Mass spectrometry detection, chemical ionization

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. 

Stan H-J, Kellner G. 1989. Confirmation of organophosphorus pesticide residues in food applying gas chromatography/mass spectrometry with chemical ionization and pulsed positive negative detection. Biomed and Environ Mass Spectrom 18(9) 645-651. 

Gimeno R.A. et al., 2002. Determination of polycyclic aromatic hydrocarbons and polycyclic aromatic sulfur heterocycles by high-performance liquid chromatography with fluorescence and atmospheric pressure chemical ionization mass spectrometry detection in seawater and sediment samples. J Chromatogr A 958 141. 

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. 

Flow injection analysis (FLA) with electrospray ionization (ESI) or atmospheric pressure chemical ionization mass spectrometry detection (FIA/ESIMS or FIA/APCIMS) (10), followed by... 

Negative chemical ionization (NCI) mass spectrometry detects ABA with a high sensitivity since the negative molecular ion M of methyl ester of ABA is more stable than the positive molecular ion [M] + due to the high electrophilicity of ABA. The NCI mass spectrum shows [M]- at m/z 278 as a base peak, and other fragment ions at m/z 310, 260, 245, 141, and 152.601 The combination of SIM with NCI gives highly selective and sensitive detection of ABA the lowest detection limit is 0.3 pg, which is 200 times lower than that... 

Byrdwell, W.C., Neff, W.E. and List, G.R. (2001) Triacylglycerol analysis of potential margarine base stocks by high-performance liquid chromatography with atmospheric pressure chemical ionization mass spectrometry and flame ionization detection. J. Agric. Food Chem., 49, 446-457. 

NBDF 4-nitrobenzenediazonium fluoroborate DBBQC 3,5-dibromo-/)-benzoquinonechlorimine OPA o-phthalaldehyde Oncolumn-TD oncolumn thermal decomposition DAD diode array detector UV UV detector MS mass spectrometry El electron ionization ESI electrospray ionization FID flame ionization detector APCI atmospheric pressure chemical ionization z-cell z-cell configuration FL fluorescence detection... 

Kubachka, K.M., et al. (2008) Detection of chemical warfare agent degradation products in foods using liquid chromatography coupled to inductively coupled plasma mass spectrometry and electrospray ionization mass spectrometry. Journal of Chromatography A, 1202,124—131. 

Improvements in the instrumentation, ionization sources, high-resolution mass analyzers, and detectors [67-69], in recent years have taken mass spectrometry to a different level of HPLC-MS for natural product analysis. Mass spectrometry detection offers excellent sensitivity and selectivity, combined with the ability to elucidate or confirm chemical structures of flavonoids [70-72]. Both atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) are most commonly used as ionization sources for flavonoid detection [73-76]. Both negative and positive ionization sources are applied. These sources do not produce many fragments, and the subsequent collision-induced dissociation energy can be applied to detect more fragments. Tandem mass spectrometry (MS , n> 2) provides information about the relationship of parent and daughter ions, which enables the confirmation of proposed reaction pathways for firagment ions and is key to identify types of flavonoids (e.g., flavones, flavonols, flavanones, or chalcones) [77-80]. 

Johnson, K. A. Shira, B. A. Anderson, J. L. Amster, 1. J. Chemical and on-line electrochemical reduction of metalloproteins with high-resolution electrospray ionization mass spectrometry detection. Anal. Chem. 2001, 73, 803-808. 

Figure 4.4 LC-ICP-MS analysis of alkyl phosphonic acids in food and beverage matrices [24]. Reprinted from Kubachka, K.M., Richardson, D.D., Heitkemper, D.T., Caruso, J.A., Detection of chemical warfare agent degradation products in foods using liquid chromatography coupled to inductively coupled plasma mass spectrometry and electrospray ionization mass spectrometer. Journal of Chromatography A, 2008, 1202, (2), 124-131, with permission from Elsevier...

Following the movement of airborne pollutants requires a natural or artificial tracer (a species specific to the source of the airborne pollutants) that can be experimentally measured at sites distant from the source. Limitations placed on the tracer, therefore, governed the design of the experimental procedure. These limitations included cost, the need to detect small quantities of the tracer, and the absence of the tracer from other natural sources. In addition, aerosols are emitted from high-temperature combustion sources that produce an abundance of very reactive species. The tracer, therefore, had to be both thermally and chemically stable. On the basis of these criteria, rare earth isotopes, such as those of Nd, were selected as tracers. The choice of tracer, in turn, dictated the analytical method (thermal ionization mass spectrometry, or TIMS) for measuring the isotopic abundances of... 

