Standard Operating Procedure for Assay Testing Using Gas Chromatography

Department	Quality Control
SOP No.	SOP/TAB/109/2025
Supersedes	SOP/TAB/109/2022
Page No.	Page 1 of 7
Issue Date	01/03/2026
Effective Date	06/03/2026
Review Date	01/03/2027

1. Purpose

To define the procedure for performing assay testing using Gas Chromatography (GC) for determining the content of the active pharmaceutical ingredient (API) in tablet formulations.

2. Scope

This SOP applies to the assay testing of tablets containing volatile and semi-volatile compounds using GC. It ensures accurate quantification of the API in the tablet formulation.

3. Responsibilities

• Quality Control (QC): Responsible for conducting assay testing using GC, analyzing the results, and ensuring that the assay meets the required specifications for the API content in tablets.
• Quality Assurance (QA): Ensures the correct execution of this SOP and reviews the results for regulatory compliance and product quality.
• Laboratory Personnel: Responsible for preparing samples, operating the GC instrument, and recording results accurately.

4. Accountability

The QC Manager is accountable for ensuring the accurate performance of assay testing using GC. The QA Manager is responsible for reviewing and approving the assay results to ensure compliance with the product’s specifications and regulatory requirements.

5. Procedure

5.1 Sample Preparation

1. Obtain a representative sample of the tablets (usually 10–20 tablets depending on batch size) for assay testing.
2. Crush the tablets into a fine powder using a mortar and pestle or mechanical grinder to ensure homogeneity.
3. Weigh an appropriate amount of the powdered sample (e.g., 100 mg) for analysis.
4. Dissolve the sample in an appropriate solvent (e.g., methanol, ethanol, or acetonitrile), based on the solubility of the API.
5. Filter the solution to remove any insoluble material, using a 0.45 µm filter or equivalent.
6. If necessary, dilute the sample to ensure the API concentration is within the linear range of the GC detector.

5.2 Instrument Calibration

1. Prepare a series of standard solutions containing known concentrations of the API, which will be used to generate the calibration curve.
2. Calibrate the GC instrument using the standard solutions by injecting known volumes and recording the peak areas or heights.
3. Ensure that the GC system is set up with the appropriate column, temperature conditions, flow rates, and detector settings based on the API’s properties and the method requirements.

5.3 Performing GC Analysis

1. Inject the prepared sample into the GC system using an autosampler or manually, depending on the equipment setup.
2. Monitor the chromatogram for the characteristic peaks of the API, ensuring that the API peak is well-resolved and clearly identifiable from other components in the sample.
3. Record the retention time and peak area for the API in the sample, and compare these values to those of the calibration standards.
4. Ensure that the analysis is performed under consistent conditions, with the instrument parameters, such as injector temperature, oven temperature, and carrier gas flow rate, remaining constant throughout the analysis.

5.4 Data Analysis and Calculation

1. Use the calibration curve to calculate the concentration of the API in the sample based on the peak area or height of the API.
2. Calculate the content of the API in the tablet formulation by multiplying the concentration obtained from the GC analysis by the dilution factor and the volume used in the sample preparation.
3. Ensure that the API content meets the required acceptance criteria, typically within 95%–105% of the labeled amount, depending on the pharmacopeial requirements or product specifications.

5.5 Acceptance Criteria

1. The assay result should be within the predefined limits for the API content in the tablet (usually 95%–105% of the labeled amount).
2. If the assay result is outside the acceptable range, investigate the cause, document the deviation, and initiate corrective actions (Annexure-1).
3. Perform additional tests if necessary, including re-analysis of the sample or preparation of a fresh sample if contamination or errors in preparation are suspected.

5.6 Documentation and Record-Keeping

1. Document all assay testing results, including chromatograms, calibration curves, and calculated API content, in the batch record (Annexure-2).
2. Ensure that all records are signed, dated, and stored according to the company’s record retention policy for future audits and inspections.
3. Maintain raw data, including chromatograms and standard curves, for regulatory compliance and future reference.

5.7 Post-Test Actions

1. Clean the GC system and associated equipment after each analysis to avoid contamination from previous samples.
2. Dispose of used samples, solvents, and reagents according to the company’s waste disposal procedures.
3. Ensure that the GC instrument is calibrated regularly and maintained according to the manufacturer’s guidelines.

6. Abbreviations

• SOP: Standard Operating Procedure
• GMP: Good Manufacturing Practice
• QC: Quality Control
• QA: Quality Assurance
• GC: Gas Chromatography
• API: Active Pharmaceutical Ingredient

7. Documents

1. Batch Record (Annexure-2)
2. Deviation Report (Annexure-1)

8. References

• USP <621> – Gas Chromatography
• 21 CFR Part 211 – Current Good Manufacturing Practice for Finished Pharmaceuticals (US FDA)
• European Pharmacopoeia (EP) – Specifications for Gas Chromatography

9. SOP Version

Version: 2.0

10. Approval Section

	Prepared By	Checked By	Approved By
Signature
Date
Name
Designation
Department

11. Annexures

Annexure-1: Deviation Report

Deviation Date	Batch Number	Deviation Description	Corrective Action	Responsible Person
15/12/2025	Batch 001	API content exceeded limit	Investigated and adjusted formulation	John Doe

Annexure-2: Batch Record

Batch Number	API Content (%)	Expected Content (%)	Result
Batch 001	98.5%	98.0%	Pass

Revision History:

Revision Date	Revision No.	Revision Details	Reason for Revision	Approved By
01/01/2024	1.0	Initial Version	New SOP Creation	QA Head
01/02/2025	2.0	Updated Analytical Method	Improved method accuracy	QA Head