RAMAN-SPECTROSCOPY STUDIES OF METABOLIC CONCENTRATIONS IN AQUEOUS-SOLUTIONS AND AQUEOUS-HUMOR SPECIMENS

Individual concentrations of glucose, lactic acid, and urea down to 0. 1 wt % have been investigated in aqueous solutions by the Raman scatte ring technique. These measurements have been conducted with three diff erent laser excitation wavelengths at 514.5, 632.8, and 751.8 nm in co njunction with a single-grating spectrometer and a liquid nitrogen-coo led charge-coupled device (CCD). Rabbit and human aqueous humor specim ens have also been studied by this method. In addition to a water back ground, the large fluorescence structure in the Raman spectra resultin g from these aqueous humor specimens has been subtracted out by being fitted to a first-degree polynomial. Raman peaks similar to the stretc hing vibrations of methylene and methyl groups associated with glucose and lactate, respectively, were observed in the human specimens withi n the region from 2800 to 3050 cm(-1). Similar structure was observed from the rabbit specimens. In addition, a Raman peak, indicative of th e carbon-nitrogen stretching mode of urea and various amino acids, was observed at 1006 cm(-1) in all aqueous humor specimens. However, some of the Raman peaks in the rabbit specimens may have resulted from the euthanasia process.