One article to understand the pipette during the verification

The pipette, also known as the pipette gun, is a device used to quantitatively transfer liquids. It is widely used in biology, chemistry and other fields and clinical diagnostic laboratories, biotechnology laboratories, pharmacy and chemical laboratories, environmental laboratories, A commonly used tool in food laboratories, commonly used are manual adjustable pipettes and electric ones. Specifically, there are many optional specifications according to the volume of liquid to be piped.

Pipettes are simple to operate. Compared with glass pipettes, they can greatly improve the efficiency of inspection and detection, and are favored by laboratory workers in food and drug inspection institutions. However, pipettes have always been used and lightly managed. Some laboratory inspectors use adjustable pipettes directly without training. In most laboratories, the inspection period for pipettes is one or six months. It should be known that the system error caused by the environment and operation of the pipette is extremely obvious, which may eventually lead to the deviation of the detection result.

Let's take a look at the use, maintenance and precautions of the pipette:

How to use the pipette

A complete pipetting cycle includes the steps of tip installation-volume setting-aspiration and dispensing-removal of the tip. Each step has operating specifications that need to be followed.

1. Installation of pipetting tips

For single-channel pipettes, insert the pipette tip vertically into the pipette tip, press lightly and turn it slightly from left to right to tighten;

For a multi-channel pipette, align the first channel of the pipette with the first tip, insert it at an angle, and shake it back and forth to tighten it.

Do not repeatedly hit the pipette to ensure the air-tightness of the tip. Assembling the tip in this way for a long time will cause the parts of the pipette to loosen due to strong impact, and even cause the knob to adjust the scale to get stuck.

2. Capacity setting

When adjusting from a large volume to a small volume, you can rotate it counterclockwise to the scale; when adjusting from a small volume to a large volume, you can adjust the set volume clockwise first, and then return to the set volume to ensure the best accuracy.

Do not turn the adjusting knob out of the measuring range, otherwise the mechanical device in the pipette will be damaged.

3. Suction and discharge

Press the button of the aspirating pipette to the first position and release the button to perform aspiration. Remember not to be too fast, otherwise the liquid will enter the tip too quickly and the liquid will be sucked into the pipette.

Discharge Close to the container wall, first press to the first level, pause for a while, and then press to the second level to drain the remaining liquid.

● Aspirate liquid vertically.

● For 5ml and 10ml pipettes, the tip needs to be immersed in the liquid surface 5mm, slowly suck the liquid, after reaching the predetermined volume, pause under the liquid surface for 3 seconds, and then leave the liquid surface.

● Slowly release the controller when aspirating liquid, otherwise the liquid will enter the tip too quickly and the liquid will be sucked into the pipette

● When absorbing volatile liquid, rinse the suction head 4-6 times to saturate the steam in the sleeve chamber to avoid liquid leakage.

4. The correct placement of the pipette

After use, you can hang it upright on the pipette holder, but be careful not to fall off. When there is liquid in the pipette tip, do not place the pipette horizontally or upside down, so as to prevent the liquid from flowing back and corroding the piston spring.

If not in use, adjust the range of the pipette gun to the maximum scale, so that the spring is in a relaxed state to protect the spring.

5. Common mistakes

1) When assembling the tip, repeatedly hitting the tip makes it difficult to remove the tip and even damages the pipette.

2) When aspirating liquid, the pipette tilts, resulting in inaccurate pipetting, and the liquid easily enters the pipette handle.

3) When aspirating liquid, quickly release the thumb, which will force the liquid to form a turbulent state, and the liquid will directly flush into the pipette.

4) Press directly to the second level to aspirate liquid (should follow the above standard method).

5) Use a large-range pipette to pipette small volumes of samples (a pipette with a suitable range should be selected).

6) Lay the pipette with residual liquid tips flat (the pipette should be hung on the pipette rack).

Check during pipetting

The inspection cycle of pipettes in most laboratories is one year or six months. It is important to know that the system error caused by the environment and operation of the pipette is extremely obvious, which may eventually lead to the deviation of the test results; regular periodic inspections can keep the test instrument under control, thereby ensuring the stability of the instrument and ensuring the measurement result Reliability.

The necessity of regular pipette inspection

Pipettes are now widely used in food and drug testing and analysis methods. However, a small error has a great influence on the total sampling amount. After a qualified adjustable pipette has been used for a period of time, due to wear and spring changes, the accuracy and precision of the pipette must be calibrated. According to reports, the misalignment rate of newly purchased pipettes is 1.56%, the misalignment rate of using less than 10,000 times is 4%, the misalignment rate of 10,000 to 50,000 times is 8.82%, and the misalignment rate is 50,000 to 100,000 times. The rate is 21.7%, and the misalignment rate of more than 100,000 times is 47.6%.

Perform a periodical check between the two calibrations of the equipment or before the instrument is put into use after maintenance to verify whether the equipment maintains the state at the time of calibration to ensure the accuracy and validity of the test results.

