We are trying to repeat the setup from J.Korf et al. Automated precolumn fluorescence labeling by Carbodiimide (N,N-dicyclohexylcarbodiimide - DCC) activation of N-AcetylAspartate (NAA) and N-AcetylAspartylGlutamate (NAAG) applied to an HPLC brain tissue analysis // Anal.Biochem. 196, 350-5 (1991). So far we could not get a clear blank. Running isocratically blank sample (v-0.6mL/min) 4mMHCl:DCC:2AA - 1:1:1 (2AA - high fluorescent label - 2-AminoAnthracene) after the switching artifacts we are getting wide noisy peak (rt 8min width ~3min) which is, we suppose, 2AA (although it should not be there according the paper) and it disappears in the absence of 2AA in a mixture. Running sample containing NAAG or NAA we are getting peaks with the retention time approximately coinciding with the one of 2AA.
If anybody dealt with relative problems or may suggest how to get rid of undesirable peak generated by the label in chromatograms we would appreciate any information.