Chemical Structural Analysis of Bone by Spectroscopy - Vibrational Spectroscopy for Tissue Analysis - page 209

is calculated and it is discovered that the phosphate-to-carbonate ions ratio for
human and sheep bone is 1.67 and 1.72, respectively.
Similarly, the ratio was calculated for the commercial hydroxyapatite
powders and the phosphate-to-carbonate ions ratios are tabulated in Table 7.3.
The phosphate ν 1 band can be observed at 961 cm −1 for both the human and
sheep bone. It is also present in the synthetic hydroxyapatite powders. The
phosphate ν 4 band exists between the 660 cm −1 and 500 cm −1 and produces
a sharp, well-defined band. The phosphate ν 4 band can be visible in both
the bone and synthetic hydroxyapatite spectra. The phosphate ν 2 band has
two or three spectral sites. In human and sheep bones, the spectral bands
are centred at 605 cm −1 and 565 cm −1 for human bone, and at 601 cm −1 and
579 cm −1 , for sheep bone. For the synthetic hydroxyapatite, the sites are cen-
tred at 633 cm −1 , 602 cm −1 , and 566 cm −1 . The splitting of the phosphate ν 4
band into two and three observed sites proves the presence of more than one
distinct site for the phosphate group.
The phosphate ν 2 band has two distinct sites for bones and is not as strong
as the ν 3 and ν 4 bands. In human and sheep bone, these sites are 467 cm −1 and
445 cm −1 , respectively. The synthetic hydroxyapatite has only one site and it
is centred on 472 cm −1 for the synthetic hydroxyapatite powders.
Spectral information on the synthetic hydroxyapatite spectra gave numer-
ous peaks parallel to that of human and sheep bone. Although this may
be the case, the spectra still indicate that there are a number of differences
between synthetic hydroxyapatite and bone. The most obvious difference
is the presence of the hydroxyl stretch on the hydroxyapatite powders
and the lack of hydroxyl stretch on the bone spectra. Also, there is a large
(or larger) amount of carbonate present in bone compared to the synthetic
hydroxyapatite; the two proofs being that the peak area is much larger in
bone and the phosphate-to-carbonate ion ratio is far larger in the synthetic
hydroxyapatite.
Summary
The quality of the structural and compositional details that can be revealed
by both the FTIR (combined with minimal PAS-FTIR spectroscopy) and
Raman spectroscopic techniques makes these two very attractive techniques
for the analysis of natural bone tissues and synthetic analogue biomaterials.
For analysing neat materials, bone, or apatite powders, PAS-FTIR offers an
attractive choice for characterisation without the need to reduce the particle
size or dilute with KBr, allowing the analysis of biomaterial in a physiologi-
cal condition. Quantitative analysis is also possible, which confirms the pres-
ence of more carbonate moiety in the natural bone compared to commercial
hydroxyapatite and substituted carbonated apatite powders.