Paul A. Flowers

Variable Path Length Transmittance Cell for Ultraviolet, Visible, and Infrared Spectroscopy and Spectroelectrochemistry

The design and characteristics of a transmittance cell for ultraviolet, visible, and infrared spectroscopy and spectroelectrochemistry are described. Through modification of a previously reported design, this cell employs threaded glass connectors as insertion ports for either quartz- or silicon-windowed tubes, thus permitting essentially continuous variation of the optical path length from ∼0.050 to 200 mm. Though the initial fabrication requires skillful glassblowing, once constructed, the cells simple design allows for rapid and reproducible disassembly/reassembly between experiments. The utility of the cell for a diversity of fluid samples is demonstrated through applications to water, aqueous ferricyanide, ferrocene in methylene chloride, and acetone vapor.

Easily Constructed Microscale Spectroelectrochemical Cell

ABSTRACT The design and performance of an easily constructed cell for microscale spectroelectrochemical analysis are described. A cation exchange polymer film, Nafion, was used as a salt bridge to provide ionic contact between a small sample well containing a coiled-wire working electrode and separate, larger wells housing reference and auxiliary electrodes. The cell was evaluated using aqueous ferri/ferrocyanide as a test system and shown to be capable of relatively sensitive visible absorption measurements (path lengths on the order of millimeters) and reasonably rapid bulk electrolysis (∼5 min) of samples in the range of 1–5 µL volume. Minor alterations to the cell design are described that could allow for analysis of sub-microliter volumes, rapid multi-sample analysis, and measurements in the ultraviolet spectral region.

Submicroliter Electrochemistry and Spectroelectrochemistry Using Standard Electrodes and a Polymer Electrolyte Salt Bridge.

The development of spectroscopic and electrochemical devices that can accommodate very small samples is of considerable importance to many areas of science and technology. We report here on the design and characteristics of a simple apparatus for the electrochemical and spectroelectrochemical analysis of submicroliter aqueous samples. The device is easily assembled from common laboratory materials and equipment, utilizing a bifurcated fiber-optic probe, standard disk electrodes of millimeter dimensions, and a polymer electrolyte film salt bridge to enable the analysis of nanoliter-scale sample volumes in a thin-layer configuration. Excellent performance has been demonstrated via measurements on aqueous ferricyanide solutions using sample volumes as low as 20 nL.

POTENTIOMETRIC MEASUREMENT OF TRANSITION RANGES AND TITRATION ERRORS FOR ACID/BASE INDICATORS

Sophomore analytical chemistry courses typically devote a substantial amount of lecture time to acid/base equilibrium theory, and usually include at least one laboratory project employing potentiometric titrations. In an effort to provide students a laboratory experience that more directly supports their classroom discussions on this important topic, an experiment involving potentiometric measurement of transition ranges and titration errors for common acid/base indicators has been developed. The pH and visually-assessed color of a millimolar strong acid/base system are monitored as a function of added titrant volume, and the resultant data plotted to permit determination of the indicators transition range and associated titration error. Student response is typically quite positive, and the measured quantities correlate reasonably well to literature values.