Monographs found in pharmacopeias, such as the one published by the United Sates Pharmacopeial Convention (USP), typically avoid specifying a particular vendor’s column in the high pressure liquid chromatography (HPLC) method. This is done to increase a method’s ease of use and also to avoid the appearance of commercial favoritism. Taking an example from the U.S. Pharmacopeia, in the monograph for theophylline, the monograph’s assay describes aHPLC method employing a 30 cm column with an inside diameter of 4 mm and containing L1 packing type. The implication to the analyst is that this column type has been tested and validated to produce acceptable separations when used under the specified HPLC conditions.
Referring to the USP’s Chromatographic Columns publication, or the chromatographic reagents section of the USP/NF, informs the reader that the L1 packing type is a stationary phase that should be between 1.5 and 10 µm in diameter and a product of chemically bonding octadecyl silane to porous silica particles. In other words, it is the C18 column commonly used in HPLC and readily available from a wide range of column manufacturers. As long as the analyst selects a C18 column of specified i.d. and length and uses it with the separation conditions stated in the method, acceptable results should be expected. As you would expect there is a wide range of packing types that extend from L1 up to well over L60. Column types and descriptions can be found by following the above link to the USP website.
Sometimes the separation mechanism is so unique that specifying a column type alone is insufficient to guarantee satisfactory results. In these cases, you may see printed in the pharmacopeia an additional note referencing a specific vendor’s column. For example, the monograph for amikacin specifies a column with L47 packing type. The L47 stationary phase is generally described as an 8 µm high-capacity anion exchange material containing trimethylamine functional groups. The description includes a note that this type of column is available as the Thermo Scientific Dionex CarboPac MA1 Carbohydrate column. Using a similar column from a different manufacturer is certainly permissible, but the analyst must accept the risk of generating unacceptable results.
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