Micropipettes are widely used in laboratories for handling small liquid volumes.

For aqueous solutions, buffers, culture media, diluted samples, and many routine applications, micropipettes are practical and easy to use for dispensing liquids in the microliter range.

However, a micropipette is not always the best choice for every liquid or workflow.

For example, you may want to consider a positive displacement syringe or dispenser when working with liquids that are:

• Highly viscous

• Volatile

• High in density

• Prone to foaming

• Dispensed repeatedly

• Handled in relatively large volumes

In these situations, a positive displacement system may offer practical advantages over a conventional air displacement micropipette.

In this article, we explain the difference between micropipettes and positive displacement syringes, the types of liquids they are suited for, and how to think about small-volume syringes such as a 0.2 mL syringe.

A Micropipette Is Not Ideal for Every Liquid

Most conventional micropipettes use an air displacement mechanism.

In an air displacement pipette, an air cushion exists between the piston and the liquid. The movement of this air cushion allows the pipette to aspirate and dispense the sample.

This system works well for water and liquids with similar physical properties, making it suitable for a wide range of routine laboratory applications.

However, when the physical properties of a liquid differ significantly from water, the air cushion may affect dispensing behavior.

For example, viscous liquids may move more slowly during aspiration and dispensing, while volatile liquids can affect the air cushion through vapor pressure.

This means that:

Just because a liquid volume falls within the range of a micropipette does not mean a micropipette is automatically the best tool for that liquid.

What Is a Positive Displacement Syringe?

In a positive displacement system, the piston acts directly on the liquid.

Unlike an air displacement pipette, there is no air cushion between the piston and the sample.

In a syringe-based system, the piston inside the syringe directly aspirates and dispenses the liquid.

Because of this design, positive displacement systems are generally less affected by properties such as viscosity, volatility, and density.

They may therefore be considered for liquids such as:

• Glycerol

• Oils

• Viscous media

• Volatile liquids

• Foaming solutions

• High-density liquids

However, positive displacement does not mean that every syringe is compatible with every chemical.

Always review the chemical compatibility of the syringe, piston, seals, and other wetted components before use.

How Much Is 0.2 mL?

When searching for small-volume syringes, you may come across products described as a “0.2 mL syringe.”

Converted to microliters:

0.2 mL = 200 µL

Similarly:

• 0.1 mL = 100 µL

• 0.2 mL = 200 µL

• 0.5 mL = 500 µL

• 1.0 mL = 1,000 µL

A volume of 200 µL is also within the operating range of many conventional micropipettes.

Therefore:

A 0.2 mL volume does not automatically mean that you need a syringe.

The more important questions are what kind of liquid you are dispensing and how the dispensing step fits into the overall workflow.

Micropipette vs. Positive Displacement Syringe

The main differences can be summarized as follows:

Comparison	Micropipette	Positive Displacement Syringe
Common operating principle	Air displacement	Positive displacement
Between piston and liquid	Air cushion	Piston acts directly on liquid
Typical consumable	Pipette tip	Syringe / piston system
Aqueous solutions	Well suited	Can also be used
Viscous liquids	May require technique adjustments	May be better suited
Volatile liquids	Can be affected by vapor	Generally less affected by air-cushion effects
Typical volume range	Mainly µL	Depends on system; µL to mL
Repetitive dispensing	Depends on pipette type	Often useful with dispenser systems
Consumable availability	Many standard tip formats	Usually requires dedicated syringes
Main strength	General-purpose small-volume handling	Challenging liquids and specific workflows

Neither system is inherently better.

A useful way to think about the difference is:

Micropipettes offer versatility for routine liquid handling, while positive displacement systems can provide advantages for challenging liquids or specialized workflows.

Positive Displacement Can Be Useful for Viscous Liquids

Viscous liquids such as glycerol or oils move more slowly than water.

With an air displacement micropipette, aspiration and dispensing may take longer, and residual liquid may remain inside the tip.

Several technique adjustments may help, such as:

• Aspirating slowly

• Pausing after aspiration

• Dispensing slowly

• Using reverse pipetting

• Using a wide-bore tip

• Using a low-retention tip

These adjustments may improve performance for some viscous liquids.

However, for highly viscous samples, consistent pipetting may still be difficult.

In these cases, a positive displacement system can be worth considering because the piston acts directly on the liquid rather than through an air cushion.

