A.J.R. Bauer, TSI, Incorporated

Articles

Raman spectroscopy provides data on bone mineral crystallinity, carbonate to phosphate ratio and extent of collagen cross-linking, all compositional information that is intimately related to biomechanical characteristics of this unique material. Key words for lead email subject line: Raman spectroscopy on bones

Raman Spectroscopic Evaluation of Bones

Raman spectroscopy is well-recognized in the art conservation and archaeology fields for the identification of pigments. This application note is a preview of a more extensive document detailing the use of TSI 

ChemLogix instruments in-situ of fresco artworks and fresco materials in the lab.

	Raman spectroscopy is a valuable tool in the arsenal of the art conservationist. Through the acquisition of a vibrational spectrum of the surface of a sample, various information is gleaned: the type of material (inorganic or organic) present in the pigment and what weathering or environmental damage has occurred, for example. Additionally, this information helps to establish authenticity and provenance of paint and pigment substances. Several TSI instruments are currently being used in this field for these purposes. We are interested in helping to develop more effective measurement methods for the other challenging pigments that are encountered in older artifacts, especially those with green and blue-green mineral pigments, which have been found in the past to have a forbidding amount of native fluorescence.

	The Raman measurements discussed in this note were made with a TSI | Chemlogix ProRaman-L instrument with 20 mW of 785 nm laser excitation and a spectral range of 100–3300 cm

. The spectra were collected with a 12-s acquisition period and 10x averaging. Room lights were excluded from the analysis by means of black plasticized cloth. The raw spectra were corrected for the native fluorescence in the material with the TSI standard background correction algorithm.

	The background-corrected Raman spectrum of a pan of vermilion water color pigment from natural pigments is shown in Figure 1 (1). It is plotted together with a Raman spectrum of cinnabar (HgS) from the RRUFFs database (University of Arizona and the California Institute of Technology) (2). Vermilion is a reddish pigment derived from crushed cinnabar (HgS) that was used as a red pigment by the ancients. In China, as early as the 4th century BC, a synthesis was developed using elemental mercury and sulfur. Due to its toxicity, vermilion has been almost completely replaced by cadmium red, starting in the 20th century. It is clear from the spectra in Figure 1 that the vermilion watercolor pan is the same material as the mineral reference, cinnabar. It is clear that this type of pigment identification can be used both to date paintings and discover frauds.


	Figure 1: Background-corrected Raman spectra of vermilion pigment and the mineral cinnabar.

	This brief application note discusses the value of Raman spectroscopy in the pursuit of pigment identification in the fields of art history and conservation. In the near future, more of this work, including the analysis of difficult green pigments, will be published.

	(2) R.T. Downs, "The RRUFF Project: an integrated study of the chemistry, crystallography, Raman and infrared spectroscopy of minerals," paper presented at the 19th General Meeting of the International Mineralogical Association in Kobe, Japan. O03-13 (2006).


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Raman Spectroscopy for Pigment Identification

Raman spectroscopy has strong potential in the identification and quantification of sugars in concentrated aqueous solutions in the food industry.

	A variety of liquid sweeteners greet consumers when they shop for toppings for toast and pancakes. At the high end of the price range one can find Grade A maple syrup and varietal honey. The predominant sugars in these aqueous solutions are sucrose and a mixture of glucose and fructose, respectively. Raman spectroscopy has been used numerous times in the literature to make measurements pertaining to mono- and disaccharide mixtures. Topics from water content in solutions to honey provenance have been reported. This application note demonstrates preliminary work on a product purity measurement for both maple syrup and honey.

	The Raman measurements discussed in this application note were made with a TSI | Chemlogix ProRaman-L instrument with 250 mW of 785 nm laser excitation and a spectral range of 100–3300 cm

. The spectra were collected with a 3-s acquisition period and 20x averaging. The raw spectra, presented in Figure 1 (secondary 

-axis), were then corrected for the native fluorescence in the material with the TSI standard background correction algorithm (results plotted on primary 

-axis). Honey and Grade A maple syrup samples were presented to the system in a standard quartz cuvette held inside the vial-holder accessory.


	Figure 1: Raw and processed Raman spectra of honey and maple syrup.

	The raw spectra of the two materials show clear differences in the background fluorescence excited at 785 nm as well as smaller but equally obvious differences in the Raman scattering signals that are present on top of the broad fluorescent curve. These differences become more pronounced when the broad fluorescence background is removed, and the spectrum is corrected for system response. The materials exhibit very clear differences in the region from 510–540 cm

 have been assigned to a C–C–O bending mode (1). C–C and C–O stretch vibrations are also observed in the region near 1050 cm

. Additionally, a feature revealed only by the signal correction is that honey has significantly more signal in the region associated with CH stretches than does the maple syrup. The sugars in maple syrup are dominated with sucrose, which is a fructose-glucose disaccharide, but all the CH bonds are retained in the disaccharide. Monitoring this feature could provide a means to determine the concentration of the sugars in aqueous solution.

	This brief application note discusses the utility of Raman spectroscopy in the differentiation of sugars in liquid materials. Although this work was performed in a quartz cuvette, it could be extended to measurements in plastic and glass containers, such as those in which these materials are sold.

	(1) S. Söderholm, Y.H. Roos, N. Meinander, and M. Hotokka, 

A.J.R. Bauer, TSI, Incorporated

Articles

Raman Spectroscopic Evaluation of Bones

Raman Spectroscopy for Pigment Identification

Raman Spectroscopic Study of Sugars in Common Liquid Sweeteners