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 CCl 4 , 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.
A compact diode laser/fiber-optic Raman spectrometer is used for quantitative detection of environmentally important dyes. This system is based on diode laser excitation at 782 nm, fiber-optic probe technology, an imaging spectrometer, and a state-of-the-art scientific CCD camera. The dyes studied include trypan blue, acid black 1, acid blue 40, and basic blue 7. Detection sensitivities (at rms S/N = 2) ranged from 0.2 ppm (3.24 × 10−7 M) for acid black 1, to 25 ppm (4.86 × 10−5 M) for basic blue 7.
Although a mature technique, Raman spectroscopy remains not widely used as a routine analytical technique. The advantages of Raman spectroscopy, such as minimal sample preparation and relatively uncomplicated spectra, combined with technical advances, including more stable diode lasers, higher quality filters, and better polychromators and array detectors, have led to a renaissance in sensitive and versatile Raman spectrometers. The lack of appropriate databases for routine analysis, which represents the last barrier to the technique's widespread use, is beginning to be overcome, as described in this review.
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