Fast separation of red colorants in beverages using cyano monolithic column in Sequential Injection Chromatography

Flexible medium-pressure Sequential Injection Chromatography (SIC) flow manifold was used for development of a fast green chromatography method. The article presents novel use of a cyano monolithic column (Merck Chromolith 50 mm × 4.6 mm) for a separation of three water soluble colorants (carmoisine, Ponceau 4R and red 2G), aiming the extension of the SIC separation capabilities for polar analytes. The separation was performed in a gradient elution mode with changing concentration (0.05-0.005% v/v) of ammonium phosphate at pH 6.0 as a mobile phase. No organic modifier was used in mobile phase, thus the green chromatography rules were fulfilled. The vis spectrophotometric detection was set at 500 nm. High performance of the separation with the cyano monolithic column was described and discussed (peak capacities 6.67-10.94, peak symmetries 1.11-1.50, resolutions ≥ 2.78 and time for one analysis 3.15 min). The method was represented by analytical parameters - LODs of 0.45 mg L− 1, a LOQs of 1.5 mg L− 1 and calibration range of 1.5-60.0 mg L− 1 (r > 0.997) for all analytes, and a method repeatability at 10 mg L− 1 of RSD ≤ 2.69% (n = 5) and system precision of RSD < 1.55% (n = 6). The developed method was used for determination of carmoisine and Ponceau 4R in red coloured beverages with red 2G as an internal standard. The results confirmed benefits of extended chromatographic selectivity of cyano monolithic column in the SIC.