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USP〈621〉tells you how chromatography must be run and what counts as a modification rather than a routine adjustment. For anyone specifying packing material the key fact is this: the stationary phase is identified by an L-code, and changing the stationary phase requires validation. That is not something a lab can do informally.
USP〈621〉is the general chapter on chromatography. It describes the basic procedures used when a chromatographic method is called out in a monograph, covering paper, thin-layer, column, gas and high-performance liquid chromatography.
For a normal-phase column the wording is specific: the solid phase is an active adsorbent — such as alumina, silica or carbon — packed into a column. That is the category chromatography silica sits in. HPLC packings are then identified through the USP L-code listing:
| L-code | Packing |
|---|---|
| L1 | Octadecyl silane (C18), chemically bonded, porous silica |
| L7 | Octyl silane (C8) |
| L9 | Nitrile groups |
Always confirm the code for your specific method — the full listing is long, and the code is part of the validated method, not a catalogue preference.
So "the lab will just switch columns" is not a small thing under USP. If a buyer runs a monograph method, the packing identity is part of that method.
If a client quotes "USP〈621〉" without a version, ask which one. The 2025 HPLC update changes parameters that affect method transfer.
For thin-layer work the chapter notes that satisfactory plates are stored over silica gel in a suitable chamber — the pharmacopoeia itself treats silica gel as the standard desiccant for protecting chromatography plates. That is the same material we also supply as a bulk desiccant, in a completely different grade. The difference is explained in chromatography silica vs desiccant silica.
| Item | What to state |
|---|---|
| Method reference | USP〈621〉plus the monograph number and the chapter version |
| Packing identity | The L-code (e.g. L1, L7, L9) — not just "silica" |
| Particle size | Commercial specification (e.g. 40–63 µm) — USP does not fix it |
| Pore diameter | Commercial specification (e.g. 60 Å) — see grades compared |
| Documentation | Certificate of analysis per batch, and a test chromatogram on request |
| Change control | Written notice if the packing batch identity changes |
Our column chromatography silica gel is quoted in the XCL-A, XCL-B and XCL-C pore grades with the particle size set to your requirement.
Written by the VEN Desiccant export team from the published text of the USP chromatography general chapter and the USP packing listing. Drafting was AI-assisted; the L-code examples and the modification-versus-adjustment rule were checked against the chapter and its published commentary and edited by our team before publication. We publish it to help buyers and their labs agree on what a packing specification has to contain. Confirm the exact code and edition against the current USP monograph before writing it into a contract.
Last checked: 11 October 2026.
Tell us the L-code, particle size and pore diameter and we will quote the grade and the documentation that goes with it.
