Semi-quantitative trace analysis of nuclear fast red by surface enhanced resonance Raman scattering

The dye nuclear fast red has been detected and determined semi-quantitative ly by means of surface enhanced resonance Raman scattering (SEARS) and surf ace enhanced Raman scattering (SEAS), using laser exciting wavelengths of 5 14.5 and 632.8 run, respectively, by employing a citrate-reduced silver col loid. A good linear correlation is observed for the dependence of the inten sities of the SEARS bands at 989 cm(-1) (R = 0.9897) and 1278 cm(-1) (R = 0 .9872) on dye concentration over the range 10(-9) to 10(-7) M, when using a n exciting wavelength of 514.5 nm. At dye concentrations above 10(-7) M, th e concentration dependence of the SEARS signals is non-linear. This is almo st certainly due to the coverage of the colloidal silver particles being in excess of a full monolayer of the dye. A Linear correlation is also observ ed for the dependence of the intensities of the SERS bands at 989 cm(-1) (R = 0.9739) and 1278 cm(-1) (R = 0.9838) on the dye concentration over the r ange 10(-8) to 10(-6) M when using an exciting wavelength of 632.8 run. Str ong fluorescence prevented collection of resonance Raman scattering (RRS) s pectra from powdered samples or aqueous solutions of the dye using an excit ing wavelength of 514.5 nn, but weak bands were observed in the spectra obt ained from both powdered and aqueous samples of the dye using an exciting w avelength of 632.8 nm. A study of the pH dependence of SEARS/SEAS and UV-VI S absorption spectra revealed the presence of different ionisation states o f the dye. The Limits of detection for nuclear fast red by SEARS (514.5 nm) , SEAS (632.8 nm) and visible spectroscopy (535 nm) are 9, 89 and 1000 ng m l(-1), respectively. (C) 2001 Elsevier Science B.V. All rights reserved.