Development of water-based liquid chromatography at the critical condition.

Liquid chromatography at the critical condition (LCCC) is a chromatographic technique that allows for the isolation of one area of the polymer matrix so that other areas of the polymer may be probed with size-exclusion or adsorptive chromatographic modes. This technique has been successfully applied to the analysis of functionality distributions in functionalized oligomers and to polymer distributions within copolymers. Herein, the critical conditions of two polar polymers, poly(acrylic acid) and polystyrene sulfonate, are determined. These conditions were identified by varying buffer concentration, organic modifier within the mobile phase, or both. At the critical condition of poly(acrylic acid), the retention characteristics of a copolymer of acrylic acid and vinyl pyrrolidinone were determined. This extension to water-based mobile phase conditions will substantially broaden the possible applications of LCCC.

Spectroelectrochemical sensing based on multimode selectivity simultaneously achievable in a single device. 5. Simulation of sensor response for different excitation potential waveforms.

The simulation of the optical response in spectroelectrochemical sensing has been investigated. The sensor consists of a sensing film coated on an optically transparent electrode (OTE). The mode of detection is attenuated total reflection. Only species that partition into the sensing film, undergo electrochemistry at the potentials applied to the OTE, and have changes in their absorbance at the wavelength of light propagated within the glass substrate of the OTE can be sensed. A fundamental question arises regarding the excitation potential waveforms employed to initiate the electrochemical changes observed. Historically, selection has been based solely upon the effectiveness of the waveform to quickly electrolyze any analyte observable by the optical detection method employed. In this report, additional requirements by which the waveform should be selected for use in a remote sensing configuration are discussed. The effectiveness of explicit finite difference simulation as a tool for investigating the applicability of three different excitation potential waveforms (square, triangle, sinusoid) is demonstrated. The simulated response is compared to experimental results obtained from a prototype sensing platform consisting of an indium tin oxide OTE coated with a cation-selective, sol-gel-derived Nafion composite film designed for the detection of a model analyte, tris(2,2'-bipyridyl)ruthenium(II) chloride. Using a diffusion coefficient determined from experimental data (5.8 x 10(-11) cm2 s for 5 x 10(-6) M Ru(bipy)3(2+)), the simulator program was able to accurately predict the magnitude of the absorbance change for each potential waveform (0.497 for square, 0.403 for triangular, and 0.421 for sinusoid), but underestimated the number of cycles required to approach steady state. The simulator program predicted 2 (square), 3 (triangle), and 5 cycles (sinusoid), while 5 (square), 15 (triangle), and 10 (sinusoid) cycles were observed experimentally.