A Drug Substance or chemical material of established quality and purity as shown by comparison to the reference standard material and used as Reference Working Substance for routine quality control analysis. The substance can be any manufacturing batch.

• A Drug Substance or chemical material of established quality and purity as shown by comparison to the reference standard material and used as Reference Working Substance for routine quality control analysis.
• Working standards play a critical role in any laboratory.

• A working standard is a material of highest purity grade available whose composition is known in relation to a certified reference material having established traceability to a recognized global standard body.
• As a working standard is to be used over a prolonged time period it is necessary to evaluate its composition periodically to verify that it does not vary beyond acceptable limits.
• Working standard also necessitates care in handling and preservation under prescribed storage conditions. Before its expiry date another working standard is prepared and its composition is compared to the existing standard.
• In this manner a record of traceability is maintained with the original certified reference material through an unbroken chain of traceability.

SOURCING

• A working standard can be prepared in-house or it can be procured from a reputed supplier or another laboratory.
• A certificate of analysis should accompany in case the material is procured from external sources.

STORAGE

• On receipt proper arrangements must be made for its storage, i.e., temperature, humidity and exposure to light. Care needs to be taken after every use to properly close and seal the container and ensure that same storage conditions are maintained. It is also helpful if a log record is maintained on its consumption.

QUALITY CHECKING

• The material should be analysed on receipt or in – house preparation. The standard is analysed by at least 3 validated analysts for its assay, and other parameters such as loss on drying, moisture content, melting point, sulphated ash, etc.
• The average of results obtained is stored for future reference. Thereafter the vial or bottle is affixed a label assigning unique number, date of analysis, storage conditions and the use by date.

WORKING STANDARD VALIDITY

• The working standard should be used only till the mentioned date on the label. Before this date a new standard should be made available.
• In case a standard gets consumed before its expiry a fresh replacement should be made available in advance.
• The list of working standards should be kept updated every time a new standard is introduced.

SHELF LIFE STUDIES

• The validity of use is based on shelf life studies and structural chemical nature of the compounds .Normally the validity of stable products is set for 3, 6, 12 and 36 months .On the basis of shelf life studies the utility period can be decided.

INTERMEDIATE CHECKS

• As a general rule the assay of a working standard including loss on drying and moisture content should be checked after 6 months for standards having expiry of 1 year or 3 months for other working standards.
• In case any unexpected variations are observed or the appearance changes the standard should be discarded even before its use by date.
• As a useful guideline the table below provide the maximum deviation acceptance criteria for different tests on working standards.