Capillary-channeled polymer (C-CP) fibers as a stationary phase in microbore high-performance liquid chromatography columns

Microbore columns utilizing polypropylene capillary-channeled polymer (C-CP) fibers as the stationary phase in high-performance liquid chromatography (HPLC) have been investigated. The polypropylene C-CP fiber diameter is ∼50 μm, with eight channels along the periphery of the fiber ranging in diameter from ∼12 to 35 μm. The polypropylene C-CP fibers were packed into fluorinated ethylene propylene (FEP) tubing, 1.3 mm inner diameter, with lengths of 500, 750, and 1,000 mm, to examine the effects of increased column length with regards to plate height, resolution and analysis time. The low backpressures characteristic of the C-CP fiber stationary phases allow the length of the column to be increased without significantly decreasing the specific permeability. The high specific permeability (∼5×10⁻⁸ cm²) of the C-CP packed microbore columns yields a relatively low backpressure of 2.35 MPa at the highest flow rate of 17 μL/s (54 mm/s) for a 1,000 mm column. Radial compression of the soft-walled FEP tubing is accomplished by pulling the 1.7 mm o.d. column through a 1.4 mm diameter orifice. Reducing the inner diameter of the column from 1.3 to 1.0 mm lowered the interstitial fraction from 47% to 42%, decreased the A-term contributions to band broadening, resulted in a significant decrease in average plate height (∼30%), and increased resolution (∼36%) at identical linear velocities. Although the lower void volume of the radially compressed column increased the backpressure from 0.57 to 2.11 MPa at a linear velocity of ∼20 mm/s, the specific permeability only decreased from ∼7×10⁻⁸ to 4×10⁻⁸ cm².