Karl Fischer titration: how to deal with tricky matrices & time wasting routines

Karl Fischer titration system with automated thermal sample preparation

Karl Fischer titration is not the labor-intensive method it used to be. These days, it can be readily automated with standard instrumentation – even for matrices and applications that regularly caused severe headaches.

At the heart of this technology: precise dosing of liquid samples into the Karl Fischer titration cell by means of the Metrohm Dosino liquid handling system. The superior performance of this technology is demonstrated by four practical examples documented in a technical poster (8.000.6089).

Example 1: automated titer determination

Ultrapure water is an excellent standard for titer determination (AB-424) but requires precise dosing volumes. A completely automated procedure using a capillary, a Dosino high precision burette, and tiamo™ software takes makes this task easier than ever.

Example 2: water content in highly viscous compounds

The setup and method described in example one may also be used to control the glycol/water ratio in highly viscous water-glycol fluids. In the example at hand, the fully automated procedure is applied to two industrial glycol-water fluids, one being a HFC (hydraulic force control) fluid.

Example 3: water content in low-boiling organic solvents

Because the water content in nonpolar organic solvents is low, coulometric Karl Fischer titration is used. The procedure was tested for n-pentane. Because of its low viscosity and surface tension, n-pentane is extremely difficult to pipette. Automated sample measurement with capillary injection using a 5 mL dosing unit overcomes this problem and allows for precise determination of the water content.

Example 4: suitability test according to Ph. Eur.

Since 2008, the European Pharmacopoeia (Ph. Eur.) requires a suitability test (chapter 2.5.12) for volumetric Karl Fischer titration. To this end, the water content of the substance is first determined. Afterwards, known amounts of ultrapure water are sequentially added and determined. From the regression line, slope, axis intercepts, and percentage mean recovery are calculated. The Metrohm system takes over the six determinations, calculates the results, ad provides a well-arranged report.