Positive- and negative-ion matrix-assisted laser desorption/ionization mass spectrometry of saccharides

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) of oligosaccharides and polysaccharides has been investigated in detail, It is demonstrated that cationized species of oligosaccharides, [M+Na](+) and [M+K](+), are dominant products under the MALDI condition, and negative ions of oligosaccharides are not formed to any significant extent in this process, The molecular masses of polysaccharides are similarly determined by positive- and negative-ion MALDI-MS with the help of column chromatography. The distinction between positive- and negative-ion MALDI mass spectra of oligo-and polysaccharides indicates that the MALDI processes for saccharides vary with molecular mass. The matrix plays a more important role in the ionization process for oligosaccharides, while in the desorption process for polysaccharides. (C) 1998 John Wiley & Sons, Ltd.

Behavior of silver cluster on laser desorption/ionization time-of-flight mass spectrometry

A successful analysis of silver was reported utilizing laser desorption/ionization time-of-flight mass spectrometry (LDI/TOF-MS) in this paper, The silver cluster ions Ag-n(+) and AgnO+ (n=2 similar to 5) were formed during laser desorption/ionization. In the presence of I-, K+ and Na+, the peaks corresponding, to the cluster ions [AgnIn-1](+) (n=2 similar to 6) and the adduct ions [AgI](+), [AgI]Na+ and [AgI]K+ were observed in the positive ion spectrum; the peaks corresponding to [AgnIn+1](-) (n=1 similar to 3) were found in the negative ion spectrum, all of which accompanied by sliver isotope distribution, The formation of silver cluster ions was accomplished through two-stage reaction: the first step was the generation of clusters, which was followed by the processes of photoionization and ion/molecule reaction.

Studies on extracting solutions of endohedral rare-earth metallofullerenes by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Thirteen extracting solutions of rare-earth metallofullerenes containing La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb respectively have been investigated by means of matrix-assisted laser desorption/ionization time-of-night, mass spectrometry. The influences of the positive-ion/negative-ion mode, laser intensity, matrix and mass discrimination to the analytical results are studied, based on which the optimal analytical conditions have been determined. The results show that the extracting solutions contain large quantities of rare-earth metallofullerenes brs;des empty fullerenes, On the basis of comparing their relative intensities, the different structure stabilities and solubilities of metallofullerenes with different rare-earth metals encapsulated into the fullerene cages, as well as some possible reasons to those differences, are discussed.

Stereochemical effects in mass spectrometry - Determination of the optical purity of enantiomers by mass spectrometry

Due to the difference in reactivity of enantiomers with chiral reagents, it was found that in the Fast Atom Bombardment (FAB) mass spectra of enantiomer mixtures of R-alpha-phenylethylamine and S-alpha-phenylethylamine with a chiral reagent S-phosphorsaeure-(1,1'-bi-naphthyl-2,2'-diylester) (BNP acid), the relative abundance of the characteristic ion is linearly related to the composition of the mixture. We have, therefore, proposed a possible method for the determination of the optical purity of enantiomers by mass spectrometry.

Mass spectral study of extractable La- and Lu-containing fullerenes

Mass spectra of LaxC2n (x = 1,2), well known endohedral metallofullerenes, and Lu2C2n (2n = 76-112), new members of extractable metallofullerenes, were studied. Positive-ion laser desorption/ionization (LDI) and electron impact (EI) mass spectra indicated that lutetium is a special lanthanide that prefers to form dilutetium fullerenes by the are-burning method. However, the signals for Lu2C2n become very weak in negative-ion LDI-MS, this is different from La-2@C-80, which has close relative abundances in positive- and negative-ion MS. The distinction between Lu2C2n and La-2@C-80 in the negative-ion LDI mass spectra may be due to the different structures of La- and Lu-containing fullerenes. (C) 1997 by John Wiley & Sons, Ltd.

Unusual polymerization behavior of water-soluble fullerenols in laser desorption ionization time-of-flight mass spectrometry

Laser desorption ionization time-of-flight mass spectrometry has been used to study the water-soluble multi-hydroxyl C-60 derivatives - fullerenols. The mass spectra exhibit unusual polymerization behavior of fullerenols. (C) 1997 by John Wiley & Sons, Ltd.

