1. Appearance and Physical Structure Inspection 

Appearance defects are the most intuitive basis for determining non-conformity, and they apply to all specifications of pipettes (10 μL, 20 μL, 50 μL, 100 μL, 200 μL, 1000 μL, 5 mL, 10 mL, etc.). 

Advanced integrity 

The tip of the suction head must be smooth and uniform, without any gaps, burrs, deformations or blockages, and the diameter of the holes must be consistent. If the tip is skewed, damaged or the hole diameter is irregular, it will directly lead to deviations in liquid intake and leakage, which is considered a serious defect. 

Main body appearance 

The entire suction head should be smooth without scratches, bubbles, shrinkage marks, oil stains, impurity spots, or obvious color differences or yellowing and brittleness. Poor suction heads produced from recycled materials are prone to have rough inner walls, poor transparency, and soft texture. They are likely to deform when exposed to high temperatures or contact with reagents, and are therefore classified as unqualified. 

Structural Consistency 

The length, taper and wall thickness of the samples of the suction heads should be highly consistent, without any variation in length or excessive deviation in taper. The suction heads with filter elements must be checked to ensure that the filter element is centered, not loose or detached, and there is no dust falling. The filter element should be of good density and without any air leakage or ventilation problems. 

Packaging and Labeling 

The packaging of the qualified suction head is intact and undamaged, without any moisture, contamination or damage. The outer packaging clearly indicates the product specifications, measurement range, material (PP polypropylene), sterilization method, enzyme-free / endotoxin-free label, production batch number, production date, shelf life and manufacturer information. Suction heads without labels, with blurred labels or damaged packaging should not be used in precision experiments.

II. Dimension Matching and Sealing Inspection 

The matching degree between the suction head and the conical surface of the pipette tip directly determines the sealing effect. Failure of sealing will lead to air leakage, inaccurate pipetting, and liquid dripping. It is a key indicator for determining the qualification of the suction head. 

Installation compatibility test 

Align the tip vertically with the conical surface of the pipette and gently rotate it until it is securely clamped. A qualified pipette tip should feel just right: not loose, not slippery, and not too tight to make installation or removal difficult; when removed, it should slide smoothly without sticking, and there should be no residual pipette tip remaining on the pipette tip. If it easily falls off, shakes, or requires violent pressing to be fixed, it indicates that the size is not qualified. 

Static sealing test 

Take the appropriate amount of deionized water and let it stand vertically for 15 to 30 seconds. Observe that there is no leakage, no continuous droplets, and no slow dripping at the junction of the tip of the pipette and the gun tip. For micro pipettes (≤ 10 μL), the sealing requirement is even higher. During the standing period, there must be no leakage at all. If there is a slight leakage, it is considered不合格 (unqualified). 

Dynamic suction and discharge test 

During normal operation, the pipette completes the entire process of liquid aspiration and drainage. During aspiration, no large bubbles enter the pipette body. During drainage, the liquid flows out smoothly without any interruption or splashing. Place the tip in water, gently press the pipette to release the air, and there should be no continuous bubbles emerging at the connection point, indicating a good seal; if there are continuous bubbles, it indicates a failed seal and the tip is not qualified. 

Negative pressure retention test 

After filling with liquid, invert the pipette and keep it for 1 minute. If there is no significant drop in the liquid level or no leakage, it indicates that the sealing of the pipette tip and the negative pressure retention ability are qualified, and it is suitable for precise pipetting and long-term static operation.