Selecting the Right C18 Stationary Phase with Parallel Array Microfluidic Column Liquid Chromatography (palmLC)

Chromatographic separation plays an essential role in medicinal research, especially for complex natural products such as traditional Chinese medicine (TCM), where selecting a suitable stationary phase is of primary importance and requires significant effort. Existing stationary phase screening (SPS) methods often necessitate inflexible and expensive instrumentation or a prolonged screening period. Despite this, efforts are mostly focused on stationary phases with significantly different properties, while those with subtle differences, e.g., various C18 stationary phases, are often overlooked, which can result in remarkably different chromatographic layouts, especially in pursuing optimum selectivity of target active components in TCM analysis. Herein, we report an efficient, low-cost, and easy-to-prototype parallel array microfluidic column liquid chromatography (palmLC) platform for SPS based on batch-prepared capillary columns and a multichannel capillary microfluidic assembly. In comparison with a standard single-column system, the developed palmLC system maintained a nondegradable chromatographic performance in terms of efficiency (5110 vs 5150 plates) and resolution (2.77 vs 3.39), ensuring reliable screening results while achieving a 600% increase in screening efficiency. In the case studies of Panax notoginseng and Gastrodia elata, among the six C18 phases screened, the C18 phase with the best separation performance was successfully identified. Finally, in SPS for Polygala tenuifolia separation, along the chromatograms, different C18 phases presented individual optimum resolutions for certain medicinal components, indicating that the six-in-one-shot palmLC strategy can effectively provide a panoramic display of the medicinal material, suggesting it is a useful tool for high definition quality control and profiling in TCM analysis.