Celebrating 1 year of the flash purification blog

It is hard for me to believe but the flash purification blog is a year old. This started as an idea within the technical group here at Biotage to share knowledge of flash column chromatography that we have learned over 30-plus years.  Though I was reticent at first, now after only a year its hard to imagine my world without this blog.

Those of you who read this blog regularly are growing in number and each time I post we set a new record for numbers of visitors, thank you.  There are certainly some posts that are popular.  I’ll spend the rest of this post sharing some details and at the end of the post, I ask that you take a couple of minutes to provide feedback in the form of an on-line survey.

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Detecting the undetectable in flash column chromatography using wavelength focusing

Sometimes it feels as if organic chemistry and chromatography are a mixture of art and science.  Maybe its because of the necessary creativity needed to address the variety of challenges that we face almost daily.  Frankly, its what I find most interesting about this world.

One of the bigger challenges facing chemists is the ability to detect and collect compounds with little or no UV absorption during flash purification.  In this post I will talk about a technique that I have found to be quite useful when trying to purify mixtures containing one or more poor absorbers.

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Acetone – a lower cost alternative to EtOAc in normal-phase flash column chromatography

Acetone, as you know, is a terrific solvent.  It dissolves many organic molecules, evaporates easily, is both water and organic soluble, and is cheap (relatively).  These attributes tell me it should be a good polar modifier for normal-phase flash chromatography.

There is one attribute that keeps chemists from using acetone in chromatography – its strong UV absorbance above 250 nm which can mask compound detection and make UV-triggered peak fractionation a challenge, especially aromatic compounds. However, with some state-of-the-art flash systems, mobile phase UV absorption is zeroed in real time enabling the use of UV absorbing solvents such as acetone.

In this post I discuss some reasons to explore switching to acetone and how modern flash chromatography equipment deals the UV-absorbing mobile phase solvents. Continue reading Acetone – a lower cost alternative to EtOAc in normal-phase flash column chromatography

How and when to insert an isocratic hold in flash column chromatography

For many chemists using generic linear gradients and even gradients based on TLC the purification results often are not selective enough to separate all of the compounds in their mix.  This is especially true if your target has a closely eluting impurity. One method used to try and increase resolution is the use of an isocratic hold or gradient pause during purification.

In this post I examine the use of the isocratic hold to determine how well it works and when/if it should be inserted into a gradient method.

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Does methanol really dissolve silica during flash column chromatography?

This is an age-old question that has been around a long time, perhaps as long as me (and I have been around a while) –  “Does silica dissolve in methanol?”  For many years I have heard from organic and medicinal chemists as well as students of organic chemistry that silica is dissolved by methanol when running a DCM/MeOH gradient.

In this post I will share the results of some tests I performed that hopefully will help clarify what is happening to the silica when in contact with methanol.

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So, what exactly is a column volume in flash column chromatography and how is it determined?

In many of my previous posts I have used the term column volume, typically abbreviated as CV, as a value used to help determine separation quality and loading capacity.  However, I recently was asked a question about this topic from a chemist who understands the column volume concept but wanted to better understand its definition and how it is determined.

In this post I will explain what a column volume is and how it is determined empirically.

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Flash column equilibration – is it a waste of time or necessary step?

Flash column chromatography has been practiced by chemists since the 1970s. That practice required the silica in the column be properly wetted to remove trapped gasses to ensure uniform flow (remember those days of not letting air into the column?). Today, with automated flash chromatography systems and pre-packed cartridges as the norm, chemists ask me – do I really need to pre-equilibrate my cartridge?

In this post I explore the impact on chromatography that equilibration, and lack thereof, has on separation performance.

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Setting the Right Flow Rate for Flash Column Chromatography

How does flow rate impact my flash column chromatography separation?  This is the kind of question I frequently get.  After all, we all know that high flow rates that are too high or too low mean bad prep HPLC chromatography.  Well, this is not necessarily true in flash chromatography.

In chromatography there are three inter-related variables which impact your separation and are represented on the  chromatographer’s triangle.

Chromatographer's triangle 2.jpgIn practice only two of these variables can be optimized.  Increasing flow rate decreases either load (if you need to maintain a purity level) or purity (if you need to maintain a throughput) because of increase sample dispersion and band-broadening.  If you increase load, you need to decrease the optimal flow rate or purity will suffer.  You get the idea.

In this post I will discuss the impact that flow rate has on flash chromatographic performance.

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How do I develop a reversed-phase flash column chromatography method?

Method transfer from reversed phase TLC (thin layer chromatography) to reversed phase flash column chromatography can be very challenging.  Because of this, I often recommend using HPLC for reversed phase flash chromatography method development. This really is a straight-forward process if you start with the right HPLC column and know a little about your HPLC system’s detector.

In this post I will share some tips on how to develop a reversed-phase flash purification method using HPLC.

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Can I use TLC for reversed-phase flash column chromatography method development?

I am often asked why reversed-phase TLC data does not translate well to reversed-phase flash column chromatography.  There are several reasons for this and in this post I will attempt to explain the challenges associated with reverse-phase TLC as a method development tool for reversed-phase flash chromatography.

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