Phenylenediamine (OPD) reacts with α-keto acids to form highly fluorescent quinoxaline derivatives. MDB is an o-phenylenediamine analogue. It is the best labeling reagent for α-keto acids because of its reactivity and sensitivity. In HPLC analysis, more than ten different α-keto acids, such as α-keto glutaric acid, pyruvic acid, and phydroxyphenyl-pyruvic acid, can be separately detected at a time, even at concentrations of only a few femtomoles per injection. The sensitivity of MDB is almost 150 times as high as OPD. The excitation and emission wavelength of the labeled materials are 367 nm and 445 nm, respectively.
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