Since its introduction, the orbitrap has proven to be a robust mass analyzer that can routinely deliver high resolving power and mass accuracy. Unlike conventional ion traps such as the Paul and Penning traps, the orbitrap uses only electrostatic fields to confine and to analyze injected ion populations. In addition, its relatively low cost, simple design and high space‐charge capacity make it suitable for tackling complex scientific problems in which high performance is required. This review begins with a brief account of the set of inventions that led to the orbitrap, followed by a qualitative description of ion capture, ion motion in the trap and modes of detection. Various orbitrap instruments, including the commercially available linear ion trap–orbitrap hybrid mass spectrometers, are also discussed with emphasis on the different methods used to inject ions into the trap. Figures of merit such as resolving power, mass accuracy, dynamic range and sensitivity of each type of instrument are compared. In addition, experimental techniques that allow mass‐selective manipulation of the motion of confined ions and their potential application in tandem mass spectrometry in the orbitrap are described. Finally, some specific applications are reviewed to illustrate the performance and versatility of the orbitrap mass spectrometers. © 2008 Wiley Periodicals, Inc., Mass Spec Rev 27: 661–699, 2008

The analysis of Stevia leaves has been demonstrated without any sample preparation using desorption electrospray ionization (DESI) mass spectrometry. Direct rapid analysis was achieved using minimal amounts of sample ( approximately 0.15 cm x 0.15 cm leaf fragment). Characteristic constituents of the Stevia plant are observed in both the positive and negative ion modes including a series of diterpene 'sweet' glycosides. The presence of the glycosides was confirmed via tandem mass spectrometry analysis using collision-induced dissociation and further supported by exact mass measurements using an LTQ-Orbitrap. The analysis of both untreated and hexane-extracted dry leaves proved that DESI can be successfully used to analyze untreated leaf fragments as identical profiles were obtained from both types of samples. Characterization and semi-quantitative determination of the glycosides was achieved based on the glycoside profile within the full mass spectrum. In addition, the presence of characteristic glycosides in an all-natural commercial Stevia dietary supplement was confirmed. This study provides an example of the application of DESI to direct screening of plant materials, in this case diterpene glycosides.

The ability to detect reactive intermediates in solution using mass spectrometry (MS) has significantly advanced in the last decade owing to the development of atmospheric pressure ionization methods such as electrospray ionization (ESI). [1,2] The recent invention of desorption electrospray ionization (DESI) [3] allows samples to be directly ionized in the open environment and introduced into the mass spectrometer without the need for sample pretreatment. These features make DESI easily amenable to high-throughput analyses and increase the variety of samples that can be analyzed by MS. [4,5,6] In DESI, charged droplets in a stream of gas are directed at an analyte of interest, which has been deposited on a surface. Upon impact, analyte molecules are extracted from the surface into secondary microdroplets, from which gasphase ions are eventually formed. [5,7] By adding reagents to the spray, it is possible to perform reactions with compounds adsorbed on surfaces and monitor the products in real time. [8] Transfer hydrogenation using Ru organometallic catalysts in the presence of a hydrogen donor is a simple, efficient, nonhazardous, and highly enantioselective approach for the reduction of multiple bonds. [9, 10,11] The asymmetric reduction of carbonyl bonds to form chiral alcohols is an important reaction in nature and in organic syntheses. [9, 12] One approach to synthesizing Ru II asymmetric transfer hydrogenation catalysts is to react [{RuCl 2 (p-cymene)} 2 ] (1) with amino alcohol ligands (L) such as (1R, 2S)-cis-1-amino-2-indanol (2; Scheme 1 a). [2, 13,14] Our research group has studied these organometallic reactions at room temperature and atmospheric pressure by placing 1 on a surface and L in the nebulizer spray of a DESI source. Herein, we demonstrate for the first time that DESI can intercept reactive intermediates formed in the secondary microdroplets on the millisecond timescale.The analysis of 1 (5 mL of 510 À3 m solution in CH 2 Cl 2 deposited on paper) by DESI using CH 3 OH as the reagent spray solution (liquid flow rate = 10 mL min À1 ; N 2 flow rate = 0.6 L min À1 ; spray voltage = 5 kV) resulted in signals corresponding to the isotopic distributions at m/z 559, m/z 579, and m/z 634, which are produced by fragmentation and reaction of 1 with CH 3 OH and H 2 O (Figure 1 a; the assignment of these signals will be discussed later). From this point forward specific isotopic distributions will be referred to using the m/z ratio of the most abundant signal. When amino alcohol 2 (10 À4 m solution in CH 3 OH) was introduced as a Scheme 1. a) Proposed mechanism for the formation of a Ru II asymmetric hydrogen-transfer catalyst from the reaction of [{RuCl 2 (pcymene)} 2 ] (1) with (1R, 2S)-cis-1-amino-2-indanol (2). The stated experimental conditions refer to reactions carried out with bulk quantities. [2,14] b) The structures of other ligands studied: (R)-2-phenylglycinol (3), 2-aminophenethyl alcohol (4), and 4-aminophenethyl alcohol (5).[

