Determination of Photodestruction Quantum Yields Using Capillary Electro-Phoresis: Application too-Phthalalde-Hyde/β-Mercaptoethanol-Labeled Amino Acids

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Abstract
Photodestruction quantum yields, ΦD, were determined for o-phthalaldehyde/ß-mercaptoethanol-labeled protein amino acids in aqueous alkaline solution using trans-azobenzene actinometry. The ΦD values ranged from 0.020 to 0.062; the highest were obtained for amide-containing amino acid derivatives (Gln and Asn; ΦD = 0.062 and 0.054, respectively). The average maximal number of fluorescent photons obtained from the chromophores ranged from 6.4 to 19.0 per molecule. We show that ΦD values can be determined with the help of an internal standard using capillary electrophoresis with laser-induced fluorescence detection. Generally, good agreement between the ΦD values obtained in this way and ΦD values obtained using trans-azobenzene actinometry was found. Furthermore, we show that knowledge of the analyte's photochemical properties assists identification of components separated by capillary electrophoresis.