Laser desorption ionization-triple

Melanson, J.E., Chisholm, K.A. and Pinto, D.M. (2006) Targeted comparative proteomics by liquid chromatography/matrix-assisted laser desorption/ionization triple-quadmpole mass spectrometry. Rapid Commun. Mass Spectrom. 20, 904-910. 

Rathore R, Coir JJ, Lebre DT, Seibel WL, Greis KD (2009) Extending matrix-assisted laser desorption/ionization triple quadrupole mass spectrometry enzyme screening assays to targets with small molecule substrates. Rapid Commun Mass Spectrom 23 3293-3300... 

Tandem mass spectrometry (MS/MS) is a method for obtaining sequence and structural information by measurement of the mass-to-charge ratios of ionized molecules before and after dissociation reactions within a mass spectrometer which consists essentially of two mass spectrometers in tandem. In the first step, precursor ions are selected for further fragmentation by energy impact and interaction with a collision gas. The generated product ions can be analyzed by a second scan step. MS/MS measurements of peptides can be performed using electrospray or matrix-assisted laser desorption/ionization in combination with triple quadruple, ion trap, quadrupole-TOF (time-of-flight), TOF-TOF or ion cyclotron resonance MS. Tandem... 

Bis- -diketones have been demonstrated to be powerful ligands in the engineering of supramolecular architectures. Pikramenou and coworkers [53a] used two bis-P-diketones of l,3-bis(3-phenyl-3-oxopropanoyl)benzene (H2L ) and l,3-bis(3-phenyl-3-oxopropanoyl) 5-ethoxy-benzene (H2L ) to synthesize neutral homodimetallic complexes [Ln2(L )3] (Ln = Eu, Nd, Sm, Y, Gd) and [Ln2(L )3] (Ln = Eu, Nd) and also an anionic dinuclear lanthanide complex [Eu2(L )4] . The detailed studies by NMR, electrospray, and MALDI (matrix assisted laser desorption ionization) mass spectrometry, by addition of chiral Pirkle s reagent, revealed that [Ln2(L" )3] and [Eu2(L )4] (see Eigure 2.38) are chiral, and have triple- and quadruple-stranded supramolecular structures, respectively, with the latter being more strongly emissive than the former. 

Recombinant wild type hIL-ip, the K138C mutant and the K138C, R4A, L6A triple mutant (mutant 1) were isolated from the soluble fraction of E. coli lysates by ammonium sulfate fractionation and hydrophobic interaction chromatography. The purified proteins were characterized by SDS-PAGE, western blots, N-terminal sequence, size exclusion chromatography (SEC), isoelectric focusing (lEF), matrix assisted laser desorption ionization mass spectrometry (MALDI-MS), and electrospray mass spectrometry (ESMS). 

Fig. 1 Schematic representation of a mass spectrometer depicting its main components and the different modes used. Abbreviations DIP direct insertion probe DEP direct exposure probe GC gas chromatography LC liquid chromatography CE capillary chromatography TEC thin-layer chromatography FEE field-flow fractionation APCI atmospheric pressure ionization El electron impact Cl chemical ionization FAB fast-atom bombardment PD plasma desorption MALDI matrix-assisted laser desorption ionization ED laser desorption TSP thermospray ESI electron spray ionization HSI hypherthermal surface ionization Q quadropole QQQ triple quadropole TOE time-of-fiight FTMS Fourier transform mass spectrometer IT ion trap EM electrom multiplier PM photomultiplier ICR ion cyclotron resonance.

Hopfgartner G, Varesio E, Stoeckli M. Matrix-assisted laser desorption/ionization mass spectrometric imaging of complete rat sections using a triple quadrupole linear ion trap. Rapid Commtm Mass Spectrom 2009 23(6) 733—736. 

Another new teehnology that shows promise as a high-throughput screening tool is FlashQuant. FlashQuant is a triple quadrupole MS/MS system that has a high-speed matrix-assisted laser desorption/ionization (MALDI) source. The MALDI souree ean provide for the very rapid assay of samples on a plate format. Beeause there is no ehromatography, the sample assay speed is about 6 s/sample (10 samples/min) this is 10—20 times a typical HPLC—MS/MS assay speed. The teehnique has potential for use in early in vitro assays that have simple matriees. At this time, it is too early to state whether or not this technique will be useful for EDM sereens. 

