In a previous post I talked about column size, specifically long-thin versus short-fat and the impact of the cartridge’s dimensions on purification performance. With that comparison I showed that in preparative chromatography, purification efficiency is more about the amount of silica than column dimensions. Cartridges of different dimensions containing the same amount of the same media will provide the same separation efficiency.
But there are other chromatographic aspects where size can impact performance. In this post I will focus on some areas where size does matter – media particle size and media surface area.
Continue reading Does Size Really Matter in Flash Chromatography? Part 2
Yes, the title is a bit salacious but it got your attention, didn’t it? I believe this is a topic worthy of discussion as it relates to flash chromatography for purification because many chemists believe longer but thinner columns perform better than short, wide columns. The facts of the matter may surprise you.
In this post I discuss the impact that cartridge dimensions have on purification performed using flash purification.
Continue reading Does size really matter in flash chromatography? Part 1
Varying the concentrations of mobile phase solvents during flash purification chromatography enhances the ability of the technique to effectively isolate the desired compound from reaction byproducts and unconsumed reagents. Choosing how these concentrations will be varied over time has a significant effect on the purity and recovery of desired compounds.
What is the best starting strong solvent %? What is the ending strong solvent %? Should the mobile-phase concentrations vary gradually in a linear manner or should they vary step-wise or something else altogether? Most separations are performed once, occasionally a handful of times. Because of this, spending effort optimizing a gradient is just not very productive unless there are aids in choosing the gradient profile that provides an effective purification with minimum effort.
Software in flash chromatography instruments, makes it simple to create a gradient. Now, what should that gradient look like?
In this post I compare isocratic, step, and linear gradients and provide some sage advice on choosing among them.
Continue reading How to choose between linear gradients and step gradients for flash chromatography
For most organic and medicinal chemists flash chromatography is just another step in the synthesis work flow – react, analyze, purify, react, analyze, purify… until the final product is made. The desired product of each reaction, and the mixture of other species present are, of course, different with each cycle. Separating the desired compound efficiently without a lot of hassle is something I have written about in this post as well as in others in this series.
In this post, I’ve written about how that TLC (thin layer chromatography) plate you use for monitoring your reaction can be used to create reliable, efficient, effective gradients.
Continue reading How do I create an efficient gradient flash chromatography method?
In all my years of working with medicinal and organic chemists, I have found that choosing how many grams of silica to use for purification by flash chromatography is something frequently guessed at. Getting the size of the column right is awfully important because using too few grams of silica will doom your purification to failure and using more an optimal mass of the stationary phase means the purification consumes excess silica, solvents, and a chemist’s time. To determine the optimal amount of silica for a purification, I rely on a factor called ΔCV (delta Column Volume) to identify the best loading capacity on any cartridge. I have also found that ΔCV this is a better loading capacity predictor for flash purification than ΔRf.
Continue reading How do I Choose the Right Column Size for Purification by Flash Chromatography?
Up to six compounds can be easily separated with an automated step-gradient optimizer embedded in modern flash chromatography systems.
Continue reading The Step Gradient Explained
For many chemists lab budgets, especially for consumable items, are limited. One way of trying to stretch their lab budget is to reuse disposable flash chromatography cartridges.
In this post I will show how regardless of the cartridge brand used, repeated use of silica flash cartridges results in loss of compound resolution and fraction purity.
Continue reading Why Reusing Flash Cartridges is Bad Science