ABSTRACT
EC detection. As with electroactive peptides, the main negative effect of preconcentrating on-column with derivatization is the baseline drift associated with impurities in the solvents (see Figure 7A for example). The large difference in the shape of drift compared to the analyte peaks allows it to be removed by appropriate data-processing. Figure 7 illustrates the effect of a median filter [41], a type of high-pass filter, on a chromatogram for trace level peptides. The chromatograms are compared to an injection of a blank containing the same solution but no peptides. The featureless background allows confident assignment of peaks even at low concentrations. Detection limits for these oligopeptides varied between 7 and 60 pM for 1 µL injection volumes [3]. The chromatograms in Fig-ure 7 illustrate that the biuret derivatization is well suited for use with preconcentration because (1) it allows narrow peaks to be obtained even with large volume injections on reversed-phase columns because it does not require organic solvents, allowing the sample to be injected in a weak mobile phase, (2) it does not produce substantial background peaks that interfere with analyte detection, resulting in surprisingly clean blank chromatograms even for large volume injections, and (3) it yields derivatization even at trace level concentrations.
