Standard Operating Procedure (SOP): Internal Calibration of Measuring Devices (Pipettes and Burettes)

1.      Purpose

To ensure the accuracy and reliability of measuring devices (pipettes and burettes) used in laboratory operations by calibrating them according to established procedures.

2.      Scope

This SOP applies to all pipettes and burettes used in the laboratory for volumetric measurements.

3.      Background

Measuring devices may have inherent or manufacturing errors. The accuracy of devices such as pipettes and burettes must be periodically verified and documented to ensure consistency and compliance with quality standards.

4.      Principle

The volume delivered by pipettes and burettes is determined by weighing the water dispensed and calculating the actual volume based on the density of water at the measured temperature.

 5. Materials Required

• Equipment:

Electronic balance (± 0.0001g precision)

Mono pan balance (1 kg capacity, ± 0.1g)

• Apparatus:

Clean 50 mL beaker

Graduated pipettes (10 mL, 5 pieces)

Bulb pipettes (10 mL, 5 pieces)

Volumetric flasks (100 mL and 250 mL, 5 pieces each)

• Consumables:

Distilled water (1 L)

Muslin cloth or blotting paper

• Reference:

Density chart for water at various temperatures

6. Procedure

6.1 Initial Preparations

1. Categorize the devices based on their stated capacity.
2. Record the temperature of the distilled water and note the corresponding density using the density chart.
3. Ensure all devices and containers are clean and dry.

6.2 Internal Calibration of Pipettes

1. Place a clean, dry 50 mL beaker on the electronic balance and tare it.
2. Using the first bulb pipette, dispense exactly 10 mL of distilled water into the beaker.
3. Record the weight of the water dispensed.
4. Empty and dry the beaker with muslin cloth or blotting paper.
5. Repeat steps 2-4 for the remaining bulb pipettes and graduated pipettes.
6. Record all observations in a tabular format.

6.3 Internal Calibration of Volumetric Flasks

1. Tare a dry 100 mL volumetric flask on the mono pan balance.
2. Fill the flask to the calibration mark with distilled water and weigh.
3. Record the weight of the water.
4. Repeat for all 100 mL and 250 mL volumetric flasks.
5. Record all observations.

7. Calculation

1.     Documentation

            Record observations in a tabular format: 

9. Results and Discussion

1. Express the error range for each category as % error ± 3×standard deviation.

Step by Step method for calculation

Step1

Step 2

Step 3

The standard deviation ($\sigma$) is 0.2586% in this case

Step 4

Step 5

2. Identify potential sources of errors, such as incorrect handling, environmental influences, or wear and tear.

 

10. Responsibilities

Lab Personnel: Perform internal calibration as per the SOP.

Lab Manager: Verify internal calibration records and ensure timely recalibration.

11. Review and Revision

SOP should be reviewed annually or whenever a change in procedure or equipment occurs.

Disclaimer:

This document is intended for guidance purposes only. Please refer to your laboratory's standard operating procedures and specific requirements to ensure compliance with applicable standards and regulations.