RP‐HPLC analysis of phenolic compounds and flavonoids in beverages and plant extracts using a CoulArray detector

Abstract

Methods were developed for the analysis of natural antioxidants including phenolic compounds and flavonoids in beverages and plant extracts using gradient HPLC with multi-channel electrochemical coulometric detection. Suitability of various reversed-phase columns for this purpose was compared; pH and mobile phase gradients were optimized with respect to the separation selectivity and sensitivity of detection. Because of different target compounds in various sample types, the overlapping resolution maps and the normalized resolution product approaches described earlier were used to select optimum columns and gradients to suit the analysis of the individual sample types. The methods were applied to the analysis of phenolic compounds and flavonoids in beer, wine, tea, and yacon extracts. 32 phenolic compounds were identified and determined, including derivatives of benzoic and cinnamic acids, flavones, and a few related glycosides. Eight-channel CoulArray detection offers high selectivity and sensitivity with limits of detection in the low microg L(-1) range, at least an order of magnitude lower than single-channel coulometric detection using the Coulochem detector. No special sample pretreatment is necessary and, because of the compatibility of the CoulArray detector with gradient elution, phenolic antioxidants of different polarities can be determined in a single run. In addition to the retention times, the ratios of the areas of the pre-dominant and post-dominant peaks to the area of the dominant peak can be used for improved identification of natural antioxidants.

Development of different comprehensive two dimensional systems for the separation of phenolic antioxidants

“…According to our previous experience [64,65] ammonium acetate and formic acid provide sufficient buffer capacity and lower gradient base-line noise in comparison to formate -formic acid or acetate -acetic acid buffers. The pH of the buffer was measured in aqueous solutions, before the addition of organic solvent.…”

Extraction, separation, and detection methods for phenolic acids and flavonoids

“…With the recent advances in electrochemical detection, multi-electrode array detection is becoming a powerful tool, compatible with gradient elution, for detecting phenolic acids and flavonoids in a wide range of samples. The multi-channel coulometric detection system may offer a highly sensitive method for the overall characterisation of antioxidants [146,147].…”

Comparison of Antioxidant Activity of Barley (Hordeum vulgare L.) and Malt Extracts with the Content of Free Phenolic Compounds Measured by High Performance Liquid Chromatography Coupled with CoulArray Detector

“…The coulometric detector was used for reversed-phase HPLC, usually with an octadecyl silica column and aqueous-organic mobile phase containing acidic buffers to suppress the dissociation of weakly acidic phenolic compounds 14 .…”