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The phosphates sodium and potassium
The terms sodium phosphate and potassium phosphate refer to a broad class of compounds with similar but different properties, depending on the amount of sodium (or potassium) counter ions and/or fluids of crystallization present. They are especially useful for creating different kinds of biological buffers.
Sodium Phosphates and Potassium Phosphates
All forms of potassium and sodium phosphates are widely used and widely accepted as safe in food, household products, medications, and pharmaceuticals. In the context of this article, “phosphate” refers to the tribasic anion salt, or [PO4]3-, that is derived from phosphoric acid. It is crucial to biochemistry and can have one, two, or three sodium counter ions.
A word about the crystallization waters, the solution ease, and the stability of long-term storage: A related molecule called water, or hydrate, is incorporated as a repeating unit with the phosphate salt in a stable crystal cell to form an extremely stable solid. The hydrate is weakly bound by hydrogen bonds. It is not actually a component of the salt. These hydrated salts can and will leak water into the atmosphere if they are not tightly sealed and the surrounding air is not humid. The anhydrous salt, which is devoid of water, can, nevertheless, “pick up” water from the atmosphere and hydrate if the ambient humidity is high. Even though salt humidity fluctuations during long-term storage are frequently gradual, properly sealing containers after opening may still be essential if the product is going to be stored for an extended period of time.
A word about ease of solution, stability in long-term storage, and crystallization waters: Rather than being a component of the salt itself, the water (hydrate), as an associated molecule weakly bound by hydrogen bonding, is actually incorporated into a stable crystal cell as a repeating unit with the phosphate salt, creating an extremely stable solid. These hydrated salts can and will leak water into the atmosphere if they are not tightly sealed and stored in a low-humidity environment. However, the anhydrous salt—which is devoid of water—can “pick up” water from the atmosphere and become hydrated in an environment with a high relative humidity. It can be important to properly seal containers after opening if one plans to store the product for an extended period of time, even though these variations in salt humidity during long-term storage are frequently gradual.
A&C supplies USP and multi-compendial excipient grade phosphates, which include the following:
A&C provides a wide range of phosphates, including extra calcium, potassium, and sodium salts. A&C also manufactures a range of phosphate buffers, one of which is A&C dissolving media concentrate, pH 6.8.
- CAS 7558-79-4, Na2HPO4, sodium phosphate dibasic anhydrous (low endotoxin), contains two sodium counter ions and no crystallization waters.
- CAS 7782-85-6 is sodium phosphate dibasic heptahydrate, which has seven crystallization waters and the same formula as above (Na2HPO4•(H2O)7).
- CAS 7558-80-7, monobasic anhydrous sodium phosphate, NaH2PO4, is a water-free compound with a single sodium counter ion.
- NaH2PO4•(H2O)2, sodium phosphate monobasic dihydrate, CAS 13472-35-0
- Sodium phosphate monobasic monohydrate, NaH2PO4•H2O, CAS 10049-21-5
- KH2PO4, potassium phosphate monobasic, CAS 7778-77-0