Gas-phase ion chromatography

Bowers. M.T.. el al. "Gas-Phase Ion Chromatography. 1 ransmon Mrul Slaie Selection and Carhon Cluslci Formation." Science. 1446 tJunc 4. 1993). 

Bo93 M. T. Bowers, P. R. Kempdr, G. von Helden and P. A. M van Koopen, Gas-Phase Ion Chromatography Transition Metal State... 

We have recently developed a gas-phase ion chromatography technique and applied it to carbon cluster cations " " and anions""". A pulse of mass-selected cluster ions is injected into a high-pressure drift cell filled with 2-5 torr of helium. The ionic mobilities of different isomeric structures depend on their different collision cross-sections with He, and the isomers are therefore separated while drifting through the cell, under the influence of a weak electric field. The absolute value of the ionic mobility for a given cluster together with computer simulations often allows unambiguous determination of the cluster... 

Four of the most powerful methods presently applied to elucidate metal cluster geometric structure will be presented in the following. These are mass-selected negative ion photoelectron spectroscopy, infrared vibrational spectroscopy made possible by very recent advances in free electron laser (FEL) technology, gas-phase ion chromatography (ion mobility measurements), and rf-ion trap electron diffraction of stored mass-selected cluster ions. All methods include mass-selection techniques as discussed in the previous section and efficient ion detection schemes which are customary in current gas-phase ion chemistry and physics [71]. 

The mechanism of spontaneous fullerene formation has been the subject of much debate and speculation [90]. One of the major advances in this area comes from gas-phase ion chromatography, which allows to separate charged carbon clusters of specific mass into families of isomers based on their mobilities through helium-filled drift tubes [91-93]. These families (e.g., monocyclic rings, bi- and tricyclic compounds, fullerenes) are identified by comparing the observed mobilities with those calculated from optimized semiempirical equilibrium geometries [92], which are aceurate enough for this purpose. Such studies lead to product distributions of the cations C as a function of n [90-93] and allow the tentative formulation of a detailed mechanism for fullerene synthesis [93]. 

Bowers, M.T. Kemper, P.R. von Helden, G. van Koppen, P.A.M., Gas-phase ion chromatography transition metal state selection and carbon cluster formation. Science 1993, 260 (June 4), 1446-1451. 

Fresh and frozen human tissue samples obtained from brain, liver, and kidney have been analyzed for hydrogen sulfide levels by sulfide-derived methylene blue determination using ion-interaction reversed-phase HPLC (Mitchell et al. 1993). This method can quantify nmol/g levels of sulfide. Gas dialysis/ion chromatography with ECD has been utilized for measurement of sulfide in brain tissue with 95-100% recovery (Goodwin et al. 1989). 

Ions that vaporize from aerosol droplets were already in solution in the chromatography column. For example, protonated bases (BH+) and ionized acids (A ) can be observed. Other gas-phase ions arise from complexation between analyte, M (which could be neutral or charged), and stable ions from the solution. Examples include... 

The coupling of liquid chromatography is more delicate because gas-phase ions must be produced for mass spectrometry. Liquid chromatography normally is used for compounds that are not volatile and are not suitable for gas chromatography. 

E/ectrospray ionisation is an atmospheric pressure ionization technique in which ions are generated in solution phase, the carrier solvent is evaporated, and a gas-phase ion is produced (see Fig. 4) [26]. An appropriate solvent (typically the effluent from a liquid chromatography system) is passed through a metal capillary to which is applied a static DC voltage. This voltage induces ionization of the... 

As mentioned above in the context of the analysis of hgnin degradation products, gas chro-matography/mass spectrometry and related methods have been developed as extremely powerful tools for the identification of phenolic compounds. Use of high-pressure liquid chromatography in combination with mass spectrometry adds to the analytical arsenal with respect to the detection of polar, non-volatile compounds but, in particular, the advent of modem ionization techniques, such as ESI and MALDI mass spectrometry, have continued to broaden the analytically governable field of organic chemistry. The latter methods diminish the need of derivatization of polar phenolics to increase the volatility of the analyte. In this section, a more or less arbitrary selection of examples for the application of mass spectrometric techniques in analytical chemistry is added to the cases already discussed above in the context of gas-phase ion chemistry. 

A prerequisite for detection, identification, and quantification of any species by MS is that all analytes must be converted into gas-phase ions before they enter the mass analyzer. API techniques are most widely used for metabolite identification, mainly due to their ability to couple to liquid chromatography and generate intact gas-phase molecular ions at very high sensitivity (Rossi, 2002 Voyksner, 1997). 

Currently, MS is primarily used in analytical apphcations. In fact, rather than the study of ion stractures, gas-phase ion-molecnle reactions, or the stracture elncidation of unknown compounds, the routine qnantitative analysis of target analytes in complex (biological) matrices using combined gas chromatography (GC-MS) or liquid chromatography (LC-MS) is by far the most important application area of MS. Nevertheless, mass spectrometers have proven to be powerful tools for studying the kinetics, mechanisms, and prodnct distribntions of gas-phase bi- and termolecular organic reactions. A wide variety of ion-molecnle reactions may be studied [1]. 

Desorption electrospray ionization (DESI) may serve as an example of the maiy atmospheric-pressure surface ionization technique that has recently been introduced [63, 76]. In DESI, the high-velocity spray of charged microdroplets from a (pneumatically assisted) electrospray needle is directed at a surface, which is mounted in front of the ion-sampling orifice of an API source (see Fig. 7.6). Surface constituents are released fiom the surface and ionized. These gas-phase ions can be introduced to and observed by MS [77]. In this way, DESI-MS enables for instance the analysis of dmgs in tablets or natural products in plant parts withont extensive sample pre-treatment or prior separation. In addition, DESI-MS and some of its related snrface ionization techniqnes enable chemical imaging of surfaces such as thin-layer chromatography (TLC) plates and tissue sections [78]. 

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