What problems have you seen with existing methods?
Note that most solvent modifiers will replace the sulfate with another counter-ion as the compound elutes through the column, unless you are using a sulfate buffer.
There seems to be a lot of information available already:
Not really. Most antibiotics have non-HPLC methods because there are many peaks (some of which are not active). Since HPLC is a comparative method you need a stable and official standard. Also most detectors are mass related you need to know the mass to IU conversion factor.