Detection of organic ionics by Ion Selective Electrodes used as an HPLC detector: application to alkaloids in plant extracts.

FERNÁNDEZ, MARCELO RAÚL1,2,*, DAEMS, DEVIN2,3, EVERAERT, JOSEPH2, VAN CAMP, GUY3, BERNIK, DELIA1 AND NAGELS, LUC2.

Santa Fe

Congreso; VI Congreso Argentino de Química Analítica; 2011

AAQA

Introduction: Some 12,000 plant secondary products have been isolated, and this amount is estimated to be only 10% of the products present. Also some 10,000 plant alkaloids were already identified. Alkaloids can be differentiated from other secondary plant metabolites by their positive charge at physiological pH. Objectives: -        Develop a sensor capable of detecting the presence of alkaloids in plant extract. -        Analyse its kinetics behaviour and applicability as HPLC detector.  Results: We developed a potentiometric HPLC detector which selectively detects the positively charged alkaloids in complex mixtures. The characteristics of the detector such as selectivity, sensitivity, calibration curve behaviour, speed of response were studied in FIA, using the sensorgram methodology. Several conditions i.e. temperature of the detection system, coating and eluent composition were varied and their effect on the response times was compared. The detector’s response is typical for a surface phenomenon dependent system showing “on” and “off” kinetics. Response speeds are described by a double exponential function. These response times (t90) were calculated for cocaine “on” and “off” kinetics being 2.15±0.06 and 1.19±0.03 seconds respectively. Alkaloids as cocaine, ergocorine, solanidine and metergoline can be easily detected at concentrations of 2.5 10-7M, 7 10-7M, 1 10-7M and 1.7 10-7M in HPLC respectively. The detector’s ability to be used as alkaloids detector in HPLC is was confirmed in several chromatograms, with UV detection for comparison.  Conclusions: Alkaloids can be sensitively detected and differentiated from other secondary plant compounds in a plant extract without pre-purification. Potentiometry and UV peak shape matching shows the applicability of this detector in HPLC. References: - Unique potentiometric detection systems for HPLC determination of some steroids in human urine. Vissers B., Everaert J., Sekula J., Malak A., Bohets H., Bazylak G., Nagels L.J. J. Sep. Sci. 2009, 32, 167. - Potentiometric Sensors for Organic Analytes: Insights to Proceed to Miniaturization. Nagels L., Vissers B., Bohets H., Everaert J., Robbens J. Current Pharmaceutical Analysis 2009, 5, 120.