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?
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?
In my role as senior technical specialist at Biotage I am often asked about compound detection options. For most flash chromatography methods, UV is the default detection tool since a majority of compounds do absorb some UV light.
Diode array UV detectors provide chemists choices in wavelength selection, providing the ability to widen or narrow the wavelength range needed to detect specific compounds and enhance their sensitivity.
When diode array detectors fail to detect compounds, it is because the compounds have no chromophore, e.g. carbohydrates, low extinction coefficients, exist in really low concentrations, or any combination of these. In these situations, alternative detectors are quite beneficial. In this post I will discuss a couple of detector options for flash chromatography.
Continue reading So, which detector should I use for flash column 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.
Continue reading 5 Steps to successful flash chromatography
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?
Flash chromatography – a purification tool for both organic chemists and natural product researchers. This tool is essential when you need to remove impurities from your targeted product, or products, in order to get them pure. To reduce the costs associated with flash chromatography, some chemists try reusing the same column over and over, not always with success.
A question I am frequently asked is “how many times can I reuse my flash column?” Although I have previously addressed this topic, I feel it is worth another look. In this post, I will attempt to address this question by providing a bit more science behind the cartridge reuse question.
Continue reading How many times can I reuse my flash chromatography column?
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).
Continue reading How can I modify my flash chromatography method to separate chemically similar compounds?