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Redesign and Performance of a Diffusion Based Solvent Removal Interface for LC/MS

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Jon G. Wilkes, National Center for Toxicological Research and Steven Colby, Scientific Instrument Services, Inc.

Introduction: In 1989 M.L. Vestel invented a device which removes HPLC solvents by diffusion of their vapors. It was used for elimination of mobile phase interferences in both LC/particle beam/MS and LC/CRIMS (LC/Chemical Reaction Interface Mass Spectrometry). The device has other potential uses for terminating HPLC with a variety of other selective and universal detectors.

The original design was technically successful, but suffered several practical limitations, including a high rate of helium gas consumption (up to 15 L/min) and excessive cost (about $20,000 retail price).

Objectives: reduced component costs; simplified electrics for gas flow or temperature control; the capability to handle HPLC flows varing from 0.05 to 1.5 mL/min; reduced consumption of helium; increased user servicability; increased efficiency of solvent removal (for lower LC/CRIMS detection limits)

Major redesign Features: heated pneumatic nebulizer (accomodate liquid flow range from micro- to analytical scale HPLC); HPLC solvent-resistant peristaltic pump flexible tubing (instrumental ruggedness); tubular PTFE porous membrane (rather than planar, as in the old design) with Pyrex outer tube coils (for visual inspection, troubleshooting, acid resistance, cheap manufacturing cost); modular, 2 stage construction of diffusion cell (optimize necessary length for each application's required amount of solvent removal; reduce helium consumption); use of clean air for carrier gas and most solvent removal; use of helium only as a stage 2 sweep.