Karl Fischer technique

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 ... 

Karl Fischer reagent analy chem A solution of 8 moles pyridine to 2 moles sulfur dioxide, with the addition of about 15 moles methanol and then 1 mole iodine used to determine trace quantities of water by titration. karl fish-or re a-jont Karl Fischer technique analy chem A method of determining trace quantities of water by titration the Karl Fischer reagent is added in small increments to a glass flask containing the sample until the color changes from yellow to brown or a change in potential is observed at the end point. karl fish-or tek nek kauri-butanol value analychem The measure of milliliters of paint or varnish petroleum thinner needed to cause cloudiness in a solution of kauri gum in butyl alcohol. kail-re byut-3n,ol, val-yu ... 

FIGURE 5 Chart for selection of Karl Fischer technique. 

Small quantities of water may be determined by the Karl Fischer technique, The method is not universally applicable but the limitations of the direct determination can be overcome by some preliminary technique. 

The end point of the reaction is conveniently determined electrometrically using the dead-stop end point procedure. If a small e.m.f. is applied across two platinum electrodes immersed in the reaction mixture a current will flow as long as free iodine is present, to remove hydrogen and depolarise the cathode. When the last trace of iodine has reacted the current will decrease to zero or very close to zero. Conversely, the technique may be combined with a direct titration of the sample with the Karl Fischer reagent here the current in the electrode circuit suddenly increases at the first appearance of unused iodine in the solution. 

The generation of iodine coulometrically at the anode has an extensive application in the Karl Fischer (KF) technique of water determination. The current... 

The near-IR technique has been used very successfully for moisture determination, whole tablet assay, and blending validation [23]. These methods are typically easy to develop and validate, and far easier to run than more traditional assay methods. Using the overtone and combination bands of water, it was possible to develop near-IR methods whose accuracy was equivalent to that obtained using Karl-Fischer titration. The distinction among tablets of differing potencies could be performed very easily and, unlike HPLC methods, did not require destruction of the analyte materials to obtain a result. 

It refers to the determination of water content titrimetrically with Karl Fischer Reagent (KFR). This technique has been used exclusively for the determination of water content in a number of pharmaceutical substances listed below (see Part II G, Chapter 14) ... 

End-point Detection The end-point of the Karl Fischer titration may be determined quite easily by adopting the electrometric technique employing the dead-stop end-point method. When a small quantum of e.m.f. is applied across two platinum electrodes immersed in the reaction mixture, a current shall tend to flow till free iodine exists, to remove hydrogen and ultimately depolarize the cathode. A situation will soon arise when practically all the traces of iodine have reacted completely thereby setting the current to almost zero or veiy close to zero or attain the end-point. 

The Karl Fischer titration is a specialised type of coulometric titration. Coloumetry itself is a useful technique, but is not used as a mainstream technique for pharmaceutical analysis. Essentially coulometry is based on the electrolytic reduction of the analyte, i.e. the analyte is reduced by electrons supplied by a source of electrical power and the amount of charge passed in order to convert the analyte to its reduced form is equivalent to the amount of analyte present in solution. 

Karl Fischer titration A sensitive technique for determining water, based on the reaction of HzO with an amine, I2, S02, and an alcohol, kelvin, K Absolute unit of temperature defined such that the temperature of water at its triple point (where water, ice, and water vapor are at equilibrium) is 273.16 K and the absolute zero of temperature is 0 K. Kieselguhr German term for diatomaceous earth, which was formerly used as a solid support in gas chromatography. 

Karl Fischer titrations - pLECTRO ANALYTICAL TECHNIQUES] (Vol 9)... 

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. 

Last and Prebble [51 ] developed a near-infrared reflectance (NIR) method for the determination of moisture in an experimental freeze-dried injection product. NIR spectra were collected through the bases of unopened product vials using a horizontal instrument accessory. The samples in these vials were then used for Karl Fischer analysis to generate a standard curve for the analysis. The NIR data must be correlated with an accepted residual moisture technique in order to yield a meaningful result. This article states that NIR accuracy and precision in this application are not consistent with allowing the use of the current method in anything but a screening role. 

Prior work (3) has indicated that a combination of 3 analytical techniques—loss of weight on ignition (LOI), Karl Fischer titration (KF), and reaction with LiAlH4—results in quantitative data on the amount of acidic OH groups in the zeolite, even in nonheated wet samples. This method discriminates between acidic and non-acidic OH... 

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