In past posts I discussed which solvents work best for sample loading in reversed-phase flash chromatography.  Recently, I was asked to provide some insight as which solvents are best in normal-phase flash column chromatography.

Liquid loading of samples onto chromatography columns is not always straight-forward. If your sample is dissolved in the mobile phase, that can work but may not be the best choice, especially if running a gradient.

In this post I show you some work I have done that opens up quite a few options for solvents used for loading samples and some surprising results with DMF.

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.

A question I hear a lot from chemists is “how much can I load”. The answer is always “it depends on your separation quality”.  At that point I begin asking about the TLC data and purification goals. Purification goal setting should be your first step and the question to answer is – what do I need this purification to achieve? Is the goal high purity, high yield, or some combination.  Remember, you will typically sacrifice purity for high yield and yield for high purity so optimization is an important consideration.

Synthetic organic chemistry is the genesis of new pharmaceutical and commercial chemical products. In short, it is based on the idea that two or more carbon-based compounds can be forced to react using heat, or other energy source, to create a new, novel product – but this we already know.

Compounds precipitating during flash chromatography is at best an inconvenience when working up your crude reaction mixture.  Precipitation during purification typically happens in the column or in the tubing exiting the column.

In this post, I will propose a strategy that can minimize and perhaps prevent this issue from occurring.

For chemists preferring or needing to dry load their crude sample mixtures to get an acceptable flash purification result, using the right ratio of sample to sorbent can be quite important.  Too much sample and solubility issues can ensue, too little sample and significant band broadening occurs, reducing the separation quality.

In this post, I propose an acceptable ratio range based on my own experimental data.

Many microwave assisted organic synthesis (MAOS) reactions use polar solvents such as alcohols, DMF, DMSO, because they absorb and transfer microwave energy very efficiently.  However, the downside of using polar, microwave absorbing solvents is that they can interfere with normal-phase flash chromatography.

In this post, I discuss why dry loading can be advantageous when purifying polar-solvated reaction mixtures.

In previous posts I have touched upon various sample loading options and how they impact flash chromatographic performance, primarily in normal-phase flash purification. As the use of reversed-phase flash chromatography has steadily increased over the past few years I thought it would be a good idea to discuss one of the most important factors impacting its success.

In this post I discuss the results of some of my original research studying the impact of injection solvent choice on reversed-phase flash separations.

Your choice of sample loading technique can, and likely will, affect the separation and purity of your targeted compound. While liquid loading is easy and often fit for purpose, it can provide some issues especially if large sample volumes are required relative to column size (> 1% of a column volume) or the dissolution solvent is too strong for the chosen purification method (e.g. injecting a methanol-solvated sample into a hexane/ethyl acetate mobile phase).

Using a “dry” loading technique with flash chromatography typically improves compound purity and overall separation quality compared to liquid loading. The reasons for this I have prophesized previously and include:

Getting the most benefit from your crude sample purification with column chromatography or flash chromatography involves optimizing many variables.  In previous posts I have talked about selecting the best solvents, their ratios, and maximizing load based on TLC Rf data. These are all important chromatography-generated variables but now I would like to share some tips on actual technique differences and their impact on purification performance.

As the popularity of prep-scale, reversed-phase flash chromatography increases, so does the frequency that I get asked this question, "How do I determine loading capacity in reversed-phase flash chromatography?"

In the world of HPLC, loading capacity isn’t normally a concern as it is primarily an analytical technique.  In the synthetic organic chemistry world, most purification is performed with silica gel where flash column purification methods are developed and loading capacity estimated from TLC data.  However, when normal-phase flash does not work and reversed-phase flash is needed, the question of how to determine reversed-phase loading capacity comes up.

In a previous post I shared results of experiments where I evaluated selected organic solvents for sample dissolution and injection for reversed-phase flash purification.  I demonstrated that DMF and DMSO both are excellent solvents for this purpose and actually provide better chromatography than methanol, acetonitrile, and acetone.

Biotage®, a pioneer in Flash Purification, launched the unique, removable cap SNAP flash chromatography columns in 2007. This beneficial column design feature continues with the newest Biotage flash columns named Sfär columns.

Various flash chromatography sample loading options are available including liquid and dry loading. Choosing the right technique is important because your sample loading choices (sample solvent and dry load sorbent), can have a major impact on the results.

In this post, I compare the two techniques and show the benefits dry loading with a form of diatomaceous earth can bring to your purification.

On July 26th, 2018, Bob Bickler, Senior Technical Specialist, recorded a webinar on A Roadmap to Successful Flash Chromatography. To learn more, read the description below as well as watch the recording!