Micropipetting is the technique of measuring and transferring very small volumes of liquid, typically less than 1 milliliter, using a handheld instrument called a micropipette. It’s one of the most fundamental skills in any biology, chemistry, or clinical laboratory, and nearly every experiment involving DNA, proteins, or chemical reagents depends on it. The volumes involved are measured in microliters, where 1,000 microliters equals a single milliliter, roughly one-fifth of a teaspoon.
How a Micropipette Works
A micropipette uses a spring-loaded piston inside a cylinder to draw up and dispense precise amounts of liquid. You attach a disposable plastic tip to the end, press the plunger down, submerge the tip in your liquid, then slowly release the plunger. The piston retracts and pulls liquid into the tip. To dispense, you press the plunger again over your target container.
There are two main mechanisms. Air displacement micropipettes, the most common type, keep a small cushion of air between the piston and the liquid. This works well for water-based solutions at room temperature, but temperature, atmospheric pressure, and the thickness of the liquid can all subtly affect accuracy. Positive displacement micropipettes eliminate that air gap entirely: the piston contacts the liquid directly. These are designed for viscous, volatile, or foaming liquids that would throw off a standard air displacement pipette.
Standard Micropipette Sizes
Most labs stock a set of four micropipettes, each covering a specific volume range. They’re labeled by their maximum capacity:
- P10: accurate from 1 to 10 microliters
- P20: accurate from 2 to 20 microliters
- P200: accurate from 20 to 200 microliters
- P1000: accurate from 200 to 1,000 microliters (1 milliliter)
Choosing the right size matters. Each micropipette is most accurate within its stated range. Setting a P1000 to dispense 10 microliters, for example, would produce unreliable results because you’d be operating far below its designed minimum. The general rule is to pick the smallest pipette whose range includes your target volume.
Where Micropipetting Is Used
Virtually every wet-lab procedure in the life sciences relies on micropipetting. When researchers run PCR to amplify DNA, they pipette reaction components measured in single-digit microliters. Diagnostic tests like ELISA, used to detect antibodies or proteins in blood samples, require dozens or even hundreds of precise liquid transfers across a plate of tiny wells. Cell culture, drug screening, forensic DNA analysis, and clinical chemistry panels all depend on the same core skill.
The reason it matters so much is that even tiny volume errors can cascade. In PCR, pipetting 8 microliters of a reagent instead of 10 can shift concentrations enough to produce a false negative. In clinical diagnostics, the same kind of error could mean a misreported lab value.
Manual vs. Electronic Micropipettes
Manual micropipettes are operated entirely by thumb pressure. They’re inexpensive, reliable, and require no batteries or charging. The tradeoff is physical strain: pressing the plunger hundreds of times a day, especially on stiff or heavy models, creates real risk of repetitive strain injury. Labs that involve extended pipetting sessions typically recommend frequent breaks for manual users.
Electronic micropipettes use a motor to drive the piston. You select the volume digitally and press a button. This reduces both physical strain and human error, producing more consistent volumes across many repetitions. Some electronic models reduce the force needed to eject tips by as much as 93% compared to manual equivalents, which makes a noticeable difference over an eight-hour workday. The downside is cost: electronic pipettes are significantly more expensive and require periodic charging.
Techniques That Improve Accuracy
Good micropipetting technique is the difference between reliable data and wasted experiments. A few practices have an outsized effect on accuracy.
Hold the pipette vertically, as close to 90 degrees as possible, when drawing up liquid. Tilting it to 45 or 60 degrees measurably changes the volume you aspirate. Immerse the tip just below the surface of the liquid, not deep into it. Going too deep pulls in extra liquid clinging to the outside of the tip. Going too shallow risks aspirating air, which leaves you short of your target volume.
Pre-rinsing the tip, meaning aspirating and dispensing the liquid two or three times before taking your actual measurement, dramatically improves accuracy. This step neutralizes capillary effects inside the tip and brings the air temperature inside the tip closer to the temperature of the liquid. It’s especially important when pipetting very small volumes, where even a fraction of a microliter matters.
Pipette Tips and Why They Matter
Micropipette tips are disposable and come in varieties matched to different tasks. Standard polypropylene tips work for most routine applications. Filter tips, which contain a small barrier plug near the top, prevent aerosols and liquids from contaminating the pipette’s internal mechanism. They’re essential when working with hazardous samples or during PCR, where a stray molecule of DNA can ruin results.
Low-retention tips have a specially treated inner surface that repels liquid, reducing the amount left behind on the tip walls after dispensing. These are valuable when working with expensive reagents, sticky protein solutions, or very small volumes where even a thin film of residual liquid represents a significant fraction of the total.
Calibration and Accuracy Standards
Micropipettes drift out of calibration with use and need regular testing. The international standard governing pipette accuracy is ISO 8655, which sets maximum permissible errors at 10%, 50%, and 100% of each pipette’s nominal volume. For a P10 pipette set to deliver 1 microliter, ISO 8655 allows a maximum error of plus or minus 0.12 microliters. Some manufacturers hold themselves to tighter tolerances: Gilson, for instance, specifies plus or minus 0.025 microliters at that same 1-microliter setting.
Most labs calibrate their pipettes annually or semiannually, either in-house using a precision analytical balance or through a third-party calibration service. If you pick up a pipette that hasn’t been checked in over a year, it’s worth confirming its accuracy before trusting it with critical experiments. A quick gravimetric check, weighing the dispensed water on a sensitive balance, can reveal whether a pipette has drifted outside acceptable limits.