Most often the question on loading is “how much can I purify” on a specific column size but once in a while I get the question above – what is the smallest amount I can purify? This is an interesting question, especially since flash chromatography is preparative chromatography technique used to purify large amounts of crude mixtures.
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Organic chemistry can be messy with not only the desired compound created but also myriad by-products. As synthetic chemists, our goal is to make these desired compounds in sufficient yield and purity to either create another compound or submit for evaluation by other departments. To purify these reaction mixtures, flash chromatography is the primary technique.
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For many years I have been publishing a blog on flash chromatography, especially related to its theory and application. It dawned on me today that one area I have not yet addressed is the impact of the flash system’s internal plumbing volume on a programmed gradient, so, here it is.
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Chromatography is as much an art as it is a science. Between synthetic reaction products and natural products, the range of compounds requiring separation, purification, and isolation is broad and diverse creating challenges from time to time. Because of this diversity, not all chromatographic separations can be performed with a “neutral” solvent system – one without added pH modifiers or buffers.
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Flash chromatography gradients need to provide as good of a separation between the target compound at its closest eluting by-products as possible in order to maximize product purity and load. Many chemists create methods based on a history with a compound class, knowing what has worked in the past. If no history with a synthetic compound class exists, then methods need developing.
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Most chemists I meet utilizing flash chromatography use linear gradients. These gradients are either very generic (X% to Y% over a certain time or volume) or can be complex with multiple slope changes and even isocratic holds. These complex gradients are often created during a purification to get the desired separation because the generic gradient does not provide enough separation for the target compound needing purification.
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Reversed-phase flash chromatography is extremely useful when purifying all types of compounds. Compounds that are charged or ionizable, however, typically need either a pH modifier (acid or base) or a buffer to better control compound retention, peak shape, and selectivity.
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I often get questions from customers about the influence of flow rate on their flash chromatography. Typically, the questions are…
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Well, it’s spring as I write this, my favorite time of year, and the foliage is in various stages of bloom. I like the rebirth of nature and the floral aromas that emanate from the blooms. These botanical aromas are the result of the various terpenes and terpenoids in the plant which can be very different between species.
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Automated flash chromatography has become an integral component of the workflows of both synthetic organic chemistry and natural product research. The most utilized chromatographic technique is normal-phase, which uses a polar stationary phase filled column (i.e. silica) and a mix of non-polar and moderately polar solvents, i.e. hexane or heptane and ethyl acetate (EtOAc), resp.
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Ensuring that the product of a reaction is pure is critical to that compound’s viability as a marketable entity. Impurities often require characterization if they are in excess of regulated limits. The isolation of these compounds can be quite challenging.
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Ever experience the problem where you load your dissolved sample into a flash column via a syringe only to encounter either resistance or “blowback”? Blowback is a term describing the situation where your sample does not stay in the column but flows back out of the column’s cap after the loading syringe is removed.
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Flash chromatography can be complex. Solvent choice, column size, stationary phase, loading technique, gradient method, flow rate, and detection parameters are all variables which factor into flash chromatography and your success with this purification technique. Of these variables, detection parameters, i.e. the type of detector, can really impact your flash chromatography results.
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For many labs on a tight budget, keeping expenses at a minimum is crucial. Many of these same labs are also required to become more sustainable, or greener, by reducing the amount of organic solvent they use. Reducing solvent also reduces expenses, but what is the impact on lab productivity?
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A fairly common question I receive is "how much of my reaction mixture can I load on my flash chromatography column?". To this question there is not a cut and dry answer because of a number of variables which influence the outcome. To help illustrate this, I will show in this post the results of a study I performed in my lab with one of my reaction mixtures.
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Gradient or isocratic elution, that is the question. Within flash chromatography these are the options afforded to separate reaction mixtures and natural product extracts and is the focus of this post.
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