Showing papers on "Permeation published in 1990"

Membrane Mass Spectrometry for the Direct Trace Analysis of Volatile Organic Compounds in Air and Water

Abstract: Very simple membrane inlets can be constructed that are selectively permeable to organic molecules while discriminating against the air or water sample matrix. The membrane thickness directly affects the flow through the membrane such that thinner membranes provide higher throughputs and shorter response times. Higher temperatures result in shortened response times and reduced selectivity of the permeation process. Comparisons of two hollow fiber membrane inlet geometries show that permeation rates are improved in the configuration where the sample flows through the inside of the hollow fiber and the permeating gases are analyzed on the outside, as opposed to the reversed configuration.

Percutaneous absorption enhancement of an ionic molecule by ethanol-water systems in human skin.

Abstract: Ethanol–water systems enhance permeation of ionic solutes through human stratum corneum. Optimum enhancement of salicylate ion permeation has been observed with ethanol volume fractions near 0.63. The mechanism of action of ethanol–water systems enhancing skin permeation was investigated by in vitro skin permeation studies combined with Fourier transform infrared spectroscopy experiments. The increased skin permeation of the ionic permeant by the ethanol–water systems may be associated with alterations involving the polar pathway. Polar pathway alterations may occur in either or both the lipid polar head and proteinaceous regions of the stratum corneum. Ion-pair formation may also contribute to increased permeation. However, the decreased permeation of salicylate ion observed at higher volume fractions of ethanol may be attributed to decreased uptake of permeant into the stratum corneum.

Contributions of drug solubilization, partitioning, barrier disruption, and solvent permeation to the enhancement of skin permeation of various compounds with fatty acids and amines.

Abstract: The contributions of several proposed mechanisms by which fatty acids and amines might increase skin permeation rates were assessed. Permeation rates of model diffusants with diverse physicochemical properties (naloxone, testosterone, benzoic acid, indomethacin, fluorouracil, and methotrexate) through human skin were measured in vitro. The enhancers evaluated were capric acid, lauric acid, neodecanoic acid, and dodecylamine. Increased drug solubility in the vehicle, propylene glycol (PG), in some cases accounted for the increases in flux in the presence of adjuvants, since permeability coefficients were unchanged. Partition coefficients of some drugs into isopropyl myristate or toluene were increased by the adjuvants, but this did not occur for combinations of an acid with a base (adjuvant-drug or drug-adjuvant). Increases in flux not accounted for by increases in drug solubility or partitioning were assumed to involve disruption of the barrier function of skin (increased skin diffusivity). All fatty acids increased skin diffusivity of naloxone, testosterone, indomethacin, and fluorouracil but not of methotrexate or benzoic acid. Dodecylamine increased skin diffusivity only for fluorouracil. Capric acid and dodecylamine, but not lauric acid or neodecanoic acid, increased the skin permeation rate of PG, suggesting that enhanced solvent penetration could also be involved as a mechanism for increased skin permeation of the drug. However, the increase in PG flux due to dodecylamine was nullified when methotrexate was added to the vehicle, possibly because of a dodecylamine/methotrexate interaction. These studies demonstrate that drug solubilization in the vehicle, increased partitioning, increased solvent penetration, and barrier disruption each can contribute to increased skin permeation rates in the presence of fatty acids and amines. The relative contributions of the mechanisms vary with the drug, the adjuvant, and the vehicle.

Transdermal delivery of narcotic analgesics: pH, anatomical, and subject influences on cutaneous permeability of fentanyl and sufentanil.

Abstract: The permeation of fentanyl and sufentanil through cadaver skin membranes was investigated using in vitro diffusion cell techniques. Neither drug influenced the permeation of the other when they were concurrently applied to the skin membrane. With respect to transdermal delivery, short diffusion lag times of less than 0.5 hr were observed for each compound. Their permeation rates through heat-isolated epidermis and dermatomed (200- to 250-µm) skin sections were essentially the same. However, when the stratum corneum was removed by tape stripping, the respective permeability coefficients were increased >30-fold, establishing the stratum corneum as the principal barrier to their skin permeation. Permeation was also studied as a function of pH. From pH 4 to pH 8 the permeability coefficients of both fentanyl and sufentanil, calculated from the total solution concentration regardless of ionization, increased exponentially. The free base is thus responsible for the relatively facile skin permeation of these drugs. Factoring of the independent permeability coefficients of the ionized and free-base forms was possible, with the latter being over two log orders larger than seen for the protonated species. Permeability coefficients of fentanyl and sufentanil through skin sections obtained from different cadavers varied four- to fivefold. Neither gender nor age was a flux-determining variable for either drug. The permeability coefficients of the drugs through skin sites as diverse as the sole of the foot, chest, thigh, and abdomen were remarkably similar. Their fluxes were sufficient for transdermal administration.

