Wide area illumination Raman scheme for simple and nondestructive discrimination of seawater cultured pearls

Abstract

Raman spectroscopy, along with discriminant partial least squares (PLS), was successfully used to discriminate among three different groups of cultured pearls (fresh water, Akoya and South seawater). The discrimination between Akoya and South seawater pearls using XRF (X-ray fluorescence), one of the most frequently adopted analytical methods in pearl analysis, has been especially difficult owing to their similar mineral compositions. The selective Raman features helped in effectively discriminating between these two pearl groups. The difference in the intensities of the CaCO 3 bands of Akoya and South seawater pearls provided a valuable clue. Along with the selective Raman feature, a reproducible Raman spectral collection achieved using a wide area illumination (WAI) scheme played an important role in the determination of the pearl groups, although the pearls were hard-surfaced, round, solid samples of different sizes and surface shapes. Unwanted spectral variation originating from sensitivity to sample placement relative to the focal plane and from unsuccessful sample representation due to the probing of a localized area, factors that could possibly deteriorate Raman reproducibility, were substantially lessened using the WAI scheme. ATR (attenuated total reflection) IR spectroscopy requiring direct contact with the pearl could be inadequate for discrimination or classification where large numbers of repeating and reproducible measurements are required. Copyright

Wide area coverage Raman spectroscopy for reliable quantitative analysis and its applications

“…With the use of discriminant-PLS, Raman spectroscopy was successfully used to discriminate three different groups of cultured pearls (fresh water, Akoya and South seawater). 80 The difference in the intensities of the CaCO 3 bands of Akoya and South seawater pearls provided a valuable clue for the discrimination. Although the pearls were hard-surfaced, round, solid samples of different sizes and surface shapes, a reproducible Raman spectral collection achieved using the WAI scheme played an important role in determining the pearl groups.…”

Shifted Excitation Raman Difference Spectroscopy Combined with Wide Area Illumination and Sample Rotation for Wood Species Classification

“…38,39 The technique has found applications for the inspection of various specimens including pharmaceutical tablets 40 or suspensions, 41 petroleum products, 40 rice varieties, 42 titanium dioxide in cream formulations, 37 and seawater cultured pearls. 43 The movement of the sample with respect to a stationary laser beam is another method to increase the probed area. Manual sample movement in conjunction with fast spectral acquisition using a charge-shifting charge-coupled device (CCD) approach has been reported to obtain representative average spectra of mineral samples.…”

“…38,39 The technique has found applications for the inspection of various specimens including pharmaceutical tablets 40 or suspensions, 41 petroleum products, 40 rice varieties, 42 titanium dioxide in cream formulations, 37 and seawater cultured pearls. 43…”

Recent advances in linear and nonlinear Raman spectroscopy. Part IV

“…Raman spectroscopy and X‐ray absorption fine structure were used by Wang et al 142 to characterize the microstructure of red decorations from the Song and Jin Dynasties to the Ming Dynasty. Park et al 143 used a wide‐area illumination Raman scheme for the simple and nondestructive discrimination of various seawater‐cultured pearls. Micro‐Raman and portable Raman spectroscopic measurements of blue pigments in selected Delft plates from the 17th to the 20th century were described by de Waal 144.…”