SOP for Operation and Calibration of Analytical Weighing Balance

SOP for Operation and Calibration of Analytical Weighing Balance

Document Type: SOP
Department: Quality Control / Analytical Laboratory
Regulatory Focus: GMP | USP | Equipment Qualification | Calibration

1. Purpose

To define the step-by-step procedure for operation, daily verification, and monthly calibration of analytical balances to ensure accurate, precise, and reliable weighing of materials.

2. Scope

This SOP applies to all analytical balances used for weighing raw materials, in-process materials, and samples for testing in the laboratory.

3. Responsibility

Role	Responsibility
Analytical Laboratory Personnel	Operate balance, perform daily verification, execute monthly calibration, and record results.
Supervisors	Review calibration and verification records; approve deviations.
Quality Assurance	Approve SOP, monitor compliance, and ensure regulatory requirements are met.

4. Definitions

• Analytical Balance: Precision weighing device, sensitivity typically 0.1 mg or 0.01 mg.
• Daily Verification: Routine check using standard weights to ensure the balance is functioning correctly before use.
• Monthly Calibration: Complete calibration including linearity, repeatability, sensitivity, minimum weight, and eccentricity, performed step-by-step as per manufacturer and USP requirements.

5. Procedure

5.1 Pre-Operation Check

• Place balance on stable, vibration-free, and level surface.
• Ensure environment is free from drafts, vibrations, and temperature fluctuations.
• Clean balance pan and surrounding area with soft brush or lint-free cloth.
• Switch on balance and allow warm-up per manufacturer’s instructions (usually 30 minutes).
• Check balance leveling bubble and internal diagnostics.

5.2 Operation Steps

1. Close draft shield doors before weighing.
2. Zero or tare the balance before placing sample.
3. Place sample gently at the pan center.
4. Record weight in logbook or electronic system immediately.
5. Remove sample and clean pan if necessary.
6. Repeat measurement if required for replicate analysis.

5.3 Daily Verification Procedure

1. Select a certified standard weight approximately 10%–50% of balance capacity.
2. Place the weight in the center of the pan.
3. Wait for the reading to stabilize.
4. Compare observed value with nominal weight.
5. Record observed weight, deviation, and pass/fail in the Daily Verification Log.
6. If deviation exceeds manufacturer tolerance, balance must not be used until corrected.

5.4 Monthly Calibration

The following steps must be performed by trained personnel:

1. Linearity Check:
   • Use at least five calibrated weights covering 0%, 25%, 50%, 75%, and 100% of the balance capacity.
   • Place each weight at the pan center and record measured value.
   • Calculate deviation from nominal weight; must be within manufacturer tolerance.
2. Repeatability Check:
   • Select a weight around 10–50% of max capacity.
   • Weigh the same weight 10 consecutive times without removing it from the pan.
   • Calculate standard deviation; must meet manufacturer specifications.
3. Sensitivity / Scale Interval Verification:
   • Use small incremental weights (e.g., 1 mg for 0.1 mg balance) to verify that the balance detects changes accurately.
   • Record actual weight increments and compare with expected value.
4. Minimum Weight Determination:
   • Start with a very small weight (e.g., 100 mg) and gradually increase.
   • Determine the smallest weight that can be measured with ≤1% relative standard deviation as per USP <41>.
   • Record result in calibration log.
5. Eccentricity Check:
   • Place a standard weight at four corners and center of the pan.
   • Record readings and calculate deviation from nominal.
   • Deviation must not exceed manufacturer limits.
6. Calibration Record:
   • Document balance ID, date, operator, weights used, observed values, deviations, pass/fail, and any corrective action.
   • Include calibration certificate if performed by external service provider.

5.5 Maintenance

• Daily: Clean pan and surrounding area; check doors and display.
• Weekly: Verify leveling and inspect pan alignment.
• Monthly: Perform complete calibration, inspect internal mechanisms per manufacturer manual.
• Annually: Preventive maintenance by qualified personnel or service provider.
• Document all maintenance activities in the balance log.

6. Deviations

• Any out-of-tolerance reading during daily verification or monthly calibration must be recorded as a deviation.
• Investigate root cause, implement corrective actions, and document resolution.
• QA must review and approve all deviations.

7. Training

• Personnel must be trained on operation, daily verification, monthly calibration, and maintenance.
• Training records must be maintained as per company policy.

8. Record Retention

All daily verification and monthly calibration records must be retained according to company policy and regulatory requirements (typically 5 years).

9. Regulatory References

• USP General Chapter <41> Weights and Balances
• EU GMP Annex 15 – Qualification and Calibration
• FDA 21 CFR Part 211 – Subpart B (Equipment)
• Manufacturer Manuals: Mettler Toledo, Shimadzu Analytical Balance User Guides
• WHO GMP Guide – Section on Equipment

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