Xylem XA00148 User Manual

Application Note

YSI, a Xylem Brand  •  XA00148

Titration of Water in Liquid Samples

VOLUMETRIC KARL FISHER SERIES

Introduction

This application can be used for many liquid samples as long as no side reactions occur and the sample dissolves in the KF reagent. Liquid samples that do not or only partially dissolve in alcohols can often still be titrated in Methanol or similar solvents. If the water is extracted from the sample dispersed in the solvent during the titration, the extraction time should be increased. The solubility of the sample can be improved by adding toluene, chloroform, long-chain alcohols or similar solvents. Various special KF solvents for oils or fats are also available. In this application, 1-component reagents are used to determine the water content. The use of 2-component reagents is also possible if the corresponding titration parameters are used.

If a sample causes side reactions, it can be recognized from the titration curve. After the water has been titrated (the steep rise in the curve at the beginning), the titration curve rises steadily until the max. time has been reached, the µA end

criterion is not met. Some side reactions can be prevented by titration with special reagents (ketones), for others it helps to titrate in the cold. Some side reactions cannot be prevented.

KF-Titration with side reaction; A: Water + side reaction; B: side reaction

B

A

	Instrument
Titrator	TL 7500 KF or higher
Exchange Unit	WA 10

Electrode, Cable, and Electrolyte

Electrode KF1100

Lab Accessories

Magnetic stirrer TM 235 KF

Karl-Fischer titration vessel TZ 1770

Glass syringe (or disposable syringe) with needle

Reagents

11-component titrant, e.g. Composite 2 or 5 or a similar reagent

21-component solvent, e.g. CompoSolver E, Methanol or a similar solvent

3Molecular sieve, dry

All reagents should be in analytical grade or better.

Titration Procedure

Reagents

Karl Fischer reagents are available as ready-to-use solutions

The molecular sieve must be replaced or dried regularly, at least every 4 weeks.

Cleaning of the electrode

The KF 1100 electrode does not require any special treatment. The two platinum pins must not touch each other. For cleaning, Isopropanol or other solvents that do not attack glass and platinum are suitable.

Sample preparation

The titration cell is filled with approx. 30 ml solvent and the conditioning is started. The solvent can be used for several titrations.

The sample is drawn into a syringe with a needle. If possible, the syringe should be rinsed with a small amount of sample before.After conditioning is finished, the sample is injected through the septum into the titration cell and the titration is started. The amount of sample is determined by weighing back.

0.5 * Titer [ mgmL ]

W (g) =

expected water content [%]

2