ABSTRACT
Stationary phase gradients formed in a single column housing or by serially connected columns are the most recently explored subset of non-uniform chromatography. Such non-uniform columns have exhibited improved separation capabilities including better resolution and reduced analysis time, particularly when compared to a traditional uniformly modified column. When combined with a mobile phase gradient, peak focusing and improved resolution of the critical pair can result. In this review chapter, both continuous and discontinuous stationary phase gradients that specifically exhibit a change in chemistry along their length are described for the first time. Stationary phase gradients are explored for a variety of different substrates including thin-layer chromatography plates, silica and polymeric monolithic columns, and particle-packed columns as well as for different chromatographic modes such as reversed-phase and HILIC. This chapter begins with an introduction into discontinuous and continuous (single-component, multicomponent) gradients, how they are constructed and characterized, their chromatographic properties, and performance, and then ends with a discussion on the incorporation of gradient stationary phases into liquid chromatography simulations for method development. The promise of unique selectivity, improved efficiency, and reduced analysis time may make these types of stationary phases a new tool for the modern chromatographer.
