Borate interference in surface-enhanced Raman spectroscopy of amines.

Interference from borate is observed in surface-enhanced Raman (SER) spectra of lysine and propylamine obtained with borohydride-reduced silver colloids. Borate bands are also observed in the spectra of other basic analytes, as well as when certain variations are made in the silver colloid preparation. The relative intensities of the analyte and borate bands depend on the pH of the colloid, the extent of oxidation of the colloid surface, and the relative adsorptivities of the analyte and borate. Benzylamine adsorbs more readily than propylamine and also competes more effectively with borate for adsorption sites. On the other hand, borate virtually excludes lysine from the surface when the solution pH is greater than or equal to 8. The formation of silver oxide in basified colloids may facilitate borate adsorption. For some basic analytes, eliminating the adsorption of borate ion and the resulting spectral interference may require using alternative SERS substrates.