We report the use of a low-cost dispersive Raman instrument with charge-coupled-device (CCD) detection, near-infrared (near-IR) diode laser excitation, and remote fiber-optic sampling to analyze mock petroleum samples which contain high benzene, toluene, ethylbenzene, and xylene (BTEX) concentrations. Partial least-squares regression (PLSR) analysis is used to correlate the individual xylene isomer concentrations to the Raman spectral signal without the use of an internal standard. The resulting PLSR model is used to predict the concentration of individual xylene isomers, and it is found that, at a 95% confidence level, samples containing between ∼1.5 and 15% xylene isomer can be predicted to better than ±0.1% for meta- and para-xylene, and to ±0.15% for ortho-xylene. The use of PLS model leverage plots provides a facile statistical method by which to identify Raman spectra which involve diode laser mode hops or significant fiber backscatter.
A comparison is made between an index-guided (Fabry-Perot type) diode laser and a distributed Bragg reflector (DBR) diode laser as excitation sources for fiber-optic Raman spectroscopy utilizing charge-coupled device (CCD) detection and an image-corrected spectrograph. The DBR diode laser was superior to the index-guided diode laser for elimination of mode hopping, elimination of frequency hysteresis as a function of both temperature and current changes, and reduction in laser broadband emission. These advantages may allow the DBR laser to be used in industrial process control applications which are too demanding for index-guided diode lasers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.