QC laboratory of the API manufacturing facility.

3. Responsibilities

• QC Analyst: Perform calibration and use the pH meter as per this SOP and record all results properly.
• QC Reviewer: Review calibration logs and ensure records are accurate and complete.
• Instrument In-Charge: Oversee routine maintenance and ensure timely calibration schedule compliance.

4. Accountability

The QC Head is accountable for ensuring adherence to this SOP and maintaining GMP-compliant pH meter operation.

5. Procedure

5.1 General Guidelines

1. Ensure the instrument is clean, calibrated, and switched on before use.
2. Use only fresh and valid standard buffer solutions for calibration (typically pH 4.01, 7.00, and 9.20 or 10.01).
3. Calibrate daily before use or as per frequency defined in the method SOP.
4. Do not use expired buffers or store them in contaminated containers.

5.2 Calibration of pH Meter

1. Rinse the electrode with distilled water and blot dry with lint-free tissue.
2. Immerse the electrode in pH 7.00 buffer solution and press “Calibrate” or “Standardize.”
3. Once stabilized, record and accept the reading (must be within ±0.05 pH units).
4. Repeat the process with pH 4.01 and 9.20 (or 10.01) buffers for multi-point calibration.
5. If the meter displays “calibration error” or drift exceeds tolerance, re-calibrate or perform maintenance.
6. Record the calibration data in the Calibration Logbook (Annexure-1).

5.3 pH Measurement Procedure

1. Verify calibration before use.
2. Rinse the electrode with distilled water between each sample.
3. Immerse the electrode in the sample solution ensuring the bulb is fully submerged.
4. Wait until the reading stabilizes, then record the pH value in the analytical worksheet.
5. Rinse and store the electrode in appropriate storage solution after use.

5.4 Maintenance of pH Meter

1. Clean the electrode weekly using electrode cleaning solution if buildup is observed.
2. Check the electrode for physical damage or clogging and replace if necessary.
3. Refill the reference electrode (if applicable) with proper electrolyte solution.
4. Store the electrode in storage solution (usually 3M KCl) and never allow to dry.
5. Perform monthly checks for instrument response time and slope (% efficiency should be 90–105%).
6. Record maintenance activity in Instrument Maintenance Log (Annexure-2).

5.5 Troubleshooting

1. If readings are unstable or drift:
   • Check electrode cleanliness
   • Ensure calibration is up-to-date
   • Check temperature sensor and cable connections
2. If still unresolved, escalate to Instrument In-Charge or service engineer.

5.6 Documentation

1. Record the following in respective logbooks:
   • Calibration details
   • Maintenance activity
   • Corrective actions taken for troubleshooting
2. Ensure all entries are signed and dated by the responsible analyst.

6. Abbreviations

• pH: Potential of Hydrogen
• QC: Quality Control
• GMP: Good Manufacturing Practices
• SOP: Standard Operating Procedure
• KCl: Potassium Chloride

7. Documents

1. pH Meter Calibration Logbook (Annexure-1)
2. Instrument Maintenance Logbook (Annexure-2)
3. Analytical Worksheet

8. References

• Instrument User Manual
• ICH Q2(R1) – Validation of Analytical Procedures
• 21 CFR Part 211

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 Meter Calibration Log

Date	pH Buffer Used	Observed pH	Status	Analyst
13/04/2025	7.00	7.01	Within Limit	Rajesh Kumar
13/04/2025	4.01	4.02	Within Limit	Rajesh Kumar
13/04/2025	9.20	9.17	Within Limit	Rajesh Kumar

Annexure-2: Instrument Maintenance Log

Date	Activity	Performed By	Remarks
12/04/2025	Electrode cleaned	Sunita Reddy	Deposits removed
01/04/2025	Electrode storage solution replaced	Sunita Reddy	Fresh KCl used

Revision History:

Revision Date	Revision No.	Details	Reason	Approved By
01/01/2022	1.0	Initial version	Equipment SOP Requirement	QA Head
13/04/2025	2.0	Updated to include 3-point calibration and maintenance log	Audit Feedback	QA Head