Karl Fischer Titration – Moisture Analysis

Karl Fischer (KF) titration is a highly specific analytical method used to determine trace and bulk water content in liquids, solids, and gases. It is widely applied in pharmaceutical, petrochemical, transformer oil, food and polymer laboratories operating under ISO 17025.

Reaction Chemistry

The Karl Fischer reaction is based on the quantitative oxidation of sulfur dioxide by iodine in the presence of water:

H₂O + I₂ + SO₂ + 3 RN → 2 HI + RNH·SO₄R

Water reacts stoichiometrically with iodine, allowing direct determination of moisture content.

Types of Karl Fischer Methods

• Volumetric KF – Suitable for moisture > 0.1%
• Coulometric KF – Suitable for trace moisture (ppm level)

Volumetric method uses standardized iodine solution. Coulometric method generates iodine electrochemically.

Calculation – Volumetric Method

Moisture (%) =

(Volume of KF reagent × KF factor × 100) / Sample weight

Where:
KF factor = mg of water per mL of reagent

Worked Example

Sample weight = 1.25 g Volume consumed = 3.2 mL KF factor = 5.0 mg/mL

Water content (mg) = 3.2 × 5.0 = 16 mg

Moisture % = (16 / 1250) × 100 = 1.28 %

This calculation must be documented with uncertainty estimation in ISO 17025 systems.

Troubleshooting Logic Flow

• High drift → Moisture contamination in cell
• Unstable endpoint → Electrode cleaning required
• High consumption → Incorrect factor
• No endpoint detection → Generator electrode issue

ISO 17025 Laboratory Relevance

• Regular standardization using sodium tartrate
• Blank correction documentation
• Drift value monitoring
• Electrode performance verification
• Uncertainty estimation and traceability

Part of Laboratory Engineering Hub

Karl Fischer moisture analysis is one of the key reaction-based analytical techniques within our complete laboratory analyzer engineering framework.

Explore the full Laboratory Engineering reference: Laboratory Analyzers – Engineering Fundamentals