## 2 Flow-based electrochemical detection
### Amperometric detection
Use of a non-metal electrode, especially the BDD electrode, can minimize the fouling effect on the electrode surface. BDD electrode has been proved to be an excellent working electrode in many analytical applications. An extremely low background current over a wide range of potentials offers a lower detection limit. Amperometric detection of acetaminophen [17], \(D\)-penicillamine [18], homocysteine [19], captopril [20], and tiopronin [21] in pharmaceutical samples using BDD electrodes has been reported. [PERSON] et. al. [22] also reported the determination of iodide in nuclear emergency tablets using BDD electrodes. A schematic diagram of flow injection manifold with amperometric detection is shown in figure 2. Moreover, this electrode can also be used to study the electrochemical behaviors of 3,6-dihydroxyphenanthrene in both non-aqueous and aqueous media [23]. The FIA manifold with a relocated detector for renewing the working electrode surface has been reported for the amperometric determination of diltiazem and nimesulfide in pharmaceutical formulations [24]. A flow system was constructed with two independent channels based on the concept of multi-site detector locations. An electrochemical cell can be relocated between the two flow channels. Each measurement that was carried out in one of the channels could alternate with the regeneration of the glassy carbon surface in the other channel through the passage of an adequate conditioning solution. A carbon paste electrode can also be used as an amperometric detector in FIA for dipyrone determination in pharmaceutical formulations [25]. This system offers a fast, simple, and precise method that is suitable for dipyrone analysis and quality control of pharmaceutical samples. The carbon paste electrode was found to be very stable over several hours without requiring any chemical or mechanical surface renovation. On-line interfacing of a rotating bioreactor and continuous-flow/stopped-flow/continuous-flow processing for the determination of lactate in milk samples has been developed. The high sensitivity can be attained using a bienzymatic system and redox polymer [Os(bpy)\({}_{2}\)ClPyCH\({}_{2}\)NHpoly(allylamine)] (Os-PAA) as a mediator. This system allows analyzing undiluted milk samples with a good stability and reproducibility with a sample throughput of 30 samples per hour [26]. Amperometric detection of carbohydrates and galactose using single-wall carbon-nanotube (CNT)-modified glassy-carbon electrodes has been reported. The amperometric response is extremely stable, with operational stability of more than 2 hours. The flow-injection response is characterized with a detection limit of 10 \(\upmu\)M and a relative standard deviation of 3.45% (n=20) [27]. A stopped-flow technique with amperometric detection of chlorate has been developed. The reaction of chlorate with excess potassium iodide and hydrochloric acid, forms iodine/triiodide that is further reduced at the glassy carbon electrode. Sensitivity can be improved by increasing the reaction time and stopping the flow while the injected zone is in a mixing coil. This can be done without increasing dispersion of the product zone. This system was successfully applied to the determination of chlorate in soil samples [28]. FIA has also been used in immunosensor applications. An amperometric immunosensor based on graphite paste has been reported for the assay of azidothymidine (AZT) [29]. The potential used for the AZT assay was 435 mV vs. Ag/AgCl electrode. The advantage of using graphite paste is that a surface regeneration for a new assay can be simply done by polishing. This immunosensor was successfully used as a detector in a sequential injection analysis system, and gave reliable results for assays of AZT purity in raw materials and AZT contents in pharmaceutical formulations. Determination of \(\beta\)-D-glucose in different commercial medical. The experimental results are in good agreement with those reported by the manufacturer.