In the first supplement for USP 30, which will
become effective on 1 August 2007, the requirements on sterile water for
inhalation, sterile water for irrigation and sterile purified water
regarding single ions and pH will be deleted and replaced by the sum
parameter of conductivity.
In detail the requirements for ammonium, calcium,
carbon dioxide, chloride and sulphate were deleted, just as the requirements
for the not very meaningful pH value in purified water. The requirements
with regard to pH, carbon dioxide as well as to the maximum concentration of
further single ions are covered by the sum parameter of conductivity. According
to USP paragraph <645> this will have to be conducted starting with step two
– that means with measuring the conductivity after the absorption of
atmospheric carbon dioxide. For containers with a nominal volume smaller
than 10 mL, a conductivity of not more than 25 µS/cm is required, and for
containers larger than 10 mL, not more than 5 µS/cm – each at 25 ±1 °C.
With this change, the US Pharmacopoeia harmonises the requirements
regarding sterile waters with the requirements on purified water and water
for injection, for which the sum parameter of conductivity replaced the requirements
regarding single ions already in 1996.