Lab Chemical-60

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Karl Fischer titration is simply a method for quantifying water content of samples. The fundamental principle behind this reaction is based on the Bunsen reaction between compounds such as iodine, sulphur dioxide to form sulphuric acid and hydrogen iodide. Karl Fischer initiated a new method based on Bunsen’s reaction. He discovered that the reaction could be modified for determining water in a non-aqueous system containing an excess of sulphur dioxide in the presence of a suitable base. He used a primary alcohol (methanol) as the solvent and a base (pyridine) as the buffering agent.

 

What is the Karl Fischer Reaction?

(1) CH3OH + SO2 + RN [RNH]SO3CH3

 

Reaction-1:  is where the alcohol reacts with sulphur dioxide (SO2) and base to form an intermediate alkylsulfite salt

 

(2) H2O + I2 + [RNH]SO3CH3 + 2RN [RNH]SO4CH3 + 2[RNH]I

 

Reaction-2: is the oxidation step where the intermediate is then oxidised to an alkylsulphate salt. This reaction consumes water.

Water and iodine are consumed in a 1:1 ratio. Once all of the water present is consumed, the presence of excess iodine is detected by the indicator electrode. That signals the end-point of the titration. The amount of water present in the sample is calculated based on the concentration of iodine in the Karl Fisher titrating reagent and the amount of Karl Fisher Reagent consumed in the titration. Depending on the type of base used the rate of reaction will vary. Classic Karl Fischer reagents contained pyridine, a noxious carcinogen, as the base. Due to its weak basicity the reaction is slow and the end point is not stable. The most common base used today is imidazole where greatest accuracy and repeatability can be achieved. Coulometry is an absolute technique so standardisation of Karl Fischer reagents is not necessary.

 

 

Coulometric Titration Method

In coulometric Karl Fischer, iodine is generated electrochemically in situ during the titration.

The anolyte contains iodide, sulphur dioxide, bases and solvents such as methanol. Electrolytic oxidation occurs when a sample is added to this anolyte.

Iodine is generated at the anode of the titration cell as shown in formula (3)

(3) 2I^--2e ---> I₂

Stoichiometrically, 1 mole of water will react with 1 mole of iodine, so that 1 milligram of water is equivalent to 10⋅71 coulombs of electricity

Comparison of volumetric and coulometric titration cells.

 

In the volumetric technique, which is used to determine higher water contents generally at levels above 5%, the iodine is introduced via a burette or similar dosing system. For lower water content detection, down to ppm levels, the coulometric technique produces the iodine

in-situ by electrolysis. Coulometry improves the Karl Fischer technique by removing the need for reagent calibration and

provides an absolute result in micrograms of water.

Low reagent usage: multiple samples can be analysed with a single charge of reagent which means less waste and less handling of chemicals, good news for Health and Safety

 

 

 Karl Fischer KF Reagent

Karl Fischer KF Reagent A is a general coulometric KF anolyte for use with generator electrodes which incorporate a frit or diaphragm to separate the anode and cathode chambers. Used in conjunction with Reagent C this formulation is supplied in a pack of 8 x 100ml bottles, 8 x 5ml cathode vials, all conveniently located in a single carton.

To conform to ASTM, API, EI, ISO (plus others) methodology for water content determination of oil and petroleum products, the anode regent must be modified with xylene to improve sample solubility and miscibility. Karl Fischer KF Reagent is pre-mixed with xylene, and other solubilizers to eliminate side reactions, so that the operator does not have to store or mix chemicals.

 

 

 

Karl Fischer KF Reagents combine speed and accuracy

VOLUMETRIC COULOMETR K.F. Titration Cell Differences

• Single shot bottles

• Safer to use

• Safer to store

• Low cost

• Faster precondition

• Reduced downtime

• Improved sample miscibility / solubility

• For use with all coulometers

[KARL FISCHER REAGENT Pyridine Free] manufacturers, suppliers, exporters in Mumbai, Gandhidham, Kolkata, Varanasi, Visakhapatnam, Chennai, Fujairah, Dubai, Canada BC, Barka, Sohar, Muscat, Oman.

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[KARL FISCHER REAGENT Pyridine Free] is available in small packing as well as in bulk. Buy premium quality [KARL FISCHER REAGENT Pyridine Free] and other lab chemicals from one of the most trusted brands.