Potassium Sorbate Permeability of Methylcellulose and Hydroxypropyl Methylcellulose Coatings: Effect of Fatty Acids

Abstract: Surface microbial stability is a major determinant of the shelf life of refrigerated meat products. Surface microbial growth has also been noticed in intermediate moisture foods exposed to temperature fluctuations. One solution to this problem is to apply edible coatings to the food surface which control diffusion of antimicrobial agents into the food. Films with such properties were identified using a permeability cell. Methyl- and hydroxypropyl methylcellulose mixed with lauric, palmitic, stearic and arachidic acid significantly lowered the potassium sorbate permeation rate relative to cellulose ether films containing no fatty acids. Permeability determinations at 5, 24, 32 and 40°C showed excellent agreement with the Arrhenius activation energy model for the permeation process.

Prediction of skin permeability of drugs. I. Comparison with artificial membrane.

Abstract: In order to measure the contribution of lipid and pore (aqueous) pathways to the total skin permeation of drugs, and to establish a predictive method for the steady state permeation rate of drugs, the relationship between permeability through excised hairless rat skin and some physicochemical properties of several drugs were compared with those through polydimethylsiloxane (silicone) and poly(2-hydroxyethyl methacrylate)(pHEMA) membranes, as typical solution-diffusion and porous membranes, respectively. A linear relationship was found between the permeability coefficients of drugs for the silicone membrane and their octanol/water partition coefficients. For the pHEMA membrane, the permeability coefficients were almost constant independent of the partition coefficient. On the other hand, the skin permeation properties could be classified into two types : one involves the case of lipophilic drugs, where the permeability coefficient is correlated to the partition coefficient, similar to the silicone, membrane; and the other involves hydrophilic drugs, where the permeability coefficients were almost constant, similar to pHEMA membrane. From the above results, the stratum corneum, the main barrier in skin, could be described as a membrane having two parallel permeation pathways : lipid and pore pathways. An equation for predicting the steady state permeation rate of drugs was derived based on this skin permeation model.

Properties of permeation pathways induced in the human red cell membrane by malaria parasites.

Abstract: The intracellular development of malaria parasites in mature erythrocytes imposes on the host cell a major demand for supply of nutrients and disposal of waste products. So as to cope with these demands, the erythrocyte membrane undergoes profound alterations in its basic permeability properties. A few hours after being invaded by Plasmodium falciparum parasites, and before any structural changes are apparent on the surface, the molecular traffic across the red cell membrane changes both in intensity and in composition of permeating substances. The changes are of a gradual nature, developmentally related and dependent on de novo protein synthesis, but do not occur concurrently for all the classes of permeants. Molecules which permeate very poorly into uninfected cells, such as hexitols (e.g., sorbitol and myoinositol), amino acids (e.g., glutamine, threonine, and histidine), a variety of organic acids and metal ions show a marked increase in their permeation rates across the host cell membrane. Likewise, substances whose normal permeation pathways conform with those of facilitated diffusion (e.g., hexoses, nucleosides, choline, and some amino acids), gain access into the host cytosol either by modified or additional permeation pathways. It has been proposed that three major new pathways are induced in the membrane of infected cells: (1) one of pore-like properties, which can accommodate most of the water soluble permeants, including anionic substances; (2) a protein-lipid interface, which can accommodate compounds of relatively higher hydrophobic character; and (3) modified constitutive transporters or modified lipid surroundings with altered transport activities. The pores are blocked by permeant bioflavonoid glycosides whose sites of binding are endofacial, and amount to less than a thousand per cell. In addition to serving as specific targets for transport blockers, the new sites of permeation can also serve as routes for enhanced delivery of cytotoxic agents into parasitized cells.

Preparation of γ-alumina thin membrane by sol-gel processing and its characterization by gas permeation

Abstract: γ-alumina porous membranes without pinholes or cracks were prepared by the sol-gel process. The boehmite sol obtained from hydrolysation of aluminium isopropoxide was applied to the inner surface of a porous supporting tube by a dipping procedure. The effects of sol concentration and the repetition number of dipping-drying-firing procedure on the membrane performance were investigated by scanning electron microscopy, X-ray diffraction and the Brunauer-Emmett-Teller method in connection with the micro-structure of the membrane. Gas permeation measurements were also conducted. The gas permeation through the thin membranes is well explained by Knudsen's flow, indicating the pores are controlled finely and homogeneously.

