57
in the first 5 minutes of the chromatogram. This mirrors a trend that is also observed in the ABTS•
antioxidant derivatisation Figure 3a
method. A number of peaks with retention times of between 6 and 17 minutes show responses to both the underivatised UV-Vis and the phenol reagent detectors. The chromatographic profiles show variation in relative response factors between the underivatised UV-Vis and the phenol reagent chromatograms. Additionally, the phenol reagent and underivatised UV-Vis chromatograms show higher response for the methanol extract compared to the water extract and no compounds responded to the phenol reagent with retention times of more than 20 minutes. The two large peaks that were detected in the conventional UV-Vis analyses at a retention time of around 25 minutes were also detected in the underivatised stream in the phenol detection experiment with retention times of 24 and 26 minutes respectively. These compounds did not respond to either the phenol reagent or the ABTS•
reagent,
indicating a lack of both phenol functionality and antioxidant activity in these compounds.
Detection using the phenol reagent showed a number of similarities and differences compared to the ABTS•
antioxidant
detection method. Given that the mobile phase composition was different in both experiments and differences in the UV-Vis chromatographic profile have been noted, additional information needs to be collected to definitively state whether the antioxidants and phenolic compounds that were detected are the same or different compounds.
Figure 3b 4. Conclusions
Bioactivity screening in NAFPs, such as the lemon myrtle leaves, is a time consuming and laborious process when carried out under conventional HPLC methods. The use of AFT-PSF columns enabled RF chromatography with PCD reagents and multiplexed detection of the underivatised central flow, allowing for fast and efficient antioxidant and phenolic screening. RF-PCD chromatography allows for the elimination of reaction coils typically utilised in most traditional PCD techniques and therefore more efficient separations, which is critical in the analysis of complex samples. Additionally, the multiplexed detection of derivatised and underivatised streams resulted in the collection of additional information from every injection.
Figure 4
Funding: This research did not receive any specific grant from funding agencies in the
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