Fiber optic thin-layer spectroelectrochemistry with long optical path

Brewster, Jeffrey D.; Anderson, James L.

doi:10.1021/ac00251a035

Cited by 56 publications

(33 citation statements)

References 38 publications

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“…The measured optical path length for this cell was 0.28 cm. This final design is very similar to that reported earlier ( 4 ) with the exception that the fibers were obtained in a ribbon form, eliminating the need to align the individual fibers.…”

Section: Methodssupporting

confidence: 64%

Spectroelectrochemical response and flow hydrodynamics in thin-layer flow detectors with long optical path lengths and fiber-optic or slab waveguide coupling

Fosdick¹,

Anderson²

1988

Anal. Chem.

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Spectroelectrochemical experiments were performed In rectangular thln-layer flow cells wlth long optical paths, for the oxldatlon of ferrocyanlde to ferrlcyanlde In phosphate buffer. The optlcal beam was coupled to the cell wlth fiber optlcs or thln-slab waveguldes as the cell sldewalls. Steady-state amperometrlc and absorptometrlc responses both depended critically on cell deslgn, agreeing well wlth theory for fully developed lamlnar flow when the cell Inlet and outlet were several mlllhneters upstream and downstream of the working electrode, but agreed better wlth theory for developlng laminar flow when the electrode completely covered one channel wall. The slgnal to noise ratio was considerably poorer for absorbance measurements than for current but considerably better than for more conventlonal thln-layer spectroelectrochemlcal cell deslgns wlth short optical paths. Flow InJectlon callbratlon curves demonstrated much greater absorbance sensttlvlty when the reactant rather than the product was the prlmary absorber. Experimental results support the potentlal use of the cells as correlatlon detectors.Thin-layer (TL) spectroelectrochemical flow cell (SEFC) detectors offer intriguing possibilities for enhanced analytical selectivity as well as assessment of flow hydrodynamics and reaction mechanisms in applications such as high-performance liquid chromatography (HPLC) or flow injection analysis (FIA). Although numerous stationary spectroelectrochemical cells (SEC) have been reported (I-@, with both short ( I , 2, 6) and long (3-5) optical paths, we are aware of only one flow application of a TL-SEFC having a short optical path length of low sensitivity in an HPLC stopped-flow coulometry configuration (6).Theory describing the current and absorbance response and optimum optical geometries for a rectangular TL-SEFC is reported elsewhere (7), demonstrating the utility of configurations with long optical paths. The present work experimentally evaluates the steady-state flow response of TL-SEFC detectors with long optical paths parallel to the electrode surface and coupled to the light beam by fiber optics or slab waveguides serving as cell side windows. Experimental data agree well with theoretical predictions. The absorptometric measurements provide a powerful means of confirming observations on the nature of channel flow hydrodynamics derived from amperometric measurements. The results show that a slight change in geometry can shift response and flow rate exponents (8) between fully developed laminar flow behavior and a behavior consistent with developing or stagnating laminar flow. The feasibility of correlation detection based on coupled amperometric and absorptometric measurements is also evaluated. EXPERIMENTAL SECTIONThe thin-layer, long optical path SEFC cell designed for this study is shown in Figure 1. The working electrode substrate consisted of either glass or a silicon wafer with a thin, thermally generated oxide insulating layer, coated with Liquid Bright Gold (Engelhard Industries), and fired in a muffl...

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Section: Methodssupporting

confidence: 64%

Spectroelectrochemical response and flow hydrodynamics in thin-layer flow detectors with long optical path lengths and fiber-optic or slab waveguide coupling

Fosdick¹,

Anderson²

1988

Anal. Chem.

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“…An electrochemical probe of concentration profiles has been reported (1,2), and optical probes include refractive index-based methods such as interferometry (3)(4)(5) and deflection spectroscopy (6,7), and absorption methods reported by our laboratory (8)(9)(10) and others (11)(12)(13)(14). An electrochemical probe of concentration profiles has been reported (1,2), and optical probes include refractive index-based methods such as interferometry (3)(4)(5) and deflection spectroscopy (6,7), and absorption methods reported by our laboratory (8)(9)(10) and others (11)(12)(13)(14).…”

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confidence: 99%

Spatially Resolved Absorption Spectroelectrochemistry: Spectra and Concentration Profiles of Species Generated and Consumed at Single and Twin Electrodes

McCreery

1989

J. Electrochem. Soc.

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A previously reported laser-based spatially resolved absorption spectroelectrochemical technique was extended to the visible wavelength range by substitution of the laser with a xenon arc source. The modified instrument permits acquisition of concentration vs. distance profiles of optically absorbing reactants and products of electrode reactions, resolved in space, time, and wavelength. The spatial resolution along the axis perpendicular to the electrode plane is ca. 5 ~m, while the time resolution is 10-100 ms, depending on the magnitude of the absorbance. The spatially resolved spectrum of chloropromazine cation radical was obtained, as were the concentration profiles for both electrogenerated and electroconsumed Fe(CN)C ~. The method was used to determine the effect of electrode orientation on diffusion layer thickness for electroconsumed Fe(CN)C ~. At times below 20s after a potential step, vertical or horizontal diffusion produced identical concentration profiles, with no evidence of density driven convection. At times longer than 20s, erratic profiles resulted, with slightly thicker boundary layers observed for horizontal diffusion. While density driven convection cannot be ruled out from these results, there is no apparent effect on experiments with typical electroanalytical time scales. Finally, the method was applied to a twin working electrode thin layer geometry, with a linear profile of Fe(CN)C 3 observed at steady state. ABSTRACTCommercially available, thermally cyclized, poly(4,4'-oxydiphenylenepyromellitimide) displays ohmic charge transport when suitably doped through an aqueous interfacial electron transfer reaction. The normally highly insulating polymer increases in conductivity by approximately 11 to 13 orders of magnitude becoming an air-sensitive semiconductor with bulk conductivities ranging from 10 -~ to 10 -7 Yt -1 cm-'. The mechanism of conduction appears to be based upon interchain electron hopping.

