Electrospray characteristic curves: in pursuit of improved performance in the nanoflow regime

Depending on its coordinates in the parameter space, an electrospray can manifest in one of several known regimes--stable, quasi-stable, transitional chaotic, and nonaxial--that ultimately impact measurement sensitivity and precision. An electrospray operating in the cone-jet regime provides relatively large and stable spray current, as well as smaller initial droplets, that are prerequisites for higher sensitivity and quality mass spectrometric analyses. However, the dynamic conditions encountered, for example, in gradient elution-based liquid separations create difficulties for continuous operation in this regime. We present a preliminary study aimed at providing the basis for stabilizing the electrospray in the cone-jet regime. On the basis of spray current measurements obtained using solvent conditions typically found in liquid chromatography-mass spectrometry, an improved description of the cone-jet stability island is provided by including transitions to and from the recently described astable regime. Additionally, the experimental conditions in which the astable regime marks the transition between pulsating and cone-jet regimes are further clarified.