Pipettes

There are two types of pipettes: Positive displacement and air pipettes. Positive displacement pipettes are commonly used for samples of high viscosity (e.g. glycerol) or high vapor pressure (e.g. volatiles like alcohol), while air-displacement pipettes can be used for a majority of laboratory applications.

Modern pipettes, also known as micropipettes, work with a piston-stroke principle – liquid is measured using the piston-cylinder system in the handle of the pipette. When the piston is depressed and then slowly released, the movement of the piston creates a vacuum in the pipette tip and thus draws liquid up inside the tip; which is called aspiration.

Since the piston in a pipette is a long way from the liquid sample, the air cushion between the piston and liquid can have a number of effects on the accuracy of this process, depending on the liquid type. Pressing down on the plunger that has a tip full of liquid expels the liquid out from the tip; this is called dispensing.

Positive displacement pipettes work on a similar principle, however the tip of the positive displacement system contains its own piston and hence there is a minimal air cushion between the piston (that is part of the tip) and the liquid surface.

Pipetting accuracy is the ability of a pipette to deliver the volume specified on the volume setting. In other words, the trueness of a measurement to the true value depends on the interplay of the elements in the system.

Pipetting precision is the ability of a pipette to consistently deliver same-sized volumes of liquid over multiple aliquots. A pipette can be precise with regard to dispensing the same volume time after time, yet inaccurate because it fails to dispense the correct volume. An accurate and precise pipette dispenses volumes at the intended volume with each dispense.

The pipette, the pipette tip, and the person operating the pipette form a 3-part system. The pipette operator, the person using the pipette to conduct research, has a high degree of influence on the accuracy of results. As such, it is important that operators are trained to use a pipette. Some powerful yet simple techniques can greatly improve pipetting accuracy. The Rainin Pipetting Technique Poster offers a good summary. Additionally, Rainin offers the Good Pipetting Practice Online Seminar to assist in learning the proper way to pipette.

Rainin offers a wide range of manual and electronic single channel, multichannel, or high throughput pipetting instruments and calibration services to ensure your results remain accurate. Rainin pipettes are available globally for purchase. Interested in purchasing a pipette? Request a quote at the top of this page.

How much a pipette costs depends on the type of pipette: single or multichannel, manual or electronic. Pipette price varies based on precision (accuracy specifications), materials, and craftsmanship. 

Pipettes are used in laboratories worldwide, including labs involved in life science research experimentation, chemical testing, petroleum, and food manufacturing. They are used in any industry that has biological testing as a requirement.

To choose the suitable pipette for the task, consider a few factors: liquid type, number of replicates, time sensitivity, and pipetting volume.

First, what type of liquid are you pipetting?

• An air-displacement pipette will work well if the liquid is aqueous or near aqueous.
• If the liquid is viscous or volatile, a positive-displacement pipette will deliver better results than an air-displacement pipette.
• Air-displacement pipettes have air inside that can be stretched or compressed when working with viscous liquids or expanded by the rapid evaporation of a volatile liquid into the pipette’s interior chamber.
• Positive-displacement pipettes have a piston extending to the syringe-like tip’s opening. This preserves pipetting accuracy by removing air from the system. 

The type of vessels involved in your application and the number of replicates are also critical factors in selecting a pipette.

• A manual single-channel pipette works well for a small number of dispenses into most tubes and plates. But if you’re pipetting into many wells or tubes, multichannel pipettes and electronic pipettes can ease the burden on the pipetting hand.
• Multichannel pipettes fill plate rows efficiently, and adjustable-spacer versions give you a convenient way to move between differently-spaced vessels like tubes and plates.
• Electronic pipettes also offer the added benefit of dispensing multiple aliquots from a single aspiration – even in a sequence of different volumes. And with a cycle counter, electronic pipettes help you track where you are in your protocol.
• Consider a high-throughput semi-automated pipetting workstation if your intended number of replicates fills multiple plates.

If your protocol is time-sensitive, consider multichannel pipettes and high-throughput pipetting platforms to accomplish the most in the least amount of time. Electronic versions of these instruments can deliver the most significant time savings.

What volume are you pipetting?

• Work between 10-100% of a pipette’s nominal volume for accurate results.
• Volumes near a pipette’s full nominal volume will deliver the highest accuracy.
• Avoid pipetting 20 µL using a 1,000 µL pipette. Instead, pipette 20 µL using a 20 µL pipette.
• Pipette sizes range from 1 µL to as large as 20 mL, and even larger volumes can be accurately transferred using serological pipettes.  

Cross-contamination can derail experiments, so adopt a strict tip-changing policy—one tip per sample. Filtered tips block aerosols and regularly wiping the pipette with ethanol removes surface residues. Maintaining a clean, orderly bench and storing pipettes properly reinforce these efforts. Rainin multichannel pipettes, with their secure tip fit and comfortable handling, make it easier to uphold these practices, ensuring each sample transfer is isolated and contamination-free.

At low volumes, even a minute droplet of leftover reagent can skew results. Be meticulous about changing tips between each reagent and consider filtered tips to prevent aerosols from contaminating the body of the pipette. Keep the pipette free of residues by regularly wiping it down with ethanol. Rainin laboratory pipettes, with pipette tips that fit consistently and eject smoothly with minimal force, make it simpler to maintain exacting cleanliness standards for each new reagent you handle.