R. Fleming

Diffusion coefficient determination using a filter-paper diaphragm cell technique

Indelicato, J. M. Norvilas, T. T., Wheeler, W. J. (1972) Lebelle, M. J., Vilim, A,, Wilson, W. L. (1979) J . Pharm. Chem. Comniun. l I62 Pharmacol. 31 : 441-443 lndelicato, J . M., Norvilas, T . T., Pfeiffer, R . R., Yamana, T., Tsi~ji, A., Kanayama, K., Nakano, 0. Wheeler, W. J., Wilham, W. L. (1974) J. Med. Chem. (1974) J. Antibiot. 28: 1000-1002 17: 523-527 Karmas, G., Spoerri, P. E. (1956) 5. Am. Chem. Soc. 74: 158@ 1584

The estimation of diffusion coefficients using the rotating diffusion cell

Abstract The rotating diffusion cell developed by Albery et al. (1976) has been used to estimate the diffusion coefficients of two esters of nicotinic acid in a selection of organic barriers. It is shown that the diffusion coefficients of these esters in some of the systems investigated are comparable to their values in the epidermis of human skin. The rotating diffusion cell is therefore proposed as a possible in vitro method for studying the percutaneous absorption of certain drugs.

Transport across a phospholipid barrier

Abstract The transport of two small organic solutes across a phospholipid barrier supported in a Millipore filter has been studied. The flux of penetrant across the barrier has been followed using two different experimental procedures with a rotating diffusion cell. In one approach, the data is analyzed by the normal reduction for rotating diffusion cell experiments; in the other, a new interpretation of the lag-time for transport across the barrier is invoked. The combination of the two analyses allows determination of the diffusion coefficient of the solute in the lipid barrier, the aqueous-lipid partition coefficient of the solute, and the interfacial transfer rate constant for the solute crossing the phospholipid-aqueous phase interface. Comparison of the transport parameters obtained with in vivo percutaneous absorption results is discussed.

Some studies of the diffusion of sodium ions through protein solutions and phospholipid sols

Diffusion of sodium‐22 in solutions containing sodium chloride, calcium chloride, bovine plasma albumin, lecithin and cholesterol has been examined by two methods which were modifications of the open‐end capillary technique of Anderson & Saddington (1949) and the continuous monitoring technique of Mills & Godbole (1958). Preliminary investigations of semi‐infinite systems consisting of lecithin sols layered on albumin solutions have been made. The activity in the capillary at various times during diffusion has been compared with the theoretical activity and good agreement has been found.

SOME ASSAY PROCESSES INVOLVING THE USE OF ION EXCHANGE RESINS

IN a recent review1 one of the authors has outlined the possible applications of ion exchange resins in assay processes of pharmaceutical interest. This paper outlines experimental details of several such processes and gives a summary of the results obtained by them. A valuable book2 dealing with the application of ion exchange resins to analytical chemistry in general, has now become available in this country.

Solution of the equations describing the flow of 22Na in a semi-infinite composite system containing a membrane

Abstract Solutions to the flow equations in a semi-infinite composite system consisting of protein solution and a phospholipid sol with a membrane at the interface are described in this paper. The composite system was contained in a length of precision bore capillary tubing and the flow rate in the system was followed by using labelled NaCl and a continuous monitoring apparatus.

Measurement of the permeability coefficient of 22Na+ through a synthetic phospholipid-protein membrane

Abstract The diffusion of 22Na+ through a composite system consisting of a layer of phospholipid sol and a layer of bovine plasma albumin have been made using a modified form of the continuous monitoring method. When 0.001 M CaCl2 and cholesterol is added to each layer a membrane is formed at the interface and affords a resistance to diffusional flow. Equations have been developed using Laplace transform theory from which the permeability coefficient of this membrane can be calculated.

Long-time solution of the equations describing the flow of 22Na+ in a finite composite system containing a synthetic phospholipid-protein membrane: Calculation of permeability coefficient

Abstract Flow equations are developed using Laplace transform theory to describe the diffusion of 22 Na + through a composite system consisting of a protein solution and a phospholipid sol with a membrane at the interface. An approximation, valid at long times (t > 1.5 × 10 5 s), is then introduced enabling calculation of an unambiguous limiting value for the permeability coefficient of the membrane.

The use of a thermoelectric osmometer to measure the osmotic coefficients of aqueous solutions of sodium salicylate at 25

The use of a thermoelectric osmometer to measure osmotic coefficients for the binary system water‐sodium salicylate at low concentrations (0·0 to 0·3 molal) is described. The accuracy and reproducibility of the instrument have been enhanced by employing a microscope to measure sample and reference drop sizes. Activity coefficients, calculated from the osmotic coefficients obtained in these experiments, have been combined with density and diffusional measurements to calculate frictional coefficients for the system.

A novel method to study the permeability of a phospholipid barrier

The development of a new filter system is described which enables the permeability of a phospholipid barrier to be determined.