We have recently in our group at the University of Copenhagen developed a robust and simple sheatless CE-ESI-MS interface (capillary electrophoresis – electrospray ionization-mass spectrometry). In this presentation the interface is characterized and compared with HPLC-MS for studying the composition of alkaloids in Cinchona bark.
One common problem for sheatless interfaces for CE-MS has been establishing a stable electric contact at the end of the separation capillary that does not induce band broadening or affect the spray stability. In our device the electric contact is generated through a submicron fracture in the capillary close the ESI tip. The fracture provides a zero dead volume and excellent conducting properties due to the large amount of ions in the electric double layer. Electric current exceeding the upper limit of CE instrumentation of up to 300 µA can easily be obtained. Furthermore, the increased conductivity of the buffer in the fracture generates field free pumping of the analytes towards the ESI spray tip.
In this study the device was used to analyze the four major alkaloids (diastereomeric pairs of quinine/quinidine and cinchonine/cinchonidine) in Cinchona bark samples, in a non-aqueous BGE system without using a chiral selector.
The separation was achieved in less than 15 min with a 75 cm capillary and a detection limit of 1 ng/mL, approximately 150-2000 times lower than the occurrence in the samples after standard sample preparation was achieved. The sheathless interface showed a 40-fold improvement of the detection limit compared to an Agilent® sheath liquid interface employing a similar non-aqueous BGE system.