3. RESULTS AND DISCUSSION The ma<strong>in</strong> task <strong>of</strong> this study was the application <strong>of</strong> the negative-ion mode MALDI-TOF MS to the determ<strong>in</strong>ation <strong>of</strong> a structure <strong>of</strong> storage oligosaccharides isolated from plants. The proper experimental conditions (the most convenient matrix, optimal concentrations <strong>of</strong> samples and matrix, optimal laser power etc.) were determ<strong>in</strong>ed for <strong>in</strong>ul<strong>in</strong> and MOSs standard samples (the details are not shown). Moreover, these <strong>in</strong>itial experiments showed a potential <strong>of</strong> negative-ion mode MALDI-TOF MS for the differentiation <strong>of</strong> reduc<strong>in</strong>g (MOSs) and nonreduc<strong>in</strong>g (<strong>in</strong>ul<strong>in</strong>) oligosaccharides, because <strong>of</strong> easy fragmentation <strong>of</strong> reduc<strong>in</strong>g end r<strong>in</strong>g (the <strong>production</strong> <strong>of</strong> <strong>in</strong>-source fragment ions [M – H – 120] – ; see Figure 1). This <strong>in</strong>-source fragmentation has already been described for negative-ion mode MALDI-TOF mass spectra <strong>of</strong> dextrans (the polymer conta<strong>in</strong><strong>in</strong>g the ma<strong>in</strong> cha<strong>in</strong> with 1–6 glycosidic bonds and different degree <strong>of</strong> branch<strong>in</strong>g) [7]. This <strong>in</strong>formation is very useful for the identification <strong>of</strong> storage carbohydrates isolated from plants as is shown below. All real samples (LGS and oligosaccharides isolated from Jerusalem artichoke and red onion) were analyzed with THAP that was <strong>selected</strong> as the most convenient matrix. While [M – H] – ions formed the dom<strong>in</strong>ant distribution for oligosaccharides from both vegetables, the ma<strong>in</strong> distribution <strong>of</strong> LGS was formed by the <strong>in</strong>-source fragment ions [M – H – 120] – (see Figure 2). LGS showed this fragmentation because <strong>of</strong> its structure that conta<strong>in</strong>s the ma<strong>in</strong> cha<strong>in</strong> formed by 1–4 glycosidic bonds and branches with 1–6 glycosidic bonds and a reduc<strong>in</strong>g end group. The mass spectra differed <strong>in</strong> the quantity <strong>of</strong> the adducts which was dependent on the amount <strong>of</strong> ions <strong>in</strong> the samples. Thus there are some important conclusions on the mass spectrometric behavior <strong>of</strong> the neutral oligosaccharides. Although the negative-ion mode MALDI-TOF MS is ignored <strong>in</strong> connection with neutral carbohydrates it is possible to determ<strong>in</strong>e the ma<strong>in</strong> characteristics <strong>of</strong> their distribution without any carbohydrate derivatization (see Table 1). In addition, the negative-ion mode MALDI-TOF mass spectra is able to differentiate reduc<strong>in</strong>g maltooligosaccharides and nonreduc<strong>in</strong>g fructooligosaccharides extracted from real samples, because <strong>of</strong> easy fragmentation <strong>of</strong> reduc<strong>in</strong>g end r<strong>in</strong>g, which is not evident <strong>in</strong> the positive-ion mode MALDI-TOF MS where both types <strong>of</strong> oligosaccharides form the alkali-ion adducts. REFERENCES [1] Harvey, D. J. Matrix-assisted laser desorption/ionization mass spectrometry <strong>of</strong> carbohydrates and glycoconjugates. Int. J. Mass Specrom. 2003, 226, 1-35. [2] Zaia, J. Mass spectrometry <strong>of</strong> oligosaccharides. Mass Spectrom. ReV. 2004, 23, 161-227. [3] Harvey, D. J. Mass Specrom. Reviews. 2006, 25, 595-662 [4] Štikarovská, M.; Chmelík, J. Analytica Chimica Acta 2004, 520, 47–55 [5] Robyt, J.D. Essentials <strong>of</strong> carbohydrate chemistry, Spr<strong>in</strong>ger, New York, 1998 [6] Laštovičkova,M; Chmelik, J. J. Agric. Food Chem. 2006, 54,5092-5097 [7] Čmelík, R.; Štikarovská, M.; Chmelík, J. J. Mass Spectrom. 2004, 39, 1467-1473. Sborník soutěže Studentské tvůrčí č<strong>in</strong>nosti Student 2006 a doktorské soutěže O cenu děkana 2005 a 2006 Sekce DSP 2006, strana 202
Figure 1 Negative-ion mode MALDI-TOF mass spectra <strong>of</strong> standard oligosaccharides: <strong>in</strong>ul<strong>in</strong> (A) and MOSs (B) where Sborník soutěže Studentské tvůrčí č<strong>in</strong>nosti Student 2006 a doktorské soutěže O cenu děkana 2005 a 2006 Sekce DSP 2006, strana 203
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