Chemical mass spectrometric detection

Simonsick, Jr., W. J. and Prokai, L., Size-exclusion chromatography with electrospray mass spectrometric detection, in Chromatographic Characterization of Polymers, Hyphenated and Multidimensional Techniques, Provder, T., Barth, H. G. and Urban, M. W., Eds., American Chemical Society, Washington, D.C., 1995, chap. 4. 

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... 

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. 

Undoubtedly, mass spectrometric detection has a substantial role to play in condensed-phase chromatographic analyses of toxic impurities. As in GC/MS, it can be highly sensitive, although this is probably more analyte-specific than in GC/MS. Selectivity can be gained by SIM on single quadrupoles or, if necessary, SRM on MS/MS instruments. What must be considered is the appropriate ionisation mode to be used in LC/MS. Most modern instruments use atmospheric pressure ionisation sources, including electrospray ionisation (ESI), atmospheric pressure chemical ionisation (APCI) and more recently atmospheric pressure photoionisation (APPI). 

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. 

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. 

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... 

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). 

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. 

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. 

CWC-related chemicals in aqueous liquid samples (water samples) are usually recovered by extraction with an organic solvent. Modem methods such as SPE and solid phase micro extraction (SPME) have also been presented 04 24). Organic extractions and these modem methods mainly recover nonpolar CWC-related chemicals, but leave behind the water-soluble and nonvolatile chemicals. These must also be recovered, however, because the agents tend to decompose (hydrolyze) rapidly under conditions in the environment. In the past few years, techniques such as CE and LC, relying on element specific or mass spectrometric detection, have been intensively developed to provide easy and effective ways of recovering these chemicals from water samples with only minor sample preparation (2S 44,1. For GC/MS analysis, the water must be displaced and the analytes derivatized. 

Prokai L, Simonsick WJ (1995) SEC with electrospray mass spectrometric detection. In Provder T, Barth HG, Urban MW (eds) Chromatographic characterization of polymers. Hyphenated and multidimensional techniques, chap 4. Adv Chem Ser. 247, American Chemical Society, Washington, DC... 

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. 

One of the early methods for mass spectrometric analysis of microdialysis samples utilized gas chromatography with mass spectrometric detection (GC/MS). Electron ionization is one type of ionization used for GC/MS. It is a hard ionization technique, resulting in a high degree of analyte fragmentation. A softer form of ionization, chemical ionization, is also available and often results in less analyte fragmentation. Selected-ion monitoring (SIM) is used frequently with... 

Jones, D.C. et al., The analysis of beta-agonists by packed-column supercritical fluid chromatography with ultra-violet and atmospheric pressure chemical ionisation mass spectrometric detection, Analyst, 124(6), 827, 1999. 

Figure 9.3. Sample preparation method proposed by Wong et al. for multiresidue analysis of pesticides in wine. (Reprinted from Journal of Agricultural and Food Chemistry 51, Wong et al., Multiresidue pesticide analysis in wines by solid-phase extraction and capillary gas chromatography-mass spectrometric detection with selective ion monitoring, p. 1150, Copyright 2003, with permission from American Chemical Society.)...

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. 

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