Chemical Structural Analysis of Bone by Spectroscopy - Vibrational Spectroscopy for Tissue Analysis - page 203

4.67

3.90

3.13

2.36

1.59

0.82

0.05
4000

3600 3200 2800 2400

Wavenumber (cm -1 )

2000 1600 1200 800 400

Figure 7.12
FTIR spectrum of carbonated hydroxyapatite.

spectra of both the synthetic and natural apatites revealed interesting findings
(Figures 7.13 and 7.14), confirming the presence of hydroxyl, carbonate, and
phosphate groups, details of which are provided in the following section.

Spectral bands

Hydroxyl

Hydroxyl stretch is observed at 3569 cm −1 in the spectra of synthetic com-
mercial hydroxyapatite and carbonated apatite powders. The hydroxyl band
at 3569 cm −1 , in the spectrum of carbonated apatite has a lower intensity
compared to that from commercial samples, which is also masked by broad
H 2 O absorptions (Figure 7.15). The large decrease in the hydroxyl band inten-
sities of the carbonated apatite powder may be attributed to the increase in
the carbonate substitution. This particular band is extremely valuable in
calculating the presence of carbonate and hydroxyl group ratios both in the
natural and synthetic apatites (Table 7.2).
The peak areas of hydroxyl stretch in the case of carbonated and P120
hydroxyapatite powders are 1.92 and 7.4, respectively, indicating that the
hydroxyl group decreases with an increase in the carbonate substitution.
The results obtained agree with the data reported by Elliott et al., who sug-
gested the replacement of carbonate ions with hydroxyl ions [28].

Carbonate Bands

Theoretically, carbonate ions have four vibrational modes, three of which
are observed in the infrared spectrum and two of which are observed in the
Raman spectrum [24]. The carbonate m4 bands have very low intensity and are