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“…Previous spectroelectrochemical cell (SEC) designs include thin-layer cells with illumination perpendicular to optically transparent electrodes (2)(3)(4), planar thin-layer cells with illumination parallel to the electrode and coupled to a spectrometer beam either indirectly by fiber optics (5,6) or directly (7), a cell with the optical path inside a narrow hole drilled through a carbon electrode (8), and planar bulk cells, with illumination from a continuum source (9, 10) or a laser (11,22) passed through a thin layer parallel to the electrode surface. These designs are for static solutions, whose spectroelectrochemical responses are described by semiinfinite (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22), thin-layer planar (2)(3)(4)(5)(6)(7), or concentric cylindrical (8) diffusion.…”

mentioning

confidence: 99%

“…These designs are for static solutions, whose spectroelectrochemical responses are described by semiinfinite (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22), thin-layer planar (2)(3)(4)(5)(6)(7), or concentric cylindrical (8) diffusion. A thin-layer spectroelectrochemical flow detector reported by Heineman and co-workers used a minigrid opt i d y transparent electrode (13).…”

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confidence: 99%

Spectroelectrochemical response and optical geometry optimization of thin-layer flow detectors with long optical path lengths: theory

Fosdick¹,

Anderson²

1988

Anal. Chem.

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Steady-state current and absorbance are characterized for a thin-layer spectroelectrochemlcal flow detector with the working electrode on one wall, using complementary Nernst diffuslon-layer-approxlmatlon and finite dlfference shnulatlon models. Both models rigorously treat the Important effects on the measured absorbance of the electrochemically Induced sample Inhomogeneity across the optical beam, requlrlng calculation of absorbance by krtegratlng local transmittances rather than absorbances over the appropriate distance coordinates, except for weakly absorbtng samples. Predicted flow rate exponents of current and absorbance are approxlmately equal and of opposite stgn: +'I3 for current and -'I3 for absorbance under fully developed laminar flow or +'I2 for current and .-'I2 for absorbance under developing lamlnar flow. Optimum optical path geometries are predlcted, havlng long optical paths parallel to the electrode surface and eRher perpendlcular or parallel to flow and lllumlnatlng the entire electrode length If shot noise Is domlnant.Detector selectivity is an important problem for determination of trace species in complex mixtures using flow techniques such as high-performance liquid chromatography (HPLC) or flow injection analysis (FIA). Liquid chromatographic identification and quantitation using a single detector of specific trace species in complex matrices may be subject to interferences by other species which have the same chromatographic retention characteristics and similar detector response. Correlation of two independent detector signals, such as electrochemical current and optical absorbance (spectroelectrochemistry) can be used to improve selectivity by ensuring that a sample component is recognized only when both detection signals yield appropriate responses simultaneously ( I ) .Previous spectroelectrochemical cell (SEC) designs include thin-layer cells with illumination perpendicular to optically transparent electrodes (2-4), planar thin-layer cells with illumination parallel to the electrode and coupled to a spectrometer beam either indirectly by fiber optics (5,6) or directly (7), a cell with the optical path inside a narrow hole drilled through a carbon electrode (8), and planar bulk cells, with illumination from a continuum source (9, 10) or a laser (11,22) passed through a thin layer parallel to the electrode surface. These designs are for static solutions, whose spectroelectrochemical responses are described by semiinfinite (9-22), thin-layer planar (2-7), or concentric cylindrical (8) diffusion. A thin-layer spectroelectrochemical flow detector reported by Heineman and co-workers used a minigrid opt i d y transparent electrode (13). Recently, an electrochemical detector for HPLC and FIA was reported that used photoexcitation to enhance sensitivity (14).This paper characterizes the steady-state flow-rate dependence of absorbance of a species either generated or consumed

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Fiber optic thin-layer spectroelectrochemistry with long optical path

Cited by 56 publications

References 38 publications

Spectroelectrochemical response and flow hydrodynamics in thin-layer flow detectors with long optical path lengths and fiber-optic or slab waveguide coupling

Spectroelectrochemical response and flow hydrodynamics in thin-layer flow detectors with long optical path lengths and fiber-optic or slab waveguide coupling

Spatially Resolved Absorption Spectroelectrochemistry: Spectra and Concentration Profiles of Species Generated and Consumed at Single and Twin Electrodes

Spectroelectrochemical response and optical geometry optimization of thin-layer flow detectors with long optical path lengths: theory

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