USP23 its 99.9 compaired to the USP25 which is 99.
Does a higher (later) Edition number necessarily mean a chemical is more pure?
No it does not. This isn’t like an octane number when you go to the gas station. Although the USP/NF is updated constantly, the specifications for most chemicals change only very rarely. Most changes involve updating methods to include the more automated equipment that is becoming more common in most labs. Also most updates include many new monographs for medicines that did not exist at the time of publication of previous editions.
Because of the nature of updates it is very likely that a chemical that received a USP24 rating is entirely good enough to receive a USP25 or USP26 rating, but just has not been retested. Furthermore because of the pass/fail nature of USP testing it is entirely possible that a chemical with a USP25 rating is more pure than one with a USP26 rating, assuming the chemical receiving a USP26 rating barely passed and the chemical receiving a USP25 rating passed with flying colors
Please Scroll Down to See Forums Below 
