Amperometric detection with flow through electrodes

Detection Methods. — A nickel-titanium alloy electrode for stable and sensitive electrochemical detection of carbohydrates has been reported." Similarly, several copper(II) oxide modified electrodes were highly sensitive for constant-potential amperometric detection of picomole levels of carbohydrates (Glc, Xyl, xylitol) in alkaline solution in flow through systems (anion-exchange h.p.l.c. and flow injection analysis), although problems with day-to lay reproducibility remained to be solved."... 

Electrochemical detection of ascorbic acid is based on the oxidation of ascorbic acid to DHA (Fig. 2). Amperometry and coulometry are the measurements of current at a constant electrode potential. The main difference between these two measurements is the amount of analyte oxidized in the detector in amperometry the oxidation and current are limited in coulometry, the analyte is totally oxidized. The structure of an amperometric detector is usually a flow-by cell, whereas in coulometry a porous flow-through cell is used. In coulometry, a higher amount of analyte is allowed in contact with the electrode surface and sensitivity increases. Working with electrochemical detector, the components of mobile phase must allow for distinct separation of ascorbic acid and be conductive to carry the charge of the analyte. However, the mobile phase must not yield too high background signal. 

For measuring the respiratory activity of the bacteria they used 5.0 mM K3[Fe (CN)6l hydrophilic mediator added to the PBS buffer electrolyte. The mediator after passing through the cell membrane could interfere with the respiration cycle and got reduced. As the formed [Fe(CN)6]" diffused back to the buffer through the gap, its mass flow could be detected recording the amperometric current at 0.6 V electrode potential. In this case the oxidative current depends on the transport and permeation rate of the mediator as well as on the metabolic activity of the culture. 

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