Summary
Physical studies carried out on a range of protein and clotting factor adsorbents
revealed marked morphological and charge differences. Their appearance in the scanning
electron microscope could be used to classify the insoluble precipitates, calcium
phosphate, barium sulphate and citrate, as either amorphorous or crystalline.
Surface charge is difficult to define but the present studies on the sparingly-soluble
salts, based on calcium and barium, have revealed that they can be subdivided on the
basis of the presence or absence of a charge reversal point in the pH-mobility curve.
The anion component appeared to determine this characteristic; it was noted that phosphate
and citrate ions had a marked effect and gave a biased negative potential at all pH
values. We concluded that where a divalent cation is cohabiting with a trivalent anion,
the greater potential-determining ability of the latter will dominate the overall
charge at the surface of a particle, even below pH7 and the absence of a positive
potential gives a monophasic pH-mobility curve.
Differences in both the physical appearance and electrophoretic mobility of the adsorbents
studied reflect the wide variation in their chemical composition, especially among
the various forms of calcium phosphate which, unlike barium sulphate, can include
substituted ions such as hydroxyl, in their crystal lattice. The definition of these
characteristics allows their behaviour towards clotting factors to be more easily
predicted.
