Electrochemical batch injection analysis

One of the benefits of electrochemical batch injection analysis is that dilution of the sample with electrolyte is not necessary, see below. A sample of volume =sl00p.L is injected directly from a micropipette, tip diameter 0.5 mm, over the centre of a macroelectrode exactly as in a wall-jet system. This is equivalent to a flow injection system with zero dispersion. During the injection, and after a short initial period to reach steady-state, the hydrodynamics is wall-jet type and a time-independent current is registered. BIA was first devised using amperometric, e.g., [31], and potentiometric, e.g., [34], detection. A typical amperometric trace is shown in Fig. 16.5. By using a programmable, motorised electronic... 

The wall-jet continuous flow system is readily modified to discrete injection mode as shown in Fig. 16.4. This is the electrochemical version of a general discrete injection technique known as batch injection analysis (BIA) [31] and is a hybrid between flow injection analysis and wall-jet in continuous flow. 

Porphyrin-modified electrodes were widely utilized for quantification of low concentrations of metals, pharmaceutical products, and species of environmental and industrial importance in association with flow techniques. This strategy enhances the amperometric response and sensitivity (the capacitive current is virtually reset), while reducing significantly the time necessary for analyses. Flow injection analysis (FIA) has been extensively explored for this purpose and a revision on the application of porphyrins and derivatives was published some years ago [203]. Alternatively, batch injection analysis (BIA) can be an interesting way for fast analyses utilizing a similar mass transport process to the electrode surface [204]. For example, citric acid was electrochemically determined by BIA using cobalt phthalocyanine modified carbon paste electrodes [205]. 

Voltammetric studies have demonstrated that thiocholine is oxidized at +0.15-0.20 V on CNT-modified GC electrodes as compared to its higher oxidation potential on unmodified GC (+0.7 V), carbon paste (+0.6 V), and gold electrodes (+0.9 V). A lower detection limit of 5 x 10 M thiocholine was obtained under the optimal batch conditions, while the detection limit was further improved down to 3 X 10 M by the electrochemical detection in flow injection analysis. 

Potentiometry is the most common method of electrochemical detection used in flow injection analysis. This methodology creates more favorable conditions for potentiometric measurements when compared to batch procedures. In FIA measurements, it is easier to avoid incidental contamination or that resulting from leakage of the solution from the reference electrode. Moreover, deactivation of the sensing surface of the indicator electrode due to adsorption, precipitation, or corrosion is minimized greatly as a consequence of the short contact time with the sample... 

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