SOP for Operation and Calibration of Conductivity Meter

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STANDARD OPERATING PROCEDURE
Operation and Calibration of Conductivity Meter

1.0 Purpose

To describe the standardized procedure for operation, calibration, and verification of the conductivity meter using USP conductivity buffer solutions to ensure accurate measurement of conductivity in pharmaceutical samples in accordance with USP <645>.

2.0 Scope

This SOP applies to all conductivity meters used in the Quality Control Laboratory for analysis of aqueous solutions, raw materials, and finished pharmaceutical products.

3.0 Responsibility

DesignationResponsibility
QC AnalystOperation, calibration, verification, and documentation
QC SupervisorReview and verification of results
QC ManagerOverall compliance and approval
EngineeringMaintenance and servicing

4.0 Accountability

The QC Manager is accountable for implementation and compliance with this SOP.

5.0 References

  • USP <645> Conductivity
  • Indian Pharmacopoeia
  • British Pharmacopoeia
  • European Pharmacopoeia 2.2.38
  • Conductivity Meter Manufacturer’s Instruction Manual

6.0 Definitions and Abbreviations

TermDescription
Conductivity (µS/cm)Measure of a solution’s ability to conduct electricity
Cell Constant (K)Factor representing the geometry of conductivity cell
ECElectrical Conductivity

7.0 Safety and Precautions

  • Handle USP conductivity buffer solutions carefully; avoid contamination.
  • Rinse electrode with purified water before and after measurements.
  • Do not immerse electrode beyond the recommended depth.
  • Perform calibration at controlled temperature (25°C ± 2°C).

8.0 Instrument Description

The conductivity meter consists of a conductivity probe, temperature sensor, and electronic display unit to measure solution conductivity accurately.

9.0 Operating Procedure

  1. Switch ON the conductivity meter and allow warm-up for 10–15 minutes.
  2. Rinse the electrode with purified water and blot dry.
  3. Immerse the electrode in the sample solution.
  4. Stir gently and allow reading to stabilize.
  5. Record conductivity in µS/cm or mS/cm.

10.0 USP Conductivity Buffer Solutions

Buffer Solution Nominal Conductivity (µS/cm) Acceptance Criteria
USP Buffer Low84± 2%
USP Buffer Medium1413± 2%
USP Buffer High12,880± 2%

11.0 Calibration Procedure (Full)

  1. Ensure all USP buffer solutions are at 25°C ± 2°C.
  2. Rinse electrode with purified water and blot dry before each measurement.
  3. Immerse electrode in USP Low buffer (84 µS/cm), allow reading to stabilize, and adjust meter to nominal value.
  4. Rinse electrode and immerse in USP Medium buffer (1413 µS/cm), stabilize reading, and adjust if necessary.
  5. Rinse electrode and immerse in USP High buffer (12,880 µS/cm), stabilize, and record value.
  6. Calibration is acceptable if all buffer readings are within ±2% of nominal values.

12.0 Verification Procedure (Post-Calibration)

  1. Rinse electrode with purified water and blot dry.
  2. Measure USP buffers: Low (84 µS/cm), Medium (1413 µS/cm), High (12,880 µS/cm).
  3. Record observed conductivity.
  4. Acceptance: Observed conductivity within ±2% of nominal values.

13.0 Calibration Frequency

  • Daily before analysis
  • After electrode replacement
  • After maintenance or abnormal readings

14.0 Deviations and Corrective Actions

  • Do not proceed with analysis if calibration or verification fails.
  • Recalibrate using fresh USP buffers.
  • Inform QC Supervisor and initiate deviation if required.

15.0 Cleaning and Maintenance

  • Rinse electrode with purified water after use.
  • Store electrode in recommended storage solution.
  • Do not scratch or rub conductivity cell.
  • Perform preventive maintenance as per manufacturer instructions.

CONDUCTIVITY METER CALIBRATION & VERIFICATION LOG

USP Buffer Nominal Conductivity (µS/cm) Observed Conductivity Acceptance (±2%) Remarks
Low84
Medium1413
High12,880

Verification After Calibration

USP Buffer Nominal Conductivity (µS/cm) Observed Conductivity Acceptance (±2%) Remarks
Low84
Medium1413
High12,880

Prepared by: _____________________    Date: ___________
Reviewed by: _____________________    Date: ___________
Approved by: _____________________    Date: ___________

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