Biomedical subjects

David A Sabatini

Publications and source records attributed to David A Sabatini.

13 recordsLinked to original sources

PubMed2006

Sorption of acetaminophen, 17alpha-ethynyl estradiol, nalidixic acid, and norfloxacin to silica, alumina. and a hydrophobic medium.

Two pure minerals and a hydrophobic medium were selected to study sorption of pharmaceuticals. The sorption of four pharmaceuticals, acetaminophen (analgesic), 17alpha-ethynyl estradiol (synthetic hormone), nalidixic acid (antibiotic), and norfloxacin (antibiotic), was evaluated with silica, alumina, and Porapak P (a hydrophobic medium). Alumina and silica were selected to represent positively charged and negatively charged aquifer mineral surfaces at neutral pH, respectively, while Porapak P was selected to represent the hydrophobic organic content of an aquifer medium. At neutral pH, acetaminophen, the least hydrophobic pharmaceutical, showed no significant sorption to any of the media, while 17alpha-ethynyl estradiol, the most hydrophobic pharmaceutical, showed significant sorption to Porapak P. Nalidixic acid, which has a carboxyl functional group that is anionic at neutral pH, showed significant adsorption to the positively charged alumina. Norfloxacin, with both a carboxyl (anionic) and a piperazynyl (cationic) group, can exist in four forms (neutral, cationic, anionic, and zwitterionic) depending on the aqueous pH. Norfloxacin also showed significant adsorption than nalidixic acid. Both nalidixic acid and norfloxacin adsorbed to silica and Porapak P to a much lower extent. The pH dependence of nalidixic acid and norfloxacin adsorption to silica and alumina was also studied by varying the pH between 4 and 11. The maximum adsorption of nalidixic acid to alumina occurred near its pKa (pH approximately 6), where the combination of cationic alumina and anionic nalidixic produced maximum adsorption. The maximum adsorption of norfloxacin to alumina was observed at pH approximately 7, which was the region where the zwitterionic form dominated. This research demonstrates that the adsorption of ionizable pharmaceuticals is strongly dependent on the system pH, the pharmaceutical properties (pKa and hydrophobicity), and the nature of the surface charge (point of zero charge). For pharmaceuticals that are uncharged at environmentally relevant pH values, the main sorption factor is their solubility or hydrophobicity; for charged forms, ion exchange is also an important adsorption mechanism.

Acetaminophen↗

PubMed2005

Field demonstration of surfactant-enhanced solubilization of DNAPL at Dover Air Force Base, Delaware.

This study reports on a surfactant-based flood for tetrachloroethylene (PCE) removal from a control test cell at the Dover National Test Site. The surfactant formulation (sodium dihexyl sulfosuccinate (Aerosol-MA or AMA), isopropanol and calcium chloride) was able to achieve a high concentration of PCE in swollen micelles (supersolubilization) without vertical PCE migration. The hydraulic system included eight screened wells that were operated in both vertical circulation and line drive configurations. After 10 pore volumes of flushing, the overall PCE removal was 68% (65% of which corresponded to the surfactant flooding alone). In addition, the residual PCE saturation was reduced from 0.7% to 0.2%, and the concentration of PCE in the groundwater was reduced from 37-190 mg/L before the flushing to 7.3 mg/L after flooding. Recycling the surfactant solution reduced the required surfactant mass (and thus cost, and waste) by 90%. Close to 80% of the total PCE removal was obtained during the first five pore volumes which were operated in an upward vertical circulation flow scheme. No free oil phase was observed during the test. Further analysis of multilevel sampler data suggests that most of the trapped oil remaining in the cell was likely localized in secluded regions of the aquifer, which helps explain the lower PCE groundwater concentration after remedial activities. In summary, this field study demonstrated the feasibility of surfactant-enhanced remediation to reduce the mass in the source zone and significantly reduce the PCE aqueous concentration and therefore the risk associated with the contaminant plume.

2-Propanol↗

PubMed2005

Modeling solubilization of oil mixtures in anionic microemulsions II. Mixtures of polar and non-polar oils.

Polar/amphiphilic oils, called lipophilic linkers, are sometimes added to oil-water-ionic surfactant microemulsions in order to increase the solubilization of hydrophobic oils. The solubilization increase has been well documented for a number of systems. However, mathematical models to calculate the solubilization increase have been proposed only for optimum microemulsions (i.e., middle phase microemulsions solubilizing equal volumes of oil and water). In this paper we propose a model, which predicts solubilization enhancement for non-optimum microemulsion systems as well. The model is an extension of the net-average curvature model of microemulsion. The net-average curvature model is combined with a surface activity model to account for the increased palisade layer solubilization due to the presence of the polar/amphiphilic oil component. New non-linear mixing rules are also incorporated to account for the optimum salinity and the characteristic length variation of the anionic surfactant microemulsion as a function of the lipophilic linker concentration. The model predicts the effect of the lipophilic linker and the electrolyte concentration on the oil solubilization in accordance with the experimental results.

