SIMPLE LASER-INDUCED FLUORESCENCE DETECTOR FOR SULFORHODAMINE-101 IN A CAPILLARY ELECTROPHORESIS SYSTEM - DETECTION LIMITS OF 10 YOCTOMOLESOR 6 MOLECULES

High sensitivity fluorescence detection was generated for capillary el ectrophoresis based on a post-column sheath-flow cuvette. An inexpensi ve 8 mW He-Ne laser operating at 594 nm was used for excitation of Sul forhodamine 101. This dye, which is commonly used for both protein lab elling and deoxyribonucleic acid (DNA) analysis, has molar absorptivit y that is matched to the laser wavelength. Collection efficiency was d oubled compared with previous work by using two microscope objectives, one located on each side of the illuminated sample stream. A series o f injections of Sulforhodamine 101 was performed; the average detectio n limit (3 sigma) was 6 +/- 1 molecule of dye injected onto the capill ary. These injections ranged from 250 to 17 molecules of dye. Both the detection limits and the amount of injection are the lowest ever repo rted in capillary electrophoresis. The mass sensitivity of this detect or is at least two orders of magnitude lower than the best on-column c apillary electrophoresis fluorescent detector.