A review of two-dimensional liquid chromatography approaches using parallel column arrays in the second dimension

Multi-dimensional liquid chromatography techniques play an important role in the analysis of complex mixtures. The keys to maximizing peak capacity in these methods are fast sampling rates and sufficient complementarity between the first- (¹D) and second- (²D) dimension separations. One way that these criteria have been met is by using ²D parallel column arrays. This review covers demonstrations of this approach in the literature that have been published over the past three decades. Two or more identical ²D columns can be operated in a sequential order to permit increased separation times and higher peak capacities in the second dimension without the concomitant decrease in sampling rate. The parallel column arrays can also be operated simultaneously to reduce total analysis time. Columns with different stationary phase chemistries can be used in the ²D column array to increase complementarity by utilizing specific stationary phases for various first dimension fractions. More recently, this type of platform has been used to automate the development of two-dimensional (2D) achiral-chiral LC methods. These strategies, as well as recent efforts toward the development of integrated, spatial multi-dimensional LC devices that include parallel column arrays, are discussed here.