Analytical Balance Performance Verification

Objective

The purpose of this SOP is to detail the procedure for verifying the performance of Analytical balances. This SOP is based on the USP chapter <41> “Weight and Balances”

Scope

The procedure applies to all Balances at QC /Analytical Laboratory of xxx (where xxx is the company name)

Responsibility

Research Scientist/Chemists/Analyst: Responsible for the Verification performance of the Balances

HOD

To ensure the implementation of this SOP in the Analytical development laboratory or Quality control Laboratory (as applicable).

Frequency

Once in six months ± five days

Performance Verification procedure

Before going to performance verification check whether the air bubble is in the correct position or not. If not, adjust air bubbles using screws.
Check the internal calibration /drift (daily test)
Perform the daily verification
Quarterly Testing
The Analytical balances must be checked with a certified calibrated set of weights at the frequency of every 3 months (quarterly) or in case of relocation, power failure or balance repair.
Procedure:
The following weights should be used based on the type of balance with acceptance criteria in the bracket
Analytical balance (readability

Table-1

Perform six weighing of each of the calibrated weights. Remove the weight and re-zero the balance after each weighing. see the weighing point on the weighing pan👇

Calculate the mean and standard deviation (SD) of the weighings. The Random error (RE) is defined as the three times standard deviation👇 RE = (3 x SD)The systematic error (E) is defined as the absolute difference between the mean of the weight and weight calibrated mass👇SE = (AVG – WCM)

Note: WCM value is obtained from the certified calibration laboratory.

Calculation method and acceptance criteria

Calculate the sum of the error according to the following formula👇:

∑=(RE+SE)WCM×100

The ∑ acceptance criteria (in %) for each taste are mentioned in Table -1 (procedure section)

Uncertainty

Perform the replicate weighing of the weights mentioned below. Remove the weight and re-zero the balance after each weighing. Calculate uncertainty by following formulae👇:

Uncertainty=Standard deviation×3 Certified weight value

Acceptance criteria = NMT 0.001

Check the uncertainty by using the weights as per balance readability.

For Analytical Balances (0.1mg readability) check of the weights of 100mg, 1gm, 10gm, and 100gm
For Semi-micro Balances (0.01mg readability) check the weights of 10mg, 100mg, 1gm, and 10gm
For Micro Balances (0.001mg readability) check the weights of 5mg, 10mg, 100mg, and1gm

If fail the test, the Balance will be labelled ” Out of order” and a service engineer should be summoned.

Documentation

The results of quarterly testing will be documented in the QA form.

Calibration of weights

The sets of weights used for calibration should be calibrated by a certified Laboratory periodically or as per the re-calibration due date given by the external agency performing the calibration.

Abbreviations:

SOP: Standard operating procedure

HOD: Head of department

RE: Random error

SE: Systematic error

mg: miligram

g or gm: Gram

NMT: Not more than

AVE: Average of the weight or mean of the weight

WCM: weight calibrated mass

References

USP; General Chapter <41> “Weights and Balances”.