Spectrometric detection, chemical ionization-mass

Barcelo D, Porte C, Cid J, Albaiges J (1990) Determination of organophosphorus compounds in Mediterranean coastal waters and biota samples using gas-chromatography with nitrogen-phosphorus and chemical ionization mass-spectrometric detection. Int J Environ Anal Chem 38(2) 199-209... 

S Lacorte, G Jeanty, JL Marty, D Barcelo. Identification of fenthion and temephos and their transformation products in water by high-performace liquid chromatography with diode array detection and atmospheric pressure chemical ionization mass spectrometric detection. J Chromatogr A 777 99-114, 1997. 

In the studies discussed above, HO radicals were detected. HO radicals are neither a reactant nor a product of the H0S02 + O2 reaction (3). Hence, these studies of the kinetics of reaction (3) are indirect. In the work of Gleason et aL (111, the reactant H0S02 and the product SO3 were monitored. This work at first glance appears to be a direct study of the kinetics of reaction (3), until one realizes that these species were monitored by chemical ionization mass spectrometiy. H0S02 was converted to SO3 and SO3 was converted to (Q SC>3) pnor to mass spectrometric detection. The detection of H0S02 and SO3 are based upon a complete understanding of the chemical ionization... 

For several years LC detectors were limited to refractive index and ultraviolet absorption systems. Recently introduced systems include the electrochemical detector and a moving belt interface allowing for chemical ionization-mass spectrometric detection. Both of these techniques provide a degree of selectivity not previously available. 

Lacker, T. SSohschein, S. Albert, K. 1999. Separation and identification of various carotenoids by C30 reversed-phase high-performance liquid chromatography coupled to UV and atmospheric pressure chemical ionization mass spectrometric detection. J. Chromatogr. A 854 37-44. 

Chemical ionization mass spectrometric detection has been explored for the detection of methyl hydroperoxides However, fluorometry has dominated the current detection schemes for the organic peroxides. Typically, a nonfluorescent substrate is oxidized by the peroxide to generate a fluorescent product. These methods are sufficiently sensitive for accurate measurement of the peroxides in the low ppt by volume. For example, the peroxidase-catalyzed dimerization of p-hydroxyphenylacetic acid (POPHA) occurs in the presence of a peroxy group at elevated pH. The formation of the fluorescent dimer, detected by excitation at 310 nm and emission at 405 nm, is proportional to the concentration of the peroxide. The most common peroxidase catalyst used for this reaction is horseradish peroxidase (HRP). Cost and stability issues with the use of HRP led to the use of other catalysts, such as metalloporphyrins or phthalocyanine complexes. Another fluorescent reaction scheme involves the oxidation of the nonfluorescent thiamine (vitamin Bi) to the fluorescent thiochrome by the peroxide group. This reaction is catalyzed by bovine hematin. This reaction is 25-fold more sensitive for H2O2 than for the organic peroxides. 

Messer, B. M., Stiestra, D. E., Cappa, C. D., Scholtens, K. W., and Elrod, M. J., Computational and experimental studies of chemical ionization mass spectrometric detection techniques for atmospherically relevant peroxides, Int. J. Mass Spectrom., 197, 219-235, 2000. 

Dost, K., Jones, D. C., Auerbach, R., and Davidson, G., Determination of pesticides in soil samples by supercritical fluid chromatography-atmospheric pressure chemical ionization mass spectrometric detection. Analyst, 125, 1751-1755, 2000. 

Retinoic acid and other retinoid carboxylic acids, however, can be readily converted to derivatives that are suitable for gas chromatography. Many of these applications have used mass spectrometry for detection (see below). Diazomethane is used, at room temperature, to prepare the methyl esters without apparent isomerization. Pentafluorobenzyl esters of retinoic acid and its analogs have also been prepared for GC-MS (280) or HPLC-MS (281). Deuterated analogs of retinoic acid or other retinoid carboxylic acids have been used as internal standards, with mass spectrometric detection (88,282) (reviewed by Napoli [283] and by De Leenheer and Lambert [89]). The pentafluorobenzyl ester of a synthetic retinoid, Ro 13-7410, was analyzed by column switching the peak of interest from a SE54 colunm was cut to an OV 240 column, with subsequent detection by negative ion chemical ionization mass spectrometry (280). 

