Aluminum Phosphate Adjuvant

Aluminum phosphate adjuvant is a white hydrogel that sediments slowly and forms a clear supernatant.


Adju-Phos; aluminum hydroxyphosphate; aluminium hydroxyphosphate; Rehydraphos.
Chemical Name and CAS Registry Number
Aluminum phosphate [7784-30-7]

Adsorbent; vaccine adjuvant.

Empirical Formula and Molecular Weight

The molecular weight is dependent on the degree of substitution of phosphate groups for hydroxyl groups.

Structural Formula

Aluminum phosphate adjuvant occurs as a precipitate of amorphous aluminum hydroxide in which some sites contain phosphate groups instead of hydroxyl. Both hydroxyl and phosphate groups are exposed at the surface. The hydroxyl groups produce a pH dependent surface charge by accepting a proton to produce a positive site, or donating a proton to produce a negative site. The pH-dependent surface charge is characterized by the point of zero charge, which is equivalent to the isoelectric point in protein chemistry.

The surface hydroxyl groups may also undergo ligand exchange with fluoride, phosphate, carbonate, sulfate, or borate anions. Aluminum phosphate adjuvant is not a stoichiometric compound. Rather, the degree of phosphate group substitution for hydroxyl groups depends on the precipitation recipe and conditions.

Functional Category

Adsorbent; vaccine adjuvant.

Applications in Pharmaceutical Formulation or Technology

Aluminum phosphate adjuvant is used in parenteral human and veterinary vaccines. It activates The immune responses, including IgG and IgE antibody responses.

Typical Properties

Acidity/alkalinity pH = 6.0–8.0 Al: P atomic ratio 1.0–1.4: 1.0
Aluminum (%) 0.5–0.75
Particle size distribution Primary particles are platy with an average diameter of 50 nm. The primary particles form aggregates of 1–10 mm.
Point of zero charge pH = 4.6–5.6, depending on the Al: P atomic ratio.
Protein binding capacity >0.6 mg lysozyme/mg equivalent Al2O3
Solubility Soluble in mineral acids and alkali hydroxides.
X-ray diffractogram Amorphous to x-rays.

Method of Manufacture

Aluminum phosphate adjuvant is formed by the reaction of a solution of aluminum chloride and phosphoric acid with alkali hydroxide.

Post a comment