Decoupling CE and ESI for a more robust interface with MS.

An interface for CE-ESI-MS that decouples both the elec. and the soln. flow rate requirements of the sepn. and ionization processes is presented. The interface uses a tapered and beveled stainless steel hollow needle surrounding the sepn. capillary terminus so that the inside of the electrode acts as the CE outlet vial and the outside tip acts as the electrospray emitter. No capillary pre-treatment is required, enabling the use of capillaries with any type of surface modification. A chem. modifier soln. is introduced through a 2nd capillary connected to the needle via a tee junction and can be used to improve the compatibility of the CE BGE with electrospray. The flow rate of modifier soln. can be >=0.1 μL/min, much less than that in a typical sheath-flow interface, thus minimizing diln. of the CE effluent to maximize sensitivity. The presence of the modifier soln. also allows the use of neutral-coated capillaries for protein anal. by CE-MS without using an assisting pressure, despite the absence of EOF under these conditions. The interface is easily integrated into a com. CE instrument, such that all operations can be carried out by the automated controls. Compared with a com. sheath-flow CE-MS interface operating under optimized conditions, LODs for amino acids were, on av., improved 5-fold. [on SciFinder(R)]