Optimization of a Flow Injection Sampling System for Quantitative Analysis of Dilute Aqueous Solutions Using Combined Resonance and Surface-Enhanced Raman Spectroscopy (SERRS)

A flow injection sampling system to analyze dilute aqueous solutions by surface-enhanced resonance Raman spectroscopy (SERRS) is described, and critical operating parameters are evaluated. A simple procedure for preparing a silver colloid, which is more homogeneous, stable, and SERS-active than that previously reported and does not require sedimentation, is presented. With the use of crystal violet (CV) as a model analyte, the flow injection system, a Raman micro-probe, and an optical multichannel analyzer (OMA) for detection, high-quality, highly reproducible (coefficient of variation = ±2.37% of mean) Raman spectra for 1 × 10⁻⁶ M solutions of CV were obtained in 1 min, and major spectral peaks were observable down to concentrations of 1 × 10⁻¹² M (∼4 × 10⁻¹⁹ g of material). SERRS enhancement and spectral quality were experimentally found to vary significantly with the method of Ag sol preparation and laser excitation wavelength. The system described can rapidly (1–240 s) provide quantitative as well as structural information about very dilute aqueous solutions.