The Correction of the Pipette
1. After using the pipette for a period of time, check if correction is needed to ensure an accurate range. Generally, it is routinely inspected for 3-6 months, and it is carried out at around 20-25 degrees. The specific operations are as follows:
1) Pipette the distilled water 3 times and discard it, then use a pipette to draw 1000 ul and 100 ul of 3 distilled water or deionized water 10 times each time, and weigh the actual weight after each weighing (on the most accurate balance). The average value of 10 times is recorded as m1. (How many volumes to choose depends on the maximum range of the pipette and 10% of the maximum range (e.g: 200ul and 20ul for two guns)
2) Check the thermometer value, find the density value of distilled water at this room temperature, and calculate the standard weight m2 of 1000 ul and 100 ul distilled water.
3) Calculate the accuracy A, the formula = (m1-m2) / m2 * 100, if it is within the allowable error range, no correction is needed, if it is exceeded, the correction is selected.
Method: According to the comparison result of the first step, if the actual weight is greater than the standard weight (m1>m2), indicating that the liquid volume removed by the pipetting gun is larger than the actual volume, the volume of the pipette should be reduced, and the actual weight is approached the standard weight. Use a tool to adjust the nut counterclockwise. The opposite is reversed. This is repeated until the standard weight is adjusted.
Correctly calibrating and verifying the accuracy of pipettes is essential to ensure precise and reliable volumetric measurements in laboratory work. Here are the key steps for the correction and calibration of pipettes:
- Initial Inspection:
- Examine the pipette for any visible damage or wear.
- Ensure that the pipette’s display (if digital) is functioning properly.
- Check that the volume adjustment mechanism is working smoothly.
- Select Calibration Standards:
- Choose a set of calibration standards that cover the range of volumes you’ll be working with. For example, if you have a 1-10 mL pipette, you might select 1 mL, 5 mL, and 10 mL calibration standards.
- Zero the Pipette:
- If the pipette has a “zero” or “tare” function, use it to set the display to zero with the pipette tip attached.
- Calibration Procedure:
- Using the selected calibration standards, pipette each standard volume multiple times (usually three to five repetitions) onto a high-precision balance capable of measuring the dispensed liquid mass.
- Record the actual masses (weights) of the dispensed liquid for each standard volume.
- Calculation of Correction Factors:
- Calculate the average (mean) mass for each standard volume.
- Calculate the expected mass for each standard based on the density of the liquid being pipetted (usually water) and the calibrated volume setting.
- Determination of Correction Factors:
- Calculate the correction factor for each standard as the ratio of the expected mass to the measured mass.
- Apply the correction factor to the volume settings. For example, if the correction factor is 1.005, you’ll need to set the pipette to 1.005 times the desired volume.
- Verification of Calibration:
- Verify the accuracy of the pipette by repeating the calibration process periodically, especially if the pipette is subjected to heavy use or significant changes in environmental conditions.
- Maintain accurate and thorough records of the calibration process, including the calibration standards used, measured masses, calculated correction factors, and dates of calibration.
- Regular Maintenance:
- Keep the pipette clean and well-maintained.
- Follow the manufacturer’s recommendations for maintenance and calibration intervals.
- In some laboratories, pipette calibration may be performed by a specialized service provider. These providers issue calibration certificates that document the accuracy of the pipette at various volumes. These certificates are often required for compliance with quality standards in regulated industries.
By following these steps, you can ensure that your pipette delivers accurate and reliable results, minimizing measurement errors in your laboratory work.