Quantification and description of photothermal heating effects in plasmon-assisted electrochemistry.

A growing number of reports have demonstrated plasmon-assisted electrochemical reactions, though debate exists around the mechanisms underlying the enhanced activity. Here we address the impact of plasmonic photothermal heating with cyclic voltammetry measurements and finite-element simulations. We find that plasmonic photothermal heating causes a reduction in the hysteresis of the anodic and cathodic waves of the voltammograms along with an increase in mass-transport limiting current density due to convection induced by a temperature gradient. At slow scan rates, a temperature difference as low as 1 K between the electrode surface and bulk electrolytic solution enhances the current density greater than 100%. Direct interband excitation of Au exclusively enhances current density by photothermal heating, while plasmon excitation leads to photothermal and nonthermal enhancements. Our study reveals the role of temperature gradients in plasmon-assisted electrochemistry and details a simple control experiment to account for photothermal heating.

Improving sensitivity in chiral supercritical fluid chromatography for analysis of active pharmaceutical ingredients.

Despite its status as the preferred method for routine enantiopurity analysis in pharmaceutical research, supercritical fluid chromatography (SFC) has historically been unsuited for the accurate and precise measurements required for release testing of active pharmaceutical ingredients (APIs) under current good manufacturing processes (cGMPs). Insufficient signal to noise, as compared to HPLC, has heretofore been the major limitation of the chiral SFC approach. We herein describe an investigation into the fundamental limitations and sources of noise in the SFC approach, identifying thermal, electronic, and mechanical sources of noise within the flow cell as key parameters contributing to reduced sensitivity. A variety of instrument modifications are explored, ultimately leading to the development of a new and improved flow cell and other instrument modifications that allow suitable sensitivity and accuracy to carry out GMP release testing for enantiopurity analysis using SFC.