Fundamental Aspects of FI On-line Dialysis

Bemhardsson et al.[4] proposed theoretical models to describe the mass transfer in online dialyzers. With typical dialyzer dimensions, the theoretical results based on laminar flow and plug flow models agreed reasonably well with experimental results, provided that hydrostatic pressures on two sides of the membrane are equal and excessive bulging of membrane is avoided. 

The phase transfer factor P (cf. Sec. 1.4.6) in on-line dialysis may be conveniently expressed by the dialysis factor, defined as the output concentration of the detector channel. Q, normalized by division with the initial sample channel concentration, Cs [5]. The phase transfer efficiency may also be described using dialysis percentage by multiplying the dialysis factor with 100. 

The dialysis factor Cd/Cs depends on several experimental parameters such as permeation qualities of the membranes, membrane area, channel dimensions, analyte concentration, flow-rates of the donor and acceptor streams and their ratios, the relative flow direction of the two streams and temperature. A brief summary on the effects of various factors under FIA conditions, based mainly on results and observations obtained by van Staden and Rensburg [6] using calcium and chloride ions as model anal)aes are given here. 

Dialysis factors are little influenced by differences in analyte concentrations within relatively wide concentration ranges below 5000 mg 1 However, other coexisting solutes may influence the dialysis efficiency, and interfere by changing the osmotic pressure. 

Relative Flow Direction of Donor and Acceptor Streams 

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