ELECTROSPRAY AS A CONTROLLED CURRENT ELECTROLYTIC CELL - ELECTROCHEMICAL IONIZATION OF NEUTRAL ANALYTES FOR DETECTION BY ELECTROSPRAY MASS SPECTROMETRY

摘要

In this paper an electrospray ion source is shown to be a controlled-current electrolytic now cell which, when operated so that three key requirements are met, can be used for efficient neutral analyte ionization (i,e,, complete analyte electrolysis) and sensitive gas-phase detection (i,e., minimized gas-phase signal suppression) in electrospray mass spectrometry (ES-MS), These three requirements are as follows: (1) the magnitude of the ES current, i(ES), must be sufficient for the oxidization of the molar equivalent of all species available for reaction in the ES capillary that are as easily or more easily oxidized than the targeted analyte, including all of the analyte; (2) the analyte must be available for reaction at the metal/solution interface in the ES capillary; and (3) the steps taken to ensure the first two requirements must not inhibit the formation of gas-phase ions from the ions generated electrolytically in solution. The means to meet these requirements are discussed, including the addition of an appropriate electrolyte to the electrosprayed solutions (e,g,, lithium triflate), the use of slower now rates (e.g., 5.0 vs 40 mu L/min), and the use of a platinum capillary in the ES device, rather than the more commonly used stainless steel capillary. Neutral metallocenes, metalloporphyrins, and polycyclic aromatic hydrocarbons are used as the model compounds, Operation of the ES ion source in the manner described expands the neutral compound types amenable to low level detection by ES-MS to include even those that are relatively difficult to oxidize (i,e,, E > 1.0 V vs SCE) and, therefore, also expands the universality of ES as an ionization source, From the electrochemical point of view, this operation of the ES ion source might be viewed as a means to provide molecular weight information, and possibly the structure, for the ionic products formed during a controlled-current electrolysis experiment. [References: 32]