How To Read Reference Standards Listings
When you access any listing of Reference Standards through the alphabetical listing, search, or PDF catalogs, you'll find some or all of the columns of information listed below.
Catalog Number: Catalog number currently assigned to each Reference Standard and Authentic Substance. Please include this number in your orders.
Description: Product description as designated in USP–NF, the product label, and/or the Drug Enforcement Administration Control Schedule, as applicable. The quantity of material per container follows the name in parentheses (all materials are in single containers unless otherwise specified).
Current Lot: Current lot designation of each official item being distributed as of the date of this catalog. If the current lot is blank, the item is not in distribution.
Purity Values: Assigned purity value as it appears on the product label. Code interpretations for the basis of purity assignments are as follows:
| Basis Code | Interpretation |
| (ai) | as is |
| (dr) | dried |
| (an) | anhydrous |
| (fb) | free base |
| (ig) | ignited |
| (sf) | solvent free |
Change Code: Codes that identify any change in USP Reference Standards status or information since the previous official USP Catalog. Code interpretations are as follows:
| Change Code | Interpretation |
| 1 | New Reference Standard |
| 2 | New lot |
| 3 | Change in package size or description |
| 4 | Correction of typographical error |
| 5 | New catalog number — use for all orders |
| 6 | Previous lot no longer official; only current lot to be used |
| 7 | Valid use date of previous lot extended |
| 8 | Change in catalog number and/or name, see cross-reference section |
| 9 | Discontinued |
Previous Lot/Valid Use Date: Lot designations for recent lots no longer being distributed. The date in parentheses indicates the month (last day of the month) through which that lot was valid as an official USP Reference Standard (e.g. "F-1 (06/00)" means lot F-1 is no longer being distributed, but was considered official through June 30, 2000).
CAS Number: Chemical Abstracts Service number, when available, for USP Reference Standards and Authentic Substances. In case of mixtures, typically, the CAS number of the analyte of interest is listed.
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