Detection systems atmospheric pressure chemical

As regards the sensitivity of the MS detection in HPLC analysis of flavonoids, this technique has proved to be the most sensitive as compared to UV and fluorescence detection. A very comprehensive comparison of the four detection systems—UV, fluorescence, and two MS systems [atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI)]—for the determination of the previously identified 3, 4, 5 -trimethoxyflavone is presented in Table 1. Fluorescence detection is 10 times more sensitive than UV detection, whereas MS detection is 50 times more sensitive than UV detection and 5 times more sensitive than fluorescence detection. 

Negative atmospheric pressure chemical ionization (APC) low-energy collision activation mss spectrometry has also been employed for the characterization of flavonoids in extracts of fresh herbs. Besides the separation, quantitative determination and identification of flavonoids, the objective of the study was the comparison of the efficacy of the various detection systems in the analysis of flavonoids in herb extracts. Freeze-dried herbs (0.5g of chives, cress, dill, lovage, mint, oregano, parsley, rosemary, tarragon and thyme) were ground and extracted with 20 ml of 62.5 per cent aqueous methanol. After sedimentation the suspension was filtered and used for HPLC analyses. Separations were carried out in an... 

MS is undoubtedly the solution of the near future for LC detection. Improvements made to interfacing devices together with a continuous and sensible diminution of instrumentation costs promote MS as a universal/selective tunable detection system. Atmospheric pressrue electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) are the most robust and popular devices for interfacing MS to LC systems. In Table 9, LC-MS data for some pesticides are given. Although ESI and APCI are more often used, other LC-MS interfaces produce reliable results in pesticide applications thermospray (TSI), particle beam (PBI) and matrix-assisted postsource decay laser desorption/ionization (CID-PSD-MALDI). 

The basic function of the mass spectrometer is to measure the mass-to-charge ratios of analyte ions, and the various designs of mass spectrometers have been described in detail in the literature. The HPLC-MS system has four main components consisting of a sample inlet, an ion source, a mass analyzer, and finally an ion detector. The sample introduction system vaporizes the HPLC column effluent. The ion source produces ions from the neutral analyte molecules in the vapor phase. Several designs of ion sources have been used over the past years including electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), thermospray ionization (TSP), continuous flow fast atom bombardment (FAB), and atmospheric pressure photoionization (APPI). The inductively coupled plasma (ICP) is a hard ionization source and is used specifically for the detection of metals and metals in adducts or in organometallic compounds. Generally, ICP-MS is used for elemental speciation analysis with HPLC, which has been described elsewhere in... 

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],... 

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