The separation performance of affinity chiral ultrafiltration systems of tryptophan enantiomers employing bovine serum albumin (BSA) as the chiral selector was experimentally examined by conducting two-stage affinity ultrafiltration. D-tryptophan was collected preferentially in the filtrate obtained in the first stage filtration performed at pH 7 due to the strong stereospecific binding of L-isomer to BSA, whilst L-tryptophan was recovered as the filtrate in the second stage filtration conducted by changing pH from 7 to 3 because of the elution of bound tryptophan. The concentration of BSA in the concentrate was markedly increased by operating with a single-pass mode at a considerably low flow rate using a hollow fibre membrane module placed vertically, based on the principle of inclined ultrafiltration, which can efficiently remove the filter cake comprising BSA molecules. The highly concentrated BSA in the concentrate led to a significant increase in the separation efficiency of L-tryptophan in the second stage filtration releasing the bound L-tryptophan from the BSA. Inclined ultrafiltration operated at a very low flow rate is considered to be a promising approach for two-stage affinity ultrafiltration employing macromolecules or nanoparticles as the chiral selector.
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