Dugo P, Kumm T, Chiofalo B, Cotroneo A, Mondello L. Separation of triacylglycerols in a complex lipidic matrix by using comprehensive two-dimensional liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometric detection. J Sep Sci 2006 29 1146—54. 

Elimination of wet chemical sample preparation enables a complete analysis to be performed and data to be quickly analyzed. The detection limits are in the low part-per-million range using mass spectrometric detection. Alternatively, detection of compounds can be achieved by all common gas chromatography detectors (flame ionization detector, electron capture detector and flame photometric detector), and detection limits are determined by the method of detection employed. 

The development of mass spectrometric ionization methods at atmospheric pressures (API), such as the atmospheric pressure chemical ionization (APCI)99 and the electrospray ionization mass spectrometry (ESI-MS)100 has made it possible to study liquid-phase solutions by mass spectrometry. Electrospray ionization mass spectrometry coupled to a micro-reactor was used to investigate radical cation chain reaction is solution101. The tris (p-bromophenyl)aminium hexachloro antimonate mediated [2 + 2] cycloaddition of trans-anethole to give l,2-bis(4-methoxyphenyl)-3,4-dimethylcyclobutane was investigated and the transient intermediates 9 + and 10 + were detected and characterized directly in the reacting solution. However, steady state conditions are necessary for the detection of reactive intermediates and therefore it is crucial that the reaction must not be complete at the moment of electrospray ionization to be able to detect the intermediates. 

Coupling of liquid chromatography with mass spectrometry provides unequivocal online spectrometric identification of tetracycline antibiotics in animal-derived foods. Typical applications of mass spectrometry in confirming tetracycline residues in edible animal products describe coupling of liquid chromatography with mass spectrometry via particle-beam (280), electrospray (292), or atmospheric pressure chemical ionization (307), using negative-ion detection interfaces. 

AC Hogenboom, J Slobodnik, JJ Vreuls, JA Rontree, BLM van Baar, WMA Niessen, UAT Brink-man. Single short-column liquid chromatography with atmospheric pressure chemical-ionization-(tandem)-mass-spectrometric detection for trace enviromnental analysis. Chromatographia 42 506-514, 1996. 

An internal standard should meet the following three requirements. First, it should have the same or very similar physical-chemical properties as the analyte, particularly hydrophobicity and ionization characteristics, so that it can mimic closely the performance of the analyte in every stage of analysis, i.e., from sample preparation, chromatographic separation, to mass spectrometric detection. In this way, any losses during sample preparation or variations in the mass spectrometry detection can be corrected. 

The positive charge of QTA and the explicit proton affinity of TTA make these cationic compounds ideal candidates for mass spectrometric detection after positive electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). 

Application of LC-MS/MS techniques to the analysis of phthalate ester metabolites in urine have also been developed. For example, Blount et al. (2000b) have developed an assay to quantify the monoester metabolites (including MEHP) of eight phthalate diesters in urine, utilizing HPLC coupled with atmospheric pressure chemical ionization and tandem mass spectrometric (APCI-MS/MS) detection techniques. Urine samples were treated with -glucuronidase to release the free phthalate monoesters followed by a two-step solid phase extraction procedure. After evaporative concentration of the eluant, the analytes in the purified samples are further separated on a phenyl reverse phase HPLC column and quantified by APCI-MS/MS, following careful optizimation of the APCI-MS/MS instrument. The limits of detection for MEHP were determined to be 1.2 ng/ml urine with recovery efficiencies of between 78 and 91%. 

Mass spectrometry involves the detection of charged particles, and, in the present case, a portion of the neutral cluster beam is ionized. Ionization essentially involves electronic excitation and occurs on the time scale of the order of 10 16 s (Haberland 1985 Mark 1987). The mass spectrometric detection of the ions is usually achieved on a microsecond time scale after the ionization event. As a result, the ionization process is taken to be time zero in the discussion of the processes which occur following the actual ionization of the neutral clusters, yet before the mass selection of the cluster ions. That is, the resulting cluster ion will incubate in the ionizer for microseconds before being accelerated into the mass filter. On that time scale, the cluster ion may lose monomer units, and the cation within the cluster may fragment or react chemically with the adjacent molecules. 

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