Matrix-assisted laser desorption/ionization biomolecules

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). 

Matrix Assisted Laser Desorption Ionization. During the development of MS, a lot of studies have been devoted to the use of laser light as an energy source for ionizing molecules. As a result, in the mid 1980s MALDI[5] was introduced and soon applied to the study of large molecules.[18] Koichi Tanaka was jointly awarded the Nobel Prize for Chemistry in 2002 for the study of large biomolecules by MALDI. 

B. Spengler. Post-Source Decay Analysis in Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry of Biomolecules. J. Mass Spectrom., 32(1997) 1019-1036. 

This proposal describes the development of a new, systematic approach for qualitatively and quantitatively studying surface-biomolecule interactions by matrix-assisted laser desorption ionization (MALDl) mass spectrometry (MS). This methodology is being developed because of the profound importance that surface-biomolecule interactions play in applications where biomaterials come into contact with complex biological fluids, it can readily be shown that undesired reactions occurring in response to surface-biomolecule contact (protein adsorption, biofouling, immune response activation, etc.) lead to enormous economic and human costs. Thus, the development of analytical methodologies that allow for efficient assessment of the properties of new biomaterials and/or the study of detailed fundamental processes initiated upon surface-biomolecule contact are of critical value ... 

Matrix Assisted Laser Desorption/Ionization (MALDI) In the MALDI procedure—used mainly for large biomolecules—the sample in a matrix is dispersed on a surface, and is desorbed and ionized by the energy of a laser beam. The matrix serves the same purpose as it does in the FAB procedure (Section 2.5.I.3.). 

Two recently developed mass spectrometric techniques have had a major impact on the analysis of large biomolecules matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and electrospray ionization mass spectrometry (ESI-MS). MALDI-MS was first introduced by Karas and Hillenkamp66 and Tanaka et al.61 in 1988 and has experienced an exponential development. It has become a widespread soft ionization technique for bioorganic samples, especially large biomolecules. Fenn and co-workers68 first published the successful soft ionization technique for... 

Matrix assisted laser desorption/ionization ion source desorption by photons proton transfer M+ < 1( 4 Pa ToF-MS, FTICR-MS tandem MS biomolecules... 

ToF mass spectrometers as dynamic instruments gained popularity with the introduction of matrix assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) as effective pulsed ion sources for the soft ionization of large biomolecules (up to 10s dalton) due to their high ion transmission.38 ToF mass spectrometers, quadrupole analyzers and/or magnetic sector fields can be combined in tandem mass spectrometers (MS/MS) for the analysis of organic compounds. 

Mass spectrometry has been revolutionalized by the advent of electrospray ionization, but, before we concentrate on this relatively recent addition to the array of ionization methods, we will first discuss two other techniques which are routinely used for the ionization of biomolecules matrix assisted laser desorption ionization (MALDI) and fast atom bombardment (FAB). These techniques share common features in that ... 

Spengler, B. (1 997) Post-source decay analysis in matrix-assisted laser desorption/ionization mass spectrometry of biomolecules. Journal of Mass Spectrometry 32, 1019-1036. 

Electrospray ionization and matrix-assisted desorption ionization were both introduced around the same time, in the late 1980s. In fact matrix-assisted laser desorption ionization (MALDI) was first mentioned in the literature in 1987 (Karas et al., 1987). In the years prior to that, there were limited reports of the application of laser desorption MS. Early developments in MALDI focused primarily on macromolecules, particularly peptides and proteins. Historically, MALDI ion sources have predominantly been coupled to time-of-flight (TOF) instruments. TOF requires precise timed ionization events, and since ions are generated in MALDI by a pulsed desorption, this combination is complementary. Mass spectra generated by MALDI can be relatively simple, containing predominantly singly charged ions. The importance of both ESI and MALDI are well proven in the analysis of biomolecules, and both techniques were awarded the Nobel Prize for chemistry in 2002 (Chapter 1). 

S. F. Ren and Y. L. Guo, Oxidized carbon nanotubes as matrix for matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis of biomolecules, Rapid Commun. Mass Spectrom., 19 (2005) 255-260. 

P. B. O Connor and C. E. Costello, A high pressure matrix-assisted laser desorption/ionization Fourier transform mass spectrometry ion source for thermal stabilization of labile biomolecules, Rapid Commun. Mass Spectrom., 15 (2001) 1862-1868. 

Most analytical studies using FT-ICR mass spectrometry, where ions have been produced inside (or just outside) the analyzer cell, have used lasers as ionization sources. Other than some very limited Cs secondary ion mass spectrometry (SIMS) studies [77], most research utilized direct laser desorption to form various organic [78] and inorganic [79] ions, including metal [80] and semiconductor [81] (including carbon) clusters. More recently matrix assisted laser desorption ionization (MALDI) has been used to form ions of high molecular weight from polymers [82] and many classes of biomolecules [83]. 

Solouki, T., Marto, J.A., White, F.M. et al. (1995) Attomole biomolecule mass analysis by matrix-assisted-laser-desorption ionization Fourier-transform ion-cyclotron resonance. 

At the beginning of the 1990s, two new ionization methods, electrospray ionization (ESI) [9] and matrix-assisted laser desorption/ionization (MALDI) coupled to time-of-flight (TOF) analysers [10] that avoided such inconveniences, were developed and continue to revolutionize the role of mass spectrometry in biological research. These methods allow the high-precision analysis of biomolecules of very high molecular weight. 

Matrix-assisted laser desorption/ionization (MALDI) On applying a high-energy laser beam to a biomolecule (co-crystallized in a matrix), it rapidly turns into a gas and ionizes. 

Matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) routinely gives MW values with an accuracy of 0.1% or better, and has become increasingly popular for the mass measurement of biopolymers [1]. The technique is simple, rugged, has a mass range in excess of 200,000 Da, and is extremely sensitive, requiring low nanomole to picomole amounts of material. Additionally, the technique is relatively insensitive to the presence of various salts and buffers that are often associated with the isolation of biomolecules. 

Matrix-assisted laser desorption ionization (MALDI) is a frequently used ionization technique, but it is rarely used as an on-line detector. The sample stream is applied to a target plate, and it is allowed to cocrystallize with the matrix, which is subsequently desorbed, ionized with a laser, and analyzed in the MS. There has been attempts of combining FFF and MALDI, and for biomolecules, MALDI is a good ion source, due to the soft ionization with high efficiency and simple mass spectra, even for heavier molecules because the majority carry only single charge. 

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