Gas separation by thin porous silica membrane of ultra fine pores at high temperature.

Abstract: For the purpose of gas separation at high temperature, a thin porous silica membrane of ultra fine pores has been prepared by the sol-gel method, where silica sol was coated near the outer surface of a porous cylindrical substrate of α-alumina, then it was dried and fired at around 450°C.Permeability measurements for H2, He and N2 through the silica membrane were carried out at various temperatures (30-270°C) to show that the permeabilities of H2 and He, which increased with the increase of temperature, were 30-300 times larger than that of N2, and that the permeability of He was appreciably larger than that of H2, These results clearly show that the activated diffusion or permeation prevails instead of the Knudsen diffusion through the silica membrane, while the permeability of N2 showed a negative temperature dependency, which is probably due to the Knudsen diffusion through some pin holes still left in the membrane. The activation energy for HZ and He were estimated to be 8.3kJ/mol and 4.0kJ/mol respectively.Separation results for H2/N2 and He/N2 mixtures at 270°C showed that large separation ratio could be obtained, and also that each gas component permeated independently without any molecular interactions among permeating molecules in the fine pores of the silica membrane, Which makes possible an estimation of separation performance from the permeation results for pure gases.

Enhancement of the in vitro skin permeability of azidothymidine (AZT) via iontophoresis and chemical enhancer.

Abstract: Azidothymidine (AZT) was used as a model drug to study the effect of iontophoresis on the skin permeation of a neutral compound. The rate of in vitro permeation across hairless rat skin was low and highly variable. With iontophoresis treatment the permeation rate was two- to threefold greater than by passive diffusion. The addition of varying amounts of sodium chloride to the donor enhanced the iontophoretic permeation rate an additional two- to threefold possibly due to convective forces. The addition of N-decylmethyl sulfoxide (C10MSO) to the donor increased the permeation rate by several hundred-fold over passive diffusion for hairless rat skin and approximately 75-fold for human skin. No additional enhancement was observed with the combination of C10MSO and iontophoresis treatment at constant current or constant voltage. It may be that the presence of C10MSO lowers the zeta potential of the skin, thus enhancement due to convective flow is minimized.

Hydrogen Permeation Through the Passivation Film on Iron by Time‐Lag Method

Abstract: The permeation of hydrogen through anodically passivated iron is measured at two values of hydrogen charging current density. The permeation transient is analyzed in terms of diffusion of hydrogen through iron in series with diffusion and migration of hydrogen ions through the anodic oxide, with local equilibrium at the metal‐oxide interface. The analysis yields the diffusion coefficient of hydrogen in the oxide, and the ratio of concentrations in the metal and in the oxide at the interface.

POTASSIUM SORBATE PERMEABILITY of POLYSACCHARIDE FILMS: CHITOSAN, METHYLCELLULOSE and HYDROXYPROPYL METHYLCELLULOSE

Abstract: Edible coatings controlling preservative migration from surface to food bulk could control surface microbial growth which is often the main cause of spoilage for many food products. In this paper we examine the potassium sorbate permeability behavior of chitosan, methyl cellulose and hydroxypropyl methyl cellulose based films. to gain an understanding of the permeation process, permeability determinations were done at 5, 24, 32 and 40°C. Permeability rates followed the Arrhenius activation energy model. A lack of breaking points in Arrhenius plots indicated that no morphological changes occur within these films in the 5 to 40°C temperature range. Activation energy values were found to be independent of film composition and were affected only by the solvent embedded in the film. This behavior was confirmed by analysis of the same permeability data using a modified Stokes-Einstein equation. Methyl cellulose was the most promising diffusion barrier with a permeability constant of 3.4 and 1.4×10−8 (mg/s cm2) (cm)/(mg/cm3) at 24 and 5°C, respectively. Electron microscopy was used to examine the morphological characteristics of these films and showed they have no visible pores or channels at magnifications up to 10,000.

Pervaporation separation of water/ethanol mixtures through polysaccharide membranes. IV, The relationships between the permselectivity of alginic acid membrane and its solid state structure

Abstract: Membranes composed of alginic acid, which is one of the anionic polysaccharides, were investigated as pervaporation membranes for the separation of water/alcohol mixtures. The selectivity of the alginic acid membrane increased markedly by more than 10,000 when the carboxyl group of alginic acid was neutralized by bases. The counter cation (Li+, Na+, K+, Rb+, and Cs+) influenced the permeation rate for the alginate membranes, which varied from 0.1 kg/m2h for the Li version to 1.0 kg/m2h for the Cs version, but the counterion had hardly any effect on the selectivity. The behavior could not be explained simply by the affinity of the alginate membranes toward water, but could be explained well by the conformation change and mobility of alginate molecules investigated by CP/MAS 13C-NMR, water mobility within the alginate membrane, and crystallinity of the membrane.

