Surface enhanced Raman spectroscopy as a molecular specific detection system in aqueous flow-through systems
Surface enhanced Raman scattering (SERS) is proposed as a molecular specific technique for direct measurements of organic molecules in aqueous solutions. An FT-Raman spectrometer was interfaced with a flow injection manifold operated in the stopped flow mode enabling reproducible collection of SERS spectra due to the automation of the analysis procedure. For SERS a solid state substrate placed in a newly developed flow-cell was used. Multiple measurements on one single SERS substrate were achieved by rinsing the substrate with reagents such as 3 M KCl or 0.1 M NaOH solutions prior to the next measurements in order to remove retained analytes from the surface of the SERS substrate. This procedure allowed for improved precision as compared with a conventional batch approach. Quantitative aspects were investigated by establishing a calibration curve for nicotinic acid which was used as a model analyte. A linear dependance of the recorded SERS intensities from the logarithm of the analyte concentration was obtained throughout the whole investigated concentration range (0.001–0.1 M, correlation coefficient r2 = 0.97). The standard deviation of the method sx0 was found to be 0.122 mM and detection limit 1.7 mM, respectively. The results demonstrate the potential of SERS spectroscopy to be used as a molecular specific detector in aqueous flow systems such as flow injection analysis.