In the fields of scientific research experiments and biomedicine, pipettes play a pivotal role as an efficient and accurate liquid transfer tool. Its accuracy and stability are directly related to the reliability of experimental data and the quality of scientific research results. However, with the accumulation of use time, the accuracy and precision of the pipette may gradually decrease due to factors such as wear and spring force changes, which will have a non-negligible impact on the experimental results. Therefore, regular in-process inspections of pipettes to verify whether they remain calibrated are crucial to ensuring the accuracy and validity of experimental data.
1. Verification conditions 1. Testing environment: Pipettes should be tested at room temperature of 15℃~25℃. The pipette to be tested and the ultrapure water used for testing should be consistent with the room temperature. 2. Detection medium: Ultrapure water is usually used as the detection medium. 3. Test items: appearance, tightness, capacity.
2. Appearance inspection 1. The surface of the plastic shell of the pipette should be flat and smooth, and there should be no obvious shrinkage marks, waste edges, cracks, bubbles, deformation, etc. 2. The coating on the surface of metal parts should be free of peeling, rust and layering. 3. The main body of the pipette should be marked with product name, manufacturer or trademark, nominal capacity (μl or ml), model specifications, factory number, etc.
3. Tightness check 1. Adjust the pipette to the maximum nominal capacity and select the suction nozzle matching the suction rod. 2. If the pipette uses a small volume (such as 10μl) suction nozzle, insert the suction nozzle 2~3mm below the liquid surface and observe whether there is liquid entering the suction nozzle. If so, the pipette's tightness does not meet the requirements. Require. For large-volume suction nozzles, you can also use the method of sucking in liquid and then hanging to observe whether there is liquid overflow.
4. Capacity verification 1. Select the detection point: For the quantitative pipette, select the quantitative volume as the detection point. For the adjustable pipette, select the maximum value of the nominal capacity, half of the maximum nominal capacity, and the minimum value of the nominal capacity. as a detection point. 2. Pre-wet the suction nozzle: At the lower end of the suction rod of the pipette, gently turn the suction nozzle to ensure the sealing of the pipette; suck and release ultrapure water back and forth 5 times to pre-wet the suction nozzle. 3. Weighing preparation: Choose a suitable container as a weighing cup and place it on the electronic balance tray and reset it to zero. Note that when measuring different volumes, use different sized weighing cups to reduce errors. 4. Aspiration and dispensing: Hold the pipette vertically, insert the suction nozzle into the container containing ultrapure water, and keep it 2mm~3mm below the liquid surface. Slowly release the button and wait for 1s~2s. Lift off the surface and rest against the side of the container to remove excess liquid. Then place the liquid outlet of the suction nozzle against the inner wall of the weighing cup at an angle of 45 degrees, slowly press the button to the first stop point, wait for 1s~2s, then press the button completely, and move the suction nozzle along the weighing cup. The inner wall of the cup moves upward. 5. Repeat measurement: Repeat the steps of aspirating and dispensing liquid multiple times (such as 5 or 6 times), and record the weighing results each time. 6. Data processing: Calculate the error of each measurement to determine whether it meets the maximum allowable error requirements of the pipette. If the allowable error is exceeded, the pipette is unqualified.
5. Handling of Inspection Results 1. If the appearance and tightness are unqualified, the pipette is prohibited from use, will be marked as "unqualified", and will be repaired or scrapped. 2. The appearance and tightness are qualified, and the errors of all used measuring ranges are less than the allowable error, and the calibration is "qualified". 3. If the appearance and tightness are qualified but the error in some ranges is greater than the allowable error, calibrate the available range. 4. If the pipette reading slips, or pressing the piston causes the value to change, a note should be made and corresponding corrective measures should be taken.
6. Verification cycle The verification cycle of pipettes is usually conducted every six months and is completed between two external calibrations. Instrument repairs or other exceptions should be promptly verified.
Periodic inspection of gun pipettes is an important link to ensure the accuracy of experimental data and the reliability of scientific research results. Through a series of rigorous and detailed verification steps, we can promptly discover and correct possible deviations in the pipette, thereby ensuring its accuracy and stability during the experiment.
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