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A paint sample from which four inorganic compounds were identified by ATR spectroscopy. The numbers indicate different layers in the sample, composed of different inorganic compounds. The boxed area shows the region within which ATR mapping occurred. Reproduced from R. Mazzeo, E. Joseph, S. Prati, and A. Millemaggi. Anal. Chim. Acta , 2007, 599 , 107. Copyright: Elsevier (2007).
Spectra of the inorganic compounds identified in the paint sample pictured in [link] . Each spectrum a-e corresponds to (a) Azurite. (Cu 3 (CO 3 ) 2 (OH) 2 ), (b) Silicate based blue pigment, (c) Lead white. (2PbCO 3 ·Pb(OH) 2 ), (d) Bole. (A natural ferruginous aluminum silicate red pigment), and (e) Gypsum. (CaSO 4 ·2H 2 O). The characteristic vibrational transitions for each compound can be seen in [link] . Alongside each spectrum is a false color image showing the location of each compound within the boxed region of [link] . The images are labelled with the layer that corresponds to its location in the paint sample. Reproduced from R. Mazzeo, E. Joseph, S. Prati, and A. Millemaggi. Anal. Chim. Acta , 2007, 599 , 107. Copyright: Elsevier (2007).
This table shows the inorganic compounds identified in the paint sample shown in [link] . Data from R. Mazzeo, E. Joseph, S. Prati, and A. Millemaggi. Anal. Chim. Acta , 2007, 599 , 107.
Compound Selected spectral bands (cm -1 ) Assignment
Cu 3 (CO 3 ) 2 (OH) 2 (Azurite) 1493 CO 3 2- asymmetric stretch
Silicate based blue pigments 1035 Si-O stretching
2PbCO 3 ·Pb(OH) 2 (White lead) 1399 CO 3 2- asymmetric stretch
A natural ferruginous aluminum silicate red pigment (Bole) 3697 OH stretching
CaSO 4 ·2H 2 O (Gypsum) 1109 SO 4 2- asymmetric stretch

The deep blue layer 3 corresponds to azurite and the light blue paint layer 2 to a mixture of silicate based blue pigments and white lead. Although beyond the ATR crystal’s spatial resolution limit of 20 µm, the absorption of bole was detected by the characteristic triple absorption bands of 3697, 3651, and 3619 cm -1 as seen in spectrum d of [link] . The white layer 0 was identified as gypsum.

To identify the binding material, the KBr embedded sample proved to be more effective than the polyester resin. This was due in part to the overwhelming IR absorbance of gypsum in the same spectral range (1700-1600 cm -1 ) as a characteristic stretch of the binding as well as some contaminant absorption due to the polyester embedding resin.

To spatially locate specific pigments and binding media, ATR mapping was performed on the area highlighted with a box in [link] . The false color images alongside each spectrum in [link] indicate the relative presence of the compound corresponding to each spectrum in the boxed area. ATR mapping was achieved by taking 108 spectra across the 220x160 µm area and selecting for each identified compound by its characteristic vibrational band.

Bibliography

  • J. Fahrenfort, Spectrochim. Acta , 1961, 17 , 698.
  • R. Mazzeo, E. Joseph, S. Prati, and A. Millemaggi. Anal. Chim. Acta , 2007, 599 , 107.
  • M. Milosevic, Internal reflection and ATR spectroscopy , John Wiley&Sons, Inc., Hoboken (2012).
  • F. M. Mirabella, Internal reflection spectroscopy: Theory and applications , 15, Marcel Dekker, Inc., New York (1993).
  • PerkinElmer Life and Analytical Sciences. N.p.: PerkinElmer Life and Analytical Sciences, n.d.  FT-IR Spectroscopy Attenuated Total Reflectance (ATR) . PerkinElmer, Inc., 2005. Web. Feb. 2014.
  • M. Schnippering, S. R. T. Neil, S. R. Mackenzie, and P. R. Unwin, Chem. Soc. Rev. , 2011, 40 , 207.

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Source:  OpenStax, Nanomaterials and nanotechnology. OpenStax CNX. May 07, 2014 Download for free at http://legacy.cnx.org/content/col10700/1.13
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