Pumps, Valves & Liquid Handling
Pipette Service & Calibration A Guide to Accurate and Reproducible Results
Savio Gadelha, Mettler Toledo Rainin
Pipettes are often the foundation of many laboratory processes and experiments, but for many researchers, pipettes require little thought to operate. Because of the simplicity of pipettes, many users overlook the need for maintenance. Like all precision tools, pipettes require regular calibration and maintenance to ensure accurate performance. A leading pipette manufacture and distributor has accumulated data suggesting that a signifi cant amount of pipettes are not serviced regularly and those that are serviced regularly experience high as found failures due to substandard service providers.
What’s Hidden Beneath the Surface?
Only a small fraction of pipette failures are evident to end users. It is estimated that 95% of pipette failures can be attributed to one or more components of the pipette’s sealing system – compromising the seal, O-ring, shaft and piston. These failures are most commonly caused by tiny cracks in the seal or a buildup of contamination inside the pipette, which can best be detected by a trained technician. A comprehensive preventive maintenance program will proactively replace seals using manufacturer approved parts, re- grease O-rings and pistons and check the shaft for damage, ensuring that the pipette can perform to its designed specifi cations.
Some service provider’s defi ne their own pipette specifi cations, which can only perform to the accuracy they have specifi ed. These specifi cations are commonly used by onsite service providers due to the challenges of meeting manufacturer or even ISO 8655 specifi cations in uncontrolled environments. Depending on the pipette and the volume setting, the difference in standards can translate to a likely gap in tolerance of 3% to 5%.
It Works, But is it Accurate?
Application use may vary, but one factor linking all labs – therefore the most important reason for everyone to regularly calibrate their pipettes – is the need to produce accurate and reproducible data. It all comes down to the accuracy of those tiny amounts of liquid transferred from one vessel to another. In this respect, it is the small, hidden faults that can have the most impact on your results.
A ± 5% variance in performance may be acceptable for one experiment and unacceptable for another. For example, when establishing a standard curve or amplifi ed serial dilution, this inaccuracy could make a fundamental difference to your data or go unnoticed and lead to incorrect results. Inaccurate results can lead to published data being challenged or, at the very least, require that the experiment be repeated multiple times.
Calibration Standard Defi nes Accuracy Level
The calibration standard used by the service provider will likely be the single most important factor affecting the accuracy of your pipettes. Because calibration standards often vary from one service provider to the next, it is wise to know the differences before selecting a service provider.
Pipettes that are calibrated to manufacturer specifi cations perform within optimal range as defi ned by the manufacturer. ISO 8655 is an international standard that governs pipette calibration. Pipettes calibrated under ISO 8655 standards – regardless of brand – may be greater than the manufacturer specifi ed performance. When calibrating a pipette to the manufacturer specifi cations or ISO 8655 standards, environmental conditions must be taken into account.
Equipment also Affects Accuracy
The most common factory-approved method for determining pipette performance uses gravimetric analysis. The weight of water in micro-grams is converted to volume in micro-litres.
Pipettes come in various types and volumes and having the right equipment is essential for accurate calibration. Small volume pipettes like a 2µL or 10 µL require a 7-digit balance, while the commonly used 200µL pipette on the other hand will require a 5-digit balance for calibration. And, multichannel pipettes should be calibrated with a multichannel balance, capable of calibrating all channels individually yet simultaneously. Pipette accuracy can be compromised when pipettes are calibrated with improper equipment.
Standard Balance Sensitivity
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