What Are Principles for Selecting Length and Inner Diameter of a FLASH Column?

Flash column components

The flash column is composed of a column tube, pressure cap, ferrule (sealing ring), sieve plate (filter), joints, screws, etc. When the pressure is not higher than 70Kg/cm2, thick-walled glass or quartz tube can also be used, and the inner wall of the tube requires a high degree of smoothness. In order to improve column efficiency and reduce tube wall effect, the inner wall of the stainless steel column is mostly polished.

Some stainless steel columns are also coated the inner wall with fluoroplastics to improve the smoothness. The effect is the same as that of polishing. There are also those using molten silicon or glass lining for thin tube columns. The column joints at both ends of the chromatographic column are equipped with sieve plates, which are sintered stainless steel or titanium alloy, with a pore size of 0.2-20um (5-10um), depending on the particle size of the filler, and the purpose is to prevent the filler from leaking. The inner diameter of the column is generally based on the column length, particle size, and the reduced flow rate, in order to avoid the wall effect.


1. Sample Size and Loading Capacity:

  • The loading capacity of the column is influenced by its size. For larger sample sizes, a longer and wider column is typically required to accommodate the sample without overloading the column. Consider the scale of your separation and the amount of sample you need to purify.

2. Resolution and Separation Efficiency:

  • Longer columns generally provide better resolution by allowing for more efficient separation of compounds. If the compounds in your mixture have similar properties, a longer column may be necessary to achieve satisfactory separation.

3. Particle Size and Packing Material:

  • The inner diameter of the column is related to the particle size of the packing material. Smaller particle sizes provide higher resolution but may result in higher backpressure. Consider the particle size of the stationary phase and choose an inner diameter that is compatible with the desired flow rate and pressure limits.

How to select the flash column’s length and inner diameter?


The longer the flash column, the higher the total column efficiency. 250-300mm is a common column length. More than half of the laboratory work uses this specification column, which is generally used to separate medium to complex mixtures of 10 to 50 components; For 500-600mm, it requires higher resolution, which is generally used to separate more than 50 components or complex samples containing difficult-to-separate materials for temperature-programming analysis.

Inner diameter

c8 chromatography flash column

The efficiency of the flash column is inversely proportional to the square of the column radius. The smaller the inner diameter, the higher the efficiency. However, the larger the inner diameter, the larger the column capacity and the more sample injection volume allowed. When the injection volume exceeds the flash column capacity, the true equilibrium cannot be established in each theoretical plate in the column, which will cause chromatographic bee distortion, lower column resolution, and poor reproducibility.

Therefore, for complex samples that require accurate separation, a small inner diameter column must be used. On the other hand, if there are compounds with very different concentrations in the sample, in order to increase the sample capacity, a column with a large inner diameter must be used.

General selection principle

Choose large-pore chromatographic columns for the analysis of large molecular weight compounds; for high pH or basic compounds, you need to choose high-end or special-end-capped chromatographic columns to improve peak shape and extend the service life of the column.

There is now a wide range of commercial flash columns. According to the parameters of the chromatographic column, we can provide us with a preliminary choice. However, due to the differences in the packing technology and bonding technology of each instrument manufacturer, even if they are all C18 flash columns, the same brand, and different series have different functions, such as those that can withstand low pH values, those that can withstand high temperatures and those that are suitable for alkaline samples. Therefore, before choosing a flash column, you must study the chromatographic column parameters carefully and read the chromatographic column instructions carefully to find a suitable column and a suitable separation method.

HAWACH provides customers with three series of flash columns, StarFlash, Flash, and DepuFlash. In StarFlash series, there are only silica gel columns, which are divided into two types: standard and advanced. Advanced silica has higher purity and better quality. Flash series is designed for the high-end market, while the DepuFlash series is more suitable for the mass market.