Atmospheric pressure chemical ionization technique

Caetano, S., Decaestecker, T., PuL R., Daszykowski, M., Van Bocxlaer, J. and Vander Heyden, Y. (2005) Exploring and modelling the responses of electrospray and atmospheric pressure chemical ionization techniques based on molecular descriptors. Anal. Chim. Acta, 550, 92—106. 

Expanded and refined discussion of sampling and ionization methods, including atmospheric pressure chemical ionization techniques. 

The effects of dentifrice components on flavor release in vitro using static head-space had previously been studied (36-37). Recently consumer emphasis on long-lasting flavor has led to extensive work in understanding the release of flavor in the oral cavity (38). Atmospheric pressure chemical ionization techniques have... 

One of the first successful techniques for selectively removing solvent from a solution without losing the dissolved solute was to add the solution dropwise to a moving continuous belt. The drops of solution on the belt were heated sufficiently to evaporate the solvent, and the residual solute on the belt was carried into a normal El (electron ionization) or Cl (chemical ionization) ion source, where it was heated more strongly so that it in turn volatilized and could be ionized. However, the moving-belt system had some mechanical problems and could be temperamental. The more recent, less-mechanical inlets such as electrospray have displaced it. The electrospray inlet should be compared with the atmospheric-pressure chemical ionization (APCI) inlet, which is described in Chapter 9. 

Thus, either the emitted light or the ions formed can be used to examine samples. For example, the mass spectrometric ionization technique of atmospheric-pressure chemical ionization (APCI) utilizes a corona discharge to enhance the number of ions formed. Carbon arc discharges have been used to generate ions of otherwise analytically intractable inorganic substances, with the ions being examined by mass spectrometry. 

Samples containing mixtures of peptides can be analyzed directly by electrospray. Alternatively, the peptides can be separated and analyzed by LC/MS coupling techniques such as electrospray or atmospheric pressure chemical ionization (APCI). 

A number of analytical techniques such as FTIR spectroscopy,65-66 13C NMR,67,68 solid-state 13 C NMR,69 GPC or size exclusion chromatography (SEC),67-72 HPLC,73 mass spectrometric analysis,74 differential scanning calorimetry (DSC),67 75 76 and dynamic mechanical analysis (DMA)77 78 have been utilized to characterize resole syntheses and crosslinking reactions. Packed-column supercritical fluid chromatography with a negative-ion atmospheric pressure chemical ionization mass spectrometric detector has also been used to separate and characterize resoles resins.79 This section provides some examples of how these techniques are used in practical applications. 

Cl is not the only ionization technique where this aspect of interpretation must be considered carefully fast-atom bombardment, thermospray, electrospray and atmospheric-pressure chemical ionization, described below in Sections 3.2.3, 4.6, 4.7 and 4.8, respectively, all produce adducts in the molecular ion region of their spectra. 

Atmospheric-pressure chemical ionization (APCI) is another of the techniques in which the stream of liquid emerging from an HPLC column is dispersed into small droplets, in this case by the combination of heat and a nebulizing gas, as shown in Figure 4.21. As such, APCI shares many common features with ESI and thermospray which have been discussed previously. The differences between the techniques are the methods used for droplet generation and the mechanism of subsequent ion formation. These differences affect the analytical capabilities, in particular the range of polarity of analyte which may be ionized and the liquid flow rates that may be accommodated. 

Particular emphasis has been placed upon electrospray and atmospheric-pressure chemical ionization (APCI) which, in addition to being the currently most widely used interfaces, are ionization techniques in their own right. 

Atmospheric-pressure chemical ionization (APCI) and electrospray ionization are both soft ionization techniques which give rise, almost exclusively, to the production of molecular species. Structural information. 

The most recent progress in MS analysis of chlorophylls has been obtained with the development of atmospheric ionization methods such as atmospheric pressure chemical ionization (APCl) and electrospray ionization (ESI). These techniques have demonstrated much more sensitivity than thermospray ionization, detecting chloro-... 

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. 

McLoughlin, D.A., Olah, T.V., and Gilbert, J.D. 1997. A direct technique for the simultaneous determination of 10 drug candidates in plasma by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry interfaced to a Prospekt solid-phase extraction system. J. Pharm. Biomed. Anal. 15 1893. 

Atmospheric pressure chemical ionization [17] shares many of the attributes of classical CL The technique has gained great popularity in recent years as one of the simple and rugged techniques for coupling... 

Thomas etal. [72] used pyrolysis gas chromatography-mass spectrometry as a fast economic screening technique for polyaromatic hydrocarbons. Thomas used reverse-phase liquid chromatography with atmospheric pressure chemical ionization mass spectrometry/mass spectrometry for the determination of polycyclic aromatic sulphur heterocycles in sediments. 

Puig et al. [450] determined ng/1 levels of priority methyl-, nitro-, and chloro-phenols in river water samples by an automated on-line SPE technique, followed by liquid chromatography-mass spectrometry (LC-MS) using atmospheric pressure chemical ionization (APCI) and ion spray interfaces. 

Other combinations of chromatography techniques with MS which may be useful in environmental studies are the coupling of high performance liquid chromatography (LC) with MS [84,384,504,506,530,585-593],LC with MS-MS [181, 594 - 599], LC with atmospheric pressure chemical ionization MS (LC-APCI-MS) [600], and Fourier transform infrared spectroscopy-fast atom bombardment coupled to LC-MS (FTIR-FAB-LC-MS) [514]. 

With the development of sophisticated ionization techniques including electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), HPLC-MS techniques have been successfully applied to the online analysis of ginsenosides in extracts and biological fluids (Fuzzati, 2004). In terms of sensitivity and specificity, an MS detector is better than UV or ELSD. Among the various MS methods, the HPLC-MS-MS (or just LC-MS-MS) technique is to date the most sensitive method for detection and quantification of ginsenosides. 

LC/MS is the ultimate analytical technique, which combines the versatility of HPLC with the identification power of MS. The weak link in LC/MS has always been the interface which connects the liquid stream at atmospheric pressure to the high vacuum present inside the mass spectrometer. The development of several atmospheric pressure interfaces, electrospray and atmospheric pressure chemical ionization (APCI), has contributed to the tremendous success and popularity of LC/MS and LC/MS/MS in bioresearch, drug discovery, combinatorial analysis and pharmacokinetic assays. This topic is covered in more depth in a later chapter. 

Rosenberg, E. (2003). The potential of organic (electrospray- and atmospheric pressure chemical ionization) mass spectrometric techniques coupled to liquid-phase separation for speciation analysis. /. Chromatogr. A 1000, 841 — 889. 

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