Coupling of capillary zone electrophoresis to mass spectrometry (MS and MS/MS) via a nanoelectrospray interface for the characterisation of some β-agonists

Capillary zone electrophoresis (CZE) was coupled to mass spectrometry (MS) via a nanoelectrospray interface (nESI), using conductively coated tips (8 µm orifice) butted to the end of a fused-silica capillary. The CZE/nESI-MS system was carefully optimised to achieve a stable operation of the arrangement in order to run also MS/MS experiments. Mixtures of β-agonists were successfully separated using 5 mmol/L ammonium acetate in 80% MeOH as a buffer. The limit of detection was 500 attomole of a substance injected. The system was also investigated from the point of view of quantification of the substances. Careful measures were taken to avoid any systematic errors (evaporative loss during the electrokinetic injection and reduction of migration times due to the electrospray pull during the CE run). The data show that the response of a mass spectrometric detector in the low-femtomole range not only depends on the concentration of the analyte but also on the properties of the nanoelectrospray process itself, that is why the linearity of the response can be compromised.