Journal Article↗

PubMed2005

Preferential solubilization of dodecanol from dodecanol-limonene binary oil mixture in sodium dihexyl sulfosuccinate microemulsions: effect on optimum salinity and oil solubilization capacity.

Solubilization of dodecanol-limonene binary oil mixtures has been studied in saturated Winsor type I and III sodium dihexyl sulfosuccinate microemulsions. The systems showed different oil solubilization behavior below and above dodecanol volume fraction 0.2. Below 0.2 dodecanol volume fraction regular Winsor type microemulsions formed. The oil solubilization was characterized in this concentration range by the optimum salinity and the maximum characteristic length. Dodecanol showed Langmuirian-type surface excess adsorption at the vicinity of the surfactant layer. Variation of the optimum salinity and middle phase characteristic length with increasing dodecanol concentration could be linked to changes in the dodecanol surface excess. These relationships were used to develop new mathematical models for the optimum salinity and characteristic length as a function of oil phase composition. Both models yield excellent agreement with the data. Above dodecanol volume fraction 0.2 regular Winsor type III microemulsions are not formed. Therefore our new models are not applicable in this concentration range.

Journal Article↗

PubMed2005

Effects of pH and cationic and nonionic surfactants on the adsorption of pharmaceuticals to a natural aquifer material.

A wide range of pharmaceutical compounds have been identified in the environment, and their presence is a topic of growing concern, both for human and ecological health. Adsorption to aquifer materials and sediments is an important factor influencing the fate and transport of pharmaceutical compounds in the environment. Surfactants and other amphiphiles are known to influence the adsorption of many compounds and may be present in the environment from wastewaters or other sources. The work described here examines the adsorption of four pharmaceutical compounds, acetaminophen, carbamazepine, nalidixic acid, and norfloxacin, in the presence of a natural aquifer material. Adsorption was studied as a function of pH and in the presence and absence of two surfactants, cetylpyridinium chloride (CPC), a cationic surfactant, and Tergitol NP9, an ethoxylated nonionic surfactant. In the absence of surfactants, results indicate a 1-2 orders of magnitude variation in adsorption affinity with changing pH for each of the two quinolone pharmaceuticals (nalidixic acid and norfloxacin) but no measurable adsorption for carbamazepine or acetaminophen. In the presence of surfactants, adsorption of acetaminophen and carbamazepine was enhanced to extents consistent with compound hydrophobicity, while adsorption of nalidixic acid and norfloxacin was not. At high pH values, the anionic species of nalidixic acid exhibited enhanced adsorption in the presence of the cationic surfactant, CPC.

Acetaminophen↗

PubMed2005

Linker-based bio-compatible microemulsions.

In this work we have studied the formulation of biocompatible microemulsions using lecithin as the main surfactant and bio-compatible linker molecules (hexyl polyglucoside asthe hydrophilic linker and sorbitan monoleate as the lipophilic linker). These bio-compatible systems are discussed as potential substitutes for chlorinated solvents in dry-cleaning applications and as solvent delivery systems for pharmaceutical applications. Formulation parameters and conditions were evaluated using isopropyl myristate (IPM) as the model oil. It was found that the proposed linker-based formulations were able to form alcohol-free microemulsions while achieving higher solubilization capacity than similar systems reported in the literature. In addition, these lecithin/linker formulations were able to form microemulsions with a wide range of oils, from polar chlorinated hydrocarbons to hydrophobic oils such as squalene. These microemulsions were achieved under isotonic conditions (0.9% NaCl) by only varying the relative proportions of the linkers. The "solvency" power of these bio-compatible formulations was tested for the removal of hexadecane (used as model oil) from cotton fabrics and compared to the solvency power of a typical dry cleaning solvent tetrachloroethylene (PCE). While PCE and the linker-based lecithin formulation removed the same amount of hexadecane at low loading ratios (less than 1% oil volume fraction), at higher loading ratios the linker-based lecithin formulation retained its oil removal capacity while the efficiency of the PCE system declined rapidly. These initial results thus demonstrate the remarkable oil solubilization capacity of these bio-compatible linker-based lecithin formulations and illustrate their potential as environmentally friendly replacements for organic solvents.

Biocompatible Materials↗

PubMed2004

Partitioning of hydrophobic organic chemicals (HOC) into anionic and cationic surfactant-modified sorbents.