Laser ionization mass spectrometry or laser microprobing (LIMS) is a microanalyt-ical technique used to rapidly characterize the elemental and, sometimes, molecular composition of materials. It is based on the ability of short high-power laser pulses (-10 ns) to produce ions from solids. The ions formed in these brief pulses are analyzed using a time-of-flight mass spectrometer. The quasi-simultaneous collection of all ion masses allows the survey analysis of unknown materials. The main applications of LIMS are in failure analysis, where chemical differences between a contaminated sample and a control need to be rapidly assessed. The ability to focus the laser beam to a diameter of approximately 1 mm permits the application of this technique to the characterization of small features, for example, in integrated circuits. The LIMS detection limits for many elements are close to 10 at/cm, which makes this technique considerably more sensitive than other survey microan-alytical techniques, such as Auger Electron Spectroscopy (AES) or Electron Probe Microanalysis (EPMA). Additionally, LIMS can be used to analyze insulating sam-... 

C. Aguilar, I. Feirer, R Bonnll, R. M. Marce and D. Barcelo, Monitoring of pesticides in river water based on samples previously stored in polymeric cartridges followed by on-line solid-phase extraction-liquid cliromatography-diode array detection and confirmation by atmospheric pressure chemical ionization mass spectrometry . Anal. Chim. Acta 386 237-248 (1999). 

I. Eeirer, V. Pichon, M. C. Hennion and D. Barcelo, Automated sample preparation with exti action columns by means of anti-isoproturon immunosorbents for the determination of phenylurea herbicides in water followed by liquid chi omatography diode array detection and liquid clrromatogi aphy-atmospheric pressure chemical ionization mass spectrometry , 7. Chromatogr. Ill 91-98 (1997). 

Analytical applications Mass spectrometry has been applied to a variety of analytical problems related to expls, some of which have already been mentioned. Identification of the principal constituents of expls has been attempted from electron impact cracking patterns (Refs 34, 50 58), as well as chemical ionization spectra (Refs 69,70 71). Such methods necessarily include vapor species analysis and are directed to detection of buried mines (Refs 50, 58, 61,... 

Table 5.2 Selected-reaction monitoring (SRM) transitions nsed for MS-MS detection of the pesticides studied in the systematic investigations on APCI-MS signal response dependence on eluent flow rate. Reprinted from J. Chro-matogr.. A, 937, Asperger, A., Efer, J., Koal, T. and Enge-wald, W., On the signal response of various pesticides in electrospray and atmospheric pressure chemical ionization depending on the flow rate of eluent applied in liquid chromatography-mass spectrometry , 65-72, Copyright (2001), with permission from Elsevier Science...

GC/MS has been employed by Demeter et al. (1978) to quantitatively detect low-ppb levels of a- and P-endosulfan in human serum, urine, and liver. This technique could not separate a- and P-isomers, and limited sensitivity confined its use to toxicological analysis following exposures to high levels of endosulfan. More recently, Le Bel and Williams (1986) and Williams et al. (1988) employed GC/MS to confirm qualitatively the presence of a-endosulfan in adipose tissue previously analyzed quantitatively by GC/ECD. These studies indicate that GC/MS is not as sensitive as GC/ECD. Mariani et al. (1995) have used GC in conjunction with negative ion chemical ionization mass spectrometry to determine alpha- and beta-endosulfan in plasma and brain samples with limits of detection reported to be 5 ppb in each matrix. Details of commonly used analytical methods for several types of biological media are presented in Table 6-1. 

Mass Spectrometry. Mass spectrometry holds great promise for low-level toxin detection. Previous studies employed electron impact (El), desorption chemical ionization (DCI), fast atom bombardment (FAB), and cesium ion liquid secondary ion mass spectrometry (LSIMS) to generate positive or negative ion mass spectra (15-17, 21-23). Firm detection limits have yet to be reported for the brevetoxins. Preliminary results from our laboratory demonstrated that levels as low as 500 ng PbTx-2 or PbTx-3 were detected by using ammonia DCI and scans of 500-1000 amu (unpublished data). We expect significant improvement by manipulation of the DCI conditions and selected monitoring of the molecular ion or the ammonia adduction. 

The chemical compositions of the isolated Au SR clusters were investigated by mass spectrometry [15,16,18, 22,32-35]. TEM was used to confirm that the species detected by the mass spectrometer represents the clusters in the sample. Figure 3a is a schematic representation of the top view of the mass spectrometer, which consists of five stages of differentially pumped vacuum chambers. The apparatus accommodates two t5 pes of ion sources, electrospray ionization (ESI) and laser-desorption ionization (EDI), and a time-of-flight (TOE) mass spectrometer with a reflectron. Details of the apparatus and the measurement protocols are described below. 

Crescenzi et al. developed a multi-residue method for pesticides including propanil in drinking water, river water and groundwater based on SPE and LC/MS detection. The recoveries of the pesticides by this method were >80%. Santos etal. developed an on-line SPE method followed by LC/PAD and LC/MS detection in a simultaneous method for anilides and two degradation products (4-chloro-2-methylphenol and 2,4-dichlorophenol) of acidic herbicides in estuarine water samples. To determine the major degradation product of propanil, 3,4-dichloroaniline, the positive ion mode is needed for atmospheric pressure chemical ionization mass spectrometry (APCI/MS) detection. The LOD of 3,4-dichloroaniline by APCI/MS was 0.1-0.02 ng mL for 50-mL water samples. 

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