Steps to verify the content during the period

Pipettes are mainly used for sampling or adding liquids in experiments or production. It uses the principle of air discharge to operate, and the capacity of the pipette is determined by the distance the piston moves in the piston sleeve. Pipettes are classified into two types: quantitative pipettes and adjustable pipettes. Its types are divided into single-head type and multi-head type. The structure is composed of a display window, a volume adjusting component, a piston, a piston sleeve, a liquid suction tube, and a liquid suction nozzle.

1. Check conditions

Testing environment: The pipette should be tested at room temperature of 15℃~25℃, and the pipette to be tested and the ultrapure water used for testing should be the same as the room temperature.

Detection medium: ultrapure water

Equipment required for testing:

Test items: appearance, tightness, capacity.

The surface of the plastic parts of the pipette should be flat and smooth, and there should be no obvious sink marks, scrap edges, cracks, bubbles and deformation, etc. The surface coating of the metal parts should be free of shedding, rusting and delamination.

The pipette body should have the following marks: product name, manufacturer or trademark, nominal volume (μl or ml), model specification, and factory number.

Piston: When the pipette piston is pressed, the up and down movement should be flexible, and the division limit should be obvious. Pressing the piston should not cause the value of the display window to change.

Regulator: The display window of the pipette should be flexibly rotated when the volume is adjusted, and the digital indication should be clear and complete.

Liquid suction nozzle: The inner wall of the liquid suction nozzle should not produce liquid droplets under normal use, and the liquid can be sucked and discharged smoothly.

2. Detection method

1. Appearance inspection Visually inspect the pipette to be inspected, and the appearance should meet the above requirements.

2. Tightness inspection Adjust the pipette to the maximum nominal capacity, and select the suction nozzle that matches the suction rod. At the lower end of the suction rod of the pipette, gently turn the pipette tip to ensure the tightness of the pipette; if the pipette uses a 200μl or 1000μl pipette nozzle, suck in the liquid and hang the pipette tip downward for 20s , Observe whether there is liquid overflowing the suction nozzle, if there is, the pipette tightness does not meet the requirements.

If the pipette uses a 10μl pipette nozzle, insert the pipette nozzle 2-3mm below the liquid surface and observe whether any liquid enters the pipette nozzle. If there is, the tightness of the pipette does not meet the requirements.

3. Capacity inspection

(1) Select the detection point, the quantitative pipette is the quantitative volume, and the adjustable pipette is the maximum value of the nominal volume, half of the maximum value of the nominal volume, and the minimum value of the nominal volume; simultaneously select and attract the rod Connect the matching suction nozzle.

(2) Turn on the electronic balance until the balance is stable.

(3) Adjust the capacity of the pipette to the point to be inspected, and select the suction nozzle that matches the suction rod; at the lower end of the suction rod of the pipette, gently rotate the suction nozzle to ensure the tightness of the pipette; Suction the ultrapure water back and forth 5 times to pre-wet the liquid suction nozzle.

(4) Select a suitable container as a weighing cup and place it on the electronic balance tray, and reset to zero.

Note: Use a 10ml plastic bottle to detect a volume above 10μl, and use a 1.5ml spiral tube to detect a volume below 10μl to reduce the error caused by the weight of the weighing cup.

(5) Hold the pipette vertically, intrude the suction nozzle into the container with ultrapure water, and keep it 2mm~3mm below the liquid surface, slowly release the button, wait for 1s~2s, then leave the liquid surface and stay in Make a stop on the container wall to get rid of excess liquid.

(6) Take out the weighing cup from the electronic balance, put the liquid suction nozzle against the inner wall of the weighing cup at 45 degrees, slowly press the button to the ground stop, wait for 1s to 2s, and then turn the button completely Press down, and then move the suction nozzle upwards along the inner wall of the weighing cup.

(7) Place the weighing cup on the electronic balance tray, record the temperature displayed by the balance at this time, and measure and record the temperature of the distilled water in the container at this time.

(8) Repeat steps (4)-(7) five times, but if the measured value is found to have exceeded the maximum allowable error, it is not necessary to repeat and directly judge it as unqualified.

4. Data processing

The actual volume value of the pipette at a standard temperature of 20°C.

5. Processing of verification results

(1) If the appearance and tightness are unqualified, the pipette is forbidden to be used, the calibration is "unqualified", repaired or scrapped.

(2) Appearance and adhesion are qualified, and the error of all used ranges is less than the maximum allowable error, the calibration is "qualified". Table 1 The maximum allowable error of the pipette When the pipette is at a standard temperature of 20°C, its capacity allowable error and measurement repeatability should meet the requirements of the following table:

(3) Appearance and adhesion are qualified but the error of some ranges is greater than the maximum allowable error, calibrate the available range.

(4) If the reading of the pipette is slippery, or the value is changed by pressing the piston, mark it.

6. Verification cycle

It is done every six months, and the time is completed between two other schools. Instrument maintenance or other exceptions should be carried out in a timely manner.

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