When to choose dry loading or liquid loading method of Flash Cartridge?

Flash cartridge has become one of the most commonly used tools for purification of crude natural products or purification of organic synthesis reaction systems. When you have an in-depth understanding of the purification method of the Flash cartridge, you will find that the loading method of the sample is one of the important factors affecting the separation effect.

In flash chromatography, samples can be loaded in two different ways: solid or liquidLiquid loading is the process of dissolving the sample in a solvent and injecting it directly into the Flash cartridge. Dry loading involves placing a solid homogeneous mixture of crude sample and support material (eg, silica gel) in front of a Flash cartridge.

How do we choose the right sample loading method?

When the sample volume is small in a single injection and is easily dissolved in the mobile phase, we usually choose the liquid loading method. The main factors to consider when using liquid loading are:

Solubility of compound in initial solvent: The sample needs to be completely dissolved.
Polarity of dissolving solvent: Usually, normal phase columns use weakly polar solvents, and reverse phase columns use polar solvents.
Volume of sample solvent: The ideal sample volume should not exceed 10% of the Flash cartridge volume.
Sample volume: Each column has a specified load volume. The ideal sample volume should not exceed the maximum loading volume of the Flash cartridge.

Then when we encounter a large amount of sample injected, or to separate viscous or multi-impurity samples that are difficult to dissolve, we need to consider using dry loading. Dry loading is typically accomplished through the following steps:

  • Dissolve the crude sample in a suitable solvent.
  • The mixture was then sonicated in an ultrasonic bath for several minutes to increase solubility.
  • The mixture was filtered to remove material that had not completely dissolved.
  • Silica gel was added to the above mixture at 2-3 times the weight of the crude sample.
  • The solvent was completely evaporated to dryness under reduced pressure by means of a rotary evaporator.
  • Finally, the mixture of crude sample and silica gel is loaded into a solid loader or empty column tube, which is then mounted on top of the Flash cartridge. Connect the solvent elution flow path.
  • The components to be separated are continuously eluted from the solid loader into the actual separation Flash cartridge.

Dry loading can effectively reduce tailing during purification, especially for samples with low solubility in elution systems or other weakly polar solvents, narrow color bands and peak shapes can be obtained. And when the sample is evenly spread when loading, the sample color band will also be flat as it descends.

Although liquid loading is simple and convenient, and dry loading is relatively cumbersome, when you encounter unsatisfactory sample peak shapes, dry loading can often improve column efficiency and sample purity.

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