Welcome to the Biotage Flash Purification Blogs.

      How does solvent choice impact flash column chromatography performance?

      October 18, 2019 at 9:44 PM / by Bob Bickler posted in Developments, Flash Theory, User Tips

      3 Comments

      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.

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      How does solvent choice impact reversed-phase flash chromatography separations?

      October 4, 2019 at 6:30 PM / by Bob Bickler posted in cartridge, chromatography, Developments, flash column, Flash Theory, gradient, isolera, Mass Detection, normal phase, reversed-phase gradient, selectivity, SNAP cartridge, solvent strength, solvents, terpene, terpenoid, User Tips

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      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. 

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      How do I choose between Normal- or Reversed-phase flash column chromatography for my compound purification?

      October 4, 2019 at 6:25 PM / by Bob Bickler posted in Developments, normal phase, reversed-phase, solubility

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      How to choose between normal- and reversed-phase flash column chromatography is an excellent question and one that my readers often ask.  Those who use column chromatography know that as long as the reaction products or compounds are fairly non-polar and near neutral pH they will have successful purifications.  However, when your mixture's chemical characteristics are more challenging (polar, non-polar, basic, acidic) there are other options that are available to successfully separate pure compounds.

      In this post, I will discuss the criteria you can use to guide your choice between normal- or reversed-phase flash chromatography.

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      Acetone – a lower cost alternative to EtOAc in normal-phase flash column chromatography

      October 4, 2019 at 6:22 PM / by Bob Bickler posted in Developments, normal phase, acetone

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      Acetone, as you know, is a terrific solvent.  It dissolves many organic molecules, evaporates easily, is both water and organic soluble, and is cheap (relatively).  These attributes tell me it should be a good polar modifier for normal-phase flash chromatography.

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      When should I use dry loading instead of liquid loading with flash column chromatography?

      October 4, 2019 at 6:17 PM / by Bob Bickler posted in cartridge, Celite, chromatography, DCM, Developments, DMF, dry load, MAOS, microwave, polar, Samplet(R), silica, synthesis, workflow

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      Many microwave assisted organic synthesis (MAOS) reactions use polar solvents such as alcohols, DMF, DMSO, because they absorb and transfer microwave energy very efficiently.  However, the downside of using polar, microwave absorbing solvents is that they can interfere with normal-phase flash chromatography.

      In this post, I discuss why dry loading can be advantageous when purifying polar-solvated reaction mixtures.

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      Detecting the undetectable in flash column chromatography using wavelength focusing

      October 2, 2019 at 5:52 PM / by Bob Bickler posted in Developments

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      Sometimes it feels as if organic chemistry and chromatography are a mixture of art and science.  Maybe its because of the necessary creativity needed to address the variety of challenges that we face almost daily.  Frankly, its what I find most interesting about this world.

      One of the bigger challenges facing chemists is the ability to detect and collect compounds with little or no UV absorption during flash purification.  In this post I will talk about a technique that I have found to be quite useful when trying to purify mixtures containing one or more poor absorbers.

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      Setting the Right Flow Rate for Flash Column Chromatography

      July 10, 2019 at 3:16 PM / by Bob Bickler posted in Developments

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      How does flow rate impact my flash column chromatography separation?  This is the kind of question I frequently get.  After all, we all know that flow rates that are too high or too low can result in bad prep HPLC chromatography.  Well, this is not necessarily true in flash chromatography.

      In chromatography there are three inter-related variables which impact your separation and are represented on the  chromatographer’s triangle.

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      Which loading method should I use for purification by flash chromatography?

      July 10, 2019 at 3:14 PM / by Bob Bickler posted in Developments

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      Getting the most benefit from your crude sample purification with column chromatography or flash chromatography involves optimizing many variables.  In previous posts I have talked about selecting the best solvents, their ratios, and maximizing load based on TLC Rf data. These are all important chromatography-generated variables but now I would like to share some tips on actual technique differences and their impact on purification performance.

      In particular in this post I will focus on the benefits and drawbacks of liquid loading and dry loading.  Both have their place in liquid chromatography but when should one technique be used over another?

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      How do I determine loading capacity in reverse phase flash column chromatography?

      July 10, 2019 at 3:01 PM / by Bob Bickler posted in Developments, Flash Theory

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      As the popularity of prep-scale, reversed-phase flash chromatography increases, so does the frequency that I get asked this question, "How do I determine loading capacity in reversed-phase flash chromatography?"