Surfactant-modified sorbents have been proposed for the removal of organic compounds from aqueous solution. In the present study, one cationic (HDTMA) and three anionic (DOWFAX-8390, STEOL-CS330, and Aerosol-OT) surfactants were tested for their sorptive behavior onto different sorbents (alumina, zeolite, and Canadian River Alluvium). These surfactant-modified materials were then used to sorb a range of hydrophobic organic chemicals (HOCs) of varying properties (benzene, toluene, ethylbenzene, 1,2-dichlorobenzene, naphthalene, and phenanthrene), and their sorption capacity and affinity (organic-carbon-normalized sorption coefficient, K(oc)) were quantified. The HDTMA-zeolite system proved to be the most stable surfactant-modified sorbent studied because of the limited surfactant desorption. Both anionic and cationic surfactants resulted in modified sorbents with higher sorption capacity and affinity than the unmodified Canadian River Alluvium containing only natural organic matter. The affinities of the surfactant-modified sorbents (K(oc)) for most HOCs are lower than octanol/water partition coefficient (K(ow)) normalized to the organic carbon content (f(oc)) and the density of octanol (K(oc) octanol); naphthalene and phenanthrene are the exceptions to this rule.

Adsorption↗

PubMed2004

Evaluating phenanthrene sorption on various wood chars.

A certain amount of wood char or soot in a soil or sediment sample may cause the sorption of organic compounds to deviate significantly from the linear partitioning commonly observed with soil organic matter (SOM). Laboratory produced and field wood chars have been obtained and analyzed for their sorption isotherms of a model solute (phenanthrene) from water solution. The uptake capacities and nonlinear sorption effects with the laboratory wood chars are similar to those with the field wood chars. For phenanthrene aqueous concentrations of 1 microg l(-1), the organic carbon-normalized sorption coefficients (log K(oc)) ranging from 5.0 to 6.4 for field chars and 5.4-7.3 for laboratory wood chars, which is consistent with literature values (5.6-7.1). Data with artificial chars suggest that the variation in sorption potential can be attributed to heating temperature and starting material, and both the quantity and heterogeneity of surface-area impacts the sorption capacity. These results thus help to corroborate and explain the range of logK(oc) values reported in previous research for aquifer materials containing wood chars.

Adsorption↗

PubMed2004

A two-state model for selective solubilization of benzene-limonene mixtures in sodium dihexyl sulfosuccinate microemulsions.

When surfactants are used to solubilize oil, the oil to be solubilized is often a mixture of components with differing properties, for example, solubilization of drug molecules in microemulsion formulations, remediation of organic polluted aquifers using surfactants, and so forth. Previous research has demonstrated that selective solubilization of one organic component over the other may occur if the organic components are dissimilar. In this research, we investigated selective solubilization from benzene-limonene mixtures in Winsor type I and III microemulsion systems containing water, sodium di-n-hexyl sulfosuccinate, and NaCl. The effect of the oil phase composition and the electrolyte concentration on the selectivity was studied. It was found that the selectivity toward benzene was highest at low electrolyte and benzene concentrations, decreasing as the electrolyte or benzene concentration increased. The results are discussed on the basis of the two-state solubilization theory and by correlating the curvature of the surfactant film in the microemulsion with changes of the electrolyte concentration and the oil phase composition. A simple mathematical model is developed for the selectivity, which combines the two-state solubilization theory and the net-average curvature model of microemulsion solubilization to yield close agreement with the experimental data.

Journal Article↗

PubMed2004

Self-assembly in linker-modified microemulsions.

Linker molecules are added to microemulsion systems to enhance the interaction between the surfactant and oil (lipophilic linkers) or water (hydrophilic linkers) phases. Previous results suggest that when lipophilic and hydrophilic linkers are combined they behave as a self-assembled surfactant at the oil/water interface. In this work we investigate this self-assembly phenomenon as a function of surfactant, linker and electrolyte concentration. We find that middle phase microemulsion appears at a specific concentration higher than the critical micelle concentration (CMC), which we denote as the critical middle phase microemulsion concentration (CmicroC). When the lipophilic linker dodecanol is added in equimolar ratio to the hydrophilic linker sodium mono- and dimethyl naphthalene sulfonate (SMDNS), the middle phase microemulsion did not appear until the surfactant sodium dihexyl sulfosuccinate (SDHS) concentration was larger than the CmicroC of the SDHS-alone system. Dodecanol is shown to segregate near the surfactant tails following a Langmuir-type adsorption process. This segregation is not affected by the electrolyte concentration but is significantly reduced when the surfactant (SDHS) concentration approaches the CmicroC. The data suggest that the self-assembly between hydrophilic and lipophilic linkers to form middle phase microemulsions is only possible if a minimum amount of surfactant is present.

Journal Article↗

PubMed2004

Improving the extraction of tetrachloroethylene from soil columns using surfactant gradient systems.