Laser light scattering studies of soluble high-performance polyimides: Solution properties and molar mass distributions

Two soluble high-performance polyimides, poly(BCPOBDA/DMMDA) and poly(ODPA/DMMDA), in CHCl3 at 25 degrees C have been studied using laser light scattering. We found that the z-average radius of gyration ([R(g)]) can be scaled to the weight-average molecular weight (M(w)) as [R(g)] (nm) = 4.95 x 10(-2)M(w)(0.52) and [R(g)] (nm) = 1.25 x 10(-2)M(w)(0.66) respectively for poly(BCPOBDA/DMMDA) and poly(ODPA/DMMDA), indicating that poly(ODPA/DMMDA) in CHCl3 at 25 degrees C has a more extended chain conformation than poly(BCPOBDA/DMMDA). Using the wormlike chain model approach, we found that the Flory characteristic ratios (C*) of poly(BCPOBDA/DMMDA) and poly(ODPA/DMMDA) are similar to 20 and similar to 31, respectively, indicating that both of them have a slightly extended chain conformation in comparison with typical flexible polymer chains, such as polystyrene, whose C-infinity is similar to 10. A combination of the weight-average molar mass (M(w)) with the translational diffusion coefficient distributions (G(D)) has led to D (cm(2)/s) = 3.53 x 10(-4)M(-0.579) and D (cm(2)/s) = 4.30 x 10(-4)M(-0.613) respectively for two soluble high-performance polyimides, poly(BCPOBDA/DMMDA) and poly(ODPA/DMMTA), in CHCl3 at 25 degrees C. Using these two calibrations, we have successfully characterized the molar mass distributions of the two polyimides from their corresponding G(D)s. The exponents of these two calibrations further confirm that both of the polyimides have a slightly extended coil chain conformation in CHCl3. The chain flexibility difference between these two polyimides has also been discussed.

Stereochemical effect in mass spectrometry .19. Determination of the optical purity of alpha-phenylethylamine by mass spectrometry

It is found that in the fast atom bombardment (FAB) mass spectra R-alpha-phenylethylamine and S-alpha-phenylethylamine can be clearly distinguished by S-1,1'-binaphthyl-2, 2'-diylhydrogenphosphate (S-BNP), Mixture of R-alpha-phenylethylamine and S-alpha-phenylethylamine also be tested and the relative abundance of the characteristic ion of mixture is related to the composition of the mixtute. We have therefore proposed a possible method to determine the optical purity of alpha-phenylethylamine.

Mass spectrometric evidence for the generation of benzyne from benzoyl peroxide in thermolysis

Benzoyl peroxide gave rise to benzoic acid (at m/z 122) in its electron impact mass spectrum, and its perdeuterated counterpart produced perdeuterobenzoic acid, C6D5CO2D, at m/z 128 under the same conditions, An intramolecular hydrogen abstraction is proposed for the formation of benzoic acid from the peroxide in thermolysis. As a result of this reaction, benzyne would be generated simultaneously. Anthracene was employed to trap any of the reactive intermediate benzyne. Collision-induced dissociation of the ion of m/z 254 from the mixture of benzoyl peroxide and anthracene indicated that triptycene was obtained by the trapping reaction, therefore confirming that benzyne is generated from benzoyl peroxide in thermolysis.

C-118 from fullerenols: Formation, structure and intermolecular nC(2) transfer reactions in mass spectrometry

In fast atom bombardment, two fullerenols C-60(OH)(x) (x=13-15) and C-60(OH)(x) (x-24-26) gave rise to a group of ions centered at C-118 with intervals of 24 mass units in the high mass region. In contrast, no such ions appeared in the mass spectra of pure C-60, C-70 and other fullerene derivatives such as C-60(C6H5)(10), under the same conditions. It is proposed that the pinacol rearrangement of C-60(OH)(2), resulting from partial rupture of the polyhydroxy molecules, produces C-59 with two carbon atoms bearing an unpaired electron, and that dimerization of this reactive intermediate is responsible for the formation of the predominant product C-118. An intermolecular nC(2) transfer process is used to explain the symmetrical abundance distribution of these product ions in the spectra of fullerenols.