If you have ever followed an HPLC method in the United States Pharmacopeia, then you have probably already encountered the problem of selecting a suitable HPLC column for the analysis. Columns are designated by a letter and number which identifies the stationary phase, e.g. L1 refers to ‘Octadecylsilane chemically bonded to porous silica or ceramic micro-particles, 1.5 to 10 μm in diameter, or a monolithic rod’. Unfortunately there are hundreds of columns that fit this description and due to selectivity differences they may not all give similar results.
The outcome of the USP Working group on HPLC Columns is that you can now look up the chromatographic column which was used to validate the procedure. The free online database provides a cumulative listing of columns referenced in gas- and liquid-chromatographic methods related to revisions made to USP–NF since January 1980. USP Chromatographic Columns can be accessed via the USP website, you will need to register to access the database, then search for the monograph in question. Once you know the actual column which was used for the method you can either use this or an equivalent. The USP Column Database provides a tool which can be used to find equivalent columns.