Cationic separation of medium strong bases by electrophoretic focusing on inverse electromigration dispersion profile. Sensitive analysis of beta-blockers in blood and water with ESI-MS detection

Electrophoretic focusing on an inverse electromigration dispersion profile is a method where the migrating profile focuses and separates the analytes and transports them to the detector. Although so far only a few anionic and cationic electrolyte systems have been reported for this technique, it has proved its separation and concentration power and potential for sensitive and selective analyses of samples with complex matrices, typically without any pretreatment. To extend its applicability, there is need for the design of electrolyte systems covering other pH ranges and potential analyte groups. This work describes the first functional cationic system for electrophoretic focusing on inverse electromigration dispersion profile in the alkaline region, based on pentamethylenediamine and acetohydroxamic acid. Computer simulation and experiments have shown that the designed electromigration dispersion profile can be split into smaller sub-profiles to reach increased performance and selectivity. The practical applicability of the system is demonstrated on the analysis of beta-blockers in capillary blood via the dried blood spot technique in combination with electrospray-ionization mass-spectrometric detection. The method allows direct injection of aqueous dried blood spot extracts and sensitive determination of metoprolol and betaxolol in real samples with limits of detection at the 2 nM (500 ngL^-1) level. Experiments with direct injection of spiked water samples show that the method can be used also for analysis of beta-blockers in waters with almost the same sensitivity.