Mathematical study on gradient formation of cetyltrimethylammonium bromide in centrifugal precipitation chromatography

Abstract

Centrifugal precipitation chromatography (CPC) is a separation system that mainly employs a moving concentration gradient of precipitating agent along a channel. Solutes of interest undergo repetitive precipitation-dissolution, and fractionate at different locations, and finally elute out from the channel according to their solubility in the precipitant solution. In the practical apparatus, two channels are formed by inserting a piece of dialysis membrane between a pair of disks with mutually mirror-imaged spiral grooves. A sample is injected into one channel and the precipitant solution is fed into another one. When the precipitant travels across the membrane to the sample channel, its concentration gradient is formed. Gradient profile of precipitant inside the sample channel is crucial to the success of CPC; therefore, it is worthwhile to investigate the formation of the precipitant concentration gradient. In this paper, an established mathematical model used to explain the steady-state gradient formation of ammonium sulfate, (NH 4 ) 2 SO 4 , in CPC was adopted for studying the gradient formation of cationic surfactant cetyltrimethylammonium bromide (CTAB). Its concentration, velocity and pressure profile obtained from the model are discussed.