Determination of Water Content By Karl Fischer Method in Phenol

Product Group

Alcohols, Phenols

Section Overview

• General Information for Water Determination in Alcohols & Phenols
• Methods for Water Determination in Phenol Sample
  
• Related Materials

General Information for water determination in Alcohols and Phenols

Water Content in Alcohols

Water determination after Karl Fischer poses no problems for most alcohols. Alcohols are easily soluble in the common Karl Fischer working media. Only alcohols with very long chains require the addition of solubilizers. Side reactions are not to be expected. Suitable methods are both the Karl Fischer volumetric titration with one or two component reagents as well as the Karl Fischer coulometric determination. The latter method is predominantly applied for low water concentrations (< 0.1%).

Water Content in Phenols

In most phenols, water determination can be carried out according to the standard methods after Karl Fischer. Some substances, however, are oxidised by the Karl Fischer reagent. This side reaction leads to unstable or dragging end points. During coulometry, interferences can accumulate to the point where analysis becomes impossible. Because the side reaction is dependent on the pH, its influence can be reduced through modification of the solvent. In a weakly acidic titration environment (e.g., through the addition of Aquastar^® buffer solution for strong bases, benzoic, or salicylic acid), easily oxidizable substances can be determined nevertheless.

Methods for Water Determination in Phenol Sample

Phenol does not cause any interferences in the Karl Fischer solution and is easily soluble in alcoholic media. Analysis can be carried out according to standard methods.

One-Component Volumetric Karl Fischer Titration

Karl Fischer Reagents:

• Karl Fischer Titrant
  Aquastar^® - CombiTitrant 5 (1.88005) - One component reagent for volumetric Karl Fischer titration, 1 mL = approx. 5 mg water
  or
  Aquastar^® - CombiTitrant 2 (1.88002) - One component reagent for volumetric Karl Fischer titration, 1 mL = approx. 2 mg water
• Karl Fischer Solvent
  50 mL Aquastar^® - CombiSolvent (1.88008) - Methanol-free solvent for volumetric Karl Fischer titration with one component reagents
  or
  50 mL Aquastar^® - CombiMethanol (1.88009) - Solvent for volumetric Karl Fischer titration with one component reagents, max. 0.01 % water

Titration Parameters:

Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min

Sample size:

5 g

Titration Procedure:

The titration medium is first placed into the cell and titrated dry by means of the titrant. Then the sample is added from a weighing boat (exact sample weight determination by weighing the weighing boat before and after addition), and the titration is started.

Two-Component Volumetric Karl Fischer Titration

Karl Fischer Reagents:

• Karl Fischer Titrant
  Aquastar^® - Titrant 5 (1.88010) - Titrant for volumetric titration with two component reagents, 1 mL = approx. 5 mg water
  or
  Aquastar^® - Titrant 2 (1.88011) - Titrant for volumetric titration with two component reagents, 1 mL = approx. 2 mg water
• Karl Fischer Solvent
  50 mL Aquastar^® - Solvent (1.88015) - Solvent for volumetric titration with two component reagents

Titration Parameters:

Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min

Sample size:

5 g

Titration Procedure:

The titration medium is first placed into the cell and titrated dry by means of the titrant. Then the sample is added from a weighing boat (exact sample weight determination by weighing the weighing boat before and after addition), and the titration is started.

Coulometric Karl Fischer Titration (With Diaphragm)

Karl Fischer Reagents:

• Catholyte
  5 mL Aquastar^® - CombiCoulomat frit (1.09255) - Coulometric Karl Fischer reagent for cells with diaphragm
  
• Anolyte
  100 mL Aquastar^® - CombiCoulomat frit (1.09255) - Coulometric Karl Fischer reagent for cells with diaphragm

Titration Parameters:

Default coulometer settings for cells with diaphragm:
For end point indication, e.g.:
I(pol) = 5 - 10 µA, U(EP) = 50 - 100 mV
Stop criterion: drift < 10 µg/min

Sample size:

1 g

Titration Procedure:

The Karl-Fischer reagent is placed into the cathode and anode compartments of the titration cell with a diaphragm. The coulometer is started, and the solvent is titrated dry. After preliminary titration and stabilization of drift, the sample is added from a weighing boat (exact sample weight determination by weighing the weighing boat before and after addition), and the titration is started.

Coulometric Karl Fischer Titration (Without Diaphragm)

Karl Fischer Reagents:

• Working medium
  100 mL Aquastar^® - CombiCoulomat fritless (1.09257) - Coulometric Karl Fischer reagent for cells with or without diaphragm

Titration Parameters:

Default coulometer settings for cells without a diaphragm:
For end point indication, e.g.:
I(pol) = 5 - 10 µA, U(EP) = 50 - 100 mV
Stop criterion: drift < 10 µg/min

Sample size:

1 g

Titration Procedure:

The Karl-Fischer reagent is placed into the titration cell without a diaphragm. The coulometer is started, and the solvent is titrated dry. After preliminary titration and stabilization of drift, the sample is added from a weighing boat (exact sample weight determination by weighing the weighing boat before and after addition), and the titration is started.