Band broadening frictional heat

The most common HPLC column diameter is 4.6 mm. There is a trend toward narrower columns (2 mm, 1 mm, and capillary columns down to 25 pm) for several reasons. Narrow columns are more compatible with mass spectrometers, which require low solvent flow. Narrow columns require less sample and produce less waste. Heat generated by friction of solvent flow inside the column is more easily dissipated from a narrow column to maintain isothermal conditions. Instruments must be specially designed to accommodate column diameters <2 mm or else band broadening outside the column becomes significant. 

The temperature gradient also affects the analyte diffusivity and retention on the column. Thus, both diffusivity and retention factors are a function of pressure and temperature. Frictional heating can cause a nonuniform increase or radial gradient in temperature inside a column, which can have a detrimental effect on the separation, resulting in band-broadening and poor peak shape (40,41). 

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