For many chromatographers, centrifugal partition chromatography feels strange at first.

There is no silica bed. No C18 column. No packed resin. No solid stationary phase that you can point to and say: this is where the separation happens.

Instead, CPC uses two immiscible liquid phases. One liquid phase is held inside the rotor as the stationary phase, while the other is pumped through as the mobile phase. The separation depends on how each compound distributes between the two liquids.

That sounds simple, but for chromatographers trained on solid stationary phases, it can feel almost suspicious.

László Frici Németh describes this through a debate that lasted around 20 years with his professor: is CPC chromatography, or is it extraction?

His answer is practical:

Scientifically, CPC is clearly chromatography. But if you want to understand it faster, think of it as extraction first.

That small shift can make CPC much less frustrating.

CPC Is Chromatography, But Not the Kind Most People Expect

CPC fits the definition of chromatography because compounds distribute between a stationary phase and a mobile phase. The unusual part is that both phases are liquids.

In classical chromatography, the stationary phase is usually solid. The chromatographer chooses a material, such as silica, C18, ion exchange resin, or another surface chemistry. The thinking often starts with adsorption, polarity, surface interaction, pore size, particle size, pressure, and gradients.

In CPC, the thinking starts somewhere else.

The key questions become:

• Which biphasic solvent system should be used?
• How does the target compound partition between the two phases?
• What is the partition coefficient?
• Which phase should be stationary?
• Is the stationary phase retained well enough during operation?
• Does the sample dissolve and behave well in the selected solvent system?

This is why CPC can feel like a nightmare. It is not because the logic is weak. It is because the logic is different.

The Better Starting Point: Think Like an Extraction Chemist

A simple liquid-liquid extraction is based on partitioning. A compound distributes between two immiscible liquids. If it prefers one phase, more of it moves into that phase. If another compound has a different preference, separation becomes possible.

CPC uses that same chemical principle, but organizes it into a chromatographic process.

Instead of shaking a separatory funnel once or repeating extraction manually, CPC creates repeated contact between the mobile liquid phase and the retained stationary liquid phase inside a rotating system. Compounds move through the system at different speeds because they spend different amounts of time in each phase.

So CPC is not “just extraction.” But extraction is often the easiest doorway into the concept.

A useful way to say it is:

Liquid-liquid extraction tells you whether separation may be chemically possible. CPC tests whether that partitioning can become a usable chromatographic method.

For chromatographers, this is often the missing mental bridge.

Why the Usual Chromatography Instincts Can Mislead You

A chromatographer approaching CPC for the first time may ask: what is the column chemistry?

That question is understandable, but it is not the best starting point.

In CPC, there is no solid surface chemistry to optimize. The “stationary phase” is one of the liquid phases. Selectivity comes mainly from how the sample components distribute between the two liquids.

This changes the development logic.

This does not mean CPC is less scientific. It means the first experimental question is different.

In CPC method development, the solvent system is central. A poor solvent system gives poor separation, no matter how good the instrument is. A good solvent system gives the target and impurities different enough partition behavior to make separation possible.

The Solvent System Is the Method

In manyCPC projects, the most important work happens before the main CPC run.

Small-scale solvent screening helps answer practical questions:

• Does the target compound prefer the upper phase, lower phase, or both?
• Are the impurities distributed differently?
• Is the partition coefficient in a useful range?
• Do the phases separate cleanly?
• Does the sample cause emulsion, precipitation, or instability?
• Are the solvents acceptable for the intended application?

This is where CPC becomes very concrete. The method is not built by guessing. It is built by testing how the sample behaves in real biphasic systems.

For a chemist, this can be refreshing. You are not only choosing from catalog column chemistries. You are designing the liquid environment that creates the separation.

For a chromatographer, it can also be uncomfortable. There are more solvent combinations to consider, and the answer is often sample-specific.

Why a Feasibility Test Makes Sense

Because CPC depends so much on sample behavior, a feasibility test is often the most useful first step when there is a real separation problem. This is not a sales shortcut. It is a technical shortcut.

A feasibility test can show whether CPC is worth developing further. It can answer questions such as:

• Can a suitable biphasic solvent system be found?
• Does the target separate from the main impurities?
• Is the sample compatible with the solvent system?
• What does the first CPC chromatogram look like?
• Are the collected fractions analytically meaningful?
• Is further method development justified?

This is also why method development support matters. CPC is not difficult because chemists are missing basic knowledge. It is difficult because the early choices require the right framework.

If the project starts with the wrong mental model, development can become slow and confusing. If it starts with partitioning, solvent behavior, and a clear target, the work becomes much more structured.

So, Is CPC Chromatography or Extraction?

The answer is: Scientifically, CPC is chromatography. It has a stationary phase, a mobile phase, and separation based on differential distribution.

Practically, CPC is easier to learn if you first think about extraction. The extraction mindset helps chemists understand why solvent system selection matters so much, why partition coefficients are important, and why the matrix can make or break the method.

The 20-year debate is useful because both sides reveal something true.

CPC is chromatography by definition but extraction-like in how chemists first understand and develop it.

This is not a contradiction. It is a better teaching sequence.

Conclusion

CPC can feel like a nightmare when chromatographers try to understand it only through the habits of classical column chromatography.

The better approach is to start with extraction.

Ask how the compound partitions. Ask which biphasic solvent system creates useful selectivity. Ask whether the sample behaves well enough to support a method.

Then return to chromatography.

CPC is not magic, and it is not a universal replacement for other purification tools. But when the chemistry fits, it can become a powerful preparative separation method.

The key is to stop looking for silica where there is none.

Next Step

If you have a defined CPC use case in mind, book a consultation with Lilichro to discuss the sample, target compound, impurity profile, and analytical method. If the case looks suitable, a feasibility test is often the most practical way to see whether CPC can deliver meaningful separation before deeper method development.