SURFACE-ENHANCED RAMAN DETECTION OF AQUEOUS CYANIDE

Cyanide ion (CN-) has been the subject of numerous studies probing the mechanisms underlying the surface-enhanced Raman scattering (SERS) ph enomenon. This work examines various aspects critical to application o f SERS for direct detection of trace cyanide in groundwater and in was tewater streams. A new method for direct quantitation of cyanide in aq ueous electrolyte has been developed that uses an ex situ oxidation-re duction cycle to precondition a planar silver electrode. Cyanide ion c an be detected in 0.1 M KCl with a linear response between 100 ppm and 10 ppb. The estimated limit of detection is approximately 8 ppb. The effects of pH, electrolyte level, and two common background ions, nitr ate (NO3-) and sulfate (SO42-), have been characterized. Cyanide respo nse was found to be sensitive to pH, with optimal performance observed at neutral to basic pH. Electrolyte concentrations of 0.001 M reduced response to cyanide by a factor of five, while levels above 0.1 M had no significant effect. The addition of 10-ppm sulfate ion decreased r esponse approximately 40%, while the presence of nitrate ion at concen trations up to 100 ppm had a negligible effect on SERS response. These results suggest that cyanide ion can be detected directly in high-ion ic-strength aqueous solutions, such as groundwater.