directly proportional to analyte concentration over a specified range.

2. Scope

This SOP applies to all analytical methods under development or validation for APIs, intermediates, drug products, and excipients at various concentration levels across a range of 80–120% of the nominal concentration or as per regulatory requirements.

3. Responsibilities

• Analytical Scientist: Prepares standard solutions, performs linearity runs, and plots calibration curves.
• Method Development Lead: Reviews data, evaluates statistical parameters, and ensures compliance with acceptance criteria.
• QA Reviewer: Verifies accuracy of linearity results and endorses inclusion in method validation report.

4. Accountability

The Head of Analytical Method Development is accountable for ensuring all linearity studies are executed as per protocol, interpreted scientifically, and documented in compliance with ICH Q2(R1) guidelines.

5. Procedure

5.1 Preparation of Standard Solutions

1. Prepare a minimum of five concentration levels (e.g., 80%, 90%, 100%, 110%, and 120%) or more as required.
2. Use a validated reference standard for solution preparation.
3. Prepare each level in triplicate and record actual concentrations.

5.2 Chromatographic Analysis

1. Inject all concentration levels into the chromatographic system (e.g., HPLC, GC, UV).
2. Ensure consistent instrument parameters for each run.
3. Record peak area or response data for each injection.

5.3 Data Compilation and Calibration Curve

1. Plot concentration (X-axis) vs response (Y-axis) using appropriate software (e.g., Excel, CDS, GraphPad).
2. Apply linear regression analysis to derive slope (m), intercept (c), and correlation coefficient (r).
3. Document the equation of the line: Y = mX + c.

5.4 Evaluation of Statistical Parameters

• Correlation Coefficient (r): Should be ≥ 0.999 for assay methods and ≥ 0.990 for impurity methods.
• Y-intercept: Should not be significantly different from zero.
• %RSD: Should be ≤ 2% for all concentration levels.
• Slope Consistency: Ensure similarity across batches or analysts.

5.5 Residual Analysis

1. Assess residual plots to confirm linearity across the range.
2. Identify systematic deviation at lower or higher concentrations if any.

5.6 Documentation

1. Record raw data in the Linearity Evaluation Worksheet (Annexure-1).
2. Include printouts of chromatograms, linearity curve, regression table, and statistical summary.
3. Attach signed validation summary for inclusion in the final report.

6. Abbreviations

• CDS: Chromatography Data System
• RSD: Relative Standard Deviation
• ICH: International Council for Harmonisation
• API: Active Pharmaceutical Ingredient

7. Documents

1. Annexure-1: Linearity Evaluation Worksheet
2. Annexure-2: Statistical Summary Template
3. Validation Protocol and Method Development Reports

8. References

• ICH Q2(R1): Validation of Analytical Procedures
• USP Chapter <1225> Validation of Compendial Procedures
• 21 CFR Part 211 – Current Good Manufacturing Practices

9. SOP Version

Version: 2.0

10. Approval Section

	Prepared By	Checked By	Approved By
Signature
Date
Name	Rajesh Thakur	Anjali Mehta	Dr. Hema Verma
Designation	AMD Analyst	QA Reviewer	Head – AMD Department
Department	Analytical Method Development	Quality Assurance	Analytical Method Development

11. Annexures

Annexure-1: Linearity Evaluation Worksheet

Concentration (%)	Theoretical Conc. (µg/mL)	Area 1	Area 2	Area 3	Mean Area	%RSD
80	80	2054	2078	2061	2064	0.58

Annexure-2: Statistical Summary Template

• Linear Regression Equation: Y = 25.31X + 3.02
• Correlation Coefficient (r): 0.9998
• Range Evaluated: 80–120%
• Analyst Initials: RT

Revision History

Revision Date	Revision No.	Details	Reason	Approved By
01/06/2025	2.0	Expanded residual analysis and documentation format	Annual SOP review	Dr. Hema Verma
15/08/2022	1.0	Initial Release	New SOP	QA Head