Flash chromatography vs prep HPLC: you want speed or precision?

I talk about flash chromatography and preparative high-pressure liquid chromatography (prep HPLC) all the time on the blog. But never have I discussed the differences of these two methods with you. To immediately change this, I have dedicated this post to breaking down adsorption chromatography and flash chromatography vs prep HPLC for you. Read on to see what we have been missing until now!

Spring just arrived and my neighbors are so excited to start gardening again. I was soaking up some early spring rays on my porch and eavesdropping on the conversation between my two neighbors as they were cleaning out their water sheds.

One pulled out a giant hose and proceeded to demonstrate that he could water a large area with a single touch of his hose. A perfect set-up for his only-grass lawn. The other pulled out a hose with a much smaller diameter and countered that although he can only water smaller areas, he is much more precise. Pretty important for the many flowers and bushes in his garden that differ in their watering needs.

Well, correct me if I’m wrong, but as I sat there, I thought to myself that is quite a good analogy to flash chromatography vs prep HPLC! And it’s not the first time gardening has made me think about chromatography. Last time I watched my nephew watering plants, I did get lost into thoughts about flow rate and column efficiency in chromatography.

But let me get back to the topic at hand.

What is the big difference in flash chromatography vs prep HPLC?

Let me start with the similarities! Both are types of adsorption chromatography. In adsorption chromatography, the separation is governed by the interactions of the sample components with the stationary and mobile phase. Compounds with different chemical properties, particularly polarities, display varying affinities towards the stationary and mobile phase. Affinity, in turn, ins influenced by two molecular properties, adsorption and desorption.

Adsorption describes the ability of a compound to stick to the stationary phase. Desorption, or solubility, describes how well a component of the mixture dissolves in the mobile phase or solvent.

The speed with which individual sample components migrate through the stationary phase depends on the adsorption/desorption properties.
Adsorption chromatography can be split into preparative or analytical chromatography.

Analytical chromatography: typically performed with smaller amounts of material to establish the presence or quantify relative proportions of components in a mixture.
Preparative chromatography: frequently used to separate or purify the components of a mixture for downstream applications.

Preparative chromatography is further divided into gravity fed chromatography (low pressure), flash chromatography (medium pressure) or prep HPLC (high pressure). These chromatography types, including flash chromatography vs prep HPLC, mainly differ by the pressure generated by the flow of the mobile phase through the stationary phase.

Let us examine the benefits and limitations of open column versus flash chromatography and prep HPLC:

Open column chromatography	Flash / prep HPLC
Pros	Pros
Low expenses for instruments, maintenance and consumables Low pressure	Fast process: - High resolution - High flow rates - High automation Low solvent consumption - High resolution High flexibility - Compatibility with a large variety of consumables and detectors High reproducibility - Stable conditions No fume hood needed (if fraction collector is enclosed)
Cons	Cons
Very time consuming - Low resolution - Low flow rates High solvent consumption - Low resolution Low flexibility - Not compatible with high performance consumables or detectors Low reproducibility - No regulated flow or pressure Fume hood needed	Instrument & maintenance cost Consumables cost

Now let us get to the juice of this post: flash chromatography vs prep HPLC.

Flash chromatography is often used as a pre-purification step to purify large sample quantities at a good resolution.
Prep HPLC is used to achieve highest resolution, or purity, under the condition of lower loading capacities.

The two techniques differ in the material used for the station phrase (different particle size), the dimension of the cartridge or column (internal diameter and length), as well as flow rate of the mobile phase. I have summarized the parameters of flash chromatography vs prep HPLC in the table below:

	Flash	Prep HPLC
Particle size	15 - 63 uM	5 - 15 uM
Column ID	12 - 115 mm	10 - 70 mm
Flow rate	15 - 250 mL/min	5 - 100 mL/min
Loading capacity	< 300 g	< 10 g
Max pressure	50 bar	300 bar

Just like with anything in life, with these two techniques you have a trade-off. Flash chromatography offers you a faster way to process more sample at once, prep HPLC is slower, but gives you a better resolution. But there is also some good news to this. There are chromatography systems that enable you to perform both flash chromatography and prep HPLC on them, so you can use both methods depending on your changing applications.

I hope I’ve watered your knowledge on flash chromatography vs prep HPLC and I have managed to give you a lot and precise information, so best of both worlds! If you are looking for additional information on chromatography types, their benefits and limitations, check out our free and very comprehensive Chromapedia guide. There is always more to discover!

Till next time,