After Getting the Sample, How do Choose Flash Column?

Column chromatography is found important in the labs due to its factors of easy packing procedure, low pressure of operation, and low costs as well. Depending on the way that the solvent flows down the column, we can find two different kinds of column chromatography: one is gravity column chromatography when the solvent flows down the column by gravity, and the other is flash column chromatography (such as Empty Chromatography Columns, Spherical Phenyl Flash Column) when the solvent is pushed down the column by positive air pressure.

In traditional column chromatography, we place a sample that is going to be purified or separated on the top of the column which contains silica gel or other solid support. After the column is filled with the solvent which runs through the solid support by gravity, the various components of the solvent will go through the column at a different speed. And we can collect them separately as we find them at the bottom of the Flash column.

Compared with gravity column chromatography, flash column chromatography is basically an air-pressure-driven hybrid of medium pressure which can speed up the flow of solvent and save the time of sample purifying in flash chromatography. Usually, it takes less than 10-15 minutes to make the column and run the separation.

spherical c18 flash column chromatography empty flash column chromatography

By using the injection formula, i.e. J = Z x 0.208% x n

1) the injection quantity is represented by J, Z is the silica gel filling quantity;
2) the difference of ORF is proposed to be accurate to 0.01, then the difference of 0.01 is set to 1 unit, which is represented by N;
3) the injection coefficient is 0.208%, which is based on the silica gel with 40-60UM particle size and 60A pore diameter, under the specific pressure condition and ideal flow rate, the ideal injection quantity is calculated Sample coefficient. Considering the factors such as uneven sample loading and large operation error in actual use, 0.2% is used instead, which is closer to reality.

For example, how many samples can be separated by the 80g column in the following conditions? If the thin layer data: RF1 = 0.19, RF2 = 0.33, then n = (0.33-0.19) + 0.01 = 14, according to the formula, j = 80 x 0.2% x 14 = 2.24g, then according to the thin layer data, the maximum injection quantity of 80g column is 2.24g.

For another example, the thin layer data: how many samples can a column with RF1 = 0.25, RF2 = 0.21120g be divided into? N = (0.25-0.21) – 0.01 = 4, injection volume J = 120 x 0.2% x 4 = 0.96g.

It is not difficult to see that the smaller the ORF difference, the less the injection volume. In the process of the experiment, we can choose which kind of column to use according to the separation degree (ORF difference) of the target and impurity. Therefore, the injection formula can be optimized as J = zx0.2xorf, that is injection amount = silica gel amount (actual grams) x0.2xrf difference.

In addition, choosing the right flash column for chromatography depends on several factors, including the sample size, the type of compound you want to separate, the expected purity level, and the available equipment. Here are some steps to help you select the appropriate flash column:

  1. Determine the sample size: Estimate the amount of material you want to purify or separate. Flash columns come in various sizes, typically ranging from a few grams to several hundred grams or even kilograms. Select a column size that accommodates your sample size comfortably.
  2. Consider the compound properties: The polarity, molecular weight, and other chemical characteristics of your compounds will influence the choice of the stationary phase. Flash columns are typically packed with silica gel, reversed-phase material (C18), or other specific adsorbents. Polar compounds are better separated on normal-phase silica, while non-polar or hydrophobic compounds may require reversed-phase columns.
  3. Set your target purity and resolution: Determine the level of purity you want to achieve. If your target compounds have similar properties or are challenging to separate, you may need a higher-resolution column or consider using a gradient elution to improve separation.
  4. Check the flow rate: Different flash columns have varying flow rates recommended by the manufacturer. Ensure that your system’s flow rate matches the specifications of the column you plan to use.
  5. Column length and diameter: Longer columns generally provide better resolution but may require higher pressures to operate. Consider the available pressure capabilities of your flash chromatography system before choosing the column length. The diameter of the column also affects the flow rate and resolution.
  6. Column compatibility: Verify that the flash column is compatible with your flash chromatography system. The column fittings and dimensions should match those of your instrument to ensure a proper fit.
  7. Budget considerations: Flash columns come at different price points. Choose a column that fits your budget and provides the desired performance for your separation needs.
  8. Brand and reputation: Consider the reputation and reliability of the column manufacturer. Well-established brands with a good track record of producing high-quality chromatography products are generally a safer choice.

Remember to consult the manufacturer’s guidelines and technical specifications for each column you are considering. Proper column selection is crucial for obtaining efficient and reproducible results in flash column chromatography.