Thiols are also called sulfhydryls. A thiol is recognized by the presence of a sulfur atom attached to a carbon backbone. Thiols can also exist in another form known as disulfides. In a disulfide, two thiols are bridged together at the sulfur atom. An example of a disulfide is homocystine, which is made of two homocysteine molecules.
Electrochemical detection can monitor the disulfide form as well as the thiol form.
It accomplishes this using two different approaches. Detection of a thiol is accomplished by an electrochemical oxidation, while detection of disulfides is accomplished by an electrochemical reduction. The difference between an oxidation and a reduction reflects what is happening at the electrode surface. During the oxidation of a thiol, an electron is lost from the homocysteine molecule and donated to the electrode. During a reduction of a disulfide, electrons are donated by the electrode to the molecule and during the process, the disulfide bridge is broken, yielding two thiols.