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 scattering technique. These measurements have been conducted with three different laser excitation wavelengths at 514.5, 632.8, and 751.8 nm in conjunction with a single-grating spectrometer and a liquid nitrogen-cooled charge-coupled device (CCD). Rabbit and human aqueous humor specimens have also been studied by this method. In addition to a water background, the large fluorescence structure in the Raman spectra resulting from these aqueous humor specimens has been subtracted out by being fitted to a first-degree polynomial. Raman peaks similar to the stretching vibrations of methylene and methyl groups associated with glucose and lactate, respectively, were observed in the human specimens within the region from 2800 to 3050 cm⁻¹. Similar structure was observed from the rabbit specimens. In addition, a Raman peak, indicative of the 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.