Why Calibrate Gravimetric Pipettes?

Right on the heels of a blog published on Laboratory-Equipment.com called “How to Improve Pipetting Techniques，”我们介绍了有关重量移液器校准的讨论。根据记录的协议，大多数实验室都需要完成仪器的定期校准。无论是由实验室工作人员还是供应商执行任务，这都是一个耗时且严格的过程。替代方案？数据和测试结果可能会受到质疑或挑战。

Considerations for Calibration

实验室执行移液器校准，以确保其移液器在给定（记录或已建立的）参数内运行。实际上，未经常规校准的移液器可能会产生与预期的分配量截然不同的，从而导致模棱两可甚至错误的数据集。

当决定如何服务你的实验室pipettes, consider these factors. First, a laboratory manager or principal investigator must consider the needs of the laboratory against any budgetary constraints. Due to the large number of pipettes commonly found in a typical lab, the cost of performing these calibrations can add up!

实验室还必须确定这些程序是否将由实验室人员定期进行内部或外部外部公司或外部公司或服务。根据ISO 17025，必须由认可的第三方代理商对移液器进行校准，并经过认证，可以在正常参数下运行。但是，实验室技术人员的周期性校准可能会在问题出现问题之前捕获差异。

使用认可的第三方实验室通常有效期为六个月，并允许实验室在常规和临床测试中使用这些移液器。这些测试程序确保已经执行了可再现和无偏测试，并确保移民达到准确性和可重复性所需的参数。

Calibration Procedures

Pipette calibrations are commonly performed using gravimetric procedures due to their simplicity, accuracy and traceability. In these procedures, an aliquot of distilled water is placed into a vessel, and the weight of the vessel is measured using a (calibrated!) analytical balance. The mass (or density) of water is a known constant, but since temperature, barometric pressure and humidity affect water’s density, these conditions are controlled and recorded for the final calculation of the exact volume. As with many experiments with variables, these procedures are repeated a number of times to ensure that the results are reproducible.

Although gravimetric calibration measurements are commonly performed by ISO-accredited testing laboratories, this does not necessarily ensure that the pipette will function within the dispensing parameters for every liquid or in every environment. Example: when the ambient temperature in the testing laboratory is different than the actual environment where the pipette will be used.

Ambient conditions in a testing environment typically will conform to a narrow range of temperature, humidity and barometric pressure set-points when performing experiments. The pipette might then be moved into a cold room or a negative pressure clean room with very different environmental conditions. The resulting density of liquid in these situations will be significantly different from that of the testing environment and data may not conform to expected results.

此外，由于水通常用于重量移液管校准，因此在使用其他具有不同毛细管压力或表面紧张张力的液体时，它并不总是确保正确的性能。因此，建议在通常使用移液器通常使用的环境中执行校准。同样，重要的是要注意分配的液体类型，与水标准相比，可以补偿任何偏差。

当发现需要校准的移液器时，根据ISO要求，最好将这些移液器的调整留给合格的专业人员。技术人员或工程师可以重新校准大多数手动空气置换移液器，但是，一些复杂的电子移液器可能需要更多的经验丰富的技术人员，这些技术人员熟悉乐器，并承担时间和精力来确保这些移液的负担在规格之内。

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