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.
Up to six compounds can be easily separated with an automated step-gradient optimizer embedded in modern flash chromatography systems.
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.
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.
Split peaks? Multiple peaks? Are they really a problem? What causes the issue?
In this post I will discuss what split peaks are and what to do to fix the problem.
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.
The newly released Biotage® Selekt flash chromatography instrument can be run at a maximum flow-rate of 300 mL/min or a maximum pressure of 30 bar. These high flowrates and pressures enable a user to perform chromatography using not only dry-packed, single-use plastic flash columns containing small (≥20 μm) spherical silica particles, but also semi-preparative, slurry-packed
HPLC columns for multiple use with smaller (≤20 μm) spherical silica particles.
When Isolera™ was launched, the maximum system pressure that could be reached was 10 bars, but reaching that pressure was a challenge since most of the Flash columns could not withstand the higher pressures. The maximum pressure rating for the Biotage® SNAP columns, for example, is limited to five or seven bars, depending on the size, and columns from most of manufacturers have the same limitation.
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.
In this post I will delve into six key factors that impact your purification success in flash column chromatography.
Previously, I have discussed the use of TLC for solvent scouting and method development and optimization. I have have also talked about cartridge size, particle size, and surface area and their impact on flash purification. Here I integrate that information into the six factors below.
Many chemists today find they need to synthesize molecules at higher temperatures in order to force difficult reactions to proceed. Solvents such as DMF, DMSO, and NMP are commonly used in these reactions as they facilitate the use of the high reaction temperatures. However, the same attributes that make these chemicals attractive as reaction solvents make compound recovery from them very difficult, including flash column chromatography. These high boiling solvents are typically polar and pose a challenge if purification is to be accomplished with normal-phase silica.
Selectivity and solvent strength are the most important factors that determine success or failure of a chromatographic separation. These two independent dynamics apply to both normal- and reversed-phase chromatography and should be optimized, especially when high fraction purity is needed.
In this post I will discuss the impact that elution solvent choice has on both normal- and reversed-phase purification.
This question is one that is increasing in frequency. Over the past 10 or so years reversed-phase flash chromatography use has increased dramatically. Likewise, reversed-phase preparative HPLC (RP pHPLC) use has also increased. Chemists need to know when to choose between the speed and low solvent use of flash column chromatography and the ultimate purification of RP pHPLC. With this as the backdrop, let me give you my thoughts on how to choose between flash chromatography and when it is best to use RP pHPLC.
I have recently posted on how solvent choice influences the separation of hard to resolve compounds using normal-phase flash chromatography. As a chemist with an inquiring mind, I thought I would expand my research beyond normal-phase and see what happens in reversed-phase.
In this post, I share my results.