Chemical Structural Analysis of Bone by Spectroscopy - Vibrational Spectroscopy for Tissue Analysis - page 208

In carbonated apatite, these sites are at 467 and 450 cm −1 , whereas in
commercial hydroxylapatite there is only one site, at 472 cm −1 [32].
FTIR spectra of synthetic commercial hydroxyapatite and synthetic
carbonated apatite powder indicate that there are a number of differences
between the two samples. The most obvious change in the spectrum of
carbonated apatite is the large decrease of the hydroxyl peak centred at
3568 cm −1 , compared to the commercial sample's spectra, which have a
well-defined, sharp peak at the same position (see Figure 7.7 and Table 7.2).
Infrared spectra of commercial hydroxyapatites have a hydroxyl band at
624 cm −1 , which is absent in carbonated apatite [33].
There is a hydroxyl stretch identified at 3568 cm −1 and 3570 cm −1 in the
spectra of the commercial hydroxyapatite powders P120 and P88, respec-
tively, but it is not observed in the spectra of bones. It can be observed that
the intensity of the hydroxyl bands for the commercial hydroxyapatite
powders are approximately the same. The amount of carbonate substitution
is calculated by measuring the peak area of the spectra of the carbonate and
hydroxyl bands. The peak area of hydroxyl stretch can be calculated for the
commercial hydroxyapatite powders since the bone does not have hydroxyl
stretch. In the case of the P120 and P88 hydroxyapatite powders, the peak
area is 6.62 and 6.78, respectively. It is apparent, even though the difference
may be small, that a decrease in the hydroxyl groups will, in turn, increase
the carbonate substitution. Obtained results are tabulated in Table 7.3.

Comparison of Natural and Synthetic apatite

The spectra of the human and sheep bone are almost identical and the same
can be said for the apatite powders.
While comparing the spectra of both the natural and inorganic matrix of
bone, it is observed that both the human and sheep bones have three different
sites present on the phosphate ν 3 band at 1096 cm −1 , 1085 cm −1 , and 1056 cm −1
(see Figure 7.14 and Table 7.3). The intensity of the ν 3 is thought to account for the
obscurity of the ν 1 carbonate bands. The phosphate-to-carbonate ions ratio can
be calculated by using the already calculated carbonate ν 3 peak area to calculate
the peak area of the phosphate ν 3 band. The phosphate-to-carbonate ions ratio

Table 7.3
Peak Area Calculation for Hydroxyl, Carbonate, and Phosphate Bands, Bone and
Hydroxyapatite Spectra

Peak
Assignments

Human
Bone

Sheep
Bone

HA
(P120)

HA
(P88)

HA
(P141)

HA
(P149)

HA
(Merck) CA

Hydroxyl stretch 6.62 6.78 6.59 6.37 5.06 1.92

Carbonate (v 3 ) 188.7 198.9 12.7 11.2 11.1 12.1 11.2 164.8

Phosphate (v 3 ) 314.9 341.8 225.8 165.7 182.0 138.1 351.6 314.5

PO 4 3− /CO 3 2− 1.67 1.72 1/17.8 14.8 1/16.4 1/11.4 1/31.4 1.9/1