Ultra-low flow rate (< 20 nL/min) nanospray ionization has demonstrated reduced ion suppression, a trend toward equimolar response, and high ionization and utilization efficiency for small molecule analytes. The majority of these experiments feature the use of offline (static) nanospray. Typically static nanospray is operated in a regime whereby the applied voltage generates or controls the effective through-emitter flow rate of mobile phase. Such static experiments are often difficult to control because the flow rate is a function of applied voltage, mobile phase composition, and emitter geometry. By decoupling through-emitter flow rate from applied voltage, it is possible to retain the benefits of static nanospray in combination with the robustness and repeatability of pumped flow (dynamic) nanospray.

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