Determination of Water Content By Karl Fischer Method in Ethanolamine

Product Group

Alcohols and Amines

Section Overview

• General Information for Water Determination in Alcohols & Amines
• Methods for Water Determination in Ethanolamine/2-aminoethanol
  
• Related Materials

General Information for Water Determination in Alcohols and Amines

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 solubilisers. 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 Amines

Weakly alkaline amines pose no problems in the water determination after Karl Fischer and can be titrated according to standard methods. For strongly alkaline amines, the buffer capacity of the Karl Fischer solution is not sufficient. A shift of pH into the alkaline range leads to a side reaction of the iodine. This can be recognized by the dragging endpoints or a continuous consumption of iodine solution, respectively. If turn-off criteria are reached nevertheless, the result is too high. This side reaction, caused by the disproportionation of iodine molecules above pH 8, can be avoided through additional buffering of the working medium with a weak acid. Aquastar^® buffer solution for strong bases, benzoic or salicylic acid, is the most suitable because, unlike acetic acid, they do not show any tendency for esterification in the Karl Fischer solution. The acids are added to the solvent prior to titration and can even be employed in excess. Some amines react with the Karl Fischer solution. Measures to suppress or overcome this side reaction are, for example, titration in methanol-free working media, utilization of small sample sizes, as well as titration to a fast end point.

Methods for Water Determination in Ethanolamine/2-Aminoethanol

Ethanolamine produces a side reaction in the Karl Fischer solution. Through treatment with acid, it is possible to largely suppress this side reaction.

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^® - CombiMethanol (1.88009)- Solvent for volumetric Karl Fischer titration with one component reagents, max. 0.01 % water
  and
  5 - 8 g  salicylic acid (1.00635) - as buffer substance

Titration Parameters:
Default titration settings, e.g.: I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion for fast titration: drift < 30 µL/min

Sample size: 0.5 - 1 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 with a syringe (exact sample weight determination by weighing the syringe before and after injection), and the titration is started. Titration is carried out to a fast endpoint.

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
  and
  5 - 8 g salicylic acid (1.00635)- as a buffer substance

Titration Parameters:
Default titration settings, e.g., I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion for fast titration: drift < 30 µL/min

Sample size: 0.5 - 1 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 with a syringe (exact sample weight determination by weighing the syringe before and after injection), and the titration is started. Titration is carried out to a fast end point.

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
  and
  20 g benzoic acid (1.00136) - as a buffer substance

Titration Parameters:
Default coulometer settings for cell with diaphragm:
For end point indication, e.g., I(pol) = 5 - 10 µA, U(EP) = 50 - 100 mV
Stop criteria for fast titration: drift < 15 µg/min

Sample size: 0.5 g

Titration Procedure:
The Karl-Fischer reagent is placed into the cathode and anode compartment 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 injected into the titration cell with a syringe (exact sample weight determination by weighing the syringe before and after injection), and the water determination is started. Titration is carried out to a fast end point.

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
  and
  20 g benzoic acid (1.00136) - as a buffer substance

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 criteria for fast titration: drift < 15 µg/min

Sample size: 0.5 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 injected into the titration cell with a syringe (exact sample weight determination by weighing the syringe before and after injection), and the water determination is started. Titration is carried out to a fast end point.