In this work, we extend the recently developed gradient approach for surfactant-enhanced remediation of dense non-aqueous phase liquid (DNAPL)-impacted sites. The goal of the gradient approach is to maximize the DNAPL solubilization capacity in swollen micelles (Type I aqueous microemulsions) while at the same time minimizing the potential for DNAPL mobilization. In this work, we introduce a modified version of the capillary/trapping curve that we refer to as the gradient curve to help interpret and/or design the gradient approach. The gradient curve presents the residual DNAPL saturation as a function of interfacial tension and microemulsion viscosity. This approach demonstrates that keeping a low viscosity of the microemulsion phase is not only important for keeping a low head loss during surfactant flooding but also to prevent oil mobilization. Eight microemulsion systems were evaluated in this research; these systems were evaluated based on their tetrachloroethylene (PCE) solubilization capacity, interfacial tension (IFT), viscosity, density, and coalescence kinetics. Two of these systems were chosen for evaluation in site-specific column tests using an increasing electrolyte gradient to produce a decreasing IFT/increasing solubilization gradient system. The column studies were conducted with media from Dover Air Force Base in Dover, DE. Both solubilized and mobilized DNAPL were quantified. During the column studies, we observed that substantial PCE was mobilized when the residual level of PCE in the column was significantly higher than the steady-state residual saturation level being approach (as predicted from the gradient curve). Four column studies were performed, three of which were used to asses the validity of the gradient curve in predicting the residual saturation after each gradient step. From these tests we observed that starting IFTs of less than 1 mN/m all produced the same mobilization potential. In the last column, we used an additional gradient step with an initial IFT above 1 mN/m to dramatically reduce the amount of PCE mobilize. Based on the good agreement between column results and projections based on the gradient curve, we propose this as a preferred method for designing gradient surfactant flushing systems.

Environmental Pollutants↗

PubMed2002

Formulating chlorinated hydrocarbon microemulsions using linker molecules.

Previously we reported on the use of lipophilic, hydrophilic, and combined linkers for formulating microemulsions of trichloroethylene and tetrachloroethylene. These linker molecules augment the interaction between the surfactant and oil phase (lipophilic linkers) or between the surfactant and water phase (hydrophilic linkers). Combining both linkers can increase the solubilization capacity several-fold. This formulation technique shows potential advantage in reducing surfactant costs and remedial times, as well as allowing the use of more environmentally friendly additives when designing surfactant-enhanced remediation systems. In this paper, we evaluate the relative importance of the surfactant and each linker in increasing the system's solubilization capacity. This interpretation is based on solubilization curves, partitioning studies, and formulation studies. The solubilization curves show that optimum linker performance is reached at an equimolar ratio of dodecanol, used as a lipophilic linker, and sodium mono and dimethyl naphthalene sulfonate, used as a hydrophilic linker. Furthermore, this equimolar combination was able to replace the anionic surfactant sodium dihexylsulfosuccinate. Dodecanol partitioning at optimum formulation shows that the poor performance of lipophilic linkers alone is due to their low partitioning into the middle phase. Adding hydrophilic linkers into this system increases the fraction of dodecanol in the middle phase, thereby further enhancing the solubilization capacity of the system. A variation of the combined linker approach is introduced by changing a lipophilic linker, oleic acid, into a surfactant (soap), with further increases in the solubilization capacity by 4- to 5-fold.

Oleic Acid↗

PubMedDate not supplied

Microemulsions of triglyceride-based oils: The effect of co-oil and salinity on phase diagrams.

Microemulsification of triglyceride-based oil is challenging due to the formation of undesirable phases such as macroemulsions, liquid crystals, or sponge phases. This research evaluates the formation of artificial sebum microemulsions using linker molecules, with the addition of co-oil to help enhance sebum solubilization. The microemulsion consists of a lipophilic linker (sorbitan monooleate), a hydrophilic linker (hexylglucocide), a main surfactant (sodium dioctyl sulfosuccinate), a co-oil, and artificial sebum. The effect of adding co-oil to the phase behavior and the microstructure of the resulting microemulsion is described. The effect of several types of co-oil is also studied; the co-oils evaluated here are squalene, squalane, isopropyl myristate, and ethyl laurate. The effect of salinity on the microemulsion phase behavior is also presented. Fish diagrams are obtained by plotting total surfactant/linker concentration as a function of sebum fraction in the oil mixture (co-oil + sebum). Different microemulsion types (Winsor Types I, II, III, and IV) are formed, depending on the total surfactant/linker concentration and the fraction of co-oil in the oil mixture. Winsor Type IV (single-phase) microemulsions are observed at high surfactant/linker concentrations. These single-phase, isotropic, and low-viscous fluids are particularly useful for cleansing and delivery of functional ingredients in skin care products. Salt addition shifts the fish diagram towards more hydrophobic oil systems and higher surfactant/linker concentrations.

Cosmetics↗