Positive Displacement Can Also Help With Volatile Liquids

Volatile liquids such as ethanol can produce vapor that affects the air cushion in an air displacement pipette.

This may contribute to issues such as:

• Liquid dripping from the tip

• Unstable aspiration volumes

• Variation between repeated pipetting cycles

Because positive displacement systems do not rely on an air cushion between the piston and liquid, they can reduce the influence of this effect.

However, when handling volatile liquids or organic solvents, always confirm the chemical compatibility of the syringe and sealing materials.

Foaming Liquids May Also Require a Different Approach

Solutions containing surfactants or certain protein-containing solutions may foam during pipetting.

Excessive foam can make it difficult to determine how much liquid has actually been aspirated and may introduce bubbles into the dispensing process.

Possible problems include:

• Air bubbles inside the liquid column

• Unclear aspiration volume

• Inconsistent dispensing

Techniques such as reverse pipetting may help in some situations.

For liquids that remain difficult to handle, a positive displacement system may be another option to consider.

Should You Use a Micropipette or Syringe for 0.2 mL?

If you need to dispense 200 µL, both a micropipette and a positive displacement syringe may be capable of handling that volume.

The choice should therefore not be based on volume alone.

A useful framework is:

Volume + Liquid Properties + Required Reproducibility + Workflow

Volume

How much liquid needs to be dispensed?

Liquid Properties

Is the liquid viscous, volatile, dense, or prone to foaming?

Required Reproducibility

How consistent does each dispensing step need to be?

Workflow

Will the liquid be dispensed once, or repeatedly into many tubes or wells?

For example, dispensing 200 µL of buffer into a small number of tubes may be straightforward with a micropipette.

Dispensing 200 µL of a viscous liquid dozens of times may be more efficient with a positive displacement syringe or dispenser.

A Dispenser Can Be Useful for Repetitive Work

With a conventional micropipette, a typical workflow involves:

1. Aspirating liquid

2. Moving to the receiving vessel

3. Dispensing

4. Returning to the source

5. Aspirating again

This cycle is repeated for each dispensing step.

Some dispenser systems work differently.

A larger volume can be aspirated into the syringe once and then dispensed in multiple smaller portions.

For workflows where the same reagent is added to many tubes or wells, this can reduce the number of repeated aspiration steps.

In repetitive work, the total number of actions required across the entire experiment can be just as important as the performance of a single dispensing step.

When Is a Micropipette a Good Choice?

A micropipette is generally practical when:

• Working with typical aqueous solutions

• Dispensing small volumes in the µL range

• Handling a relatively small number of samples

• Routinely dispensing buffers or reagents

• Using widely available pipette tips

• Adjusting between several volumes with a variable-volume pipette

For many routine laboratory liquid handling tasks, a micropipette remains the most convenient option.

When Should You Consider a Positive Displacement Syringe or Dispenser?

A positive displacement system may be worth considering when:

• Frequently handling viscous liquids

• Working with volatile liquids

• Handling high-density samples

• Working with foaming liquids

• Micropipette performance is difficult to stabilize

• Dispensing the same liquid into many containers

• Handling a broader range of volumes from µL to mL

• You want to reduce the influence of an air cushion

The syringe volume alone should not determine the choice.

The properties of the liquid and the overall workflow are equally important.

The Best Liquid Handling Tool Is Not Determined by Volume Alone

It may seem logical to think:

“I need to dispense 0.2 mL, so I need a 0.2 mL syringe.”

But that is not always the most appropriate way to choose a liquid handling tool.

Since 0.2 mL is equal to 200 µL, it is also within the working range of many micropipettes.

A better question is:

What are you dispensing, how are you dispensing it, and how many times will you repeat the process?

For routine small-volume aqueous solutions, a micropipette is often the most practical choice.

For challenging liquids, or for workflows involving repeated dispensing, a positive displacement syringe or dispenser may offer advantages.

Selecting the tool according to both the liquid properties and the workflow can help make liquid handling more efficient and consistent.

WATSON’s Micro Dropper is a positive displacement liquid dispenser designed to work with interchangeable syringes.

It supports nine syringe sizes covering a range from 0.1 mL to 50 mL and does not require electrical power for operation.

When reviewing workflows involving liquids that are difficult to handle with conventional air displacement micropipettes, or procedures that require repeated dispensing of the same liquid, a positive displacement liquid handling tool may be worth considering alongside a conventional micropipette.