Karl Fischer moisture analyzer and Karl Fischer Moisture Works
Overview: Using the Karl Fischer method for determination of moisture content of material in electrochemical devices. Karl Fischer: Germany, in 1935 invented a determination of moisture.
Karl Fischer Moisture Analyzer The new method: the use of iodine and sulfur dioxide in redox reactions, organic base and methanol in the environment, quantitative reaction with water.
CH3OH + SO2 + RN - [RNH] SO2CH3 RN is an organic base, such as pyridine. This step response is the reaction of sulfur dioxide and methanol, an ester, the ester was Alkali.
I2 + H2O + [RNH] SO3CH3 + 2RN - 2HI + [RNH] SO4CH3 + 2 (RNH) I step reaction is quantitative fat and water should be: under the action of sulfide anion was iodine in the water oxidation of alkyl sulfate , quantitative reaction of iodine with water 1:1.
Titration with iodine reagent continuously samples to determine the end point is to observe the color change when iodine excess. This is the first of the Karl Fischer titration.
Advantages and disadvantages
Advantages: rapid analysis, high precision
Disadvantages: Relative infrared moisture analysis with conventional methods, the operation is relatively complex, requiring reagents for supplies, and waste pollution on the environment, a small promise, instrument costs are higher.
Categories
Coulometry
Uses: used to measure trace substances in water
Reagent: mainly methanol (or ethylene glycol ether) and iodine
Electrolytic cell: electrolytic cell structure more complex, not only measure the direct pole, a pair of electrolytic electrodes, but also points the anode and cathode pool pool, the sample is injected into the pool anode and cathode pool is also divided and undivided diaphragm The.
The difference between iodine: iodine reagents are wrapped. To the solution, power, replacement of iodine, and the solution of the water reaction.
Volumetric method
Uses: used to measure the water content of conventional materials
Reagent: methanol, pyridine (or ethylene glycol ether), sulfur dioxide, iodine (in fact, the solution is in the form of iodide) and so on.
Electrolytic cell: a simple electrolytic cell, only the measurements indicate a very
The difference between iodine: iodine reagent in water samples is a direct response.
Major manufacturers
Metrohm, Mettler
Karl Fischer Moisture Works
Karl Fischer moisture determination principle is the use of iodine oxidation of sulfur dioxide, the need - to participate in the quantitative reaction of water: 12 S02 ten ten ten 2H2O = 2HI H2SO4 (1)
The reaction is reversible. In order to respond to the positive direction and quantitative shall be carried out by adding alkaline substances. Experiments show that pyridine is the most appropriate reagents, while pyridine also has combined with iodine and sulfur dioxide vapor pressure to reduce the role of the two. Therefore, the reagents must be added to methanol or another solvent with active OH-based, so that stability of sulfuric acid anhydride, methyl pyridine into pyridine hydrogen sulfate.
Theoretical molar ratio of reagents of iodine: sulfur dioxide: pyridine, methanol = 1:1:3:1. |
