Roosevelt University, Biological, Chemical, and Physical Sciences, Schaumburg, IL 60173
Analytical Chemistry
AN ANALYSIS OF THE ARSENATE ANION AND SIMILAR OXOANIONS USING RAMAN AND SURFACE ENHANCED RAMAN SPECTROSCOPY (SERS), K. Leckrone*, and
S. Adhikari, Department of Biological, Chemical and Physical Sciences, Roosevelt University, Chicago, IL, 60605 kleckron@roosevelt.edu
Raman spectroscopy can be used as a tool for quantitatively measuring oxoanion concentrations, but it has relatively poor detection limits. Surface Enhanced Raman Spectroscopy (SERS) can improve detection limits for a variety of analytes by orders of magnitude. The goal of this study was to determine whether SERS can be used to quantify arsenate and similar oxoanions at lower concentrations. We first examined the effect of pH on the Raman spectra of arsenate, arsenite, phosphate, nitrate, carbonate and sulfate. The experimental results were compared with theoretical expectations based on alpha plot diagrams. The detection limit and linearity of response for arsenate in a pH-9 (NH3/NH4+) buffer were determined based on peak height. The reproducibility of the results was checked using statistical analysis. Furthermore, the detection of arsenate was investigated at lower concentrations using colloidal (silver) SERS in the same buffer solution. Signal enhancements greater than two orders of magnitude were observed for the colloidal SERS analysis (mean = 501733+/- 131099 Counts/M) compared to the normal Raman (mean = 2917+/- 45 Counts/M), However, quantitation was complicated by the formation of aggregates when silver colloid was added to the arsenate solution. Even though linearity was not observed using colloidal SERS, future investigations may include the linearity of SERS spectra at different pH levels and/or the use of surface-bound SERS substrates.
[Abstract (DOC)]