Rapid separation of microcystins and nodularin using a monolithic silica C₁₈ column

A monolithic C₁₈-bonded silica rod column (Merck Chromolith) was compared to particle-based C₁₈ and amide C₁₆ sorbents in the HPLC separation of eight microcystins and nodularin-R. Two gradient mobile phases of aqueous trifluoroacetic acid modified with acetonitrile or methanol, different flow-rates and different gradient lengths were tested. The performance of the Chromolith column measured as the resolution of some microcystin pairs, the selectivity, efficiency (peak width) and peak asymmetry equalled, or exceeded, the performance of traditional particle-based columns. The Chromolith column allowed a shortening of the total analysis time to 4.3 min with a flow-rate 4 ml min^-1.