Jeffrey DeHart

Enzymatic Determination of Ethanol Using ‘Reagentless’ Electrocatalyzed Luminol Chemiluminescence

Abstract Flow analysis methodology is presented for the determination of aqueous ethanol in concentrations between 3–340 μM. Alcohol oxidase catalyzes the production of hydrogen peroxide which is detected by luminol chemiluminescence. Adjustment of the pH to alkaline conditions and addition of the luminophore are implemented using in-line flow-through beds containing crystalline media. The requirement for a homogeneous catalyst is eliminated by electrochemical initiation of luminescence. Traditional laboratory reagents are replaced by packed beds containing immobilized enzyme, solid phase basification media, and crystalline luminol. The methodology is suitable for application in both continuous flow and flow injection analysis configurations.

Magnetically Assisted Gasification of Solid Waste

A variety of techniques, including supercritical water oxidation, fluidized bed combustion, and microwave incineration have been applied to the destruction of solid wastes produced in regenerative life support systems supporting long duration manned missions. Among potential problems which still deserve attention are the need for operation in a variety of gravitational environments, and the requirement for improved methods of presenting concentrated solids to the reactor. Significant improvements in these areas are made possible through employment of the magnetically assisted gasification process. In this paper, magnetic methods are described for manipulating the degree of consolidation or fluidization of granular ferromagnetic media, for application in a gravity independent three step solid waste destruction process. Solids are first concentrated from an aqueous slurry using a depth filter in which the particles of filtration media are stratified according to size and consolidated for maximum filtration efficiency using magnetic forces. The organic material within the entrapped solids is destroyed by a combination of pyrolysis, isomerization, and oxidation reactions in a fluidized bed reactor. Finally, inorganic solids are removed by reverse-flow fluidization and collected on a downstream filter.

Dissolved Oxygen Determination by Electrocatalysed Chemiluminescence with In-line Solid Phase Media

Dissolved elemental oxygen is determined in a flowing aqueous stream using glucose oxidase to catalyse the reaction between D-glucose and O2 to produce hydrogen peroxide. The levels of the resulting H2O2 are detected and quantified by luminol chemiluminescence using in-line solid phase media for pH adjustment of the reagent stream and for controlled release of the luminophore. The reaction is initiated by electrochemical catalysis. By the use of excess D-glucose in the reagent flow stream, the intensity of chemiluminescence is rendered proportional only to fluctuations in the dissolved O2 concentration. The methodology provides a means for the detection of aqueous O2 in the range 0-10 mg/L.

A CHEMICAL AMPLIFICATION SYSTEM FOR CONDUCTIOMETRIC MONITORING OF AIRBORNE CO2 PARTIAL PRESSURES

A novel method for the detection and quantitation of airborne carbon dioxide is described. The method is based upon membrane transport, chemical amplification, and conductimetric detection. Gas phase CO2 is equilibrated across a hydrophobic hollow fiber membrane with a primary, secondary, or tertiary alkanolamine containing aqueous phase. The resulting dissolved carbon dioxide reacts reversibly with both water and the alkanolamines to form a variety of ionic species, including: carbonate, bicarbonate, carbamates, and protonated amines. At equilibrium, the CO2 holding capacities of the alkanolamine solutions are several orders of magnitude greater than that of pure water, resulting in a substantial amplification of the conductivity signal for solutions in equilibrium with a given atmospheric pCO2.

Reagentless chemiluminescence-based fiber optic sensors for regenerative life support in space

The initial feasibility demonstration of a reagentless chemiluminescence based fiber optic sensor technology for use in advanced regenerative life support applications in space and planetary outposts is described. The primary constraints for extraterrestrial deployment of any technology are compatibility with microgravity and hypogravity environments; minimal size, weight, and power consumption; and minimal use of expendables due to the great expense and difficulty inherent to resupply logistics. In the current research, we report the integration of solid state flow through modules for the production of aqueous phase reagents into an integrated system for the detection of important analytes by chemiluminescence, with fiber optic light transmission. By minimizing the need for resupply expendables, the use of solid phase modules makes complex chemical detection schemes practical. For the proof of concept, hydrogen peroxide and glucose were chosen as analytes. The reaction is catalyzed by glucose oxidase, an immobilized enzyme. The aqueous phase chemistry required for sensor operation is implemented using solid phase modules which adjust the pH of the influent stream, catalyze the oxidation of analyte, and provide the controlled addition of the luminophore to the flowing aqueous stream. Precise control of the pH has proven essential for the long-term sustained release of the luminophore. Electrocatalysis is achieved using a controlled potential across gold mesh and gold foil electrodes which undergo periodic polarity reversals. The development and initial characterization of performance of the reagentless fiber optic chemiluminescence sensors are presented in this paper.