Determination of Water Content By Karl Fischer Method in Kerosene

Product Group

Hydrocarbons, Petroleum products

Section Overview

• Water Determination in Hydrocarbons and Petroleum Products
• Methods for Water Determination in Kerosene sample
• Related Materials

General Information for Water Determination in Hydrocarbons and Petroleum Products

Water content in hydrocarbons

Saturated hydrocarbons can, in most cases, be titrated according to standard methods. To overcome solubility problems of unpolar or weakly polar substances, the addition of a solubilizer to the Karl Fischer Solvent is necessary. In the case of long-chain and cyclic hydrocarbons, long-chain alcohols (e.g., propyl alcohol or decyl alcohol) or chloroform are thus recommended. Toluene, xylene, or chloroform improve the solubility of aromatic compounds. Unsaturated hydrocarbons can usually be titrated in the same way. Interferences due to double bonds only occur with some very reactive compounds. In the case of interferences (unstable end point or none at all), a methanol-free, alcoholic solvent (e.g., CombiSolvent or CombiSolvent Keto) should be utilized instead of methanol. Recommended methods are both the volumetric titration with one or two component reagents, as well as the coulometric analysis. The latter is predominantly applied for low water concentrations (< 0.1%).

Water Content in Petroleum Products

Petroleum products are mixtures of long-chain or aromatic hydrocarbons. They are hardly soluble in methanol. Water determination by Karl Fischer method therefore requires the addition of solubilisers. For light oils, long-chain alcohols are suitable. For dissolving heavier oils, toluene, xylene, or chloroform are added. For the volumetric titration, specific KF solvents for oils are available. Due to the very low water concentration, titrants with a low factor (2 mg/mL or 1 mg/mL) are recommended. During coulometric determination without a diaphragm, 20% solubilizer can be added to the working medium, or 40% solubilizer to the anolyte in the case of coulometry with a diaphragm. Note that oils are often heterogeneous compounds with uneven distribution of water and should thus be homogenized (e.g., with Ultra-Turrax) prior to Karl Fischer water determination. Additives in oils can cause side reactions during KF determination. Here, the direct coulometric analysis is not possible, the volumetric titration is only conditional. As an alternative, the Karl Fischer oven method can be utilized in combination with coulometry, whereby the release of water is best achieved at temperatures between 120 and 140°C.

Water determination can be carried out volumetrically or coulometrically. The addition of solubilizers (long-chain alcohols or chloroform) is necessary.

 

Methods for Water Determination in Kerosene sample

One-Component Volumetric Karl Fischer Titration

Karl Fischer Reagents:

• Karl Fischer Titrant
  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 Oil (1.88020) - Solvent for volumetric Karl Fischer Titration with one-component reagents for oils
  or
  25 mL Aquastar^® - CombiMethanol (1.88009) - Solvent for volumetric Karl Fischer Titration with one-component reagents

Titration Parameters:
Stirring time: 60 sec.
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min

Sample Size: 
10 mL

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 without a hollow needle (exact sample weight determination by weighing the syringe before and after injection), and the titration is started. A stirring time of 60 seconds is recommended.

Two-Component Volumetric Karl Fischer Titration

Karl Fischer Reagents:

• Karl Fischer Titrant
  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 oils and fats (1.88016) - Solvent for volumetric Karl Fischer titration with two-component reagents for oils & fats
  or
  25 mL Aquastar^® - Solvent (1.88015) - Solvent for volumetric Karl Fischer titration with two component reagents

Titration Parameters:
Stirring time: 60 sec.
Default titration settings, e.g.: 
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min

Sample Size: 
10 mL

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 without a hollow needle (exact sample weight determination by weighing of the syringe before and after injection), and the titration is started. A stirring time of 60 seconds is recommended.

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
  80 mL Aquastar^® - CombiCoulomat frit (1.09255) - Coulometric Karl Fischer reagent for cells with diaphragm
  and
  20 mL Chloroform (1.02445) - as a solubilizer

Titration Parameters:
Stirring time: 60 sec.
Default coulometer settings for cell 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: 
2 mL

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 injected into the titration cell with a syringe without a hollow needle (exact sample weight determination by weighing the syringe before and after injection), and the water determination is started. A stirring time of 60 seconds is recommended.

Coulometric Karl Fischer Titration (Without Diaphragm)

Karl Fischer Reagents:

• Working Medium
  80 mL Aquastar^® - CombiCoulomat fritless (1.09257) - Coulometric Karl Fischer reagent for cells with or without diaphragm
  and
  20 mL Chloroform (1.02445) - as solubilizer

Titration Parameters:
Stirring time: 60 sec.
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: 
2 mL

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 without a hollow needle (exact sample weight determination by weighing the syringe before and after injection), and the water determination is started. A stirring time of 60 seconds is recommended.