Standard Operating Procedure (SOP)

Here’s a detailed Standard Operating Procedure (SOP) for Preparation of Working Standards used in analytical laboratories:

1. Purpose

To describe a standardized procedure for the preparation, labeling, storage, and usage of working standards derived from primary reference standards for use in quality control testing.

2. Scope

This SOP applies to all analysts involved in the preparation and use of working standards in the Quality Control Laboratory at [Company Name]. It covers pharmaceutical substances, chemicals, and reagents used as reference materials for analysis.

3. Responsibilities

• Analyst: Prepare, label, and document working standards as per this SOP.

• Quality Control Supervisor: Verify and approve working standard preparation.

• Quality Assurance (QA): Review and archive related records as per documentation practices.

4. Definitions

• Primary Standard: A certified reference material obtained from pharmacopoeias or qualified sources.

• Working Standard: A standard prepared from a primary standard, used routinely in analytical testing.

• LOD: Limit of Detection

• LOQ: Limit of Quantification

5. Materials and Equipment Required

• Primary reference standard (certified)

• Analytical balance (calibrated)

• Volumetric flasks, pipettes, and glassware

• Suitable solvent (as per test method)

• Labels and marker

• Desiccator (if required)

• Storage vials (amber, airtight)

• Documentation logbook or electronic system

6. Procedure

6.1 Handling of Primary Standards

1. Use certified reference standards (USP, EP, BP, etc.) or in-house validated materials.

2. Ensure the material is within its validity period and stored as per label.

6.2 Preparation of Working Standard

1. Weighing:

   • Accurately weigh the required quantity of the primary standard on a calibrated analytical balance.

   • Record the exact weight to 4 decimal places.

2. Dissolution:

   • Dissolve in a suitable solvent using clean, dry volumetric glassware.

   • Dilute to the required volume to prepare the standard stock solution.

3. Mixing:

   • Ensure complete dissolution by gentle swirling or using a sonicator (if applicable).

4. Aliquoting:

   • Divide the prepared solution into small portions and store in clean, labeled amber vials to avoid repeated thaw-freeze cycles.

6.3 Labeling

Each working standard vial should be labeled with:

• Name of the compound

• Concentration (e.g., 100 µg/mL)

• Solvent used

• Date of preparation

• Expiry date

• Prepared by (initials)

• Storage conditions

6.4 Storage

• Store prepared standards as per stability data (e.g., 2–8°C, protected from light).

• Avoid repeated exposure to air, moisture, or light.

6.5 Validity/Requalification

• Assign a validity period based on stability data (usually 1–6 months).

• Requalify if required by comparison with a fresh primary standard.

7. Precautions

• Ensure glassware is clean and dry before use.

• Avoid contamination of stock or working solutions.

• Record all observations and deviations, if any.

8. Documentation

• Enter details in the Working Standard Preparation Logbook, including:

  • Batch number of the primary standard

  • Quantity weighed

  • Preparation and expiry dates

  • Assigned working standard ID

  • Signature of preparer and reviewer

9. References

• Pharmacopeial guidelines (USP, EP, BP)

• ICH Q7: Good Manufacturing Practice for Active Pharmaceutical Ingredients

• Internal Quality Manual

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