Quantitative analysis using Raman spectroscopy without spectral standardization

Compared with other spectroscopic techniques, Raman spectroscopy has not generally been applied to problems of quantitative analysis, primarily because it is assumed that spectral irreproducibility due to source, sample or optical parameters requires standardization of the Raman signal. However, a custom-built Raman spectrometer with a 785 nm excitation source has yielded a spectral peak height reproducibility of 0.5% relative standard deviation. Quantitative studies of glucose in water, ethanol in water and p-xylene in m-xylene, described here, illustrate the linearity and precision of the Raman system. In order to estimate the linear dynamic range of the instrument, detection limits were determined for benzene in water and in CCl₄, demonstrating a range from sub-ppm to 100% concentration. Specific factors affecting spectral reproducibility, and therefore quantitative results, are discussed. The quality of the results presented indicates that Raman spectroscopy should be a more common quantitative spectroscopic technique.