Column Dimensions and Materials

During the initial years of HPLC, the most common internal diameter of conventional analytical columns was 2 mm, except for columns for size exclusion chromatography that often used to be 7-8 mm. Soon, the standard inner diameter changed to 4.6 mm, the standard length was reduced from 60 to 15-25 cm, and the particle size of the column packing materials was reduced from 40-50 to 5-10 pm. The dimensions of the columns were initially related to the commercial availability of stainless steel tubing. Today, the internal diameters of conventional HPLC columns and microbore HPLC columns are in the range of 2-5 and 0.5-1 mm, respectively. Capillary columns typically have 0.1-0.5 mm ID and nanoflow columns have 0.1 mm ID (Table 3.1). 

Smaller internal diameters give more concentrated bands (less dilution). If there is a limitation on the available amount of sample, smaller ID columns wUl improve the detection limit with concentration-sensitive detectors. Typical concentration-sensitive detectors are UV, fluorescence, and electrospray ionization mass spectrometers (ESI-MSs). 

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