Improved recycling chromatography – how to make faster and automatic separations of peak pairs

Recycling chromatography is an interesting technique to separate two close eluting peaks by increasing the column bed length. It can be applied as an alternative strategy when other optimization approaches as decreasing the flow rate or changing the solvent gradient do not result in separation of the target peaks. Two recycling systems have been described in literature: close loop recycling and alternative pumping recycling. The first is a classic and simple method which uses one column, the second is an improvement of the first one by using two identical columns and a 2-position valve. Here, we describe an optimization of the latter method by the addition of a second UV detector resulting in faster method development. The method was further improved allowing automated recycling which works also with changes in sample concentration under the PurityChrom® 6 software. These changes significantly improved the recycling chromatography technique.