title: Direct RP-HPLC determination of underivatized amino acids with online dual UV absorbance, fluorescence, and multiple electrochemical detection.
abstract: The combined use of a dual-UV detector, a fluorimetric one and of a multiple electrochemical (EC) detector equipped with a dual electrode, consisting of a conventional size 3 mm diameter glassy carbon electrode (GCE) and of a pair of 30 mum thick carbon microfibers, is proposed for the determination of 15 amino acids, two dipeptides and creatinine. This online coupling of the above detection modes could partially replace amino acid analysis by derivatization methods, since it solves problems concerning the direct detection of selected underivatized amino acids. Additionally, it was proved that the use of multiple-detection allows positive peak identification in a single chromatographic run, yields more information for free amino acids and solves in some cases the problem of chromatographic resolution. In order to optimize the detection conditions of the underivatized amino acids and related compounds by different detectors, their detection characteristics were determined by adequate preliminary experiments. The electro-oxidation characteristics of the underivatized compounds of interest were determined by hydrodynamic voltammetry using a flow cell with a macrodisc GCE and by ex-situ voltammetry using both a GCE of conventional size and a carbon fiber disk microelectrode. Important practical advantages of microfiber and microdisk electrodes with respect to macroelectrodes were demonstrated.
authors.affiliation: Laboratory of Physical Chemistry, Department of Chemistry, Aristotle University of Thessaloniki, Thessaloniki, Greece.
authors.forename: Panagiota
authors.initials: P
authors.lastname: Agrafiotou
authors.forename: Sotiris
authors.initials: S
authors.lastname: Sotiropoulos
authors.forename: Adriani
authors.initials: A
authors.lastname: Pappa-Louisi
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid / Q000295:instrumentation* / Q000379:methods*; D055664:Electrochemical Techniques; D057927:Hydrophobic and Hydrophilic Interactions; D009862:Online Systems / Q000295:instrumentation*; D013053:Spectrophotometry / Q000295:instrumentation* / Q000379:methods*
chemical_list: D000596:Amino Acids