Sodium and Potassium Phosphates
Sodium Phosphate or Potassium Phosphate is a term that refers to a whole library of compounds with varying but similar properties based on the number of sodium (or potassium) counter ions and/or waters of crystallization that are present. They are very useful in the preparation of many different biological buffers.
All Sodium Phosphates and Potassium Phosphates are generally recognized as safe and have wide use in food, household products, in medical and pharmaceutical applications. In our case phosphate refers to the anion salt derived from phosphoric acid with formula [PO4]3-, it is tribasic and can have one, two or three sodium counter ions and play key roles in biochemistry.
A note about waters of crystallization, long term storage stability and ease of solution: the water (hydrate) is not part of the salt per se; it is actually an associated molecule weakly bound by hydrogen bonding but incorporated into a stable crystal cell as a repeating unit with the phosphate salt forming a very stable solid. These hydrated salts can and do lose water to the atmosphere if they are not stored tightly sealed and if the ambient humidity is low. On the other hand, the anhydrous salt (no water) can ‘pick up’ water from the air and become hydrated if the ambient humidity is high. These changes in salt humidity on long-term storage are usually slow but it can be important to properly seal containers after opening if one intends to store the product long-term. Once the salts are dissolved in aqueous solution at similar molar strengths then there is no chemical difference between hydrates of salts with the same number and type of counter ion. In general, it is found that hydrated phosphate salts are more easily brought into aqueous solution (speed-wise) than their anhydrous counterparts.
At A&C we have the following USP and multi-compendial excipient grade phosphates available:
- CAS 7558-79-4, sodium phosphate dibasic anhydrous (low endotoxin) with formula Na2HPO4, which has two sodium counter ions and no waters of crystallization
- CAS 7782-85-6, sodium phosphate dibasic heptahydrate with formula Na2HPO4•(H2O)7, which is the same as above except it has seven waters of crystallization
- CAS 7558-80-7, sodium phosphate monobasic anhydrous, NaH2PO4 this has just one sodium counter ion with no waters
- CAS 13472-35-0, sodium phosphate monobasic dihydrate, NaH2PO4•(H2O)2
- CAS 10049-21-5, sodium phosphate monobasic monohydrate, NaH2PO4•H2O
- CAS 7778-77-0, potassium phosphate monobasic, KH2PO4
A&C has a wide array of phosphates available including other sodium, potassium, and calcium salts. In addition, A&C also manufactures many phosphate buffers such as A&C dissolution media concentrate pH 6.8.