When changing the HPLC columns used in USP methods, some consideration must be taken for any allowable changes.

If changing any dimension (length or inner diameter) or particle size of HPLC Columns provided in United States Pharmacopeia USP methods, attention and care must be taken for any allowable alterations.

For isocratic separations, it is reported that the particle size and / or the length of the column may be modified provided that the ratio of the column length (L) to the particle size (dp) remains constant or into the range between −25% and 50% of the prescribed L / dp ratio.

For gradient separations, changes in length, column inner diameter, and particle size are not allowed.

Please refer to the USP <General Chapters, {621} Chromatography> for up-to-date information, further clarifications, and other allowable changes.   

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