The procedure used here has been previously described
(Mengerink et al., 2002; Kutlán and Molnár-Perl, 2003). Briefly, the
derivatisation was performed by mixing 100 L sample or standards
solutions, 20 L of daily prepared methanolic OPA (5 mg/mL),
75 L borate buffer (pH 9.9) and 5 L MPA. The resulting solution
was vortexed and analyzed after 1-min at room temperature.
2