A new technique for measuring the temporal characteristics of the carbon fibre microelectrodes in in vivo voltammetry at millisecond time intervals

A common approach to test the time-response of carbon fibre microelectrodes entails the use of a flow injection system which allows delivery of a bolu s of test compound in the flow stream to a detector electrode. The introduc ed bolus is distorted from its original form by convective and dispersive f orces during the period of transport from the injector to the detector elec trode in the connection tubing and couplings. Thus, the flow injection syst em allows one to change the medium in the vicinity of the electrode in abou t 100-200 ms. We describe here a simple falling drop system, which is an ea sy to use for calibration of the carbon fibre microelectrodes with respect to their sensitivity and time-response. This system does not have a loop in jector and minimizes problems associated with convective and dispersive bol us distortion. It allows one to change the medium in the vicinity of the el ectrode in less than 10 ms. With this system, the sensitivity and the tempo ral resolution of the electrodes may be easily and rapidly estimated in a s ingle experiment. The temporal resolution of the untreated, uncoated carbon fibre cylinder electrode of 300 mu m tip length in response to dopamine wa s estimated as 1.49 +/- 0.1 mu M/ms (M +/- SEM, n = 36, rise) and 0.051 +/- 0.003 mu M/ms (n = 36, wash-out) on the half of amplitude of electrochemic al response which was monitored by constant potential amperometry. (C) 1998 Elsevier Science B.V. All rights reserved.