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When should I use a “high-performance" flash chromatography column?

December 29, 2020 at 5:00 PM / by Bob Bickler


The evolution of flash column chromatography has brought chemists many new and exciting options for crude mixture purification. Among them are so-called high-performance flash columns or cartridges.  These high-performance purification tools are typically filled with silica or other media 15 to 30 microns in particle diameter (versus 40-63 micron for standard flash media) and provide the expectation of better separations and higher purity fractions.  That’s really enticing but how often do you need these types of columns especially since they are, of course, more expensive?  Well, that question is what I address below.

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Why is TLC Rf important for flash column chromatography optimization?

December 28, 2020 at 4:10 PM / by Bob Bickler


Many chemists I talk to understand that TLC data is useful for flash chromatography method development. Most also know that they should try to get their target compound to elute with an Rf between 0.15 and 0.4 by adjusting TLC solvent strength. Have you ever wondered why this is important and how Rf values impact flash chromatography results?

In this post I will explain the relationship between TLC Rf and flash elution volumes (CV) and why having your target compound elute in the Rf range is needed.

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Why does my silica flash chromatography column get hot?

December 23, 2020 at 3:16 PM / by Bob Bickler


Silica is the most commonly used sorbent for flash column chromatography. When solvent is pumped through a column packed with dry silica you may notice it gets warm and sometimes down right hot!

In this post I will attempt to explain why this phenomena occurs.

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Which sample solvents work best with normal-phase flash column chromatography?

December 22, 2020 at 4:15 PM / by Bob Bickler


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.

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What impact do buffers have on APCI mass detection?

December 18, 2020 at 1:08 PM / by Bob Bickler


APCI (atmospheric pressure chemical ionization) and ESI (electrospray ionization) are the two most frequently utilized mass detection tools for automated flash chromatography.  In a previous post, I discussed differences between the two detectors and the compound types best suited for each source.

Because these two sources ionize differently, there are cases when additives are needed in the make-up solvent and cases when they should not.  In this post, I will show the impact that adding a buffer or acid has on APCI detection.

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Using adducts and fragments to identify compounds in mass-directed flash chromatography

December 17, 2020 at 11:57 PM / by Bob Bickler


Over the past several years, automated flash chromatography has evolved to include in-line mass detection.  Typically, these single-quadrupole mass detectors are outfitted with either an atmospheric pressure chemical ionization source (APCI) or an electrospray chemical ionization source (ESI). 

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Why Reusing Flash Cartridges is Bad Science

December 14, 2020 at 10:08 AM / by Bob Bickler


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.

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In-line mass detection to find the undetectable in flash column chromatography

December 11, 2020 at 2:04 PM / by Bob Bickler


In previous posts I have discussed some options and techniques to improve detection of poorly absorbing or UV-transparent compounds – by wavelength focusing and by evaporative light-scattering (ELS).

In this post I will talk about a third alternative technique – using an in-line mass detector.

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Using pH to optimize reversed-phase flash chromatography separations

December 8, 2020 at 8:51 PM / by Bob Bickler


I have previously posted on the topic of normal-phase optimization by evaluating different solvent blends or mixtures. I have also touched on reversed-phase method development as well suggesting chemists use HPLC to optimize their purification.

In this post, I will look at the impact modifying mobile phase pH can have on reversed-phase separations.

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Does mass detection make-up solvent choice matter?

December 7, 2020 at 4:18 PM / by Bob Bickler


An interesting question, at least to me. Depending on the detector brand, some mass spectrometer manufacturers recommend acetonitrile while others recommend methanol. Is there a real difference between these solvents?

In this post I look at how acetonitrile and methanol compare when used with an APCI source.

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Can reversed-phase flash column chromatography be greener?

December 3, 2020 at 7:24 PM / by Bob Bickler


In previous posts I offered some suggestions to improve the “greenness” of normal-phase flash purification.  As the use of reversed-phase flash purification has increased the past few years I thought I would explore how to potentially make it greener too.

So, with that in mind, let's take a look at the use of acetone in place of acetonitrile as a reversed-phase flash chromatography solvent.

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Detecting the undetectable in flash column chromatography, part 2

December 1, 2020 at 2:19 PM / by Bob Bickler


Compound detection challenges are, for many chemists, a part of life. In a previous post I discussed how wavelength focusing can help your flash system detect and fractionate compounds with poor chromophores. However, compounds naked to UV-Vis light,  such as carbohydrates, are impossible to detect by UV when separating by liquid chromatography.

There are some alternatives, however, and in this post I will discuss the application of evaporative light scattering detection (ELSD) to flash purification.

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