Chemical Structural Analysis of Bone by Spectroscopy - Vibrational Spectroscopy for Tissue Analysis - page 198

A significant finding of this work was the appearance of peaks in the bone
tissue (organic phase) spectra in the region 3000-2880 cm −1 . The peaks at
2934 and 2935 cm −1 (symmetric C-H) stretch mode in the spectra of normal
bone tissue were due to an organic substance, judging by the virtual elimina-
tion of these peaks upon deproteination (Figure 7.2). The peak at 2915 cm −1
(symmetric C-H) in the deproteinated spectra was due to the organic bone
tissue after the deproteination procedure. The current results confirm that
complete deproteination of bone tissue by hydrazine was not achieved.
The only shared peak between the spectra for synthetic hydroxyapatite
spectrum and bone tissue was that at 952 cm −1 (Figures 7.3, 7.4, and 7.5, and
Table 7.1), which was associated with the phosphate (symmetric) stretch mode.
Other regions of these spectra did not match each other as closely. The P120 HAP
sample used in this study produced considerable signals at 774 and 690 cm −1 ,
which were assigned as phosphate vibrational modes. Previously, it was
thought that there were strong chemical and structural similarities between
hydroxyapatite with natural bone [22]. It was reported that there are significant
structural differences between the spectral details of synthetic hydroxyapatite
and the inorganic matrix of the natural bones. The only shared peak at 952 cm −1
had a higher relative intensity for the bone samples, which indicated more of a
symmetric P-O stretching mode than that associated with synthetic hydroxy-
apatite. No other peaks in all of the spectra matched.
The broad band in the region of 900 and 600 cm −1 , which dominated the
spectrum of synthetic hydroxyapatite, was a combination of two peaks,
774 and 690 cm −1, respectively (Figure 7.3). Tudor et al. [23] suggested two
possibilities for the breadth of this band, one being the overlapping of two
hydroxide bands and other a combination of carbonate and hydroxide
bands. To evaluate these possibilities, the spectrum of hydroxyapatite was
compared with the spectra of calcium hydroxide, calcium carbonate, and cal-
cium phosphate. It was established that the broad peaks at 774 and 690 cm−l −l
were not due to calcium hydroxide or calcium carbonate, as the peaks were
at different positions (Figure 7.4 and Table 7.1). Calcium hydroxide had two
broad peaks centred at 801 and 721 cm −1 , which were completely absent in
the spectrum of hydroxyapatite.
A comparison of the spectra of hydroxyapatite with calcium phosphate
indicated that in both cases the broad bands matched very well in the region
of 900 and 600 cm −1 (Figure 7.4). Both of these peaks were due to asymmetric
P-O modes. Hence, it may be concluded that there are two possibilities for the
broadening of the peaks: (1) the presence of multicrystalline phases of the phos-
phate moiety in the hydroxyapatite, and (2) phosphate bands that are subject to
interference from the hydroxide group of the hydroxyapatite. The second pos-
sibility is unlikely, as a broad band was also observed in the case of the calcium
phosphate spectrum (Figure 7.4). However, the first possibility was confirmed
by comparing the hydroxyapatite spectra with the spectrum of sodium hydrox-
ide, which indicated that sharp, well-defined hydroxide bands also appeared at
a much lower wavenumber, centred at 293 and 207 cm −1 , which were completely