Article pubs.acs.org/ac
Microfluidic Dual Emitter Electrospray Ionization Source for Accurate Mass Measurements Andrew G. Chambers† and J. Michael Ramsey*,† †
Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States S Supporting Information *
ABSTRACT: A glass microfluidic device with two independent electrospray ionization (ESI) emitters has been designed to sequentially generate ions from different solutions for mass analysis. Rapid modulation between the emitters is accomplished by turning on and off the voltage that simultaneously generates the fluid flow rate and ESI potential. The time required to switch between the two electrospray signals is less than 70 ms. Using the second emitter to introduce a reference compound for internal calibration, accurate mass measurements (less than 3 ppm mass error) were obtained with a time-of-flight mass spectrometer.
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extra-column band broadening at low flow rates.8 An alternative approach for introducing a reference standard that does not impair the quality of the separation is to use independent emitters for the analyte and reference solutions.9−11 It is also advantageous to introduce the analyte and reference independently to the mass spectrometer in succession to avoid interferences that may arise if both materials have the same nominal m/z value. To ensure adequate sampling of the column eluant the duty cycle for acquiring data for the reference material should remain comparatively small. Numerous methods have been reported for sequential introduction of analyte and reference solutions into a single mass spectrometer inlet using two different capillary ESI emitters. They include repositioning of the emitters at the inlet,5,12−14 the use of a mechanical baffle to temporarily block the electrospray from one emitter at a time,15,16 dynamic control of the ESI voltage,17,18 and modification of external electric fields to gate ions in the gas phase.19−21 Both mechanically based and electrically based strategies for sequentially operated, dual ESI systems are capable of accurate mass measurements (
