Two configurations have been tested which are suitable for field-portable instrumentation. The system at left uses a reaction chamber for ion desolvation. In the reaction chamber design, total gas flow, Q (400–800 sccm) includes a heated desolvation and modifier gas flow, Qd, of about 100 sccm at about 100°C, with the balance of gas aspirated from the ESI plume region. The ESI liquid infusion, q, is 50–600 nL/min, with an emitter voltage drop V-V1 in the ±1400–2000 V range for Proxeon metal emitter tips. The voltage across the reaction chamber, V2-V1 (not critical) is typically ±40 to 100 V, and V2 is set to the mean DMS potential. At right is shown the configuration with very low flow and no additional desolvation. The reaction chamber allows more complete breakup of ion-solvent clusters, provides more stable intensities, and works at higher liquid flows. A full curtain-gas system (Qd > Q, for net outflow toward the ESI source for complete control of desolvation and modifier effects) is not discussed here, but is used in the AB SCIEX commercial DMS-MS and is shown in Schneider et al (2010a)..