Detection of nitrate and sulfate anions by normal Raman spectroscopy and SERS of cationic-coated, silver substrates

The use of normal Raman spectroscopy and surface-enhanced Raman spectroscop y (SERS) of cationic-coated, silver substrates to detect nitrate and sulfat e ions in aqueous environments is examined. For normal Raman spectroscopy u sing near-infrared excitation, a linear concentration response was observed with detection limits of 260 and 440 ppm for nitrate and sulfate, respecti vely. Detection limits in the low parts-per-million concentration range for these anions are achieved by using cationic-coated, silver SERS substrates . Adsorption of the anions on the cationic-coated SERS substrates is descri bed by a Frumkin isotherm.