SOP FOR OPERATIONS AND CALIBRATION OF ANALYTICAL BALANCE

1. OBJECTIVE:

1. To lay down the procedure for Operation and Calibration of Analytical Balance.

2. SCOPE: 

1. This procedure is applicable for Operation & Calibration of Analytical Balance being used in Quality Control Laboratory .

3. RESPONSIBILITY:

1. Quality Control Officer / Executive are responsible to follow procedure as per the procedure mentioned in this SOP. 

2. QC Head is responsible for implementation and compliance of the procedure as per this SOP.

4. ABBREVIATIONS

1. SOP    :    Standard Operating Procedure

2. QC    :    Quality Control

3. SD        :    Standard Deviation

4. CC    :    Change Control

5. NMT    :    Not More Than 

6. QC    :    Quality Control

7. Mg    :    Milligrams

8. g        :    Grams

9. S. No.    :    Serial Number

5. PROCEDURE: 

1. Procedure For Operation

1. Ensure that working bench and balance is clean.

2. Ensure that the balance is calibrated.

3. All the windows are closed and balance is leveled properly.

4. If it is not leveled turn the leveling screw of the balance in clockwise or anti-clockwise direction to get the air bubble in the sprit level exactly in the middle position of the circular marking of the level window. 

5. Switch on the balance.

6. Before weighing the material the balance is allowed to stabilize for at least 30 minutes.

7. Press the ‘tare’ button before weighing; ensure that 0.0000/0.00000 g is displayed on the digital display board of balances having Model No.ATX224 & AUW220D.

8. Open the balance window and place the butter paper/Container on the weighing pan.

9. Weigh the paper or tare weight, press tare button to minus the paper weight/ Container.

10. Then weigh the required quantities of the sample.

11. Close the window; wait till a stabilized weight is obtained.

12. Record the weight or takeout the print. 

2. Precautions

1. To avoid condensation of moisture, refrigerated materials must be allowed to come to room temperature before the container is opened.

2. Before cleaning the balance or its pan ensure that the balance is in the OFF mode.

3. Object to be weighed on the balance should be placed gently on the weighing pan. Jerks must be avoided.

4. While weighing ensure that the object weight does not exceed the max. limit of the balance.

3. Procedure For Calibration

1. Daily verification of Analytical Balance

1. During calibration, the weighing pan must be unloaded.

2. Daily verification of Analytical Balance

3. Set the balance to auto zero

• Place the standard weight as per the table-I on the weighing pan with help of forceps.

• Note the displayed weight after the display is stable and take out the prints.

• Put each individual standard weight carefully on the pan, wait for stabilization and record the observations.

2. Monthly Calibration 

1. Accuracy:

• Check accuracy using different standard weights as per below table.

• Acceptance criteria: As per table given below.

• Actual weight should be as per outside calibration party calibration of weight box. 

Standard Weights
0.1g	2.0g	50.0g
0.2g	5.0 g	100.0 g
0.5g	10.0 g	200.0g
1.0g	20.0 g

2. Linearity:

• Check the linearity by using weight of 0.1g, 0.2g., 0.5g, 5.0g, 50.0g, 100.0g with actual & observe weight.

• Plot a graph of actual weights against observed weights. It should be linear.

• Calculate correlation coefficient.

• Acceptance criteria: Correlation coefficient should not be less than 0.999.

3. Precision :

• Check 5 times weight as selected for linearity by loading & unloading the specific weight 0.1g, 0.2g., 0.5g, 5.0g, 50.0g, 100.0g.

• Calculate % RSD for observed weights.

• Acceptance criteria: NMT 0.5%

4. Eccentricity:

• Check eccentricity by 100g weight in the four corners and middle of the pan of the balance. 

• Calculate % RSD for observed weights.

• Acceptance criteria: NMT 0.1%

5. Measurement Uncertainty

• Check 10 times weights of 100 g & 2g.

• Calculate Standard deviation for observed weights.

• Uncertainty can be calculated using formula 2*SD / weight taken.

• Acceptance criteria: NMT 0.10%

2 X Standard Deviation (SD) X 100/

Measurement Uncertainty=  (NMT 0.10%) Reported mass Weight (g)   (as per certificate)

4. Calibration Frequency: Monthly

5. Documentation

1. Record the results of Daily verification as per Daily verification of Analytical Balance (Annexure I) and Monthly calibration as per Monthly Calibration of Analytical Balance (Annexure II).

2. If the instrument is out of calibration, tag the instrument with the following label. And inform to the service engineer for rectification.

5.  Calibrate the instrument after rectification.