DAPCI

DGE a AC AMS APCI API AP-MALDI APPI ASAP BIRD c CAD CE CF CF-FAB Cl CID cw CZE Da DAPCI DART DC DE DESI DIOS DTIMS EC ECD El ELDI EM ESI ETD eV f FAB FAIMS FD FI FT FTICR two-dimensional gel electrophoresis atto, 10 18 alternating current accelerator mass spectrometry atmospheric pressure chemical ionization atmospheric pressure ionization atmospheric pressure matrix-assisted laser desorption/ionization atmospheric pressure photoionization atmospheric-pressure solids analysis probe blackbody infrared radiative dissociation centi, 10-2 collision-activated dissociation capillary electrophoresis continuous flow continuous flow fast atom bombardment chemical ionization collision-induced dissociation continuous wave capillary zone electrophoresis dalton desorption atmospheric pressure chemical ionization direct analysis in real time direct current delayed extraction desorption electrospray ionization desorption/ionization on silicon drift tube ion mobility spectrometry electrochromatography electron capture dissociation electron ionization electrospray-assisted laser desorption/ionization electron multiplier electrospray ionization electron transfer dissociation electron volt femto, 1CT15 fast atom bombardment field asymmetric waveform ion mobility spectrometry field desorption field ionization Fourier transform Fourier transform ion cyclotron resonance... 

There are some variants that have emerged in the wake of DESI. By replacing the electrospray emitter by a metal needle and allowing solvent vapor into the coaxial gas flow desorption APCI (DAPCI) can be performed [106], Other versions are atmospheric-pressure solids analysis probe (ASAP) where a heated gas jet desorbs the analyte, which is subsequently ionized by a corona discharge [107], and electrospray-assisted laser desorption/ionization (ELDI) where a laser ablates the analyte and charged droplets from an electrospray postionizes the desorbed neutrals [108],... 

One of the most significant developments in mass spectrometry in the recent years is the introduction of a new class of ionization methods where samples in either solid or liquid state can be directly ionized in their native environment under ambient conditions (rather than inside a mass spectrometer) without any sample preparation. This new class of ionization methods is often referred to as ambient ionization methods [1,2], Because these methods generally ionize analytes on the surface or near the surface of the samples at atmospheric pressure, they have also been called atmospheric pressure surface sampling/ionization methods or direct/open air ionization methods [3], Since the first reports on ambient ionization with desorption electrospray ionization (DESI) [4] and direct analysis in real time (DART) [5], numerous reports have been published on the applications of these new ionization methods as well as the introduction of many related ambient ionization methods such as desorption atmospheric pressure chemical ionization (DAPCI) [6], atmospheric solid analysis probe (ASAP) [7], and electrospray-assisted laser desorption/ionization (ELDI) [8], Recently, two reviews of the various established and emerging ambient ionization methods have been published [2,3],... 

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. 

Several other ionization methods have been developed based on DESI, including desorption atmospheric pressure chemical ionization (DAPCI), desorption atmospheric pressure photo-ionization (DAPPI), laser ablation electrospray ionization (LAESI), and extractive electrospray ionization (EESI). Each technique uses variations of the solvent, how the charged beam is formed, and how the beam is nsed to facilitate the prodnction of analyte ions. Because these are surface methods (except EESI), they are incompatible with LC. 

DAPCI desorption atmospheric pressure chemical ionization... 

The first method for liquid chromatography-mass spectrometry analysis of TATP by APCI-MS was reported by Widmer et al. [59]. The atmospheric pressure chemical ionization (APCI) was operated in the positive ion mode and resulted in a TATP LOD of 100 pg/pL. A lower LOD, 3.3ng, has been reported for a method that couples HPLC with an APCI-MS/MS full-scan method [52]. The LOD was reduced to 0.8 ng when SRM was employed with quantitative analysis on ions m/z 223, 132, 91, and 74 [52]. Detection limits in the low nanogram range has been reported for TATP analyzed by desorption atmospheric pressure chemical ionization (DAPCI), a technology similar to DESI [27]. 

Various ionization sources are employed in the analysis of explosives by MS. APCI is used with GC-MS, LC-MS, and LC-MS/MS systems for explosives analysis [200-204] this source is chosen because lower LOD can be found with APCI over El sources. However, El remains the ionization source used most often in GC-MS analyses of explosives [12,134-137,139-143,205], DESI, desorption atmospheric pressure chemical ionization (DAPCI), and direct analysis in real time (DART) sources are used to detect explosives, including emerging explosive threats like TATP and as part of field-deployable MS systems [163,206-209],... 

Most of the mass spectrometry analyses are conducted under vacuum environment. However, ambient mass spectrometry is a rapidly growing field that provides fast and direct analysis of solid sample surfaces or liquid samples introduced on a suitable surface (Alberici et al. 2010 Weston 2010 Huang et al. 2010 Chen et al. 2010). For that, different ambient ionization MS methods, such as atmospheric pressure desorption/ionization on porous silicon (AP-DIOS) (Huikko et al. 2003), desorption electrospray ionization (DESI) (Takats et al. 2004), direct analysis in real time (DART) (Cody et al. 2005), desorption atmospheric pressure chemical ionization (DAPCI) (Takats et al. 2005), and desorption atmospheric pressure photoionization (DAPPI) (Haapala et al. 2007), have been successfully used in the direct analysis of compounds fi"om various samples, such as body fluids (Cody et al. 2005 Chen et al. 2006), finiits, plant leaves (Luosujarvi et al. 2010), milk (Yang et al. 2009), banknotes (Cody et al. 2005), textiles (Cody et al. 2005 Chen et al. 2007), and pharmaceutical formulations (Ifa et al. 2009 Gheen et al. 2010), just to mention a few, without any sample pretreatment. 

