Biomedical subjects

John A Bergendahl

Publications and source records attributed to John A Bergendahl.

3 recordsLinked to original sources

PubMed2004

Observations on solid phase micro-extraction for MTBE analysis.

In a recent study of aqueous phase methyl tertiary butyl ether (MTBE) adsorption onto hydrophobic molecular sieves, the solid phase micro-extraction gas chromatography analytical technique was used to measure MTBE concentrations in water. The method was especially beneficial in measuring MTBE concentrations in the microg/l range, but anomalies were observed that investigators should be aware of before employing this technique. Specifically, it was observed that the calibration of the extraction fiber with known MTBE concentrations was non-linear over all concentration ranges. The technique was not suited to higher concentrations, and dilutions were necessary to increase the working range of the technique. Lastly, the fiber was observed to extract increasingly less MTBE from known standard solutions over time, requiring repeated calibrations to obtain reliable concentrations of unknown samples.

Calibration↗

PubMed2004

Fenton's oxidation of MTBE with zero-valent iron.

Methyl tert-butyl ether (MTBE) has become a contaminant of increasing concern in the U.S. Traditional remediation technologies are successful in removing MTBE from contaminated water, but usually transfer the contaminant from the aqueous to another phase. Fenton's oxidation of MTBE provides a promising alternative to traditional remediation techniques in that it may mineralize the contaminant rather than just phase transfer. This bench-scale study investigated the feasibility of Fenton's oxidation of MTBE using zero-valent iron as the source of catalytic ferrous iron. The oxidation reactions were able to degrade over 99% of the MTBE within 10 min, and showed significant generation, and subsequent degradation, of the MTBE oxidation byproduct acetone. Second-order rate constants for MTBE degradation were 1.9 x 10(8) M(-1) s(-1) at pH 7.0 and 4.4 x 10(8) M(-1) s(-1) at pH 4.0. The total organic carbon was reduced by over 86% when a H2O2:MTBE ratio of 220:1 or greater was used.

Carcinogens↗

PubMed2003

Mechanistic basis for particle detachment from granular media.

Colloids may become detached from surfaces in environmental systems as a result of chemical and physical conditions. Many researchers reporting on colloidal detachment in natural and model systems have stopped short of mechanistically and quantitatively describing their observations. In this work, a mathematical construct is presented that quantitatively determines the effect of thermodynamics and hydrodynamics on particle detachment from surfaces in granular media. Using the Buckingham pi theorem, a mathematical model is structured based on governing dimensionless groupings. Determining dimensionless numbers elucidates conditions conducive for detachment in engineered and natural porous media. Published detachment data are compared to the mathematical model developed herein and provide support for its utility. Extensions of this technique have utility in many applications where fluid interaction with particulate-laden porous media is encountered.

Colloids↗