Working Standards
Working Standards
Working Standards – Cleanchem Laboratories
A drug substance or chemical material that meets established standards of quality and purity, confirmed by comparison with a reference standard, is used as a Reference Working Substance for routine quality control analysis. This substance may be derived from any qualified manufacturing batch.
Importance of Working Standards
Working standards are essential tools in every analytical laboratory. A working standard is the purest available material whose composition is verified against a certified reference standard with traceability to recognized international agencies. Since working standards are used over extended periods, their composition must be periodically re-evaluated to ensure they remain within acceptable limits. Proper handling and storage under defined conditions are critical, and before expiry, a replacement must be prepared and cross-checked to maintain an unbroken traceability chain to the original certified reference standard.
Sourcing
Working standards may be prepared in-house at Cleanchem Laboratories or procured from reputed suppliers or accredited laboratories. When sourced externally, a Certificate of Analysis (CoA) should always accompany the material.
Storage
Upon receipt, appropriate storage arrangements must be ensured — including controlled temperature, humidity, and light protection. After every use, the container should be tightly sealed and stored under the prescribed conditions. Maintaining a usage log helps track consumption and quality consistency.
Quality Verification
Each working standard should be analyzed upon preparation or receipt. At Cleanchem Laboratories, the standard is tested by at least three validated analysts for assay and parameters such as moisture content, loss on drying, melting point, and sulphated ash. The average of these results is documented for reference. Containers are then labeled with a unique identification number, date of analysis, storage conditions, and expiry date.
Validity of Working Standards
Working standards must only be used until their labeled expiry date. A new standard should be prepared or procured before the current one expires or is fully consumed. An updated register of working standards must be maintained.
Shelf Life Studies
The validity of a working standard depends on stability data and the chemical nature of the compound. Generally, stable compounds may have shelf lives of 3, 6, 12, or 36 months. Shelf life studies guide the determination of appropriate validity periods.
Intermediate Checks
For working standards with one-year validity, assay and moisture content are typically re-evaluated after six months; for shorter validity, checks are done every three months. Any unexpected changes in assay results or physical appearance warrant immediate discontinuation of the standard, even before expiry.
Acceptance Criteria for Deviation
| Test Parameter | Acceptance Criteria |
|---|---|
| Assay by HPLC | ± 0.5% |
| Chemical Assay | ± 1.0% |
| Microbiological Assay | ± 2.0% |
| Water Content | ± 0.5% |
| Loss on Drying (LOD) | ± 0.5% |