Ambient MS is another advance in the field. It allows the analysis of samples with little or no sample preparation. Following the introduction of desorption electrospray ionization (DESI) [108,109], direct analysis in real time (DART) [110], and desorption atmospheric pressure chemical ionization (DAPCI) [111, 112], a number of ambient ionization methods have been introduced. They include electrospray-assisted laser desorption/ionization (ELDI) [113], matrix-assisted laser desorption electrospray ionization (MALDESI) [114], atmospheric solids analysis probe (ASAP) [115], jet desorption ionization (JeDI) [116], desorption sonic spray ionization (DeSSI) [117], field-induced droplet ionization (FIDI) [118], desorption atmospheric pressure photoionization (DAPPI) [119], plasma-assisted desorption ionization (PADI) [120], dielectric barrier discharge ionization (DBDI) [121], and the liquid microjunction surface sampling probe method (LMJ-SSP) [122], etc. All these techniques have shown that ambient MS can be used as a rapid tool to provide efficient desorption and ionization and hence to allow mass spectrometric characterization of target compounds. 

Desorption electrospray ionization (DESI) [1] was introduced at the end of 2004, and direct analysis in real time (DART) [2] soon after in 2005. The apparent potential of both DESI and DART in high-throughput applications soon led to the development of some derivatives with the intention to broaden the field of applications or to adapt the underlying methodology to specific analytical needs. Now, the repertoire of methods includes variations of the DESI theme such as desorption sonic spray ionization (DeSSI) [3], later renamed easy sonic spray ionization (EASI) [4] or extractive electrospray ionization (EESI) [5,6]. Then, there are the DESI analogs of APCI and APPI, i.e., desorption atmospheric-pressure chemical ionization (DAPCI) [7,8] and desorption atmospheric pressure photoionization (DAPPI) [9]. 

Hi) Gas phase charge transfer means that ion formation occurs after volatilization or desorption of neutral species from the surface into the gas phase through ionization via proton/electron transfer or other ion-molecule reactions at atmospheric pressure. Indeed, the assumption of ion-molecule reactions, eventually purely in the gas phase above the sample, has led to the development of an DAPCI source (Chap. 13.2), in the first place to prove this mechanism of ion formation [7]. The solvent pH can be used to positively affect the vapor pressure of the analyte, e.g., the vapor pressure of volatile plant alkaloids is increased by addition of abase. 

It has been shown that addition of solvents can be avoided if the moisture of the ambient air is sufficient to generate HsO reagent ions [8,24]. The setup for DAPCI (using ambient air only) is shown in Fig. 13.9. A comparison of spectra of Proctosedyl, an ointment containing cinchocaine (Mr = 343 u) and hydrocortisone (Mr = 362 u), as obtained by DESI, DAPCI with ambient air, and DAPCI with solvent is presented in Fig. 13.10. 

Fig. 13.9. Schematic of a DAPCI source for operation with moist ambient air as reagent gas. The sharp needle discharge electrode is coaxially centered in a capillary of 3 mm i.d. delivering humidiiled nitrogen gas if the ambient air is below 20% relative humidity. Adapted fromRef. [24] with permission. John Wiley Sons, Ltd., 2007.

Fig. 13.10. Comparison of DESI, solvent-free DAPCI and DAPCI of Proctosedyl ointment, (a) Positive-ion DESI spectrum with the intensity of m/z 363, protonated hydrocortisone, 16-fold expanded to show the low-abundant ion. (b) Positive-ion DAPCI spectrum of the ointment obtained without solvent and same expansion as above, c) Positive-ion DAPCI spectrum obtained with solvent. Reproduced from Ref. [8] with permission. John Wiley Sons, Ltd., 2006.

DESI works best with polar analytes that are easy to protonate or deprotonate, although analytes of low polarity are accessible to a certain extent. This was the rationale for developing DAPCI. In order to improve the efficiency of ambient MS in the regime of low-polarity compounds even further, desorption atmospheric... 

This section on direct analysis in real time (DART) [2] has not been placed at the end of this chapter because it would be inferior to the preceding techniques, but because DART relies on much different phenomena. In fact, DART delivers analytical results very similar to those of DESI, even more so to those of DAPCI or DAPPI, and thus presents an alternative concept of ambient MS. 

DAPCI Desorption atmospheric pressure chemical ionization Sample surface exposed to APCI [17]... 

Used for separating 1-O-glycopyranosyl sinapate from rapeseed liquid-assisted surface desorption atmosphmc pressure chemical ionization mass spectrometry (DAPCI-MS) to detect sinapine in radish taproot tissue Sinapine formed a coloured complex with titanium tetrachloride Based on the yellow colour of sinapine in alkaUne media and the weakening of the intensity of the red coloured Fe-sulphosalicylic acid complex in the presence of phytic acid. 

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