Monolithic columns—a new concept of separation in the sequential injection technique

Abstract

In this contribution, the coupling of monolithic column with sequential injection technique (SIA), as a new possibility of implementation of a separation step in SIA is described. Monolithic columns were developed based on a new sol–gel technology. Due to the presence of macropores, the monolithic columns possess a much higher porosity than conventional particulate high pressure liquid chromatography (HPLC) columns. Consequently, monoliths can be coupled to the SIA system without loss of performance or limitations due to the very low column back-pressure. The aim of our study was to develop and test the new SI separation manifold and to demonstrate its functionality in the simultaneous determination of four different compounds (methylparaben, propylparaben, sodium diclofenac and internal standard butylparaben) in standard solutions and in a topical emulgel. A Chromolith ® Flash RP-18e, 25 mm×4.6 mm (Merck, Germany) column and a FIAlab ® 3000 system (USA) with an eight-port selection valve and 10 ml syringe were used for sequential injection chromatographic separations in our study. The mobile phase used was acetonitrile:water (40:70 (v/v)) + 0.05% triethylamine, pH 2.5, gradient flow rate 8–20 μl s −1. A novel reversed-phase sequential injection chromatography (SIC) technique with UV spectrophotometric detection was optimised and validated. The validation parameters showed very good results. The analysis time was less than 8 min. The method was found to be applicable for the routine analysis of the active compound sodium diclofenac and preservative propylparaben in a pharmaceutical product, topical diclofenac emulgel 1%. The coupling of the monolithic columns with sequential injection manifold provides an excellent tool to solve the separation problems without using HPLC instrumentation and with low cost per analysis and low consumption of organic solvents (non-continuous flow).