1J: Chemically selective self-assembled monolayers for lowered limits of detection of Cr(VI)

Abstract

Chromium most often exists in two natural oxidation states, Cr(III) necessary for life and Cr(VI) a carcinogen. Differentiating between the two states in public drinking water is crucial to determining whether or not that water is safe for public usage. In order to detect lower concentrations of the heavy metal and to distinguish between its two oxidation states, sensors employing pyridine self-assembled monolayers (SAMs) to a gold surface with Total Reflection X-Ray Fluorescence (TXRF) were proposed using a new protocol. It is hypothesized that these sensors will lower limits of detection and increase detection selectivity between Cr’s two common oxidation states. Electrochemical cycling of the gold surface prior to SAMs addition increased surface area to 2.40 * 10^-14 µg/Ų, leading to an increase in the functional pyridine groups used to isolate Cr(VI). Data was confirmed by enhanced peak current from potassium ferrocyanide electrochemical cycling and quartz crystal microbalance (QCM) mass addition studies, with the increase in gold surface area allowing for 408.1% increase in Cr(VI) signal­. Future TXRF analysis can be applied to view the amplified signal of isolated Cr(VI), using the gold surface of the sensor as an internal standard. With electrochemical removal of Cr(VI) and use of the pyridine SAMs, these sensors are hypothesized to be reusable and chemically selective for Cr(VI) detection with improvement to limits of detection.