Hi: I thought that I would give you some useful information, which you can use now or when working on future USP methods.
USP has loosened method parameters quite a bit, giving plenty of room to change columns, mobile phase, etc. See the chromatography section in the USP for the allowable changes, etc. There is a way to eliminate or reduce the number of instances where one does not meet USP requirements.
Always include mobile phase modification and/or different vendor/brand of column in the alternate chromatography section of the validation. If only one brand/vendor's column is validated and written into the method, you are typically bound to use that column; however, by validating a second vendor column of the same type, you give yourself leeway, just in case the primary vendor is out of stock, having QA issues, etc. Also include modification of the mobile phase for a different brand of column, or even the same brand, but a different lot. Mobile phase modification is typically not an issue within one brand and one packing lot; however, if working with ionic compounds using a column made with older type A silica gel, difference in residual silanol sites from one batch of silica get to another can affect chromatographic separation. If possible, it is always better to use newer technology columns, those made with type B silica gel.
Check the USP website to determine which type and brand of column was used to establish the method. USP use to publish a book titled; "Columns Used in USP and NF Methods". They stopped printing this book several years ago, but it is now an online program at USP without any cost. In this program one can look up the monograph of interest, which will list the brand name of the column used for the method, whether it is the assay, purity, etc. As a part of this program, that was typically in the back section of the former book, is a list of all manufacturing qualifying columns, L1 and L7 being a very long list. Keep in mind that the description that USP gives in the monograph is general, not specific to differences in carbon load, type of endcapping bonding chemistry, etc. This leads us to the next program on USP's website.
USP also has a column comparison program that is used to determine the difference in the same type of column from one brand to another, such as C8, C18. It can be quite useful in determining which brand of column should work similarly to one you may already have in house. For example, there is a huge list of C18 columns that quality as L1; however, not all C18 columns perform the same. It has to do with differences in the type of silica gel, A or B, bonding chemistry, endcapped or not endcapped, type of endcapping, carbon load, surface area, ligand density, etc. A C18 phase is not going to change, but differences as mentioned above can create differences in performance. Be proactive and check the USP monograph column used for the method, and if you do not wish to use this column, check to see which column qualifies from another vendor and do the column comparison program before starting a new method.
Both of these programs are free, but you must register to use them.
Regards,
Linda
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