This research substantially improved the differentiation of rice of two geographical origins utilizing a wide area illumination (WAI) scheme capable of collecting Raman spectra of a large sample area (28.3 mm 2 ) synchronously without sample rotation. For the purposes of comparison, we also employed a conventional scheme in which the laser illuminated only small areas. Principal component analysis (PCA) was used to differentiate the two geographical origins using the Raman spectra collected through both the conventional and the WAI schemes. The WAI scheme exhibited improved differentiation, primarily due to the fact that the WAI scheme could efficiently produce Raman spectra with a more reliable sample representation, as well as better reproducibility. The spectral feature obtained using the conventional scheme appeared to be more variable; however, this variation resulted more from unsuccessful sample representation than from an actual change in the sample composition. We conclude that the WAI scheme has a good potential for the analysis of diverse agricultural samples that consist of solid granules.

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We have determined the urea concentration in an aqueous solution using Raman spectroscopy by incorporating a Teflon tube as an effective intensity correction standard as well as sample container. A non-overlapping Teflon band was used as the reference peak to correct Raman intensity variations that occasionally resulted from changes in laser power. To increase the sensitivity, we positioned a copper reflector inside the Teflon tube to maximize the collection of Raman scattering. The obtained accuracy using Raman spectroscopy was 0.53 mM, close to the range of accuracy of previous NIR studies (0.15-0.52 mM).

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