Direct Ionization

There is a strong similarity between the mechanism shown m Eigure 5 12 and the one shown for alcohol dehydration m Eigure 5 6 The mam difference between the dehy dration of 2 methyl 2 butanol and the dehydrohalogenation of 2 bromo 2 methylbutane IS the source of the carbocation When the alcohol is the substrate it is the correspond mg alkyloxonmm ion that dissociates to form the carbocation The alkyl halide ionizes directly to the carbocation... 

Since the sample is ionized directly from solution it is protected from heat and many thermally labile analytes may be studied with httle or uo degradation. 

Tandem mass spectrometry (MS/MS) is another common approach used for protein identification. In this method, proteins are digested and the resulting peptides are ionized directly from the liquid phase by... 

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... 

The second example was the pyruvate decarboxylase catalyzed formation of (ll )-l-hydroxy-l-phenyl-2-propanone (PAC) with benzaldehyde as substrate (Fig. 5 a) [64]. This second reaction shows one potential limitation of this method. Some compounds are too volatile for direct measurement by MALDl mass spectrometry or they do not ionize directly due to their nonpolar character. In this case, these compounds have to be derivatized prior to their measurement in order to reduce their volatihty and to introduce ionizable functions. This is, however, often very easy using well estabhshed quantitative reactions, e.g., formation of oximes from aldehydes and sugars (Fig. 5b). 

There are, initially, at least three types of molecular ions from which other ions may be derived. These are formed by electron ionization, direct desorption, and ion/molecule processes, especially cat ionization/anionization. The means by which these... 

The molecular component of the heteroclusters with the lower IP may be ionized directly. In this case, the ionization threshold of the heteroclusters would correspond to the IP of the polyatomic molecule and the amount of internal energy deposited would be relatively small at the ionization threshold, leading to negligible fragmentation (Gover et al. 1991). 

Peptide Mixture ionized directly for MS/MS by ESI or Mixture Mixture separated by LC ionized for MS/MS ... 

The observed spectrum probably results from the superposition of several phenomena evaporation of the sample with rapid ionization, direct ionization on the surface of the filament, direct ion desorption and, at higher temperature, pyrolysis followed by ionization. 

Thermoionization. A fraction of the large hydrocarbon molecules and soot particles, both represented by R, can be ionized directly via the reaction ... 

Neutrons which are uncharged particles. Therefore, they do not produce ionization directly. But, their interaction with the atoms of matter can give rise to alpha, beta, gamma, or X-rays which then produce ionization. Neutrons are penetrating and can only be stopped by thick masses of concrete, water, or paraffin. 

Multiphoton absorption leads to electrons in the irradiated molecules raised to highly excited states. The excitation may be such that the sample is ionized directly, as in the plasma which is the basis of laser desorption ionization (LDI). Generally, there is only a small excess of ions formed in this way, and a secondary ionization is necessary to obtain a better yield of charged species. 

Only a small portion of secondary particles ( 1 % of total secondary particles) are ionized and become the secondary ions that are analyzed in SIMS. A sputtered particle faces competition between ionization and neutralization processes when it escapes a sample surface. Ionization probability represents the chance of a sputtered particle being an ion. The ionization probability is strongly affected by the electronic properties of the sample matrix. Ionization directly affects the signal intensity of secondary ions as shown in the basic equation of secondary ion yield. 

Electrospray Generation of charged Ionization directly from sample solution... 

This diagram represents ionization of a core electron via a shape resonance orbital. In the first step the core electron is excited to an orbital above the ionization threshold that has a large amplitude n the vicinity of the molecule. The second step represents separation of the electron from the molecule. The subsequent relaxation then is identical to the situation where the core electron is ionized directly. These channels, depicted in Table II, are Auger decay... 

Mass spectrometry (MS) is one of the most powerful detection techniques used in liquid-phase analyses,1 mainly due to the ease of interfacing with separation techniques such as capillary electrophoresis (CE)2,3 and high-performance liquid chromatography (HPLC).4 Due to its sensitivity and applicability to a wide variety of chemical and biochemical species, MS is also used for the analysis of (bio)chemical molecules processed in microfluidics devices.5,6 Electrospray ionization (ESI)7 10 is often used to transfer samples from microfluidics chips to a mass spectrometer, involving analyte ionization directly from solutions and operating at flow rates typically used in microfluidics devices.11 Due to its effectiveness, the use of chip-MS coupling has rapidly spread in many research areas with bioanalytical applications,12 such as the... 

One unique development in relation to electrospray is paperspray, a soft ionization method in which the sample is ionized into the IMS in an nncomplicated manner without the need for a pump or capillary. The advantage is that an analyte can be ionized directly from filter paper containing the sample or after separation by paper chromatography. Examples of the nse of paperspray-lMS inclnde chlorpromazine, reserpine, and 2,6 Di-t-butylpyridine. 

Cold ions can also be formed by two-photon ionization directly behind the nozzle of a supersonic neutral molecular beam [486]. These cold ions can then be further investigated by one of the laser spectroscopic techniques discussed above. The combination of pulsed lasers and pulsed nozzles with time-of-flight spectrometers gives sufficiently large signals to study not only molecular excitation but also the different fragmentation processes [487 89]. 

All these chromatographic mass spectrometric techniques are time consuming because a separation has to be made before the sample can be ionized. Direct analysis of biological samples by MS without... 

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