GIT&T: Micro-LC Capillaries

Choosing the Correct Inner Diameter

  • Fig. 1: Separation of a mixture on a 300 μm ID column and an Eksigent ExpressLC ultra-system with  a) Capillary-ID: 25 μm, b) Capillary-ID: 50 μm, c) Capillary-ID: 100 μm and d) Capillary-ID: 100 μm.  (©Terence Hetzel IUTA)
  • Equation1_G.I.TNT

Thorsten Teutenberg1, Terence Hetzel1, Denise Loeker1, Juri Leonhardt1

Typically, columns with an inner diameter of 300 µm are used for micro-LC applications. To achieve high separation performance the inner diameter of the capillary has to be in optimal alignment with the column.

In principle - the smaller the capillary’s inner diameter, the lower the influence of the resulting extra-column volume on the separation performance. However, consideration should be given to the fact that the back pressure is inversely proportional to the fourth power of the radius as can be seen from equation 1:

(see equation 1)

Reducing the inner diameter can therefore have a dramatic effect on the overall system pressure. Before assembling the system, one needs to investigate the influence that the capillary connection will have on the separation performance. Figure 1 shows a separation using a 5 cm long column with an inner diameter of 300 µm. Only a very low loss in separation efficiency is observed when the capillary with an ID of 25 µm is exchanged for one with an ID of 50 µm. However, if the ID is increased to 100 µm or even 250 µm (data not shown), the separation efficiency is affected dramatically, as can be seen by the peak width and signal intensity. As a result, it is recommended to use 50 µm ID capillaries for the connection of 300 µm ID columns. When compared to 25 µm ID capillaries, the decrease in separation performance is negligible but the back pressure is reduced significantly.

1 Institut für Energie- und Umwelttechnik e. V. (IUTA), Duisburg, Germany

Do you have problems with micro- or 2D-LC? Ask the experts at:


Dr. Thorsten Teutenberg

Institut für Energie- und Umwelttechnik e. V. (IUTA)

Department Head Research Analysis

Duisburg, Germany





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