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Can reversed-phase flash chromatography purify better than normal-phase?

The answer to this question is yes, reversed-phase can sometimes provide a better separation and thus better purification than normal-phase.  When is reversed-phase likely to be the better choice is a different, and likely better, question.

In this post I will try to demonstrate when reversed-phase is likely the better purification mode.

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How can I reduce flash column purification time and cost?

This is a question being asked of my colleagues and me more and more frequently, especially in pharma accounts.  Why?  Well, you are familiar with the adage – Time is Money, right.  Well this really applies to them. A new molecular entity (NME) created as a pharmaceutical can take up to a decade and a billion dollars to bring to market.  Granted, the biggest costs are in the clinical trials but the synthetic route and the time to discover and make the compound – and purify it – plays a major role within drug discovery and development. This timeline is not helped by the ever increasingly difficult-to-synthesize compounds being investigated as drug candidates today.

With that in mind, this post focuses on ways to speed the purification process without sacrificing purity and yield. Continue reading How can I reduce flash column purification time and cost?

How can I perform normal-phase and reversed-phase column chromatography on one flash system?

For chemists, flash chromatography is part of their everyday synthesis workflow. For most syntheses, crude reaction mixtures are purified by normal-phase (aka adsorption) chromatography.  There are times; however, where the crude mixture’s complexity and polarity make normal-phase chromatography very challenging.  For these situations, reversed-phase (aka partition) chromatography may be a preferred option.

But, if you have only one flash system available, can you, should you, and how do you efficiently switch from non-polar, normal-phase solvents to polar, reversed-phase solvents – and back again without issues? In this post I’ll attempt to shed some light on the topic. 

Continue reading How can I perform normal-phase and reversed-phase column chromatography on one flash system?

How do particle size and flow rate affect normal-phase flash column chromatography?

Media particle size and solvent flow rate play major roles in chromatographic separations including flash purification.  This is true in both reversed-phase chromatography (aka partition chromatography) as well as normal-phase chromatography.

The roles played are related to the overall compound mass-transfer kinetics and diffusion/dispersion as they migrate through the column.  Smaller particles reduce sample dilution by reducing interstitial volume, while flow rate impacts the ability of molecules to efficiently pass through the porous particles.

In this post, I will show how both particle size and flow rate impact flash chromatography.

Continue reading How do particle size and flow rate affect normal-phase flash column chromatography?

5 Steps to successful flash chromatography

The bane of organic synthesis for most chemists is purification rather than synthesis. Synthetic reaction mixtures are rarely devoid of impurities so some type of purification is necessary.  Most often flash chromatography is used but for many chemists, it is less well understood than their chemical reaction and provides some level of anxiety.

In this post, I will summarize the five most important steps to creating a successful flash chromatography method and thus the anxiety associated with it.

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How does solvent choice impact reversed-phase flash chromatography separations?

I have recently posted on how solvent choice influences the separation of hard to resolve compounds using normal-phase flash chromatography. As a chemist with an inquiring mind, I thought I would expand my research beyond normal-phase and see what happens in reversed-phase.

In this post, I share my results. 

Continue reading How does solvent choice impact reversed-phase flash chromatography separations?

How to efficiently scale-up flash column chromatography

For synthesis and medicinal chemists, compounds are typically made only once en route to a final product. Once that compound shows activity toward a particular target, then the synthesis is scaled up meaning that purification too requires scaling. The same is true in natural product research where once a high-value compound is isolated at small scale, there is a need to isolate it at larger scale.

Both of these scenarios can be problematic to scale-up/ process chemists when other, non-chromatographic purification techniques are not successful. When this happens, either a different synthetic route or extraction process is needed or large scale chromatography is employed. In this post, I will explain how flash chromatography can be successfully scaled while minimizing time and solvent consumption. Continue reading How to efficiently scale-up flash column chromatography

How can I modify my flash chromatography method to separate chemically similar compounds?

The challenges organic, medicinal, and natural product chemists face are many: from designing reactions, to optimizing synthesis, work-up / extraction, and purification / isolation of the desired compound or compounds. Among those issues related to purification / isolation is the common problem of separating compounds with similar chemistry that either co-elute or separate poorly.

In this post I will discuss some tips on how to “resolve” this issue (yes, pun intended).

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Ionizable compound purification using reversed-phase flash column chromatography

With most chromatographic purifications, only two solvents are needed to adequately separate compounds from each other. Unfortunately, there are instances where the separation is either poor or cannot be accomplished with “normal” elution conditions such as those with ionic or very polar organic molecules.

In this post I offer some solutions to this issue.

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How do I purify ionizable organic amine compounds using flash column chromatography?

For most organic reaction mixture purifications the process is fairly straightforward. Use hexane/ethyl acetate or, for polar compounds, DCM/MeOH.  But what do you do if this doesn’t work and your compounds are basic organic amines?

In this post, I re-examine the options available to achieve an acceptable organic amine purification when typical separation methods are insufficient. Continue reading How do I purify ionizable organic amine compounds using flash column chromatography?