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 multi-channel 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 (approximately 4 × 10^-19 g of material). The system described can rapidly (1-240 s) provide quantitative as well as structural information about very dilute aqueous solutions.