Rapid, Efficient Quantification of Water in Solvents and Solvents in Water Using an Ionic Liquid-based GC Column

Oct 01, 2011
Volume 24, Issue 10, pg 516–529

Developing versatile, rapid and accurate analytical techniques for the detection and quantification of water in a variety of materials remains an important and ubiquitous analytical problem. This article describes an effective and sensitive ionic liquid (IL)-based capillary gas chromatography (GC) method with a thermal conductivity detector (TCD) to determine the water content in liquid samples. The open tubular capillary columns, coated with specific ILs developed in this study, increased the sensitivity and significantly increased the ruggedness of this technique. The lower limit of detection (LOD) of this method is ~2 ng water. Samples containing high levels of water are also readily analysed without pretreatment. Conversely, organic solvents can be measured in water by the same approach using either a TCD or a flame ionization detector (FID). Standardization was performed with National Institute of Standards and Technology (NIST) reference materials and the accuracy was compared with another independent method (Karl Fischer titration). The developed method is highly sensitive, fast, and is not affected by interferences and side reactions common with existing Karl Fischer Titration (KFT) methods.

The determination of water content in solvents and consumer products, including foods, pharmaceuticals and industrial materials is of great importance. Analytical testing for the presence and concentration of water is one of the most frequent, important and ubiquitous measurements made in modern industrial society. Thus a versatile, simple and efficient analytical technique for the accurate quantification of water is imperative. The essentially universal presence of water requires accurate, easy and sensitive techniques to quantify it. Various techniques such as gravimetry (1), Karl Fischer Titration [KFT] (2,3), gas chromatography (GC) (4–13), near infra red spectroscopy [NIRS] (4,14–16), solvatochromic sensing (17,19), fluorine nuclear magnetic resonance spectroscopy (F-NMRS) (18), isotope ratio mass spectrometry [IRMS] (19) and others have been reported in the literature, but only few methods are widely accepted and used.

Currently, the most commonly used method for water analysis is the KFT, which was first reported in 1935 (2). In this titrametric method, I2 is reduced to HI in the presence of water (9). There are four components in the Karl Fischer reagent consisting of: iodine, sulphur dioxide, a suitable base (RN), (originally pyridine was used, but now imidazole is more common); and a suitable solvent (methanol, ethanol, diethylene glycol monomethyl ether, etc) (20).

The accepted mechanism of this two-step reaction is (20,21):

The end point is determined potentiometrically. Two types of KFT methods are used: coulometric titration and volumetric titration. The former is used to detect trace amounts of water, ranging from 10 µg to 99 µg (1 ppm – 5%), and it requires ~5 g or more of sample (22). Volumetric titration is used to detect higher water quantities greater than 1 mg (10 ppm – 100%) and the amount of sample required varies from 0.1 mg to 500 mg (23). Therefore, prior knowledge of the approximate amount of water present in the sample is required in choosing the correct KF method of analysis.

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