The calibration operation is roughly described as follows:
1. In a constant temperature and humidity environment, peel off the weighing container on the analytical balance;
2. Absorb the distilled water of the nominal range (that is, the maximum range), pour it into the weighing container for weighing, and obtain the weight Δm of the discharged distilled water;
3. Under the corresponding water temperature, the Kt value of water converts the weight Δm of distilled water into volume, that is, V=Kt*Δm. The Kt value formula can be found in the corresponding measurement standard. It can be seen from the formula that the main factor affecting the Kt value is the density of water.
Secondly, in terms of measurement methods, the volume calibration method for pipettes and pipettes is almost the same. If the nominal accuracy is the same, do liquids other than distilled water actually operate with exactly the same accuracy? the answer is negative.
In order to understand this, we need to understand the difference between pipette and pipette structure and the principle of pipetting.
The pipette is a simple physical structure, generally made of glass, and the volume is determined by the scale. When calibrating the corresponding scale of the corresponding volume, the method used is the above calibration method. The corresponding mass of the corresponding volume of distilled water is fixed. If the quality of distilled water discharged after absorption is "correct", the volume of distilled water discharged after absorption is "correct (within the allowable error range of the nominal value)", then the suction volume represented by the lowest concave shape where the distilled water is located during suction The liquid level point is "correct" and this point is where the corresponding volume scale is located. Once this is determined, the volume inside the pipette is physically determined and then this volume hardly changes with external factors such as liquid density,
Pipettes in the general sense are air-piston pipettes. When the pipetting button is moved, the position of the internal piston changes, which in turn creates a negative pressure that draws liquid into the tip. The determination of the suction volume is determined by a series of factors such as the internal and external pressure difference, but the main determinant is the internal and external pressure difference. When calibrating, if the quality of distilled water extracted is "correct" (weighing method), it means that the volume of distilled water extracted is "correct (within the nominal allowable error range)", which means the pipetting volume is "correct". Therefore, when determining the pipette volume with distilled water,
At this time, it is easy to understand that the pipette will perform differently in different types of liquids and in different environmental conditions. For example, under the condition of constant environmental conditions, that is, the same pressure difference, if the density of the liquid is different from that of distilled water, that is, the quality of the same volume of liquid is different from that of distilled water, in order to balance the internal and external pressure, the amount of liquid suction will vary different.
