SOP on Working Standards

SOP on Working Standards


To establish a quality system and guidelines for the preparation, characterisation and establishment of working reference standards/materials. 

Standard Reference Material

SRM is a certified material issued by any recognised/accredited body to be used for development and validation of accurate methods of analysis ensuring traceable measurement results of working level.

Working Reference Standard

Working Reference Standard which serves as a substitute for standard reference material are materials, which are evaluated against the SRM for suitability of use. 

Working reference standards are prepared by the analytical laboratories In house for their routine analytical work for regular day to day use. Working reference standards are generally used for the calibration of the instrumental techniques, evaluation of the accuracy of the analytical methods used and verification of the test results to ensure their accuracy and consistency. It is very important that the guidelines for the preparation of the In-house working reference standards may have to be established and documented. Such guidelines will ensure that the In-house working reference standards are fit for their intended purpose and of appropriate quality.


The composition of the In-house standard reference material should resemble in parameters as closely to that of samples, which will be tested against it. Also the purity of the material should be such that no substances are present in it that would interfere with the methods/procedures by which the material is being tested.

The bulk material (5 to 50gm) should usually be procured from a single source or it may be prepared by pooling a number of different batches of the material. It should be ensured of homogenity by mixing, grinding, sieving, drying and packing in a suitable container. These steps should be accomplished without undue contamination or chemical change in the material. Analytical grade or G.R. grade materials may also be used subject to their availability

Store the prepared and homogenised material in a suitable container.  


Tests performed for evaluation should be adequate to assure the identify, strength and purity of the material. Also complete testing should be performed as indicated in the active substance specification.

Complete testing of the material is undertaken for all the tests as per relevant applicable specification. The Analytical data with respect to identity, loss on drying/ moisture, assay/potency by Chemical/Instrumental techniques as applicable, relevant impurities, metallic contaminants etc. should be undertaken.
For the assay/potency certification, three independent determinations should be undertaken using a single definative method. The method used should be highly accurate, validated so that the data being generated have negligible systematic errors relative to end use requirements. The average of these determinations is computed as the assay/potency value. The obtained value represents the best estimate of the true/assigned value to the material. Generally it is 100 percent minus content of moisture and volatiles (L.O.D.)


It should be ensured to safeguard and maintain the integrity of the prepared working reference standard. The current GMP requirements should be observed in packing materials and should be controlled to avoid any contamination effect of the containers.


Distribute the prepared working reference standard in three sealed glass bottles/containers and store in conditions, which do not effect its stability.

- One portion to be released for routine analysis.
- Second portion to be kept for stability studies.
- Third portion to be kept for preparing further working standards.

Stability of the prepared working standard

The stability of the prepared working standard is necessary in order to determine the length of time for which the standard used for quantitative purposes are expected to retain its strength/ potency under the storage conditions to establish its validation period.

The potency and degradation of the prepared working reference standards is verified at six months for antibiotics/vitamins and for others of an interval of one year. 


An identification mark/code no. may assigned to the containers filled with reference standards. Also each container must be labelled to show the following details:

- Name of the product
- Code No./Batch No.
- Date, Month of Establishment
- Assay/ Potency
- Water/ L.O.D.
- Date of validity
- Storage conditions

Records and Documentation

Details of the analytical data generated in the establishment of the working reference standards must be recorded and document. Also the traceability of the standard reference materials against, which the working reference is prepared should be documented.

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