Analytical Balance Calibration (Updated)

1. Introduction

Analytical balances are precision instruments used in pharmaceutical laboratories to measure mass with high accuracy (up to 0.1 mg or better). Calibration ensures the balance is providing correct readings, complying with GMP, GLP, and pharmacopoeial standards.

2. Objective

• To verify that the analytical balance provides accurate and reproducible measurements.

• To maintain compliance with USP <41> and ISO 9001 requirements.

3. Principle

Calibration is performed using traceable standard weights (Class E2/F1 as per OIML) with known certified mass. The displayed reading is compared with the true value to determine accuracy, sensitivity, and repeatability.

4. Types of Calibration

1. Internal Calibration – Performed automatically by the balance using built-in weights.

2. External Calibration – Using certified standard weights.

5. Equipment Required

• Analytical balance (calibrated and clean)

• Standard weights (E2/F1 class, traceable to national standards)

• Gloves or forceps (to handle weights without contamination)

6. Procedure

A. Preparation

1. Place the balance on a vibration-free, stable surface.

2. Level the balance using the leveling bubble.

3. Ensure temperature, humidity, and air flow are within specified limits.

4. Clean the weighing pan.

B. Calibration Steps

1. Warm-up the balance (usually 30 min after powering on).

2. Zero Check – Ensure display reads “0.0000 g” before starting.

3. External Calibration:

   • Place the first standard weight on the pan.

   • Record displayed value.

   • Repeat for all selected weights across the balance’s range.

4. Internal Calibration:

   • Initiate as per balance manufacturer instructions.

5. Repeatability Test:

   • Weigh the same standard weight multiple times (minimum 5 readings).

   • Calculate standard deviation.

6. Eccentricity Test:

   • Place the same weight in different positions on the pan and check variation.

7. Acceptance Criteria (USP <41>)

• Accuracy: Difference between displayed mass and standard weight ≤ tolerance for the balance’s resolution.

• Repeatability: Standard deviation ≤ 0.41 × readability (d) of the balance.

• Eccentricity: All positions within tolerance.

8. Frequency

• Daily: Performance check before use (zero, repeatability).

• Monthly/Quarterly: Full calibration with standard weights.

• After Relocation/Repair: Immediate recalibration.

9. Documentation

• Balance ID, model, location

• Date/time of calibration

• Weight IDs and nominal values

• Displayed values and deviations

• Pass/Fail status

• Analyst and reviewer signatures

10. References

• USP <41> “Balances”

• USP <1251> “Weighing on an Analytical Balance”

• ISO/IEC 17025

• OIML R111