RESUMEN
Direct desorption ionization of various types of biomolecules on metal substrates without the need of matrices was observed by a time-of-flight mass spectrometer. It provides a new convenient method for detection of small biomolecules without the confusion of ion peaks from matrix compounds. Simple commercial Al foil can be used as the substrate to obtain mass spectra of biomolecules without the need of an etching process to produce a porous surface such as with direct ionization on silicon (DIOS). The desorption and ionization mechanism is also discussed.
Asunto(s)
Aluminio/química , Ácidos Grasos/química , Espectrometría de Masas/métodos , Oligonucleótidos/química , Péptidos/química , Polisacáridos/química , Óxido de Aluminio/química , Láseres de Estado Sólido , Espectrometría de Masas/instrumentaciónRESUMEN
Desorption and ionization efficiencies of matrix-assisted laser desorption/ionization (MALDI) for various biomolecules with different dihydroxybenzoic acid isomers were studied. No clear relationships were observed between MALDI biomolecule signals vs. gas-phase basicity, proton affinity and ionization potential. This indicates the the gas-phase protonation mechanism is not adequate to explain the observed results.
Asunto(s)
Hidroxibenzoatos/química , Espectrometría de Masa por Láser de Matriz Asistida de Ionización Desorción/métodos , Isomerismo , Oligonucleótidos/química , Péptidos/química , Polisacáridos/químicaRESUMEN
So far, there have been only a few matrices reported for detection of polysaccharides with molecular weight higher than 3000 Daltons by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). In this work, we found that 2',4',6'-trihydroxyacetophenone (THAP) is a good matrix for MALDI time-of-flight MS analysis of polysaccharides with broad mass range. Large polysaccharides, dextrans, glycoproteins and polysialic acids have been successfully detected by MALDI-MS with THAP as matrix.
Asunto(s)
Acetofenonas/química , Espectrometría de Masas/métodos , Polisacáridos/análisis , Espectrometría de Masa por Láser de Matriz Asistida de Ionización Desorción/métodos , Estructura Molecular , Polisacáridos/química , Polisacáridos/clasificaciónRESUMEN
Although matrix-assisted laser desorption/ionization (MALDI) was developed more than a decade ago and broad applications have been successfully demonstrated, detailed mechanism of MALDI is still not well understood. Two major models; namely photochemical ionization (PI) and cluster ionization (CI) mechanisms have been proposed to explain many of experimental results. With the photochemical ionization model, analyte ions are considered to be produced from a protonation or deprotonation process involving an analyte molecule colliding with a matrix ion in the gas phase. With the cluster ionization model, charged particles are desorbed with a strong photoabsorption by matrix molecules. Analyte ions are subsequently produced by desolvation of matrix from cluster ions. Nevertheless, many observations still cannot be explained by these two models. In this work, we consider a pseudo proton transfer process during crystallization as a primary mechanism for producing analyte ions in MALDI. We propose an energy transfer induced disproportionation (ETID) model to explain the observation of an equal amount of positive and negative ions produced in MALDI for large biomolecules. Some experimental results are used for comparisons of various models.