High-performance liquid chromatography with contactless conductivity detection for the determination of peptides and proteins using a monolithic capillary column

Gradient programs were applied to the determination of peptides and proteins in HPLC with contactless conductivity detection. A monolithic capillary column was used for the fast and sensitive determination of the biochemical species in acidic mobile phases consisting of acetic acid or trifluoroacetic acid in various concentrations of acetonitrile in water. The drift in baseline, which is caused by conductivity changes during the elution program, was minimized by careful optimization of the composition of the mobile phase and remaining drift was removed by computational baseline normalization. The flow rate from a conventional HPLC pump was reduced to a flow rate suitable for capillary systems using a pre-column flow splitter and a final total flow rate of 1.65 μl/min was used for all capillary HPLC separations. The contactless conductivity detector was positioned directly on the outlet capillary of the separation column and positively charged peptides and proteins were determined as sharp and symmetrical peaks. Detection limits in a concentration range from 3.7 × 10−8 to 5.1 × 10−7 M and a reproducibility of peak areas and peak heights between 2.3% and 7.3% were achieved for all biochemical species tested.