from procurement to application in study sample analysis.

3. Responsibilities

• Bioanalytical Scientist: Responsible for the selection, justification, and usage of internal standards during method development and sample analysis.
• QA Officer: Verifies that the internal standard procedures are followed, documented, and traceable.
• Lab Technician: Prepares internal standard solutions as per protocol and maintains inventory.

4. Accountability

The Bioanalytical Department Head is accountable for ensuring compliance with this SOP and verifying that the internal standard strategy aligns with regulatory expectations.

5. Procedure

5.1 Selection of Internal Standards

1. Select an internal standard (IS) that closely resembles the chemical and physical properties of the analyte.
2. Preferred internal standards include stable isotope-labeled analogs (e.g., deuterated compounds) or structurally similar compounds.
3. Document justification of IS selection in method development records using Annexure-1: Internal Standard Selection Justification Form.

5.2 Procurement and Storage

1. Source internal standards from certified suppliers with certificate of analysis (CoA).
2. Upon receipt, verify the CoA for purity, molecular structure, and batch details.
3. Store IS stock solution at recommended conditions (typically -20°C, protected from light).
4. Record storage information in Annexure-2: Internal Standard Inventory Log.

5.3 Preparation of Internal Standard Solution

1. Weigh required quantity of IS using calibrated analytical balance and dissolve in appropriate solvent (e.g., methanol or acetonitrile).
2. Prepare intermediate and working solutions as per validated method SOPs.
3. Label all prepared solutions with:
   • Name of IS
   • Concentration
   • Date of preparation
   • Expiry date
   • Prepared by
4. Document preparation details in Annexure-3: Internal Standard Solution Preparation Log.

5.4 Use During Sample Preparation

1. Add a fixed volume of IS working solution to each calibration standard, quality control (QC) sample, and study sample prior to extraction.
2. Ensure consistent mixing and processing to maintain uniformity.
3. Record volumes and sample IDs in the extraction worksheet or Annexure-4: Sample Extraction Log.

5.5 Monitoring and Troubleshooting

1. Review peak shape, retention time, and area response of the IS in each chromatogram.
2. Investigate deviations such as inconsistent IS response or peak shifts.
3. Document any issues and corrective actions taken in Annexure-5: Internal Standard Performance Review Log.

5.6 Disposal of Expired Standards

1. Dispose of expired IS solutions as per hazardous waste SOPs.
2. Record disposal activity in Annexure-6: Internal Standard Disposal Log.

6. Abbreviations

• IS: Internal Standard
• LC-MS/MS: Liquid Chromatography Tandem Mass Spectrometry
• BA/BE: Bioavailability/Bioequivalence
• CoA: Certificate of Analysis
• QC: Quality Control
• SOP: Standard Operating Procedure

7. Documents

1. Internal Standard Selection Justification Form – Annexure-1
2. Internal Standard Inventory Log – Annexure-2
3. Internal Standard Solution Preparation Log – Annexure-3
4. Sample Extraction Log – Annexure-4
5. Internal Standard Performance Review Log – Annexure-5
6. Internal Standard Disposal Log – Annexure-6

8. References

• ICH M10: Bioanalytical Method Validation
• US FDA Guidance on Bioanalytical Method Validation (2022)
• WHO Guidelines for Bioanalytical Laboratories

9. SOP Version

Version: 2.0

10. Approval Section

	Prepared By	Checked By	Approved By
Signature
Date
Name
Designation
Department

11. Annexures

Annexure-1: Internal Standard Selection Justification Form

Analyte	Selected IS	Justification	Selected By	Date
Drug A	Drug A-d5	Stable isotope, same retention time	Dr. Rajesh Kumar	15/04/2025

Annexure-2: Internal Standard Inventory Log

IS Name	Batch No.	Received Date	Expiry Date	Quantity	Location
Drug A-d5	DAI-1125	10/04/2025	09/04/2026	25 mg	Freezer-1

Annexure-3: Internal Standard Solution Preparation Log

Date	IS Name	Concentration	Solvent	Prepared By
12/04/2025	Drug A-d5	1 µg/mL	Methanol	Sunita Reddy

Annexure-4: Sample Extraction Log

Sample ID	IS Volume Added	Operator	Date
PL-101	50 µL	Ajay Verma	14/04/2025

Annexure-5: Internal Standard Performance Review Log

Date	Run ID	IS Peak Area	Observation	Action Taken
15/04/2025	BAE-097	325000	Consistent	None

Annexure-6: Internal Standard Disposal Log

Date	IS Name	Quantity Disposed	Disposed By	Verified By
17/04/2025	Drug A-d5	5 mg	Mahesh Patil	QA Officer

Revision History:

Revision Date	Revision No.	Details	Reason	Approved By
01/01/2022	1.0	Initial Issue	New SOP	QA Head
17/04/2025	2.0	Expanded procedure and annexures added	ICH M10 Alignment	QA Head