Reintroducing Countercurrent Chromatography to the Chemist

Ever since chemists began using separating funnels to isolate compounds by partitioning, they have understood the potential benefits of liquid/liquid chromatography, known today as countercurrent chromatography (CCC). Yet despite this knowledge, solid/liquid chromatography techniques, such as HPLC or flash, have become the workhorses of purification. Until recently, CCC was primarily a technique for natural products or academic research and was hardly used in mainstream purification. Unfortunately, early CCC instrumentation was poorly engineered and suffered from slow speed of separation, a combination that led to negligible adoption as a complementary and orthogonal chromatography technique. However, a new generation of high-performance countercurrent chromatography (HPCCC) instrumentation (see Figure 1) has led to the rebirth of liquid/liquid chromatography in the 21st century. This paper discusses the development and application of these instruments, and the benefits that CCC offers to the chemist. CCC can significantly improve a chemist’s productivity and separate compounds that were previously very difficult to isolate or uneconomical to produce. Due to the large difference in accessible stationary phase between liquid/liquid to solid/liquid chromatography—typically 70–80% compared to 5–10%—the loadings are dramatically higher, shortening the number of sample injections needed to process a batch. Furthermore, because both mobile and stationary phases are liquids, we gain two further important productivity benefits. First, sample solubility issues are reduced because one’s options for injecting sample onto the column have been tripled. Using CCC, one can inject sample into either of the individual mobile or stationary phases or a mixture of the two, whichever combination provides the highest loading per injection. The use of two liquids is also beneficial once the sample is on the column, because even if the sample crashes out of solution, it does not cause the column to block, stopping the chromatography.