Diode laser-based concentration gradient imaging detector for capillary isoelectric focusing

A diode laser-based, real-time, universal concentration gradient imaging detector was constructed and tested for capillary isoelectric focusing (CIEF). The detector indicates sample zones by measuring refractive index gradients created by the concentration gradients of samples. An imaging detection system is the best detection approach for CIEF because all samples are focused inside the capillary column after separation. A diode laser was found to be an ideal light source for the imaging detector because of its small size, low cost, and light beam characteristics. The detector can be operated at any wavelength and does not need a high-intensity light beam. In order to focus the non-circular, non-Gaussian diode laser beam through the capillary, the optical geometry of the imaging detector was optimized. Because of the short analysis time (2–4 min), good reproducibility for determining isoelectric points, and the universality of the detector, the CIEF-imaging detector system has many possible applications, such as analysis of human hemoglobin variants and peptide mapping. This is the first report of a diode laser-based imaging detection system for analytical chemistry.