Detection of Fragments

Reactions (19)-(21) represent the dissociation of benzene and reactions (22)-(26) represent the detection of fragments by VUV laser photoionization. The line-shape images resulted from these reactions. 

In this paper, the photofragmentation of transition metal cluster complexes is discussed. The experimental information presented concerning the gas phase photodissociation of transition metal cluster complexes comes from laser photolysis followed by detection of fragments by ionization (5.). Ion counting techniques are used for detection because they are extremely sensitive and therefore suitable for the study of molecules with very low vapor pressures (6.26.27). In addition, ionization techniques allow the use of mass spectrometry for unambiguous identification of signal carriers. 

Mass spectrometry Detection of fragments by charge/mass Mass number, plus fragmentation patterns 10—9 Pa (lO-11 ton) Useful for characterization of species in a vapor, complicated by reactions in spectrometer. Does not differentiate isomers directly. Important for detecting hydrogen in a... 

CGE separation of dsDNA fragments was performed on a PMMA chip using a near-IR dye (TOPRO-3). This allows the LIF detection of fragments (603-1353 bp) as low as 0.1 [tg/mL. DNA sizing of hepatitis C virus (HCV) amplicon was demonstrated [149]. 

Grasl-Kraupp B, Ruttkay-Nedecky B, Koudelka H, Bukowska K, Bursch W, Schulte-Hermann R. In situ detection of fragmented DNA (TUNEL assay) fails to discriminate among apoptosis, necrosis, and autolytic cell death A cautionary note. Hepatology 1995 21 1465-1468. 

ISD fragmentations lead to product ions that are always apparent in the MALDI spectra, whereas the observation of product ions from PSD fragmentation needs certain instrumental conditions. For example, a MALDI source coupled to a linear TOF analyser allows detection of fragment ions produced in the source at their appropriate m/z ratio. On the contrary, fragment ions produced after the source cannot be resolved from their precursor ions and are detected at the same apparent m/z ratio. This induces a broadening of the peaks with a concomitant loss of mass resolution and sensitivity. 

Flow Cytometry (see also Chapter 4). The detection of fragmented nuclei by flow cytometry is now a widely used and accepted method for the detection and quantitation of apoptosis (28,53). The methods rely on the use of DNA binding dye (usually PI), which intercalates stoichiometrically with DNA and allows the quantitation of DNA content. A sub-Gl peak is reliably found to be indicative of apoptosis (because of the DNA fragmentation) and the peak size reflects the amount of apoptosis in the sample. The method is easily applied to cell suspen-... 

In general, MSn is also highly effective for differentiation of isobaric compounds. The detection of fragment ions [M-162]+ (Y0+), [M-324]+ (due to consecutive losses of two sugar residues), [M-204]+, [M-308]+... 

Huang, X. A contig assembly program based on sensitive detection of fragment overlaps. Genomics 1992, 14, 18-25. 

Detection of fragments by Mass number, plus — l0- Pa Useful for characterization... 

As shown before, ions of interest were isolated and analyzed by DADI/MIKE spectrometry for the detection of fragmentation pathways or structure elucidation. This means that even in chemically pure compounds, an analysis of the mixture must... 

One special ion type may be generated by different precursor species. This is especially true if a mixture of homologous compounds has to be analyzed. In this case, the analyst woud like to know where the ion of interest does originate from and the methods for the detection of fragment ion origins may be applied (see 4.2). The following examples may illustrate some possible applications. 

Structural information on dendritic polyurethanes was obtained by PSD experiments, which allowed the detection of fragment ions arising from the cleavage of ester or amide bonds. 

Dissociation and ionization by means of one or several lasers. Sensitive detection of fragments and ions with resonance photoionization and mass spectrometric techniques (tunable lasers). Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) with pulsed ablating laser sources. High lateral resolution enables molecular microprobing of biological cell compounds... 

Photoassociation of like atoms to form homonuclear molecules, emphasizing the widely studied alkali metals, is treated first. The simple one-color experiments are described in detail, including the variety of techniques used for detection trap loss (decrease in atomic fluoresence), direct detection of excited molecule ionization, detection of fragments by resonance-enhanced multiphoton ionization, and detection of ground or metastable molecules (formed by decay of the upper photoassociation level) by resonance-enhanced multiphoton ionization. 

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