Sensing performance, amperometric

Sensing performance for H-,. Sensing performance of the amperometric sensor was examined for the detection of H2 in air. Figure 3 shows the response curve for 2000 ppm H2 in air at room temperature. The response was studied by changing the atmosphere of the sensing electrode from an air flow to the sample gas flow. With air the short circuit current between two electrodes was zero. On contact with the sample gas flow, the current increased rapidly. The 90% response time was about 10 seconds and the stationary current value was 10yUA. When the air flow was resumed, the current returned to zero within about 20 seconds. 

N. Barsan, J.R. Stetter, M. Findlay, and W. Gopel. High performance gas sensing of CO Comparative tests for semiconducting (Sn02-based) and for amperometric gas sensors . Analytical Chemistry 71 (1999), 2512-2517. 

Long Term Performance of Sensors. The sensors showed excellent long term stability stored in buffer at 4 °C. Table 1 shows the long term performance of four typical biosensors. The usual current response to 6 mM glucose for a new biosensor is about 2 fiA. The precision of the absolute current response to 6 mM glucose remains within 15 % for up to four months. This level of precision is unusual for amperometric biosensors. Normally, variations in current are compensated by calibration. The sensitivity of the biosensors, as indicated by the slope of the response, is also stable. This stability is due to the film which maintains the ferrocene within the sensing layer. Biosensors with adsorbed mediator and immobilized enzyme but without film are not stable for any period of... 

Amperometric sensing of selected species in liquids is widely extended with an enormous variety of materials and applications, which include electrochemical detection coupled with high-performance liquid chromatography and flux injection analysis. In these cases, high sensitivity and high reproducibility are required. These properties are conditioned by electrode fouling associated to formation of solid deposits and adsorbates on the electrode surface. As a result, the electrode experiences memory effects with concomitant loss of analytical performance. 

Analyses of responses aiming to define the characteristics of the electrode deposit and the details of the mechanism operative in anodic oxidations or cathodic reductions are also very challenging and rare in the case of amperometric sensing on modified electrodes, due to the complexity of most systems with respect to the bare ones. On the other hand, the superior performance of new computers may lead to unprecedented sophisticated simulations. In the case of composites based on nanosized materials, studies of the diffusion to micro- and nano-electrode systems may be exploited [234]. Similarly, calculations regarding the reaction mechanisms based on density functional theory have been exploited to give a rationale to the performance of a number of electrocatalysts [235]. 

The preparation technique of the disposable sensing elements used in this flow-injection amperometric immunofiltration system demonstrated high reproducibility of the analytical parameters. The variation between the responses to a standard concentration of mortalized cells (100 cell/ml) obtained with membranes prepared from one and the same batch was 16 %. It should be noted that the data points in Figures 4, 5 and 6 (curves a) are obtained as an average of 4 independent measurements, eadi performed by an individual sensing element. The error bars in Figures 4,5 6 represent the standard deviation obtained from these 4 independent measurements. 

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