Development (AMD) department. It ensures accurate, reproducible, and regulatory-compliant pH determination that supports preformulation, stability, and quality assessment activities.

2. Scope

This SOP applies to pH method development and optimization of all APIs handled in the AMD laboratory, including new chemical entities (NCEs), generic actives, and intermediates requiring aqueous or partially aqueous pH measurement.

3. Responsibilities

• Analytical Scientist: Conducts method development, documents procedures and performs validation.
• Reviewer: Verifies method accuracy, precision, linearity, and robustness results.
• QA: Reviews method validation report and ensures alignment with ICH guidelines.
• Head – AMD: Approves finalized method and validation report for regulatory filing.

4. Accountability

The Head of AMD is accountable for ensuring all pH methods developed for APIs are scientifically justified, validated, and traceable as per applicable GMP and ICH requirements.

5. Procedure

5.1 Pre-Method Considerations

1. Obtain API solubility and dissociation profile from literature or preformulation data.
2. Select appropriate solvent system:
   • Water or buffer (0.1N HCl, 0.1N NaOH, phosphate buffers)
   • Maintain ionic strength where necessary
3. Use Annexure-1: pH Method Development Plan to document method rationale and objectives.

5.2 Preparation of Sample Solutions

1. Weigh accurate quantity of API (e.g., 100 mg) into a beaker.
2. Dissolve in required volume of solvent or buffer (e.g., 100 mL water or pH 7.0 phosphate buffer).
3. Filter using Whatman No. 1 filter paper if needed to remove insoluble matter.
4. Label all test samples clearly with strength, solvent, and API name.

5.3 Instrument Preparation

1. Ensure pH meter calibration with standard buffers (pH 4.01, 7.00, and 9.21).
2. Document calibration in Annexure-2: pH Meter Calibration Log.
3. Check electrode condition and refill electrolyte (if applicable).

5.4 pH Measurement Procedure

1. Transfer approx. 50 mL of prepared API solution to a clean 100 mL beaker.
2. Immerse electrode in solution, ensuring no air bubbles around the bulb.
3. Allow reading to stabilize for 30–60 seconds before recording.
4. Record temperature of measurement (e.g., 25°C ± 2°C).
5. Rinse electrode with deionized water between samples.
6. Perform measurement in duplicate and report average.

5.5 Method Optimization Parameters

1. Assess stability of pH over 2 hours (interval: 0, 30, 60, 120 minutes).
2. Determine pH in different solvent systems to simulate degradation or solubility behavior.
3. Evaluate temperature influence by performing trials at 20°C, 25°C, and 30°C.
4. Document data in Annexure-3: pH Optimization Worksheet.

5.6 Method Validation Criteria

1. Linearity: Prepare known acidic/basic dilutions and assess pH response.
2. Precision: Perform repeatability (6 readings from same analyst) and intermediate precision (2 analysts, 2 days).
3. Accuracy: Compare with expected theoretical pKa or known reference value.
4. Robustness: Alter buffer strength, temperature, and assess effect on pH.
5. Document validation results in Annexure-4: pH Method Validation Report.

5.7 Final Method Documentation

1. Consolidate method SOP including:
   • Sample preparation
   • Solvent system
   • Electrode care
   • Acceptance criteria
2. Submit method and validation report to QA and retain approved copy in DMS.

6. Abbreviations

• AMD: Analytical Method Development
• API: Active Pharmaceutical Ingredient
• ICH: International Council for Harmonisation
• DMS: Document Management System
• QA: Quality Assurance

7. Documents

1. pH Method Development Plan – Annexure-1
2. pH Meter Calibration Log – Annexure-2
3. pH Optimization Worksheet – Annexure-3
4. pH Method Validation Report – Annexure-4

8. References

• ICH Q2(R1) – Validation of Analytical Procedures
• USP <791> – pH
• 21 CFR Part 211 – Subpart I: Laboratory Controls
• Ph. Eur., JP – General Notices on pH Measurement

9. SOP Version

Version: 2.0

10. Approval Section

	Prepared By	Checked By	Approved By
Signature
Date
Name
Designation
Department

11. Annexures

Annexure-1: pH Method Development Plan

API	Solvent System	Expected Range	Prepared By
API-X	0.1N HCl	2.5–3.5	Ajay Mehra

Annexure-2: pH Meter Calibration Log

Date	Buffer Used	Reading	Calibrated By
01/05/2025	pH 4.01	4.02	Sunita Reddy
01/05/2025	pH 7.00	7.01	Sunita Reddy

Annexure-3: pH Optimization Worksheet

Time (min)	pH Reading	Temperature (°C)	Remarks
0	3.10	25.1	Stable
60	3.08	25.0	Negligible change

Annexure-4: pH Method Validation Report

Parameter	Acceptance Criteria	Result	Status
Precision	RSD ≤ 1%	0.45%	Pass
Robustness	pH change ≤ ±0.1	±0.06	Pass

Revision History:

Revision Date	Revision No.	Details	Reason	Approved By
04/05/2025	2.0	Included method validation and optimization sections	Regulatory Filing Requirement