Quantitative trace analysis of interleukin‐3, interleukin‐6, and basic model proteins using isotachophoresis‐capillary zone electrophoresis with hydrodynamic counterflow

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Abstract
A quantitative analytical technique to determine trace concentrations of recombinant human interleukin‐3 (rhIL‐3), recombinant human IL‐6 (rhIL‐6), and various basic model proteins is described using isotachophoresis‐capillary zone electrophoresis (ITP‐CZE). Proteins were separated on coated fusedsilica capillaries using a commercial capillary electrophoretic system modified for the application of isotachophoretic preconcentration with hydrodynamic counterflow. The effect of injection time and isotachophoretic focusing time was investigated and compared with predictions from existing mathematical models. Good linearity of the calibration graphs (r > 0.995) was observed for all investigated proteins. The limit of quantification was in the 10−8M range using UV detection at 200 nm. Within‐day and between‐day precison of peak area ranged between 1 and 6%. Precision was unaffected by isotachophoretic preconcentration. In conclusion, the described method is feasible to quantify trace concentrations of rhIL‐3, rhIL‐6, and basic proteins. Potential applications comprise issues of pharmaceutical quality control.