ABSTRACT
The use of light has also shown promise as a derivatization agent. This technique simplifies the derivatization procedure and is not characterized by the drawbacks associated with chemical methods, including interference from unreacted derivatizing agent. The method may be implemented on-line (e.g., in a post-column reactor following a separation) with limited band broadening. However, photolysis derivatization is limited to detection of peptides composed of aromatic or sulfur-containing amino acids. Photolysis increases selectivity at a number of applied potentials. For example, with peptides containing tryptophan and tyrosine, no electrochemical signal is seen at +0.60 V without photolysis, but a response is identified at +0.80 V versus Ag/AgCl [143]. In comparison, with photolysis a signal is observed at +0.60 V and the signal obtained at +0.80 V vs. Ag/AgCl is two or three times higher than without photolysis [143]. This is attributed to the fact that the stable photoproducts of some electroactive amino acids, including 3-hydroxytyramine (DOPA, the major product of tyrosine photolysis), are readily oxidized [144]. A similar increase in selectivity after photolysis is exhibited with peptides containing methionine and cystine [143]. In comparison, cysteine displayed decreased sensitivity following photolysis [143, 144].
