Experimental evaluation of chromatographic performance of capillary and microfluidic columns with linear or curved channels.

We prepared 0.3 or 0.15mm i.d. columns from both fused silica capillaries and planar titanium wafers with machined grooves. Both types of devices were packed with sub-two micron C18 sorbent. Chromatographic efficiency and peak capacity were tested using LC instruments with low extra column dispersion (300nL2 or 30nL2 for 0.3 or 0.15mm i.d. columns, respectively). Micro column testing in gradient mode was less affected by extra column (pre-column) dispersion. To exploit this feature we developed a method for estimation of column efficiency from gradient analysis using the theoretical relationship (Pc-1)=N0.5×const. The validity of this relationship was experimentally verified using 2.1mm i.d. and 0.3mm i.d. columns. The (Pc-1) versus N relationship was experimentally determined with straight columns, which in turn was employed for the estimation of microfluidic column efficiency. Microfluidic devices with serpentine channels exhibited lower isocratic efficiency than straight capillary columns, but the loss of peak capacity was less significant. The loss chromatographic efficiency due to zone dispersion in serpentine microfluidic channels was more apparent for 0.3 than 0.15mm i.d. devices. Gradient performance of 0.15×100mm microfluidic columns was comparable to state-of-the-art 2.1×100mm columns packed with the same sorbent.