A comparison of the performance of the cupric reducing antioxidant potential assay and the ferric reducing antioxidant power assay for the analysis of antioxidants using reaction flow chromatography

Abstract

The cupric reducing antioxidant capacity (CUPRAC) assay is an established procedure used to measure antioxidant content. Recently, the CUPRAC assay was adapted for use in post column derivatisation coupled with high performance liquid chromatography (HPLC-PCD). In prior works reported in the literature, CUPRAC HPLC-PCD assays used large post column mixing coils leading to a deterioration in the observed separation efficiency. In this work we used the CUPRAC PCD assay with reaction flow (RF) chromatography. No reaction loop was required, thus preserving the efficiency of the separation. We subsequently compared the performance of the CUPRAC assay to that of an antioxidant assay that we have previously converted to RF chromatography, namely the ferric reducing antioxidant potential (FRAP) assay, both in RF mode. The relative response factor with respect to trolox was measured for both RF assays via the separation of a standard mixture of 16 compounds. Sample analysis of coffee and green tea via both RF assays was used to compare their ability to screen for bioactive candidates in complex natural products. In general, the CUPRAC assay is recommended as the RF PCD methodology of choice as it provided a higher level of performance compared to the FRAP assay, demonstrating less baseline noise interference, greater sensitivity, wider linear dynamic range and better assay precision.