Dependence of thermal mismatch broadening on column diameter in high-speed liquid chromatography at elevated temperatures

In this paper, we compare a narrow-bore column (2.1-mm i.d.) to a conventional-bore column (4.6 mm i.d.) at elevated temperatures under conditions where thermal mismatch broadening is serious and show that narrow-bore columns offer significant advantages in terms of efficiency and peak shape at higher linear velocities. We conclude that the so-called thermal mismatch broadening effect is largely due to a radial retention factor gradient and not a radial viscosity gradient. The lower volumetric flow rates inherent with the use of narrower columns lead to lower linear velocity in the heater tubing and longer eluent residence times in the heater. Thus, with the same heater tubing at the same column linear velocity, narrow-bore columns give better thermal equilibration between the eluent and the column compared to wider bore columns. This means that high-temperature, ultrafast liquid chromatography no longer requires excessively long preheater tubing to thermally equilibrate the eluent to the column temperatu...