Ion mobility spectrometry after electrospray nebulization and ionization was investigated as a method for the detection of components dissolved in liquids. While electrosprary operating conditions proved promising, greater sensitivity was achieved when the electric potential applied to the sample introduction needle was increased above breakdown potential and a corona discharge was established. Passing the liquid through the corona discharge established a "coronaspray" that efficiently nebulized and ionized the solvent and analytes. In this initial investigation of coronaspray ion mobility spectrometry (CIMS), ion current as a function of potential, temperature, and liquid flow rate was studied; several IMS spectra were obtained; and a continuous monitoring mode of operation was demonstrated. The results from this study indicated that CIMS has potential as a versatile and sensitive detection method for a variety of analytical procedures involving liquid flowing streams such as flow injection analysis, liquid chromatography, capillary zone electrophoresis, and field flow fractionation.
Abstract. Coronaspray ion mobility spectrometry was used in sample detcction following reversed-phase liquid chromatographic separation. Samples were introduced by coronaspray using a fused silica transfer line that was inserted through a stainless steel needle. Ion mobility spectra and chromatographic responses via monitoring of reactant-ion depletion in the software second gate mode were shown for esters of para-hydroxy benzoic acid, isomers of nitroaniline, and a mixture of acetaminophen, caffeine, and phenacetin.
Key words: ion mobility detection. ion mobility spectrometry, HPLC, coronaspruy
INTRODUCTIONAlthough many different methods have been employed to detect components following liquid chromatographic separation, ultraviolet (UV) detection is still used most often, even though its response is limited to compounds with appropriate chromophores. Thus, the search continues for sensitive liquid chromatographic detectors that perform reliably and respond to non-light absorbing species, Yeung has summarized the current status of research with regard to detectors that are available for LC (1). As attention shifts to microcolumn LC, the need is increasing for detectors that can detect small quantities of material, are compatible with low flow rates, and will respond to compounds lacking chromophores. Ion mobility spectrometry (IMS) potentially satisfies these three requirements.An ion mobility spectrometer contains an ambient pressure region where a neutral gas is ionized, typically by beta emission from a b3Ni source (2). These ions, called reactant ions, drift through a uniform electric field at velocities that are based on their gas phase mobilities. When small quantities of organic compounds are present near the ionization source, charge transfer processes occur between these neutral organics and the reactant ions and produce a second set of ions called product ions that change the nature of the charge-carrying species in the spectrometer. Use of an orthogonal electric field as a "gate" at either end of a section of the spectrometer allows the drift time of the ions to be determined.
SummaryIon mobility monitoring has been used for detection in gas, supercritical fluid, and liquid chromatography, illustrating its potential as a method of detection for unified chromatography.
Applications presented include GC-IMD of dioxins in fly ash, SFC-IMD of vitamin E, and HPLC-IMD of alkylamines.Ion mobility spectra of several mixed supercritical fluid mobile phases are also presented. Use of methanol, acetonitrile, and dichloromethane as modifiers of supercritical carbon dioxide, and use of supercritical dichlorodifluoromethane and chlorodifluoromethane as mobile phases had little effect on the reactant ion pattern at the flow rates and concentrations used in this study. Only when acetone was used as a modifier of carbon dioxide did the positive reactant ions change significantly. No effect of modifiers or mobile phase was observed for the negative reactant ions.
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