Basic Calcium Orthophosphate

StJBMITTBD BY A. PERLOFF AND A. S. PoSNERf Checked by Norman E. MillerJ 

Methods for the synthesis of calcium hydroxyapatite have been reported in the past,1,2 but all of them produced either poorly crystallized or somewhat impure products. The following procedure produces a very well-crystallized compound which has a high degree of purity. The reaction is simply the hydrolysis of calcium monohydrogen phosphate to hydroxyapatite in a closed system. The major disadvantage is the small amount of material obtained from each hydrolysis because of the small capacity of the bombs used. Larger reaction vessels would minimize this objection. 

An orthophosphoric acid solution, 1 volume of reagent-grade 85% phosphoric acid to 5 volumes of distilled water, is saturated with reagent-grade calcium phosphate. After allowing the excess calcium phosphate to settle, the clear, saturated solution is decanted into a beaker. This solution is heated to its boiling point and well-crystallized calcium 

The presence of certain cation impurities can strongly influence the final product. During some preparations the platinum lining developed cracks, and iron and chromium ions from the steel bomb were introduced into the water. When this happened, the final product contained a large proportion of well-crystallized whitlockite [/3-Ca3(P04)2]. 

With the recommended procedure well-developed, clear hexagonal dipyramidal crystals of hydroxyapatite, ranging up to 0.3 mm. in length, have been obtained. The crystals are uniaxial negative with index of refraction e = 1.643 0.002 and a — 1.649 + 0.002. Atomic parameters and unit cell dimensions as measured by x-ray diffraction are published elsewhere.6 

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K-XRF methods are typically calibrated using phantoms of known Pb level comprised of plaster of Paris or similar mineral material (Chettle et al., 2003 Todd and Chettle, 2003). Todd et al. (2002) observed that such simulations of bone matrix provide potentially erroneous calibrations since they are not true bone matrix. The former is mainly calcium sulfate hemihydrate while bone mineralogy is a heterogeneous matrix of hydroxyapatite (basic calcium orthophosphate, among other formulations). 

Durapattte. Hydroxylapatite calcium phosphate hydroxide calcium orthophosphate, basic hydroxyapatite Alveograf Ossopan Periograf. 3Ca3(P04)a.Ca(0H)2 Or... 

Potassium orthophosphates.—The normal salt, potassium orthophosphate, K3P04, is obtained by heating basic slag or native calcium phosphate with charcoal and potassium sulphate. The potassium sulphide simultaneously formed is converted into phosphate by addition of phosphoric acid, or the potassium phosphate is precipitated by addition of alcohol. The aqueous solution of the salt is very alkaline in reaction, owing to hydrolytic dissociation. The heat of formation from the elements in solution is 483-6 Cal.4... 

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