Analytical Balance Performance Verification: Procedure, Tests & Acceptance Criteria

Analytical balance performance verification

Analytical balance performance verification ensures accurate and reliable weighing by routinely checking accuracy, repeatability, linearity, and drift using certified calibration weights. Daily checks require measured values to remain within ±0.1% of the standard, with the balance properly levelled, draft shield doors closed, and environmental conditions controlled. All results must be documented and reviewed to comply with GMP, GLP, ISO, and USP <41> requirements.

Key verification tests include drift, evaluated by multiple readings of a single weight over time; repeatability, assessed by repeated weighing and standard deviation calculation; and linearity, verified by weighing certified standards across the balance’s operating range. Together, these tests confirm the balance’s suitability for precise and compliant analytical measurements.

Related: Pharmaceutical Analysis

Objective

This article outlines a standard procedure for verifying the performance of analytical balances, focusing on key metrics such as random error (RE), systematic error (SE), uncertainty, and overall performance. It is designed to help laboratories ensure consistent, compliant weighing results.

Scope

The performance verification procedure described here applies to all analytical balances used in QC, analytical development, or related laboratory areas that require high-precision weighing.

Responsibility

• Analytical Scientists / Chemists / Analysts
  Perform balance verification and document results.
• Head of Department (HOD)
  Ensure implementation of this procedure in the laboratory.

Verification Frequency

• Routine performance verification should be conducted every six months ± five days.
• Additional checks are recommended if the balance is relocated, repaired, or experiences a power failure.

Performance Verification Procedure

Before beginning official verification:

1. Balance Setup:
   • Verify that the air bubble level indicator is centred; adjust levelling feet if needed.
   • Perform internal calibration or drift checks as daily preliminary tests.
2. Routine Checks:
   • Conduct daily verification prior to use.
   • Perform quarterly performance testing using a certified set of weights.

Weighing and Error Calculation

Test Weights and Weighings

• Use certified calibration weights appropriate to the balance readability (e.g., 100 mg, 1 g, 10 g, 100 g for a 0.1 mg balance).
• For each weight:
  • Perform six consecutive weighings.
  • Remove the weight and re-zero the balance between measurements.

Note:

• The following weights should be used based on the type of balance, with acceptance criteria in the bracket
• Analytical balance (readability

Error Metrics

• Random Error (RE):
  Calculated as 3 × standard deviation (SD) of the weighings.
• Systematic Error (SE):
  Defined as the absolute difference between the average measurement and the certified weight (WCM).

Overall Error

The total error percentage is calculated using:

Σ = {(RE+SE) × 100} ÷ WCM

Acceptance criteria for each weight are defined based on the balance type in the procedure tables. (

Uncertainty Assessment

Uncertainty is assessed by repeated weighings of a certified standard at least six times, with re-zeroing between each measurement. Calculate uncertainty using:

Uncertainty} = (Standard Deviation×3) ​÷ Certified Weight Value

Acceptance Criterion:

• Uncertainty should not be more than 0.001.

Recommended weight sets for uncertainty testing:

• Analytical Balances (0.1 mg readability):
  100 mg, 1 g, 10 g, 100 g
• Semi-micro Balances (0.01 mg readability):
  10 mg, 100 mg, 1 g, 10 g
• Micro Balances (0.001 mg readability):
  5 mg, 10 mg, 100 mg, 1 g

Out of Specification (OOS)

If any part of the verification fails:

• Label the balance as “Out of Order”.
• Notify service support for inspection, adjustment, repair, or recalibration.

Documentation

• All results, including raw weighings and calculated errors, must be documented in a QA performance verification form or electronic log.
• Ensure traceability of the calibrated weight certificates and their calibration validity.

Weight Calibration

The reference weights used for verification must be calibrated periodically by a certified external laboratory according to their scheduled re-calibration due dates to maintain traceability.

Summary

Analytical balance performance verification is essential for ensuring precision, accuracy, and compliance in laboratory weighing activities. Proper verification not only supports regulatory requirements (such as USP <41> and ISO/IEC 17025) but also guarantees reliable results for analytical and quality control processes.

Further reading: 〈41〉 BALANCES