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|Title:||Singlet-Delta Molecular Oxygen as a Tool for Selective Chemiluminescent Detection in Chromatography|
|Department / Program:||Chemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Chemiluminescence induced by the singlet-delta state of molecular oxygen has demonstrated its potential as a tool for selective detection in high-performance liquid chromatography (HPLC). Excited molecular oxygen, formed for this work in the chemical reaction between hydrogen peroxide and hypochlorite, brings about sample luminescence by energy transfer to an analyte or by chemical reaction with it to form excited molecular fragments.
Luminescence occurs in a three-liquid confined-spray aspirator cell. This unit displays dead-volume behavior dependent on gas and liquid flow rates; its best dead volumes rival those of standard ultraviolet-absorption liquid chromatography detectors. Utilizing a relatively simple housing assembly, the cell respresents a straightforward "add-on" to any chromatography setup. Signal processing can occur by either digital or analog means; mounting the cell by the entrance slit to the polychromator of a diode-array spectrometer permits accumulation of luminescence spectra.
Optimizing reagents and flow conditions for best signal-to-noise ratio (S/N) and dead volume involves fairly common substances and control of only a few parameters. The best source of hypochlorite has been undiluted household bleach, adjusted to pH 10. Hydrogen peroxide gives best results when diluted in methanol from stock 90% solution. Tests with an energy-transffer dye have established optimum concentrations of 0.72 M OCl('-) and 0.02 M H(,2)O(,2), given flow rates of 2.5 ml min('-1) for each reagent. Choosing reagent flow rates appears to involve a tradeoff between increasing S/N and depleting reagents more rapidly; once we fix reagent flow rates, sample-stream flow rate primarily determines dead volume. Gas flow rate has only a small effect on dead volume within the range of flow rates available. Temperature control to counter evaporative cooling has a positive effect on S/N, but would require more engineering for its convenient incorporation into the spray-cell design.
Strengths and weaknesses of the singlet oxygen spray call are apparent from several kinds of results. Response tests show that most common solvents are acceptable as carriers, and that both energy-transfer and chemical reaction responses occur. Chemiluminescence spectra for several example compounds suggest ways of choosing spectral observation windows and reactive mechanisms to explore for detection. Chromatography of green-leaf pigments and of a dye mixture demonstrates the spray cell's performance in practical HPLC detection. Preliminary working curves, on the other hand, show only a limited linear range and a high detection limit; the method requires more work to decrease noise.
Detailed analysis of spray-cell system performance suggests ways of improving its ability to serve as a practical detector. A series of engineering details, with proper attention, may make for better cell design and heating technique. Choice of photomultiplier tubes and wavelength selection filters, as well as use of photomultiplier cooling, offer ways to extend the system's sensitivity and selectivity. Careful examination of luminescence mechanism would possibly suggest different optimum chemical conditions depending on the analyte of interest.
Results to data have demonstrated the unique selectivity, and potential practical utility, of detection by singlet oxygen-induced luminescence in the spray cell, as well as other avenues to explore. With some appropriate improvements, the current technique can provide information of interest in the environmental, medical, and textile fields. Further exploring reactions of singlet-delta oxygen may provide different means for generating analytical signals for HPLC detection; gas-phase singlet oxygen reactions should provide a new method for selective gas chromatography detection, and other luminescence systems are available for use in the spray cell.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.
|Date Available in IDEALS:||2014-12-13|