      In the world of HPLC, loading capacity isn’t normally a concern as it is primarily an analytical technique.  In the synthetic organic chemistry world, most purification is performed with silica gel where flash column purification methods are developed and loading capacity estimated from TLC data.  However, when normal-phase flash does not work and reversed-phase flash is needed, the question of how to determine reversed-phase loading capacity comes up.

      In this post I will attempt to provide some guidelines to help you understand and determine reversed-phase flash chromatography loading capacity.

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      How do I develop a reversed-phase flash column chromatography method?

      July 10, 2019 at 2:53 PM / by Bob Bickler posted in Developments

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      Method transfer from reversed-phase TLC (thin layer chromatography) to reversed-phase flash column chromatography can be very challenging.  Because of this, I often recommend using HPLC for reversed-phase flash chromatography method development. This really is a straight-forward process if you start with the right HPLC column and know a little about your HPLC system's detector.

      In this post, I will share some tips on how to develop a reversed-phase flash purification method using HPLC.

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      How much DMF or DMSO can I inject on my reversed-phase flash chromatography column?

      June 13, 2019 at 5:05 PM / by Bob Bickler posted in Developments

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      In a previous post I shared results of experiments where I evaluated selected organic solvents for sample dissolution and injection for reversed-phase flash purification.  I demonstrated that DMF and DMSO both are excellent solvents for this purpose and actually provide better chromatography than methanol, acetonitrile, and acetone.

      In this post I report some surprising results from follow-on work evaluating the impact of increased injection volume using DMF and DMSO as the sample diluent/injection solvent.

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      How do I Choose the Right Column Size for Purification by Flash Chromatography?

      June 13, 2019 at 4:59 PM / by Bob Bickler posted in Developments, Flash Theory

      6 Comments

      In all my years of working with medicinal and organic chemists, I have found that choosing how many grams of silica to use for purification by flash chromatography is something frequently guessed at. Getting the size of the column right is awfully important because using too few grams of silica will doom your purification to failure and using more an optimal mass of the stationary phase means the purification  consumes excess silica, solvents, and a chemist's time. To determine the optimal amount of silica for a purification, I rely on a factor called ΔCV (delta Column Volume) to identify the best loading capacity on any cartridge. I have also found that ΔCV this is a better loading capacity predictor for flash purification than ΔRf.

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      Benefits of acetonitrile over methanol in normal-phase flash column chromatography

      June 13, 2019 at 4:57 PM / by Bob Bickler posted in Developments

      2 Comments

      When it comes to the purification of polar organic compounds many chemists turn to normal-phase flash chromatography with dichloromethane and methanol as the mobile phase. This solvent system often can be challenging to optimize due to methanol’s high polarity and protic chemistry.

      I have found that acetonitrile can often replace methanol as the polar modifier in DCM-based solvent systems.  In this post I will show an example where this is true.

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      Determining solvent strength in flash column chromatography

      May 7, 2019 at 5:23 PM / by Bob Bickler posted in Developments, selectivity, solvent strength

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      Recently, one of our readers wrote and asked how to determine solvent strength in normal-phase flash chromatography. This is an excellent question because solvent strength is one of several factors impacting flash chromatography performance.

      In this post I will explain how solvent strength can easily be determined.

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      How to Choose Between Linear Gradients and Step Gradients for Flash Chromatography

      April 12, 2019 at 12:51 PM / by Bob Bickler posted in Developments, efficiency, linear gradient, step-gradient

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      Varying the concentrations of mobile phase solvents during  flash purification chromatography enhances the ability of the technique to effectively isolate the desired compound from reaction by-products and unconsumed reagents.  Choosing how these concentrations will be varied over time has a significant effect on the purity and recovery of desired compounds.

      What is the best starting strong solvent %?   What is the ending strong solvent %?  Should the mobile phase concentrations vary gradually in a linear manner or should they vary step-wise or something else altogether?  Most separations are performed once, occasionally a handful of times.  Because of this, spending effort optimizing a gradient is just not very productive unless there are aids in choosing the gradient profile that provides an effective purification with minimum effort.

      Software in flash chromatography instruments, makes it simple to create a gradient.  Now, what should that gradient look like?

      In this post I compare isocratic, step, and linear gradients and provide some sage advice on choosing among them.

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      Does methanol really dissolve silica during flash column chromatography?

      April 9, 2019 at 11:23 PM / by Bob Bickler posted in Developments, methanol, dichloromethane, dissolve

      8 Comments

      This is an age-old question that has been around a long time, perhaps as long as me (and I have been around a while) –  “Does silica dissolve in methanol?”

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