Atmospheric pressure chemical ionization photoionization

The most important techniques belonging to this class are electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI) and, more recently, atmospheric pressure photoionization (APPI). At present the latter does not have applications in cultural heritage, so it will be not described here. 

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... 

Keski-Hynnilae, H., Kurkela, M., Elovaara, E., Antonio, L., Magdalou, J., Luukkanen, L., Taskinen, J., and Kostiainen, R. (2002). Comparison of electrospray, atmospheric pressure chemical ionization, and atmospheric pressure photoionization in the identification of apomorphine, dobutamine, and entacapone phase II metabolites in biological samples. Anal. Chem. 74, 3449-3457. 

W. A. Comparison of atmospheric pressure chemical ionization, electrospray ionization, and atmospheric pressure photoionization for the determination of cyclosporin a in rat plasma. Anal Chem 2005, 77, 541-548. 

The real breakthrough in LC/MS development was achieved with the broad introduction in the 1990s of atmospheric pressure ionization (API) techniques, such as electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), which enable the analysis of a wide variety of molecular species. The spectrum of available API techniques has been amended meanwhile by the introduction of sonic spray ionization (SSI) and atmospheric pressure photoionization (APPI). 

Figure 2.4 Comparison of (a) sensitivity, (b) variability, (c) selectivity, and (d) pricing between various chemical and immunological analyses for the presence of PPCPs in the environment. FID = flame ionization detector and EC = electrochemical detection. Note that GC-MS-MS can have mass detectors such as triple quadrupole and ion trap with ionization from El = electron ionization or Cl = chemical ionization, whereas LC-MS-MS with ionization from ESI = electrospray ionization, APCI = atmospheric pressure chemical ionization, or APPI = atmospheric pressure photoionization. (Adapted from Ingerslev and HaUing-Sprensen, 2003.)...

Notes AA, acetic acid AAc, ammoniuin acetate ACN, acetonitrile AH, airnnonium hydroxide FA, formic acid MeOH, methanol TFA, trifluoroacetic acid THF, Tetrahydrofuran APCI, atmospheric pressure chemical ionization APPI, atmospheric pressure photoionization ESI, electrospray ionization IS, ion spray IT, ion trap Q, single quadrupole QqQ, triple quadrupole TOF, time of flight. 

Rauha JP, Vuorela H and Kostiainen R, Effect of eluent on the ionization efficiency of flavonoids by ion spray, atmospheric pressure chemical ionization, and atmospheric pressure photoionization mass spectrometry../ Mass Spectrom 36 1269-1280 (2001). 

Lien G, Chen C, Wang G (2009) Comparison of electrospray ionization, atmospheric pressure chemical ionization and atmospheric pressure photoionization for determining estrogenic chemicals in water by liquid chromatography tandem mass spectrometry with chemical derivatizations. J Chromatogr A 1216 956-966... 

These direct ion sources exist under two types liquid-phase ion sources and solid-state ion sources. In liquid-phase ion sources the analyte is in solution. This solution is introduced, by nebulization, as droplets into the source where ions are produced at atmospheric pressure and focused into the mass spectrometer through some vacuum pumping stages. Electrospray, atmospheric pressure chemical ionization and atmospheric pressure photoionization sources correspond to this type. In solid-state ion sources, the analyte is in an involatile deposit. It is obtained by various preparation methods which frequently involve the introduction of a matrix that can be either a solid or a viscous fluid. This deposit is then irradiated by energetic particles or photons that desorb ions near the surface of the deposit. These ions can be extracted by an electric field and focused towards the analyser. Matrix-assisted laser desorption, secondary ion mass spectrometry, plasma desorption and field desorption sources all use this strategy to produce ions. Fast atom bombardment uses an involatile liquid matrix. 

Different methods are used to tackle these problems [10-13], Some of these coupling methods, such as moving-belt coupling or the particle beam (PB) interface, are based on the selective vaporization of the elution solvent before it enters the spectrometer source. Other methods such as direct liquid introduction (DLI) [14] or continuous flow FAB (CF-FAB) rely on reducing the flow of the liquid that is introduced into the interface in order to obtain a flow that can be directly pumped into the source. In order to achieve this it must be reduced to one-twentieth of the value calculated above, that is 5 pi min. These flows are obtained from HPLC capillary columns or from a flow split at the outlet of classical HPLC columns. Finally, a series of HPLC/MS coupling methods such as thermospray (TSP), electrospray (ESI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) can tolerate flow rates of about 1 ml min 1 without requiring a flow split. Introducing the eluent entirely into the interface increases the detection sensitivity of these methods. ESI can accept flow rates from 10 nl min-1 levels to... 

Earlier methods of ionization applied to carotenoids, including electron impact (El), chemical ionization (Cl), a particle beam interface with El or Cl, and continuous-flow fast atom bombardment (CF-FAB), have been comprehensively reviewed elsewhere (van Breemen, 1996, 1997 Pajkovic and van Breemen, 2005). These techniques have generally been replaced by softer ionization techniques like electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), and more recently atmospheric pressure photoionization (APPI). It should be noted that ESI, APCI, and APPI can be used as ionization methods with a direct infusion of an analyte in solution (i.e. not interfaced with an HPLC system), or as the interface between the HPEC and the MS. In contrast, matrix-assisted laser desorption ionization (MALDI) cannot be used directly with HPEC. 

S. Ma, S. K. Chowdhury, and K. B. Alton, Thermally induced N-to-O rearrangement of ferf-V-oxides in atmospheric pressure chemical ionization and atmospheric pressure photoionization mass spectrometry Differentiation of V-oxidation from hydroxylation and potential determination of V-oxidation site. Anal. Chem. 77 (2005), 3676-3682. 

Cai SS, Syage JA. Comparison of atmospheric pressure photoionization, atmospheric pressure chemical ionization, and electrospray ionization mass spectrometry for analysis of lipids. Anal. Chem. 2006 78 1191-1199. 

In the current LC-MS interfaces, i.e., ESI and atmospheric-pressure chemical ionization (APCl), interfacing and analyte ionization are closely interrelated. The column effluent is nebulized and ionization takes place in the aerosol generated, either with or without a primary external source of ionization. Ionization mechanisms of ESI, APCl, and atmospheric-pressure photoionization (APPl) are discussed in this chapter. 

Note El is electron ionization, Cl is chemical ionization, FI/FD is field ionization/field desorption, APPI is atmospheric pressure photoionization, and APCI is atmospheric pressure chemical ionization. 

---