Characterization of Mobile Phase Flow Inhomogeneity in Micro-structured Fibres: Towards the Development of Multi-channel Supports for Open Tubular Liquid Chromatography
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Despite the prominent role played by open tubular columns in gas chromatography, they have enjoyed comparatively little success as supports for open tubular liquid chromatography (OTLC), owing to impractical channel diameters (3-5 μm) required to facilitate retention in the liquid phase. In an effort to circumvent the technical issues associated with such narrow diameters, columns with multiple parallel channels have been suggested as alternatives – to this end, micro-structured fibres (MSFs) have been proposed as supports for OTLC. Much research has been conducted using MSFs for chromatography in the Oleschuk group, and although some success has been achieved, performance has been continuously hindered by flow velocity variation among the channels stemming from differences in channel sizes (or channel variance) as well as differences in stationary phase coverage, which serve to degrade column efficiency. Recent efforts have focused on devising a novel method for assessing the channel variance of MSFs. This method seeks to determine hole tolerance through evaluation of the extent of band broadening that occurs when performing chromatography in the absence of a retentive mechanism. Using this method, a linear correlation between the relative standard deviation of the channel diameters and the amount of broadening was revealed. To supplement the results, computational fluid dynamics was employed to simulate fluid flow through multi-channel columns. The results of these simulations again provided a linear correlation between the RSD of the channel diameters and the extent of flow velocity variation among the channels.