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Double the Light, Double the Spectra

Photonics Spectra
Oct 2001
Daniel Woolls

Spectroelectrochemistry offers researchers a peek into numerous material properties and reaction mechanisms of organic and inorganic systems. Now a team at the University of Burgos has devised a technique that doubles the amount of data from an experiment.

The team, led by Jesus Lopez-Palacios, an analytical chemist at the university, says this double-barreled approach yields a wealth of data on what happens when an electrode and compounds in solution exchange electrons. The researchers have demonstrated that by shining light beams simultaneously from two directions they can obtain a pair of spectroscopic signals.


The bidirectional spectroelectrochemistry system doubles the data from a sample run. The light from the source is split in the fiber so that it simultaneously illuminates the electrode in the cell from the perpendicular and parallel directions.

Traditionally, spectroelectrochemical methods for planar electrode experiments have aimed the probe light either perpendicularly or parallel to the electrode surface. In each case, the compound interacting with the electrode absorbs the light in a characteristic way, providing a spectrum for analysis. This and separate electrochemical data allow chemists to monitor the reaction taking place at the electrode's surface.

The new technique, known as bidirectional spectroelectrochemistry, incorporates a custom-made gold electrode, a halogen and deuterium double lamp, and a bifurcated optical fiber. The lamp's light is split and directed through the fiber to the electrochemical cell. The resulting pair of beams passes through the cell to individual spectrometers and thence to 2048-element detectors.

Until now, scientists have used one or the other configuration to determine a given parameter, such as standard potential or electron transfer rate. Lopez-Palacios said that sampling with both beams, however, reveals new data.

"When the two signals are obtained and compared at the same time, extremely important information emerges about how the electrode reaction is taking place," he said, such as electrode reaction mechanisms, electrochemical parameters and processes such as electropolymerization.

Moreover, Lopez-Palacios said that obtaining and analyzing both kinds of data simultaneously is the only way to fully understand the electrochemical behavior of systems with complex mechanisms such as those involving adsorption, or the formation of deposits on the electrode surface. Sequential sampling at each direction is not advisable because the time window for the measurements is approximately a millisecond. Firing the beams simultaneously is the only way to observe the phenomenon from two angles, he said.

Commercial system

Although the technique is in the experimental stage, the researchers hope to market a bidirectional spectroelectrochemistry system in the future. First, they plan to broaden the spectral range to include the infrared instead of just the visible and ultraviolet, as in the current system.

One key achievement is that the custom spectroelectrochemical cell fits inside a standard 45 × 10 × 10-mm spectrophotometric cuvette, so the setup is compatible with commercially available holders and accessories.

The research team reported its findings in the July 1 issue of Analytical Chemistry.

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