An interesting question for synthesis chemists as the need for reversed-phase flash chromatography for both intermediates and final compounds increases. Historically, normal-phase flash chromatography has been the “go-to” purification tool for synthetic intermediates. Today, however, intermediates and final products are increasingly polar. These polar reaction mixtures cause purification challenges in both separation and recovery with normal-phase (silica) thus requiring use of reversed-phase flash chromatography.
Over the course of my career, I have had terrific interactions with a multitude of chemists discussing chromatography. When it comes to flash chromatography the approaches from these chemists ranged from running generic 0-100% ethyl acetate in hexane gradients to modeled gradients based on tribal knowledge for a type of synthetic molecule to always using TLC for method development to prep HPLC. Each of these techniques are used because they provide some level of success. To me, though, if I spend time and resources synthesizing a highly valuable and unique molecule, then I want to purify the reaction mixture with the best possible method.
The term “Green Chemistry” has become a major part of the science community’s lexicon. When I think about green chemistry and its relationship to flash column chromatography I think of two specific areas where it applies...
Applying green chemistry principals to flash purification is becoming increasingly important. In this post, I discuss ways to make flash column chromatography greener by reducing solvent use through optimization of gradient shape.
This is a follow-on to my earlier post where I presented some greener alternatives to DCM as a solvent in flash column chromatography.
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.
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.
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.
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.
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.
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).
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.
In this post I will talk about a third alternative technique – using an in-line mass detector.
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.
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.
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.
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.