Less conventional electrochemical detection methods in HPLC analysis of
food materials.
Luc J. Nagels
University of Antwerpen, Chemistry Department, Groenenborgerlaan 171, B-2020
Antwerpen, Belgium. lnagels@ruca.ua.ac.be
Special HPLC/electrochemical methods for application in food analysis are shown.
Electrochemical detection in HPLC can be subdivided in 5 parts: amperometric,
potentiometric, voltammetric, conductometric, and mixed methods (e.g. spectroelectrochemical). The most widely used in HPLC in general, and in HPLC for food analysis in
particular, are amperometric and conductometric detection. Conductometric detection (very
popular in ion chromatography), voltammetric and spectroelectrochemical methods will not
be dealt with here. Amperometry is used for the determination of a restricted class of
(electrochemically active) compounds. A less well-known but very interesting amperometric
technique (especially in food- and in biomedical analyses) makes use of post-column enzyme
reactors, converting non-electroactive substances to electroactive ones before amperometric
detection. Examples from the group will be shown on the determination of oligosaccharides
[1, 2]. Such reactors are very robust and efficient, and their selectivity can be tuned by the
proper choice of enzymes, which is advantages when compared to pulsed amperometric
detection (“PAD”). Enzyme reactors are not yet commercially available. This is also the case
for potentiometric HPLC detection. The potentiometry/HPLC combination has only recently
been explored in research labs. It is a very sensitive and promising mode of detection,
especially for ionizable organic substances. New results from the group are shown for the
determination of food related hydroxycarboxylic acids [3], for drugs known to occur
frequently in the food chain such as clenbuterol and many other basic drugs [4], for amines
and aminoalcohols.
References.
[1] L.J. Nagels and P.C. Maes, Post-column enzyme reactors for the HPLC determination of
carbohydrates, in “Carbohydrate analysis”, Journal of Chromatography Library – volume 58,
Ziad El Rassi Editor, Elsevier, Amsterdam 1995, Chapter 16.
[2] L.J. Nagels, Enzyme reactors and enzyme electrodes for the liquid chromatographic
determination of carbohydrates, in “Carbohydrate analysis” 2nd Ed., Ziad El Rassi Editor,
Elsevier, Amsterdam. In print.
[3] D. Zielinska, I. Poels, M. Pietraszkiewicz, J. Radecki, H.J. Geise, L.J. Nagels
Potentiometric detection of organic acids in liquid chromatography using polymeric liquid
membrane electrodes incorporating macrocyclic hexaamines
Journal of Chromatography A, 915 (1-2) 25-33 2001
[4] G. Bazylak, L.J. Nagels, Potentiometric detection of exogenic beta-adrenergic substances
in HPLC, Journal of Chromatography A, in print.