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What Do We Know about Determination of Amino Acids with Orthophthalaldehyde?
Author(s) -
Zuman Petr,
Salem Nuha,
Kulla Eliona
Publication year - 2009
Publication title -
electroanalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 128
eISSN - 1521-4109
pISSN - 1040-0397
DOI - 10.1002/elan.200804426
Subject(s) - isoindole , chemistry , imine , amino acid , aqueous solution , ion , reaction mechanism , hemiacetal , schiff base , combinatorial chemistry , catalysis , stereochemistry , organic chemistry , biochemistry
Mechanisms of the formation of the fluorescent species widely used for determination of amino acids, based on reaction with orthophthalaldehyde (OPA) were unknown. Attempts to elucidate this mechanism based solely on product identification were unsuccessful. Analytical methods based on reaction of OPA with amino acids in the presence of RS − or CN − ions were developed empirically. The reaction conditions reported in more than 700 papers differed considerably. In aqueous solutions OPA exists in three different forms in equilibrium – the unhydrated form Ia (20%), monohydrated acyclic form Ib (8%) and cyclic hemiacetal form Ic (72%). These forms are in equilibria, the rate of establishment of which is acid and base catalyzed. Reactions of OPA and NH 3 and 2‐aminoethanol (colamine) take place in a series of equilibria depicted in Scheme 1. The isoindole derivatives are formed in cyclization of the carbinolamine. Formation of an imine is a side reaction.