Karl Fischer titration standardization

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. 

Ordinarily water content may be determined by a Karl Fischer titration, but for the low concentrations in aliphatic hydrocarbons this method is filled with difficulties. To obtain even modest accuracy such as 5 ppm at HtO levels about or below 30 ppm as specified by the German Standard DIN S1777 relatively large eluent volumes (>2001 ) are required. On the other hand, the absolute and relative retentions are sensitive to 1 to 2 ppm of water consequently, two different batches of eluent with identical water content according to the above mentioned Karl Fischer titration can yield different retention values. Therefore, it is impossible to use titration as the sole method for eluent standardization. The reproducibility of adsorption chromatography, however, can be increased by continuously recycling a sufficiently lapge volume in a closed system to maintain equilibrium. 

Karl Fischer Titrators These titrators measure moisture (water) in a variety of samples. The titrant s concentration is usually expressed as titer, or grams of water consumed per milliliter of titrant. Standardization involves a certified primary standard (a material containing a known amount of water). This standard is purchased in ampules and is accompanied by a test certificate indicating traceability to a reference material. In addition, the titrator should be calibrated for the titrant volume measurement. The moisture can be measued by weight loss upon drying and checked against the Karl Fischer results. 

Example Standardization and Blank Correction in 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%. 

For the reasons that we have just described, the measurement of residual moisture within an isolated vial or ampoule is a difficult undertaking. Joan May, in this book, also deals with this topic and she explains how the FDA developed very accurate standardized techniques to execute these determinations by chemical Karl Fischer titration or thermogravimetric techniques. The only drawback is that, in both cases, the material is destroyed. 

Correlation of total, bound, and surface water in raw materials was the topic of a paper by Torlini and Ciurczak in 1987.The NIR was calibrated by Karl Fischer titration, differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA) for the various water types. NIR could distinguish surface from bound water, whereas standard loss on drying (LOD) could not. 

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 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... 

Free water in jet fuels can be detected by the use of the Karl Fischer titration method (ASTM D-1744) or by observing color changes when chemicals go into aqueous solution (ASTM D-3240). The standard water reaction test for jet fuel (ASTM D-1094, IP 289) is the same as for aviation gasoline, but the interface and separation ratings are more critically defined. Test assessment is by subjective visual observation and, although quite precise when made by an experienced operator, the test can cause rating difficulties under borderline conditions. As a consequence, a more objective test, known as the water separometer test, is now included in many specifications (ASTM D-2550). 

Kerosene, because of its higher density and viscosity, tends to retain fine particulate matter and water droplets in suspension for a much longer time than gasoline. Free water in kerosene can be detected by the use of a Dean and Stark adaptor (ASTM D-4006, IP 358) (Fig. 7.3), by the Karl Fischer titration method (ASTM D-1744, ASTM D-6304), by the distillation method (ASTM D-95, IP 74), or by a series of alternate tests (ASTM D-4176, ASTM D-4860). The standard water reaction test method (ASTM D-1094, IP 289) can also be used. 

In addition to the air-oven methods for moisture measurement, there is also a Karl Fischer titration method. In this method, moisture is considered to be the moisture that is extracted by methyl alcohol in a sealed container with ground soybeans for a specified time period (Paulsen, 1991). This water-alcohol extract is placed in a reaction chamber where the water reacts with iodine. The amount of iodine used in titration is a measure of the amount of water in the soybeans. Soybean samples tested with the Karl Fischer method usually show about 0.2 percentage points lower moisture than those tested with the USDA air-oven method (Paulsen, 1991). The standard deviations of differences from duplicate samples were lower (0.07 percentage points) for the USDA air-oven method than for the Karl Fischer method (0.11 percentage points) (Paulsen, 1991). 

Karl Fischer titration is specified for use in plasticizers. The method determines free and Itydration water in solid and liquid samples. In most cases, automatic titration is used and this is the main subject of standard but manual titration method is also included in the appendix. The sample containing a maximum of 100 mg of water is dissolved in a suitable solvent and titrated with Karl Fischer reagent which consists of iodine, sulfur dioxide, organic base, and solvent. The titration end-point is determined amperometrically. The ASTM method lists numerous substances in which the presence of water can be determined. There is also a list of substances which interfere with measurements. 

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. 

In this Karl Fischer titration procedure a methanol extract of the sample is titrated with standardized Karl Fischer reagent to a visual end-point. 

Karl Fischer Reagent—Standard commercially available reagents for coulometric Karl Fischer titrations. 

ISO standard 893 covers analysis of alkanesulfonates, specifying assay by gravimetry, alkane monosulfonates by titration or extraction (Sections 2(a) and 2(c), below), neutral oil by petroleum ether extraction of an isopropanol/water solution, pH of a 5% aqueous solution, water by Karl Fischer titration or azeotropic distillation, sulfate by titration with lead nitrate, sulfite by iodometric titration, and chloride by potentiometric titration (99). The value for neutral oil can be checked for losses due to evaporation by confirming that the weight of the sulfonates and other salts in the 2-propanol/water phase plus the water content and weight of neutral oil is equal to 100%. 

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. 

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. 

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. 

Determination of Moisture in NG by Karl Fischer Reagent. Place a 5—lOg sample of the NG into a fared narrow-necked stopperable flask and retare. Titrate directly with standardized Karl Fischer Reagent until a brown color remains for 30 sec, or use a potentiometric endpoint. Then,... 

It is routine to standardize Karl Fischer reagents, or even a coulometer, with a standard such as lincomycin hydrochloride monohydrate, which contains 3.91 wt% H20. The coulometer is run until the end point is reached, indicating that the Karl Fischer reagent is dry. A port is opened briefly to add solid lincomycin, which is then titrated to the same end point. Then an unknown is added and titrated in the same manner. Find the wt% HzO in the unknown. 

Standardize Karl Fischer reagent 1. Set up titration assembly per manufacturer s instructions. 

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