Ethanol extraction by supported liquid membrane during fermentation.

Abstract: A supported liquid membrane system was developed for the extraction of ethanol during semicontinuous fermentation of Saccharomyces bayanus. it consisted of a porous Teflon sheet as support, soaked with isotridecanol. This assembly permitted combining biocompatibility, permeation efficiency, and stability. The removal of ethanol from the cultures led to decreased inhibition and, thus, to a gain in conversion of 452 g/L glucose versus 293 g/L glucose without extraction. At the same time, the ethanol volumetric productivity was enhanced 2.5 times, due to an improvement of yeast viability, while the substrate conversion yield was maintained above 95% of its theoretical value. Besides these improvements in fermentation performances, the process resulted in ethanol purification, since the separation was selective towards microbial cells and carbon substrate, and likely selective to mineral ions present in the fermentation broth. For pervaporation, a concentration of ethanol four times greater was obtained in the collected permeate.

Oxygen permeability of low density polyethylene as a function of limonene absorption: an approach to modeling flavor "scalping".

Abstract: A procedure was developed to measure adsorption (scalping) of limonene by low density polyethylene. The polymer was mounted on an oxygen electrode. Limonene absorption produced an increase in oxygen permeability which appeared proportional to limonene concentration. Diffusion coefficients calculated from permeation curves were similar to diffusion coefficients calculated on a weight change basis.

The separation of water–ethanol mixtures by pervaporation through hydrophilic—hydrophobic composite membranes

Abstract: A new kind of polymer composite membrane, which we refer as hydrophilic–hydrophobic composite membrane, is prepared by the concentrated emulsion polymerization method6,7 and employed to separate permselectively ethanol–water mixtures. This composite contains polyacrylamide as the dispersed phase and crosslinked polystyrene as the continuous phase. The swelling in water of this composite membrane is around 4 g water/g polymer and its swelling in ethanol is negligible. The permeation of the composite membrane by pervaporation decreases with increasing ethanol concentration in the feed and increases with increasing polyacrylamide fraction in the composite. The rate of permeation is in the range of 30–103 g/m2 h. The selectivity of the membrane ranges between 2 and 50 and increases with increasing ethanol concentration in the feed and increasing polyacrylamide fraction in the composite. The permeation increases and the selectivity decreases with increasing feed temperature. The activation energy of permeation varies between 1.8 and 4.9 kcal/mol, depending upon the compositions of the feed and membrane.

Chemical modification of poly(substituted‐acetylene): II. Pervaporation of ethanol / water mixture through poly(1‐trimethylsilyl‐1‐propyne) / poly(dimethylsiloxane) graft copolymer membrane

Abstract: Poly(1-trimethylsilyl-1-propyne)/poly(dimethylsiloxane) (PTMSP/PDMS) graft copolymer was prepared to evaluate the permeation characteristic at pervaporation of aqueous ethanol solution through the graft copolymer membrane. For the preparation of PTMSP/PDMS graft copolymer, an improved synthetic procedure was released in this paper, which comprised a one-pot reaction of PTMSP in lithium bis(trimethylsilyl)amide followed by treatment with hexamethylcyclotrisiloxane and trimethylchlorosilane. PDMS content of the graft copolymer was controlled in the range 5–74 mol%. Very tough and thin membranes could be prepared from these copolymers having various PDMS content by the solvent casting method. The permselectivity of the membranes was investigated by pervaporation of ethanol/water mixture at 30°C. Preferential permeation of ethanol was observed for the membranes. It was also found that the selectivity of every copolymer membrane was higher than that of the PTMSP membrane. Moreover, the selectivity depended on the PDMS content of the graft copolymer. The separation factor and permeation rate assumed the maximum values at 12 mol% PDMS content. At the maximum point, 7 wt% aqueous ethanol solution was concentrated to about 70 wt% ethanol solution, and the separation factor and permeation rate were 28.3 and 2.45 × 10−3g · m/m2 · h, respectively. Such a high permselectivity for ethanol might be due to a delicate alteration of membrane structure, which was induced by the introduction of a short PDMS side chain into a PTMSP backbone.