Coupling of monolithic columns with sequential injection technique: A new separation approach in flow methods Original Research Article

Sequential injection chromatography (SIC) system was created by incorporating a monolithic chromatography column into a standard sequential injection analysis (SIA) manifold. The system was successfully used for separation of salicylic acid (SA) and its ester methylsalicylate (MS) and for determination of these compounds in a topical pharmaceutical preparation. The separation was performed on Chromolith® SpeedROD RP-18e, 50–4.6 mm column (Merck, Germany) placed between the selection valve and the detection cell with acetonitrile–water (35/60 (v/v)), pH 2.5 as the mobile phase. The eluted compounds were detected by diode array Ocean Optics spectrophotometer at 240 nm. Propylparaben (PP) was chosen as a suitable internal standard for quantification of the desired substances. The relation between the absorbance signal and concentration was linear in the range 0.17–43.2 μg ml−1 for SA, 0.24–60.2 μg ml−1 for MS and 0.24–58.8 μg ml−1 for PP. The detection limits were 0.04 μg ml−1 (SA) and 0.15 μg ml−1 (MS), respectively. The recoveries of the determined compounds in the pharmaceutical paste were found above 96%. The values of common chromatographic parameters obtained by the proposed system (resolution, number of theoretical plates and peak asymmetry) are presented.