On-Line Radioisotope Detection for Capillary Electrophoresis

Two simple, on-llne radloactlvlty detectors for Capillary electrophoreds are descrtbed. The first caplllary electrophoresls/radioisotope detector system utlllres a commerclally available semlcMKhtctor devloe, which is positioned external to the Separation channel and whlch responds dlrectly to lmpkrshrs y or hlgh-energy @ radlatlon. The second caplllary electrophoreds/radtope detector uttllzes a commerclally avalable plastk bclnullator materlal that completely surrounds (360') the separation channel, thereby Improving the efflclency of detectlon. The system performance Is evaluated for both detectlon schemes by uslng synthetlc mixtures of "P-labeled sample molecules. The efflclency of the semlconductor detector (planar geometry) Is determlned to be approximately 2696, whereas that of the plastic sckrtllator Is found to be approxhately 65%. The detectlon lhnlts are deterrnlned to be In the low-nanocurle range for separations performed under standard conditions (an lnjqcted sample q u a m of 1 &I correspods to 110 X md of 9%). The lower lhnll of detectlon Is extended to the subnanocurle level by use of flow (voltage) programming to Increase the resldence tlme of labeled sample components In the detectlon volume.