Analysis of aromatic and terpenic constituents of pepper extracts by capillary electrochromatography

An original method based on capillary electrochromatography (CEC) has been developed for the identification and determination of aromatic and terpenic compounds in extracts of spices obtained from Piper nigrum. The method is based on the use of a fused silica capillary (effective length: 23.5 cm, internal diameter: 100 µm) packed with a C18 sorbent (packing length: 23 cm, particle size: 5 µm). The mobile phase is a 50 mM, pH 6.0 ammonium acetate / acetonitrile (10/90, v/v) mixture. Applying a 30 kV voltage, within a 22-min electrochromatographic run the following eleven compounds are separated and analysed: the terpenes terpinen-4-ol, caryophyllene oxide, limonene, beta-pinene, 3-carene, alpha-pinene, alpha-humulene, beta-caryophyllene and alpha-phellandrene and the aromatic eugenol and piperine. Compound determination is carried out using a diode array detector set at 265 and 338 nm for alpha-phellandrene and piperine, respectively, and at 210 nm (reference subtraction at 282 nm) for all other analytes. The optimised method has been validated with good results in terms of linearity, limits of quantitation and detection and precision. The CEC method was successfully applied to the analysis of essential oils and methanolic extracts of “black”, “white” and “green” pepper. The results show that the samples can be analysed without any pre-treatment, in fact a simple dilution with the mobile phase allows good analyte separation to be obtained without any significant interference from the oil or methanolic matrices.