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...
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.
A baseline that rises or drops when using flash chromatography with a UV detector can be a problem, especially if you are trying to collect compounds with poor detectability or that exist in low quantities.
In this post I will talk about the causes and solutions for a rising (or even dropping) baseline.
With most chromatographic purifications, only two solvents are needed to adequately separate compounds from each other. Unfortunately, there are instances where the separation is either poor or cannot be accomplished with “normal” elution conditions such as those with ionic or very polar organic molecules.
In this post I offer some solutions to this issue.
Flash chromatography is a standard part of an organic chemist’s workflow. It is utilized after most reaction steps in order to remove most of the generated by-products and excess reagents.
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.
Recently, I posted an article explaining why high performance TLC plates are not needed for method development for high-performance flash chromatography. Based on some excellent feedback, I see a need to discuss silica chemistry and its impact on chromatography.
The challenges organic, medicinal, and natural product chemists face are many: from designing reactions, to optimizing synthesis, work-up / extraction, and purification / isolation of the desired compound or compounds. Among those issues related to purification / isolation is the common problem of separating compounds with similar chemistry that either co-elute or separate poorly.
In this post I will discuss some tips on how to "resolve" this issue (yes, pun intended).
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.
For most organic reaction mixture purifications the process is fairly straightforward. Use hexane/ethyl acetate or, for polar compounds, DCM/MeOH. But what do you do if this doesn't work and your compounds are basic organic amines?
In this post, I re-examine the options available to achieve an acceptable organic amine purification when typical separation methods are insufficient.
There are many factors which influence successful flash column chromatography. One of those factors is sample load, which itself is influenced by things like selectivity, efficiency, dissolution solvent, and load technique. Several of these factors I have addressed in previous posts. Of these, selectivity and efficiency are specific to a media's physical and chemical characteristics.
In this post I will show if particle size and/or particle shape can influence loading capacity. Additionally, I will show the positive impact that surface area has on flash column chromatography purification.
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.
slash column chromatography has been practiced by chemists since the 1970s. That practice requires the silica in the column be properly wetted to remove trapped gasses and ensure uniform flow (remember those days of not letting air into the column?). Today, with automated flash chromatography systems and pre-packed columns as the norm, chemists ask me – do I really need to pre-equilibrate my column?
In this post I explore the impact on chromatography that equilibration, and lack thereof, has on separation performance.
Plate count is a theoretical number describing the separation efficiency of a chromatography column. In short, it is a measure an eluting compound's bandwidth at the time it elutes from a column, Equation 1.
For chemists needing to purify natural product extracts or synthesis reaction mixtures flash chromatography is typically the tool of choice. In previous posts I have discussed various ways to optimize the purification to obtain the highest purity compounds with maximum load in minimal time.
Sometimes, though, chemistry gets in the way in the form of solubility issues. When this happens most often dry loading is recommended for these sample types. In this post I will show the impact various dry load sorbent options have on chromatography.
One of the more challenging purifications is that of water-soluble, ionizable compounds. Typically, normal-phase with silica is not used because of the probable non-reversible interactions, especially between the ionized amines interacting and the ionizable silanols. With normal-phase out of the purification solution that leaves ion exchange and reversed-phase as chromatographic options.
In this post I will discuss the use of reversed-phase and the influence pH and buffers have on the chromatography of some ionic, water soluble compounds.