Ambient pressure ionization

Chemical ionization can be used at ambient pressures. Chemical ionization was used in tandem MS, using a triple quadrupole instrument, to characterize the antipsychotic agent 2-amino-N(4-(4-(l,2-benzisothiazol-3-yl)-l-piperazinyl)butyl)benzamide from human plasma.5... 

Ion mobility spectrometry (IMS) [3,12] is the most widely used instrument for drug detection. The sample is heated to vaporize the analyte, which is then ionized by atmospheric (ambient) pressure chemical ionization (APCI) [3]. The resulting gas-phase ions travel through a drift tube and are separated by their distinct velocities (mobilities) in a weak electrostatic field. IMS instruments use ambient air or nitrogen as the carrier gas, making it particularly adaptable to field applications. 

G.A. Eiceman, J.H. Kremer, A.P. Snyder and J.K. TofFeri, Quantitative assessment of a corona discharge ion source in atmospheric pressure ionization-mass spectrometry for ambient air monitoring. International Journal of Environmental Analayrical Chemistry 33 (1988) 161—183. 

Electrospray (ESI) is an atmospheric pressure ionization source in which the sample is ionized at an ambient pressure and then transferred into the MS. It was first developed by John Fenn in the late 1980s [1] and rapidly became one of the most widely used ionization techniques in mass spectrometry due to its high sensitivity and versatility. It is a soft ionization technique for analytes present in solution therefore, it can easily be coupled with separation methods such as LC and capillary electrophoresis (CE). The development of ESI has a wide field of applications, from small polar molecules to high molecular weight compounds such as protein and nucleotides. In 2002, the Nobel Prize was awarded to John Fenn following his studies on electrospray, for the development of soft desorption ionization methods for mass spectrometric analyses of biological macromolecules. ... 

Sulfur probe An ionization probe coated with a thin layer of molten sulfur on its conducting tip is used for measurement of shock velocity (Figure 3.18b). This is a special probe which is used in the conducting medium (Sulfur is non-conducting at ambient pressure but becomes conducting at shock pressures as its resistance decreases drastically at such pressures). This property of sulfur allows the R-C network to generate an electrical pulse at the time of arrival of shock wave. 

Some altitude effects on the operation of chromatographic instruments are anticipated. To achieve reproducible retention times for identifying compounds, mobile-phase flows need to be controlled so that they are independent of ambient pressure. Detectors may also respond to changes in pressure. For example, the electron capture detector is a concentration-sensitive sensor and exhibits diminished signal as the pressure decreases. Other detectors, such as the flame ionization detector, respond to the mass of the sample and are insensitive to altitude as long as the mass flow is controlled. 

Dwivedi P, Hill HH Jr (2008) A rapid analytical method for hair analysis using ambient pressure ion mobility mass spectrometry with electrospray ionization (ESI-IMMS). Int J Ion Mobil Spec 11 61-69... 

Ion mobility spectrometry (IMS) is an instrumental method where sample vapors are ionized and gaseous ions derived from a sample are characterized for speed of movement as a swarm in an electric field [1], The steps for both ion formation and ion characterization occur in most analytical mobility spectrometers at ambient pressure in a purified air atmosphere, and one attraction of this method is the simplicity of instrumentation without vacuum systems as found in mass spectrometers. Another attraction with this method is the chemical information gleaned from an IMS measurement including quantitative information, often with low limits of detection [2 1], and structural information or classification by chemical family [5,6], Much of the value with a mobility spectrometer is the selectivity of response that is associated with gas-phase chemical reactions in air at ambient pressure where substance can be preferentially ionized and detected while matrix interferences can be eliminated or suppressed. In 2004, over 20000 IMS-based analyzers such as those shown in Fig. 1 are placed at airports and other sensitive locations worldwide as commercially available instruments for the determination of explosives at trace concentration [7],... 

The solubility measure describes the concentration reached in solution, when a pure phase of the material is allowed to dissolve in the solvent for a defined period of time, at a defined temperature (and pressure). Most often for pharmaceutical purposes, the pure phase is a solid, ideally a crystalline solid, and the liquid is water or a buffered aqueous solution, at a controlled temperature (often 25 or 37 °C) and ambient pressure. The purity of the solid can have a large effect on measured solubility. Solubility can be measured in water or in pH-controlled buffers. In water, the extent of solubility for ionizable compounds will depend upon the p fCa values and the nature of the counterion. In pH-controlled aqueous buffered solution, at equilibrium, the solubility will depend upon the compound s intrinsic solubility, its plQ, and the ionic strength. It may also depend upon the relative solubility of the initial added compound and the solubility of the salt formed by the compound with the buffer salts, with which the solid may equilibrate. In any buffer or solvent system, the measured solubility may depend on the time of sampling, as solubility kinetics... 

The need for an ionization source that provided both softer ionization, i.e., less fragmentation of the molecular ion, and a convenient interface with liquid chromatography (at ambient pressure) to mass spectrometry (at high vacuum) helped spur the creation of atmospheric pressure ionization. Two techniques fall under the heading of API, electrospray and atmospheric pressure chemical ionization (APCI), and the technical aspects of each are discussed individually. However, many of the fundamental principals that describe these ionization mechanisms can be applied to both electrospray and APCI sources. 

TAS) energies or between pressure-induced electron delocalization and temperature-induced electron ionization, reflected on stabilities of phases and the phase boundaries. These pressure-temperature induced changes are unique, establishing an entirely different set of periodic behaviors in crystal stmcture and electronic and magnetic properties not found in the conventional periodic table. In return, this is what makes the Mbar chemistry" unique from any ambient-pressure combinatorial chemistry based on variation of chemical composition and temperature. New opportunities to discover interesting phenomena and exotic materials exist in both liquids and solids at high pressures. 

A new generation of mass spectrometer inlets allow for direct sampling of a substrate under ambient conditions. Theoretically, this eliminates the need for any sample preparation. Examples include direct analysis in real time (DART) and desorption electrospray ionization (DESI), as well as desorption atmospheric-pressure chemical ionization (DAPCI) and atmospheric solids analysis probe (ASAP). These techniques utilize a source of energy interacting directly with a sample surface at ambient pressure, causing molecules of interest to desorb, ionize, and be sampled by a mass spectrometer. 

Selectivity and versatility of measnrements have been enhanced through the use of a range of ion sources operated at ambient pressure and easily combined with drift tubes. Techniques to measure samples as liquids and solids, not only gases, have been incorporated significantly into IMS technology during the past decade and have transformed IMS from a vapor analyzer with niche applications to a measurement technique broadly applicable to semivolatile or nonvolatile substances. Indeed, a reason for the increase in visibility of mobility spectrometry as an analytical method is the combination of electrospray ionization (ESI) with drift tubes and the combination of mobility analyzers with mass spectrometers. This combination of ESI-IMS-MS with drift tnbes at ambient pressure and at reduced pressures of... 

Sukumar, H. Stone, J.A. Nishiyama, T. Yuan, C. Eiceman, G.A., Paper spray ionization with ion mobility spectrometry at ambient pressure, Int. J. Ion Mobil. Spectrom. 2011, 14,51-59. 

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