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.