Multiple pulse amperometry in low pressure chromatography for parallel determination of oxidizable and reducible compounds. Analysis of a green coffee extract as a case study

In this paper, the determination of both oxidizable and reducible compounds within a single chromatographic run is exploited for the first time, using a low-pressure chromatographic system and multiple pulse amperometric detection. The case study selected focussed on the analysis of green coffee extracts. The separation of the compounds was carried out using a 1-cm length monolithic column and an eluent prepared by mixing an aqueous solution of an ion-pair reagent, perfluoroheptanoic acid (PFHpA), and acetonitrile. The parallel determination of oxidizable and reducible compounds was performed by application of two consecutive pulses, E1 = +1.6 V and E2 =-1.5 V. At anodic conditions, the chromatographic peaks for 5-caffeoylquinic acid (5-CQA), caffeine and 5-feruloylquinic acid (5-FQA) were detected, while at cathodic conditions, a chromatographic peak was ascribed for trigonelline. In the developed methodology, the use of multiple pulse amperometry provided better sensitivity if compared to previously described amperometric methodologies determining either oxidizable or reducible compounds. Detection limits for the referred compounds of ca. 1 x 10-5 mol L-1, an analysis rate of 12 h-1 and an acetonitrile consumption of 0.07 mL per analysis were achieved. The approach presented demonstrates the possibility of combining low pressure chromatographic systems and multiple pulse amperometry, in the devel-opment of new, low-cost and fast methodologies for multi-analyte determinations.