Residual charge reduction

The most important multiply charged polyatomic positive ions are compounds with two or more basic groups which when protonated lead to doubly or poly-charged ions. Typical examples are diamines such as the double protonated a, to alkyldiamines, H3N(CH2)pNH2+, and the most important class, the polyprotonated peptides and proteins, which have multiple basic residues. Charge reduction for these systems occurs through proton transfer from one of the protonated basic sites to a solvent molecule. Such a reaction is shown below for the monohydrate of a doubly protonated diamine ... 

Residual Current Even in the absence of analyte, a small current inevitably flows through an electrochemical cell. This current, which is called the residual current, consists of two components a faradaic current due to the oxidation or reduction of trace impurities, and the charging current. Methods for discriminating between the faradaic current due to the analyte and the residual current are discussed later in this chapter. 

The residual current, in turn, has two sources. One source is a faradaic current due to the oxidation or reduction of trace impurities in the sample, i . The other source is the charging current, ich> that is present whenever the working electrode s potential changes. 

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