title: Quantitative aspects in electrospray ionization ion trap and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of malto-oligosaccharides.
abstract: Mass spectrometry is widely applied in carbohydrate analysis, but still quantitative evaluation of data is critical due to different ionization efficiencies of the constituents in a mixture. Different size and chemical structure of the analytes cause their uneven distribution in droplets (electrospray ionization, ESI) or matrix spots (matrix-assisted laser desorption/ionization, MALDI). In addition, instrumental parameters affect final ion yields. In order to study and optimize the latter, an equimolar mixture of malto-oligosaccharides (DP1-6) was analyzed using varying target masses for ESI as well as different matrices and laser power for MALDI. The sodium adducts and derivatives for positive ion mode (hydrazones with Girard's T Reagent, GT) and negative ion mode (reductively aminated with o-aminobenzoic acid, oABA) were studied. Negatively charged oABA-labeled malto-oligosaccharides turned out to be unsuitable for quantification of the malto-oligomeric composition. Best agreement was achieved when applying target masses in the range of the highest homolog in the mixture in electrospray ionization ion trap (ESI-IT) (1-2% deviation with GT label or as Na(+) adducts). Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) gave best results when the laser power was adjusted significantly over the desorption/ionization threshold (1% deviation with GT label). Both parameters show significant influence on the determined oligomeric composition. Consequently, estimation and even quantitative determination of amounts of oligosaccharides in a mixture can be achieved when the analytes are labeled and the proper instrumental parameters are used.
authors.affiliation: Technische Universität Braunschweig, Institut für Lebensmittelchemie, Schleinitzstr. 20, D-38106 Braunschweig, Germany.
authors.forename: Inga
authors.initials: I
authors.lastname: Unterieser
authors.forename: Julia
authors.initials: J
authors.lastname: Cuers
authors.forename: Kristin
authors.initials: K
authors.lastname: Voiges
authors.forename: Jonas
authors.initials: J
authors.lastname: Enebro
authors.forename: Petra
authors.initials: P
authors.lastname: Mischnick
mesh_terms: D010129:4-Aminobenzoic Acid / Q000737:chemistry; D009844:Oligosaccharides / Q000737:chemistry*; D017670:Sodium Compounds / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
chemical_list: D009844:Oligosaccharides; D017670:Sodium Compounds; C021705:maltooligosaccharides; D010129:4-Aminobenzoic Acid