Registration Dossier

Physical & Chemical properties

Endpoint summary

Administrative data

Description of key information

Additional information

Typically the purity of sodium dihydrogenorthophosphate is > 90% (dry weight, after excluding water). All impurities present at >1% are other inorganic phosphates or other related inorganic substances, similar to the Registered substance, and which do not significantly affect its toxicological and ecotoxicological properties. There are no hazardous impurities present within the substance at levels >0.1%.


Sodium dihydrogenorthophosphate has a melting point of >450°C and is considered to be very soluble (>50.2 <52 % (w/w) at 20°C). The pH of this solution, observed in the water solubility study, was between pH3.6 to pH 4. The water solubility study conducted on sodium dihydrogenorthophosphate made the following observations:

The test material studied is essentially sodium dihydrogenorthophosphate following a degree of basification. For example, if an existing, acidic sample solution of sodium dihydrogenorthophosphate was adjusted towards a basic pH by the addition of sodium hydroxide, the resulting salt formed would be that of disodium hydrogenorthophosphate. As water solubility data for this analogous salt exists (>23.8 < 25.1 % (w/w) at 20°C, pH 9.2. O’Connor BJ, 2009, Harlan Laboratories Ltd, 2920/0004) and as it incorporates the environmentally relevant pH of interest, it can be concluded that the solubility of the sodium dihydrogenorthophosphate would decrease slightly as the pH increased over the pH range of 4 to 9. However, it must be noted that solubility would still remain high (in the range 23.8 to 25.1% w/w at 20°C, pH 9.2) and such a decrease would only be observed if significant buffering capacity was present which prevented the formation of an acidic solution as formed on dissolution of the test material.The temperature range of 10 to 30°C had no significant influence on the observed solubility of the test material.


Sodium dihydrogenorthophosphate is not considered to possess any of the following hazardous physico-chemical properties: autoflammability and/or self-ignition, flammability, explosiveness and oxidising properties.