Universal detection in capillary electrophoresis with a micro-interferometric backscatter detector

An optically simple, inexpensive, micro-volume refractive index detector wa s applied to capillary electrophoresis (CE), allowing universal solute dete ction at the sub-picogram level. The micro-interferometric backscatter dete ctor (MIBD) employs direct, side illumination of an unmodified capillary by an He-Ne laser, producing a 360 degrees fan of scattered light that contai ns a set of high contrast interference fringes. These light and dark spots are viewed on a flat plane in the direct backscatter configuration. A slit- photodetector assembly accomplishes signal interrogation of the time-depend ent fringe shifts, produced or imparted by refractive index (RI) changes. U sing an unfocused laser beam to prove the unmodified separation capillary p roduces a detector volume of 4.7 x 10(-9) L. The separation and quantificat ion of a mixture of organic dyes and simple sugars demonstrate the system's utility. Submicromolar concentration detection limits of 0.46, 1.1 and 0.7 2 mu M for Bromothymol Blue, Thymol Blue and Bromocresol Green, respectivel y, are achievable with CE-MIBD in the simplest configuration. The 3 sigma R I concentration detection limits are 2.5 times superior to those obtained b y UV/VIS detection performed under the same conditions. Several carbohydrat es (maltose, lactose and D-ribose) are separable and detectable at the ppm level, using no active thermal stabilization. Further demonstrating the uti lity of MIBD for universal detection with CE.