Transfer in Biology and Medicine

The descriptions of mass transfer developed in this book are detailed and accurate because they were developed for well-defined problems in the chemical industry. In that highly competitive industry, small improvements in chemical processing can mean large increases in profits. This promise of higher profits led engineers to examine the details of mass transfer and to get highly quantitative results. 

This chapter tries to bridge this gap. It gives an overview of mass transfer for those with little mathematics beyond elementary differential equations. This chapter does not completely stand alone it probably will require the complete novice to consult other sections to understand completely the basic ideas involved. Still, it can give the biologist an easier introduction, and the engineer a good review. 

We begin the review as follows. Mass transfer describes the amount of solute moving from one region to another. For example, it describes how a solute like glucose moves from the lumen of the small intestine into the blood. The solute flux N is the amount of solute per area per time. It is given by 

Any flux includes transport both by convective flow and by diffusion. However, in general, one of these routes is much more important than the other. For example, glucose transport along the length of the small intestine is almost completely by flow, but glucose transfer across the intestinal wall is almost completely by diffusion. 

The overall mass transfer coefficient is a rate constant, a measure of how fast the process occurs. It is a close parallel to the rate constant of a first-order chemical reaction, or to the half life of radioactive decay. It is different from these chemical rate constants in two important ways. First, K is defined per unit area, and chemical rate constants are normally defined per unit volume. One consequence is that we will sometimes work with Ka, where a is the interfacial area per system volume. The product Ka has the same units of reciprocal time as a first-order chemical rate constant. 

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P. Khanna, Energy transfer immunoassays using phycobiliproteins. Presentation at Conference of Phycobiliprotein in Biology and Medicine, Seattle, Washington, September 9-10, 1985. 

Applications of photophysics in biology and medicine are very extensive and only a few topics can be mentioned in this review. A survey of the use of lanthanide ions as luminescent probes of biomolecular structure and a general account of long distance electron transfer in proteins and model systems are very helpful. The methods applicable to the synthesis and activation of a number of photoactivable fluoroprobes have been described and photoactivation yields measured . 

Steeghs, M. (2007) Development of proton-transfer reaction mass spectrometry techniques. Detection of trace gases in biology and medicine. PhD thesis. Radboud University Nijmegen, Netherlands. 

In this section, we use four examples to illustrate the use of mass transfer coefficients. These examples, which supplement those given in Chapter 8, have a basis in biology and medicine. They serve to introduce the ideas involved. They are an overview, and for the complete novice, may require referring to earlier sections of the book. 

Mass transfer is much better explained here than it was earlier. I believe that mass transfer is often poorly presented because it is described only as an analogue of heat transfer. While this analogue is true mathematically, its overemphasis can obscure the simpler physical meaning of mass transfer. In particular, this edition continues to emphasize dilute mass transfer. It gives a more complete description of differential distillation than is available in other introductory sources. This description is important because differential distillation is now more common than staged distillation, normally the only form covered. This edition gives a much better description of adsorption than has been available. It provides an introduction to mass transfer applied in biology and medicine. 

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