Standard Operating Procedure for Calibration of pH Meter Used in Production in API Manufacturing
| Department | API Manufacturing |
|---|---|
| SOP No. | SOP/API/088/2025 |
| Supersedes | SOP/API/088/2022 |
| Page No. | Page 1 of 10 |
| Issue Date | 13/04/2025 |
| Effective Date | 15/04/2025 |
| Review Date | 13/04/2026 |
1. Purpose
To define the procedure for routine calibration of pH meters used in production areas for accurate and reliable pH measurements in process solutions during API manufacturing.
2. Scope
This SOP applies to all benchtop and portable pH meters installed or used in production environments for in-process pH monitoring during synthesis, extraction, purification, or cleaning activities.
3. Responsibilities
- Production Operator: Perform daily or before-use calibration of pH meter and record in calibration log.
- QC/QA Officer: Verify calibration records and ensure traceable standard solutions are used.
- Engineering/Instrument Team: Perform preventive maintenance and annual calibration certification.
4. Accountability
The Production Head is accountable for proper execution of calibration. The QA Head is responsible for ensuring compliance with calibration standards.
5. Procedure
5.1 Calibration Frequency
- Daily before first use or before any batch-wise measurement.
- After each maintenance or probe replacement.
- Whenever abnormal readings or drift is observed.
5.2 Required Materials
- Standard buffer solutions (pH 4.00, 7.00, and 9.20 ± 0.02 at 25°C).
- Clean beakers, distilled water, tissue paper, labeling pen.
- Calibration Logbook or Electronic Log System.
5.3 Calibration Steps
- Switch ON the pH meter and allow it to stabilize for 5 minutes.
- Rinse the electrode with distilled water and gently blot dry.
- Immerse the electrode in pH 7.00 buffer first and wait until reading stabilizes.
- Set or confirm the reading at pH 7.00 and press “calibrate” or “enter.”
- Repeat with pH 4.00 and pH 9.20 buffers following the same steps.
- Rinse the electrode between each buffer and avoid contamination.
- After completing 2 or 3-point calibration, recheck with a standard buffer to confirm accuracy.
- If readings deviate > ±0.05 pH units, repeat calibration or inform Engineering/QC.
5.4 Documentation
- Record the following in the pH Meter Calibration Log (Annexure-1):
- Date
- Instrument ID
- Buffer values and observed readings
- Calibration result (Pass/Fail)
- Name and signature of the person performing calibration
- Retain calibration records as part of batch documentation or instrument history file.
5.5 Precautions
- Use fresh buffer solutions; discard opened buffers after 30 days or as per label.
- Ensure the pH probe is stored in recommended storage solution when not in use.
- Do not wipe probe with tissue after calibration—rinse and blot gently.
6. Abbreviations
- pH: Potential of Hydrogen
- SOP: Standard Operating Procedure
- QA: Quality Assurance
- QC: Quality Control
7. Documents
- pH Meter Calibration Log (Annexure-1)
- Instrument Calibration Certificate
- Batch Manufacturing Record (where applicable)
8. References
- USP General Chapter <791> – pH
- ICH Q7 – GMP for APIs
- 21 CFR Part 211 – US FDA cGMP Guidelines
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 | Instrument ID | Buffer 4.00 | Buffer 7.00 | Buffer 9.20 | Calibrated By | Remarks |
|---|---|---|---|---|---|---|
| 13/04/2025 | PHM-102 | 4.01 | 7.00 | 9.19 | Pass |
Revision History:
| Revision Date | Revision No. | Details | Reason | Approved By |
|---|---|---|---|---|
| 01/01/2022 | 1.0 | Initial SOP Release | New Instrument SOP | QA Head |
| 13/04/2025 | 2.0 | Updated procedure and added third buffer option | GMP Alignment | QA Head |