Comparison of On-line Preconcentration Methods for Determination of Derivatized Serotonin by CE-LIF

A method combining CZE–LIF and derivatization of 5-HT with 3,4 dimethoxybenzylamine has been developed for determination of 5-HT at very low concentrations. To improve sensitivity of detection, preconcentration techniques such as stacking and use of a dynamic pH junction were evaluated; a full-factorial design was used to determine the most relevant experimental conditions. Running buffer of high pH and low sample pH resulted in the highest response and it was shown that stacking was not an efficient method of preconcentration. Another focusing approach, sweeping, was evaluated by adding an ion pairing agent, heptanesulfonic acid (HSA), to the separation buffer. This approach resulted in a tenfold increase in sensitivity; peak efficiency was also clearly improved by addition of 75 mM HSA. Linearity of response was demonstrated. The limit of detection was less than 10 fmol μL−1 of sample.