl ether. 

The main objective of the lEA PYRA Round Robin was to determine the interlaboratory precision and methods applied for elemental composition, water, pyrolytic lignin and main cotiqjounds. Two poplar oils were analysed by the lEA PYRA participants. It was concluded that the precision of carbon and hydrogen was very good, liquid sample handling plays a very important role in the C, H analysis, water by Karl-Fischer titration was acceptable, but should be checked carefully, and the method for the determination of pyrolytic lignin should be improved (3). 

Essential oils - Determination of water content - Karl Fischer method... 

Water in these oils is measured over the wavelength range of 3400-3250 cm with no baseline correction applied. This range shows sensitivity to both the baseline shift due to low levels of water contamination and the hydrogen-bonded OH stretch response characteristic for higher levels of water contamination in these oils. The IR response for this lubricant class is insufficient to determine low levels of water contamination. Karl Fischer titration is recommended for low-level water determination for petroleum turbine and hydraulic oils. 

In current industrial practice gas chromatographic analysis (glc) is used for quality control. The impurities, mainly a small amount of water (by Karl-Fischer) and some organic trace constituents (by glc), are determined quantitatively, and the balance to 100% is taken as the acetone content. Compliance to specified ranges of individual impurities can also be assured by this analysis. The gas chromatographic method is accurately correlated to any other tests specified for the assay of acetone in the product. Contract specification tests are performed on product to be shipped. Typical wet methods for the determination of acetone are acidimetry (49), titration of the liberated hydrochloric acid after treating the acetone with hydroxylamine hydrochloride and iodimetry (50), titrating the excess of iodine after treating the acetone with iodine and base (iodoform reaction). 

Determination of water content—Karl Fischer method ISO 11021) A reagent (Karl Fischer reagent without pyridine) is used for the reaction of the absorbed water from an essential oil. The reagent is produced by titration, using a Karl Fischer apparatus. The nal result of the reaction is obtained by an electronic method. 

ISO/DIS 11021 , Essential oils—Determination of water content—Karl Fischer method, ISO, 1999, Geneva, Switzerland, www.iso.org (accessed January 2014). 

Squirrel has also reported on the fact that with some polymers, in addition to the initial free water content of the polymer, water is produced during heating. He observed this in the case of polyethylene terephthalate and for this reason, prefers to determine water by Karl Fischer titration. 

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. 

Methods for analysis of AE are well established. ASTM standard D4252 specifies determination of water by Karl Fischer titration, pH of a 1% aqueous solution, hydroxyl number by phthalation, and PEG by extraction, as well as other tests (19). NMR determination of ethoxy content is the subject of CTFA Method J 3-1 (96). 

An ISO standard, 6384-1981, specifies methods of analysis for ethoxylated fatty amines Apparent pH is determined at a 5% concentration in 50 50 methanol/water, water by Karl Fischer titration, amine types by sequential titrations, EO content by HI cleavage, corrected, and PEG by ion exchange chromatography (30). Most of these procedures are discussed in Section II of this chapter. A note on apparent pH the method of calibration is with buffers prepared in methanol/water. This differs from the practice in most chemical laboratories. 

Karl Fischer reagent A mixture ofU and SO2 dissolved in pyridine - MeOH used as a titrant for water with which HI is liberated and the pH determined with a meter. 

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. 

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]. 

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. 

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. 

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

For the determination of small amounts of water, Karl Fischer (1935) proposed a reagent prepared by the action of sulphur dioxide upon a solution of iodine in a mixture of anhydrous pyridine and anhydrous methanol. Water reacts with this reagent in a two-stage process in which one molecule of iodine disappears for each molecule of water present ... 

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. 

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... 

Experiment Ten different positions within the conditioner representing typical and extreme locations relative to the air inlet/exhaust openings were selected for analysis. Eight tablets were picked per position their water content was accurately determined on a tablet-to-tablet basis using the Karl Fischer technique. Table 4.7 gives an overview of all results ... 

MOISTURE.dat Section 4.4 At 10 selected locations inside a dryer samples of eight tablets each were drawn to determine water content by the Karl Fischer method using MULTI, the hypothesis Ho is tested that all 10 sample means and standard deviations are indistinguishable. 

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

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. 

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