Sublimation of near-racemic samples of serine yields a sublimate which is highly enriched in the major enantiomer; this simple one-step process occurs under relatively mild conditions, and represents a possible mechanism for the chiral amplification step in homochirogenesis.

We have applied an ambient ionization technique, desorption electrospray ionization MS, to identify transient reactive species of an archetypal C-H amination reaction catalyzed by a dirhodium tetracarboxylate complex. Using this analytical method, we have detected previously proposed short-lived reaction intermediates, including two nitrenoid complexes that differ in oxidation state. Our findings suggest that an Rh-nitrene oxidant can react with hydrocarbon substrates through a hydrogen atom abstraction pathway and raise the intriguing possibility that two catalytic C-H amination pathways may be operative in a typical bulk solution reaction. As highlighted by these results, desorption electrospray ionization MS should have broad applicability for the mechanistic study of catalytic processes.mass spectrometry | transient intermediates | C-H oxidation | catalysis C atalytic methods for selective C-H oxidation rely on the exquisite choreography of a series of ligand substitution and redox events (1, 2) and in some instances, the controlled generation of a hyperreactive electrophile (3-5). The Du Bois laboratory has developed an amination protocol that uses the catalyst bis [rhodium(α,α,α′,α′-tetramethyl-1,3-benzenedipropionic acid)], hereafter designated as Rh 2 (esp) 2 , to promote both intra-and intermolecular oxidation reactions (1, 2). Indirect evidence has implicated a reactive Rh-nitrene intermediate that oxidizes saturated C-H bonds through a concerted asynchronous two-electron insertion event (6-10). Studies of the reaction mechanism suggest the generation of a one-electron oxidized form of the catalyst, [Rh 2 (esp) 2 ]+ , which appears to result from reaction of the nitrenoid oxidant (4, 5, 11). The fast rates of the on-and off-path steps in this catalytic process and the transient nature of the reactive Rh-nitrene have confounded direct detection of many of the proposed reaction intermediates.A preponderance of experimental and theoretical data (7-10, 12, 13) supports the mechanism for Rh-catalyzed C-H amination depicted in Fig. 1. Sulfamate 2 and iodine oxidant 3 condense to form iminoiodinane 4 (14, 15). The iminoiodinane is a ligand for Rh 2 (esp) 2 , which react to generate [Rh 2 (esp) 2 ]•PhINSO 2 OR 5; subsequent loss of iodobenzene (PhI) furnishes nitrenoid 6. Oxidation of adamantane by 6 gives the sulfonamide product 7 and regenerates the dirhodium catalyst 1. The structures of intermediates 5 and 6 were postulated through analogy to carbenoid intermediates in reactions of dirhodium catalysts with diazo compounds, and to the best of our knowledge, have not been observed spectroscopically (6-10, 12, 13). In our experience, the oxidation of substrate by Rh-nitrene 6 seems to correlate with competitive formation of a mixed-valent (Rh 2+ /Rh 3+ ) dimer 8 that visibly colors the reaction solution red. Previous studies show that this red species is generated when Rh 2 (esp) 2 1, sulfamate 2, and oxidant 3 are mixed in solution (e.g., 0.3 mM 1 in chlorobenzene) (4,5,11). In this report, we provide direct...