High-resolution laser desorption mass spectrometry of peptides and small proteins.

Abstract

Matrix-assisted laser desorption/ionization (MALDI) has been used with an external ion source Fouriertransform mass spectrometer to obtain the highest mass resolution ever, to our knowledge, demonstrated for laserproduced ions (r/Am = 1,100,000 for [Arg8Jvasopressin, 228,000 for melittin, and 90,000 for bovine insulin). The peaks in the isotope cluster for bovine insulin are fully resolved, and the mass measurement accuracy is an order of magnitude better than can be achieved with time-of-flight mass spectrometry. With the method described here, analyte is applied to a sample probe and mixed with a solution containing a matrix material (2,5-dihydroxybenzoic acid) that strongly absorbs ultraviolet light. Upon irradiation with a pulse from an excimer laser (353 nm, 2 mJ), a large number of intact protonated molecular ions are produced. The ions are focused by a 117-cm-long quadrupole ion guide and injected into an ion cyclotron resonance analyzer cell located inside the bore of a 6.5-T superconducting magnet. A pulse of argon buffer gas cools the ions prior to detection. One of the principal advantages of an external ion source Fourier-transform mass spectrometer is that the ion formation and ion detection processes are separated and can be independently optimized.In 1988, Karas and Hillenkamp introduced a mass spectrometry method called matrix-assisted laser desorption/ionization (MALDI) for measuring the molecular weights ofbiopolymers (1-3). The key idea is to isolate and surround analyte biomolecules with a matrix material that strongly absorbs laser light.When an incident laser pulse strikes the solid matrix/ biomolecule mixture, ablation and ionization of the surface layer occurs very rapidly. One might expect that fragile biomolecules would not survive such a violent event, but, remarkably, they remain intact and appear as the main peaks in a mass spectrum. Selection of an appropriate matrix material has proven to be critical to the success of MALDI. Beavis and Chait screened hundreds of possible matrices and found that cinnamic acid derivatives are excellent for the analysis of peptides and proteins (4,5). With the introduction a few years ago ofinexpensive MALDI mass spectrometers, the technique has become an essential tool in many protein biochemistry laboratories (6, 7).Most MALDI applications use time-of-flight mass spectrometry (TOF-MS) to mass analyze and detect the laserproduced ions. Although this method is rapid and has picomolar sensitivity, the mass measurement accuracy is somewhat limited. Several processes that limit the mass resolution and mass measurement accuracy ofTOF mass spectrometers have been identified (8). One cause of peak broadening is the considerable energy spread of the ions. Even at the threshold for ionization, the energy spread can be as large as 30 eV, and as the laser power is increased the spread increases further (9-11). This causes there to be a distribution of arrival times and a broadening of the peaks in the TOF mass spectrum. Further peak broadening can occur...

Compound W, a 3,3′-Diiodothyronine Sulfate Cross-Reactive Substance in Serum from Pregnant Women—A Potential Marker for Fetal Thyroid Function

“…Dried samples were dissolved in 0.02 N NaOH and purified by HPLC. The purified product was analyzed by T 2 S RIA and high-resolution mass spectrometry (MS) (9,10). RIA analysis revealed a T 2 S-reactive peak, the elution time of which coincided with W peak on HPLC.…”

Evaluation of different combinations of gated trapping, RF-only mode and trap compensation for in-field MALDI Fourier transform mass spectrometry

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Mass spectrometry in systems biology: An overview

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