An IM-quadMS was the first hybrid instrument used to detect nitrotoluene compounds with a radioactive ionization source [189]. Later work uses laser desorption ionization (LDI) to detect TNT, DNT, RDX, and HMX with an IM-quadMS [190]. Recently, the formation reaction mechanism of RDX response ions in an atmospheric pressure GDI source is now better understood with the use of an IM-triple quadrupole mass spectrometer [179]. 

Because of the advances in the gas-phase ionization of biomacromolecules, such as electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI), mass spectrometry (MS) has become a powerful tool for detection, identification, and structural analysis of proteins, peptides, and polynucleotides. The molecules ionized in a gas phase by these methods are subsequently analyzed by sector, quadrupole, ion-trap, or time-of-flight mass spectrometers. In particular, the MS systems consisting of ESI and triple-stage quadrupole (ESI/TSQ) or ion-trap (IT) mass spectrometry and MALDI time-of-flight (MALDl/TOF) mass spectrometry have been most widely applied to the field of protein chemistry for the accurate determination of molecular mass of proteins and peptides, determination of amino acid sequence, identification of proteins by peptide mass databases, and analysis of posttranslational modifications such as phosphorylation and glycosylation. In general, current techniques allow detenni-... 

Triple quadrupole MS instruments have been the most common ones in studies involving lipid analysis, butnovel hybrid (quadrupoletime-of-flight, etc.)instruments are rapidly gaining popularity due to their ability for multiple precursor ion scans simultaneously. Besides ESI, atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI), and matrix-assisted laser desorption ionization (MALDI) have been employed in analysis of lipids. However, these methods seem to have an advantage over ESI only in special cases. For instance, APPI and APCI allow analysis of sterols without derivatization, which is needed for ESI. 

Perchalski PJ, Yost RA and Wilder BJ (1982) Structural elucidation of drug metabolites by triple quadrupole mass spectrometry. Analytical Chemistry 54 1466. Spengler B (1997) Post-source decay analysis in matrix-assisted laser desorption/ionization mass spectrometry of biomolecules. Journal of Mass Spectrometry 32 1019. 

The typical wavelengths of lasers used in LDl experiments are shown in Table 6.1. Generally speaking, unless unusual resonances are available in the molecule of interest, the UV lasers are more amenable to LDl, while the IR lasers are amenable to desorption, but not ionization. By far, the most common lasers are the nitrogen laser at 337 nm and the frequency-tripled Nd YAG laser at 355 nm, because these lasers efficiently ionize molecules using the matrix-assisted laser desorption/ionization method discussed in Section 6.4. 

With the move toward higher mass additives to reduce volatility, Johlman et al. examined additives with masses between 500 and 1300 Daltons and compared the results with spectra obtained employing FAB ionization. Using direct laser desorption FTMS in a 3 T system, spectra were found to be "superior" to the FAB spectra produced using both sector and triple-quad mass spectrometers, particularly in terms of reduced fragmentation. 

Another LDI instrument that was similar in principle to LAMMA was developed by Perchalski (1985) that featured the additional selectivity of two stages of mass analysis provided by a triple quadrupole mass spectrometer (QqQ). The LDI QqQ was shown to have potential for use as a probe-type analyzer for molecular analysis of mixtures, as demonstrated by the detection of a mixture of nine antiepileptic drugs by monitoring the precursor ion/product ion pair for each drug (Perchalski et al., 1983). The LDI—QqQ, however, was determined to be too slow to adequately characterize molecules ionized by cationization or anionization after desorption by a single-shot laser. Also, the vaporization/ionization process on the LDI—QqQ was unable to ionize polar, nonvolatile, and/or thermally unstable molecules (Perchalski, 1985). 

The desorption/ablation aspect of MALDl has been the object of an excellent review by Dreisewerd. Among the most basic functions of the matrix is absorption of the laser energy and conversion of most of it to heat. Subsequent matrix vaporization is sufficiently forceful that it entrains and ejects analyte that has been cocrystaUized in or on the matrix. The time scale is not as short as in fast atom bombardment (FAB) or secondary ionization mass spectrometry (SIMS) because the typical MALDl lasers used emit pulses of a few to hundreds of nanoseconds duration (e.g., N2 337 nm, 3 ns or tripled Nd YAG, 355 nm, 4—7 ns, Er YAG, 2.98 pm, 200 ns, although a range of pulse lengths has been studied ). This is slow compared to intramolecular motions. In UV MALDl, the energy conversion step is... 

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