Matrix assisted laser desorption measurements

Ens, W. Mao, Y. Mayer, F. Standing, K.G. Properties of Matrix-Assisted Laser Desorption. Measurements Wifli a Time-to-Digital Converter. Rapid Commun. Mass Spectrom. 1991, 5, 117-123. 

The ablated vapors constitute an aerosol that can be examined using a secondary ionization source. Thus, passing the aerosol into a plasma torch provides an excellent means of ionization, and by such methods isotope patterns or ratios are readily measurable from otherwise intractable materials such as bone or ceramics. If the sample examined is dissolved as a solid solution in a matrix, the rapid expansion of the matrix, often an organic acid, covolatilizes the entrained sample. Proton transfer from the matrix occurs to give protonated molecular ions of the sample. Normally thermally unstable, polar biomolecules such as proteins give good yields of protonated ions. This is the basis of matrix-assisted laser desorption ionization (MALDI). 

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... 

Considering these situations, the observation of molecular weights, particularly by matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF MASS), is essential [33]. The operation is simple and enables us to observe the molecular ion peaks of CPOs with molecular weights exceeding 10,000. The quahty of the measurement is strongly dependent on the choice of the matrix. Therefore, the search for the best matrix for each CPO should be pursued. 

Meyer-Dulheuer [55] has analysed the pure additives (phenolic antioxidants, benzotriazole UV stabilisers and HALS compounds) of Table 9.8 in THF solutions by means of MALDI-ToFMS. As it turns out, polar molecules in the mass range of below 800 Da, which have a high absorption coefficient at the laser wavelength used, can often be measured without any matrix [55,56]. In this case, there is no matrix-assisted laser desorption and ionisation (MALDI) process any more. It is a simple laser desorption/ionisation (LDI) process. The advantage of this method is a matrix-free mass spectrum with the same mass resolution as in the MALDI case,... 

We have used accurate mass measurements obtained by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOFMS) to differentiate and profile saponins from M. truncatula roots. An example is provided (Fig.3.11) showing the MALDI-TOFMS spectra of a solid-phase extract of M truncatula root tissue. In this spectrum, we can identify multiple saponins. 

A modified version of 2DE and gel image analysis, with silver staining, autoradiography, and protein identification and measurement of peptide mass, uses matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) as a rapid and sensitive technique for identifying peptides. MALDI-TOF-MS applies well to protein detection in biological fluids.56 A second advantage of this technique is... 

S. Ring and Y. Rudich. A Comparative Study of a Liquid and a Solid Matrix in Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry and Collision Cross Section Measurements. Rapid Commun. Mass Spectrom., 14(2000) 515-519. 

The development of mass spectroscopic techniques such as matrix assisted laser desorption (MALDI) and electrospray mass spectrometry has allowed the absolute determination of dendrimer perfection [7,8], For divergent dendrimers such as PAMAM and PPI, single flaws in the chemical structure can be measured as a function of generation to genealogically define an unreacted site of or a side reaction producing a loop at a particular generation level. Mass spectromet-ric results on dendrimers, not only demonstrate the extreme sensitivity of the technique, but also demonstrate the uniformity of the molecular mass. The polydispersity index of Mw/Mn for a G6 PAMAM dendrimer can be 1.0006 which is substantially narrower than that of living polymers of the same molecular mass [7],... 

Fig. 6. Protein identification using a peptide map measured with a matrix-assisted laser desorption time-of-flight mass spectrometer. All the peptide extracted from the gel is measured and the set of masses is used in the database search. The mass resolution is in the order of 10,000. Individual isotopes of a 2.5 kDa peptide are clearly resolved.

Matrix-assisted laser desorption ionization mass spectrometry (MALDI) uses a matrix, typically of aromatic acids, whose molecular weight is similar to those of typical metabolites and thus disallows the mass spectrometric measurement of the latter. 

Quist, A.P. Huth-Fehre, T. Sundqvist, B.U.R. Total Yield Measurements in Matrix-Assisted Laser Desorption Using a Quartz Crystal Microbalance. Rapid Commun. Mass Spectrom. 1994, 8, 149-154. 

The product was identihed by a number of spectroscopic methods. Dioxygen uptake was measured by spectrophotometric titration. MALDI-TOF-MS (matrix-assisted laser desorption/ionization-time of flight-mass spectrometry), an MS method particularly suited to determining molecular masses of biopolymers and synthetic materials with relative masses up to several hundred kilodaltons, determined that the product contained stoichiometric amounts of the heme starting material, the copper complex, and dioxygen in a 1 1 1 ratio. 

There are at least three possibile ways in which the inhibitor can bind to the active site (1) formation of a sulfide bond to a cysteine residue, with elimination of hydrogen bromide [Eq. (10)], (2) formation of a thiol ester bond with a cysteine residue at the active site [Eq. (11)], and (3) formation of a salt between the carboxyl group of the inhibitor and some basic side chain of the enzyme [Eq. (12)]. To distinguish between these three possibilities, the mass numbers of the enzyme and enzyme-inhibitor complex were measured with matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI). The mass number of the native AMDase was observed as 24766, which is in good agreement with the calculated value, 24734. An aqueous solution of a-bromo-phenylacetic acid was added to the enzyme solution, and the mass spectrum of the complex was measured after 10 minutes. The peak is observed at mass number 24967. If the inhibitor and the enzyme bind to form a sulfide with elimination of HBr, the mass number should be 24868, which is smaller by about one... 

Kang, M.-J., Tholey, A., Heinzle, E. Application of automated matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for the measurement of enzyme activities. Rapid Commun. Mass Spectrom. 2001, 15, 1327-1333. 

Powell, K.D. Fitzgerald, M.C. Measurements of protein stability by H/D exchange and matrix-assisted laser desorption/ionization mass spectrometry using picomoles of material. Ancd. Chem. 2001, 73, 3300-3304. 

Fukai, T., Kuroda, J., and Nomura, T., Accurate mass measurement of low molecular weight compounds by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, J. Am. Soc. Mass Spectrom., 11, 458, 2000. 

Matrix-assisted laser desorption ionization time of flight (MALDI-TOFF) measures the mass of the peptides... 

In 1974, Comarisov and Marshall60 developed Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). This technique allows mass spectrometric measurements at ultrahigh mass resolution (R = 100000-1000000), which is higher than that of any other type of mass spectrometer and has the highest mass accuracy at attomole detection limits. FTICR-MS is applied today together with soft ionization techniques, such as nano ESI (electrospray ionization) or MALDI (matrix assisted laser/desorption ionization) sources. 

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