For chromatographic systems, instru

For chromatographic systems, instrument calibration standards should be chosen from highly purified materials that are well characterized and can be accurately weighed. Standards can be compendial (from USP) or non-compendial (e.g., from NIST, a chemical supplier, or produced in-house). Substances obtained from a chemical supplier or produced in-house should be purified and characterized using validated purification processes and validated characterization methods. Purification is necessary because impurities can add variation and interfere with analytical methods. Finished dosage forms generally should be avoided as standards because excipients in the finished dosage form may interfere with analysis.