Karl Fischer titration moisture content determination

Karl Fischer Titration Moisture content of reference standards is commonly and accurately determined by Karl Fischer (KF) titration. KF titration determines total water content, including both the free water and water of hydration trapped in the crystal structure. Coulometric KF-titration is the most sensitive application of the method and is normally used for the small amounts of water found in reference standards. A volumetric technique is available for samples containing large amounts of water. Interference is a relatively common problem in KF titration and thus, due caution must be exercised in the interpretation of KF results. Reagents have been designed to cope with interfering functional groups.48-50... 

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. 

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. 

Moisture in solid sugars is determined generally by oven drying in liquid products, by Karl Fischer titration. Inorganic content is determined by either conductivity in solution, or sulfated ash gravimetric procedures. 

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. 

The amount of water present is fundamental to the stability of confectionery products. Unsurprisingly, therefore, measuring water content is an important exercise. Various methods are used. Some oven drying moisture content determinations are still carried out. This sort of work is difficult since the moisture contents are normally low and the samples can only be dried with difficulty. In particular, there are problems in drying the product in a reasonable time without charring it. Various other methods of water content determination are in use. One such is the Karl Fischer titration. 

Moxalactam disodium reference standards are equilibrated under controlled humidity conditions to raise the moisture content to a level where the material can be handled by ordinary means. This is accomplished by spreading a thin layer of material in a wide mouth weighing bottle which is placed in a 42% relative humidity chamber for about 16 hours before use. The 42% relative humidity chamber is prepared by storing a saturated aqueous solution of potassium carbonate in a desiccator or closed chamber held at room temperature. After a 16 hour equilibration period, the water content of the standard is determined by Karl Fischer titration. The activity of the standard is then corrected for the water content of the equilibrated reference material. Experience indicates that the water content of a properly equilibrated reference material should be in the range of 10 to 12%. 

This study of methods to determine the moisture content of humic substances has yielded no absolute values for moisture content. The loss on drying shows no end point for water loss and the potential interferences of the Karl Fischer titration prevent definition of absolute values. Certainly, additional research needs to be done in this area. For example, techniques such as NMR and IR might be utilized to define and correlate the moisture status of these substances. In many cases it is sufficient to have a reference point to bring these substances to for comparison purposes. Based on Figure 1, loss on drying at 60°C should be the most consistent reference point, however, the interlaboratory study results showed very poor agreement. Based on this limited study we conclude that the Karl Fischer method gives more consistent results on these samples. 

During the collection of the material, three samples were taken at the beginning, middle and end of the procedure for moisture determination by Karl Fischer titration. Furthermore, samples were taken from each bag before sealing and analysed for their microbe content and insolubility index at 24°C. The results indicated that no microbial contamination occurred during the preparation of the material and that the moisture content achieved (ranging from 2.4 to 3.3% mass fraction) was suitable to avoid microbiological growth [30,31]. 

The moisture content of the material was determined by Karl Fischer titration on ten samples selected during the bottling procedure. The mean moisture mass fraction measured was (2.24 0.36)%. 

Measurement of moisture uptake is typically done by either of two general methods. The classical approach involves equilibration of solid at several different humidities and the subsequent determination of water content either by gravimetric or analytical methods such as Karl Fischer titration or loss on drying. Moisture adsorption or desorption may be measured by use of this method and the pro-... 

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]. 

Water content above a threshold value is critical because water reacts with isocyanate to form urea in a reaction competitive to urethane group formation. The determination is a straightforward application of the Karl Fischer titration, but precautions are necessary when weighing and transferring the sample because of the ease with which the polyol absorbs moisture from laboratory air. Usually, the sample is weighed out by difference from a disposable syringe. 

In 2009, the ASTM International Committee D02 on Petroleum Products and Lubricants has approved a new ASTM method which covers the determination of moisture content in new and in-service lubricants and additives by relative humidity sensor. The method, D7546 - 09 Standard Test Method for Determination of Moisture in New and In-Service Lubricating Oils and Additives by Relative Humidity Sensor, offers users an alternative to moisture testing by Karl Fischer titration. 

The presence of any appreciable amount of moisture in solvents used in a two-component polyurethane system can react with isocyanate crosslinkers and thus impair crosslinking efficiency. Therefore, moisture content is one of the important properties of solvents such as ketones and esters, which are used in two-component polyurethane coatings. Moisture content is normally determined by the Karl-Fischer titration method. 

Moisture content determination of an essential oil can be carried out by Karl-Fischer titration, GC, spectroscopy, or electrometric methods. Drying of an essential oil is realized by the addition or filtering through a desiccating agent (e.g., anhydrous sodium sulfate). A simple test to check the presence of moisture in an essential oil is carried out by mixing 0.5-mL essential oil with 1-mL carbondisulfide. A clear solution indicates the absence of moisture. 

Moisture content has been classically determined by Karl Fischer titration using semi-automated apparatus as described in ASTM E 203. This has been largely replaced in routine operations by weight loss determination using automated balances, often with microwave heat input (see Volatile Loss in the foregoing). Such operations are covered in ASTM D 6980. With suitable columns and detectors, GC methods can be used, particularly in combination with TGA loss of water. Proton NMR is also sensitive and can distinguish between water of hydration and physically adsorbed moisture. 

The pnirity of ILs was checked by IH NMR, 13C NMR and IIB NMR spectroscopy. The water content was determined by Karl-Fischer titration, and were found to be less than 100 ppan. Before use, the support material and ILs were subjected to vacuum treatment with heating to remove traces of adsorbed moisture. 

Ammonium chloride is analyzed by treatment with formaldehyde (neutralized with NaOH) and the product HCl formed is analyzed by titration using an acid-base color indicator such as phenolphthalein. Alternatively, it may be mixed with caustic soda solution and distdled. The distillate may be analyzed for NH3 by titration with H2SO4 or by colorimetric Nesslerization or with an ammonia-selective electrode (APHA, AWWA, WEF. 1995. Standard Methods for the Examination of Water and Wastewater. 19th ed. Washington, DC, American Pubhc Health Association). The presence of ammonia or any other ammonium compound would interfere in the test. The moisture content in NH4CI may be determined by Karl—Fischer method. 

Refs l)K.Van Keuren, "A Procedure for Chemical Analysis of Composition A-3 , NAVORD Report 1781, US Naval Ordnance Laboratory, White Oak, Md. (1951) la)S.M. Kaye, PATR 1936 (1953) (Nonaqueous titration method for detn of RDX content in Comp A-3) 2)Anon, Military Explosives , TM 9-1910 (1955), 271 (Identification of Composition A-3) 3)Purchase Description X-PA-PD-940 (1956) (Karl Fischer moisture detn) 4)Federal Test Method Std No 141 (1958), Method 4082 (Karl Fischer moisture detn) 4a)C.C.Jamison, "Determination of Nitrogenous Coumpounds of Ordnance Interest by Chromous Chloride Reduction , PicArsn, FRL TechMemo ACS-3-60 (I960) 5)U.S. 

The chemical methods of water determination invoke the concepts of direct titration of the water or a chemical reaction between the water and specific reagents that causes the evolution of gases the water is determined by measurement of the volume produced. Chemical methods used for determining moisture also include (1) application of the Karl Fischer method of determining water content, and (2) reaction of quicklime with water in coal and subsequent measurement of the heat generated by the reaction. 

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