Figure 5. Electropherograms of ΦX 174 DNA restriction fragments obtained using (a) 4.0, (b) 1.0, and (c) 0.2 µM dye in the running buffer. See Figure 3 for experimental details.
Conductivity detectors sufficiently small for deployment in capillary analytical systems can be fabricated very simply and reproducibly from commonly available micro assemblies of multiconductor ribbons. It results in a unique geometry for the conductivity detection cell where the fluid does not flow between the electrodes. Interface circuitry for a personal computer (PC)-based bipolar pulse conductance detector is described. The cell can be used with this or commercial detectors. Results obtained with the new cell and electronic design in a suppressed conductometric capillary electrophoresis separation system are presented.
A fiber-optic ammonia gas sensor designed for neurochemical applications is presented. Parameters evaluated in terms of effect on the steady-state and dynamic response of this sensor include the indicator dye, concentrations of indicator and total ammonia nitrogen in the internal solution, volume of the internal solution, structure of the gas-permeable membrane, and temperature. The final ammonia sensor responds over the concentration range from 7 to 3000 nM with a limit of detection of 7 nM and response times ranging from 2 to 5 min. Glutamate oxidase is immobilized at the tip of this ammonia sensor to provide a glutamate biosensor with a detection limit of 0.1 microM when operated at pH 7.8. In addition, this ammonia sensor is used to measure extracellular ammonia levels in perfused retinal and eye-cup tissue preparations. These measurements indicate a calcium-dependent, potassium-evoked release of ammonia during these depolarization conditions.
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