Atmospheric-pressure chemical ionization mass spectroscopy

Homogenized garlic was extracted by SF-CO2 and the major thiosulfinates were characterized with liquid chromatography/ atmospheric pressure chemical ionization mass spectroscopy (LC/APCI/MS) [59]. In addition to the thiosulfinates, small quantities of ajoene were also found in the SF extracts of garlic homogenates. The identified thiosulfinates are listed in Table (1). 

Combs, M.T. Ashraf-Khorassani, M. Taylor, L.T. HPLC/atmospheric pressure chemical ionization-mass spectroscopy of eight regulated sulfonamides, J.Pharm.BiomedAncd., 1999, 19, 301-308. [LOD 0.05-6 ng sulfathiazole sulfamethazine sulfamerazine sulfapyridine sulfadimethoxine sulfadiazine sulfaquinoxaline sulfachlorpyridazine]... 

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. 

El-Hela, A.A., Al-Amier, H.A., and Ibrahim, T.A. 2010. Comparative study of the fla-vonoids of some Verbena species cultivated in Egypt by using high-performance liquid chromatography coupled with ultraviolet spectroscopy and atmospheric pressure chemical ionization mass spectrometry. J. Chromatogr. A 1217 6388-6393. 

Towards this goal, there have been extensive studies that have compared PTR-MS measurements of atmospheric VOCs with those obtained by other atmospheric analytical techniques, such as GC-MS [17], GC-FID [21-26], atmospheric pressure chemical ionization mass spectrometry (AP-CIMS) [27], differential optical absorption spectroscopy (DOAS) [24,28] and Fourier transform infrared (FTIR) spectroscopy [17,29], in addition to offline sampling methods coupled to GC analysis [30-34], These studies have shown that PTR-MS is capable of accurately measuring concentrations of VOCs providing that there is no contribution to the miz of interest in a mass spectram by interfering species. If other compounds are present in the atmospheric sample which can lead to ions (protonated parent compounds, cluster ions or fragment ion species) at the nominal mJz of the protonated VOC of interest, then the lack of specificity associated with PTR-MS requires that the actual identity of the compound still needs to be confirmed by other analytical techniques, such as GC-MS. 

G. J. Lehr, T. L. Barry, G. Petzinger, G. M. Hanna, S. W. Zito, Isolation and identification of process impurities in trimethoprim drug substance by high-performance liquid chromatography, atmospheric pressure chemical ionization liquid chro-matography/mass spectrometry and nuclear magnetic resonance spectroscopy, J. Pharm. Biomed. Anal. 19 (1999), 373-389. 

Rezanka, X, Identification of Very Long Chain Fatty Acids by Atmospheric Pressure Chemical Ionization Liquid Chromatography-Mass Spectroscopy from Green Alga Chlorella Kesslerii. J. of Sep. Set. 25 1332—1336 (2002). 

Sandra, P. Medvedovici, A. Zhao, Y. David, F. Characterization of triglycerides in vegetable oils by silver-ion packed-column supercritical fluid chromatography coupled to mass spectroscopy with atmospheric pressure chemical ionization and coordination ion spray. J. Chromatogr. 2000, A 974, 231-241. 

Grosjean, E., P.G. Green, and D. Grosjean Liquid chromatography analysis of carbonyl (2,4-dinitrophenyl)hydrazones with detection by diode array ultraviolet spectroscopy and by atmospheric pressure negative chemical ionization mass spectrometry. Analytical Chemistry, 71 (1999) 1851-1861. 

The typical atmospheric concentrations of OH and HO2 radicals in the daytime are 10 and 10 molecules cm ( 0.1 pptv and a few pptv), respectively. The detection techniques whose accuracy is thought to be satisfactory for their measurements are laser-induced fluorescence (LIF) at low pressure which is called Fluorescence Assay by Gas Expansion (FACE), and chemical ionization mass spectrometry (CIMS), and they have recently been used widely. In either of the methods, directly measured is OH, and HO2 is measured by converting to OH utilizing the reaction of HO2 -I- NO —> OH -I- NO2 (reaction (7.10)) adding NO to the atmospheric samples just before the introduction to the detector. Other than these methods, differential optical absorption spectroscopy (DOAS) is also used for the measurements of OH in fields and smog chambers. 

A detailed description of sources used in atmospheric pressure ionization by electrospray or chemical ionization has been compiled.2 Atmospheric pressure has been used in a wide array of applications with electron impact, chemical ionization, pressure spray ionization (ionization when the electrode is below the threshold for corona discharge), electrospray ionization, and sonic spray ionization.3 Interferences potentially include overlap of ions of about the same mass-charge ratio, mobile-phase components, formation of adducts such as alkali metal ions, and suppression of ionization by substances more easily ionized than the analyte.4 A number of applications of mass spectroscopy are given in subsequent chapters. However, this section will serve as a brief synopsis, focusing on key techniques. 

Chemical/Physical. Atkinson et al. (2000) studied the kinetic and products of the gas-phase reaction of 2-heptanone with OH radicals in purified air at 25 °C and 740 mmHg. A relative rate constant of 1.17 x 10 " cmVmolecule Sec was calculated for this reaction. Reaction products identified by GO, FTIR, and atmospheric pressure ionization tandem mass spectroscopy were (with respective molar yields) formaldehyde, 0.38 acetaldehyde, L0.05 propanal, X0.05 butanal, 0.07 pentanal, 0.09 and molecular weight 175 organic nitrates. 

Carboxylic acids The smallest carboxylic acid, formic acid, can be measured using infrared spectroscopy (Table 11.2), since it has characteristic absorption bands. As discussed earlier and seen in Fig. 11.33b, mass spectrometry with chemical ionization using SiF5 also revealed HCOOH in an indoor environment (Huey et al., 1998). However, since the sensitivity in these initial studies was about two orders of magnitude less than that for HN03, the detection limit may be about the same as that for FTIR and TDLS. Formic and acetic acids have been monitored continuously from aircraft (Chapman et al., 1995) and their surface flux determined by eddy correlation (Shaw et al., 1998) using atmospheric pressure ionization mass spectrometry. Detection limits are about 30 ppt. 

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