Soft ionization method coupling

A different experimental approach to NRMS is embodied in the tandem quadrupole acceleration-deceleration instrument that uses quadrupole mass filters for mass selection and analysis of low-energy (70-80 eV) ions whereas collisional electron transfer is carried out after ion acceleration to 4-8 keV kinetic energies (Fig. 5) [10, 50]. The reionized products are decelerated back to 70-80 eV for mass analysis. The quadrupole instrument achieves unit mass resolution of NR products and it is versatile enough to allow variable-time and photoexcitation experiments described briefly below. Coupling with soft ionization methods... 

A possible solution to the above problems would be the triple-dimensional analysis by using GC x GC coupled to TOFMS. Mass spectrometric techniques improve component identification and sensitivity, especially for the limited spectral fragmentation produced by soft ionization methods, such as chemical ionization (Cl) and field ionization (FI). The use of MS to provide a unique identity for overlapping components in the chromatogram makes identification much easier. Thus MS is the most recognized spectroscopic tool for identification of GC X GC-separated components. However, quadru-pole conventional mass spectrometers are unable to reach the resolution levels required for such separations. Only TOFMS possess the necessary speed of spectral acquisition to give more than 50 spectra/sec. This area of recent development is one of the most important and promising methods to improve the analysis of essential oil components. 

An impetus in the field of mass spectrometry (MS) analysis occurred in the early 1990s with the invention of two novel and soft ionization methods, electrospray ionization (ESI) by John Fenn and matrix-assisted laser desorption ionization (MALDI) by Koichi Tanaka, who both shared the Nobel Prize in Chemistry in 2002. A second impetus, which is more diffuse, is currently occurring and consists of miniaturization. Whereas the intrinsic sensitivity of mass spectrometers has roughly remained the same for a couple of decades, the amount of material required for recording one spectrum has... 

The inductively coupled plasma ion source was developed to accomplish exactly the opposite of the two soft ionization methods just described. Molecules are reduced to their atomic (i.e. elemental) components through the application of intense energy. Masses corresponding to elements of interest (e.g. 30.974 for phosphorus) are then specifically monitored. 

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. ... 

Much data on the structure of flavonoids in crude or semipurified plant extracts have been obtained by HPLC coupled with MS, in order to obtain information on sugar and acyl moieties not revealed by ultraviolet spectrum, without the need to isolate and hydrolyze the compounds. In the last decade, soft ionization MS techniques have been used in this respect, e.g., thermospray (TSP) and atmospheric pressure ionization (API). However, the most used methods for the determination of phenols in crude plant extracts were the coupling of liquid chromatography (LC) and MS with API techniques such as electrospray ionization (ESI) MS and atmospheric pressure chemical ionization (APCI) MS. ESI and APCI are soft ionization techniques that generate mainly protonated molecules for relatively small metabolites such as flavonoids. 

Currently, the most commonly used method for determining drug impurities is HPLC-MS. Such analysis requires proper preparation of the sample, adequate adjustment of separation parameters, and use of an ionization method. The use of soft ionization produces the molecular ion of the impurity and enables its molecular weight to be established. Use of tandem MS/MS spectrometry allows the chemical structure of the impurity to be established by marking its fragmentation schemes. Liquid chromatography coupled with MS detection was used in purity studies of zaleplon [63], etoricoxib [64], ethanediol, diacetate [65], dicloxacillin [66], quinapril [67], and others described in several review articles [68-70]. 

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