Fast analysis of proteins by isoelectric focusing performed in capillary array detected with concentration gradient imaging system.

Isoelectric focusing of several protein samples is performed simultaneously in an array of 2-4 short capillaries (4-10 cm long). The separated proteins are detected by either an on-line concentration gradient imaging detection system, or a single point concentration gradient detector which requires a mobilization step following the focusing process. The application of the capillary array increases the throughput of the capillary isoelectric focusing (CIEF) technique, and makes the technique comparable in sample throughput to the gel slab isoelectric focusing technique, but with much faster speed of separation and quantitation. The analysis is completed in 2-3 min with the imaging detection system, which is about 100 times faster than the conventional gel slab isoelectric focusing and 10 times faster compared to conventional CIEF. The resolution of the separation is 0.02 pH units or better. All separated proteins in the capillary array are detected by the universal concentration gradient detector, which eliminates the need for sample derivatization. The concentration limit of detection for the inexpensive instrument described in this work is about 30 micrograms/mL and can be reduced by using higher quality components in the system, such as a more stable laser, higher optical quality capillaries and a faster computer A/D board. The sample consumption is 400 nL for the 4 cm long, 100 microns ID square capillary. The isoelectric point (pI) values of the samples can be directly determined without internal pI markers from their positions inside the capillary after focusing when the imaging detection system is used.