entrance lens 35 can be operated at ground potential and the es needle assembly maintained at ground potential during operation ions entering capillary annulus 14 can be driven uphill against the entrance kilovolt potential by gas collisions and delivered into vacuum at whatever voltage is set on capillary exit electrode 15 consequently the dielectric capillary entrance and exit potentials are decoupled and can be set independently of one another when conductive capillary tubes or orifices are used instead of dielectric capillary 13 the electrostatic potential set on these elements must be set to the voltage required for ion acceleration and focusing into vacuum typical es chamber operating voltages which have previously been reported for positive ion production when es needle tube rip 32 to endplate nosepiece 42 distance is set at 1 5 cm are given below ______________________________________ conductive dielectric capillary capillary or orifice______________________________________es liquid introduction tip 32 0 v 5 0 kv cylindrical lens 33 3 0 kv 2 0 kv endplate 34 4 0 kv 1 0 kv capillary entrance lens 35 5 0 kv 100 v______________________________________ for negative ion production the voltage polarities are reversed it was discovered that increased es mass analyzer signal could be attained by increasing the relative cylindrical lens potential 33 to a value greater than.