Effect of sample preparation methods on the analysis of dispersed polysaccharides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Quantitative analysis capability of DIUTHAME mass spectrometry verified by acetylcholinesterase enzyme-catalyzed reaction assays

Matrix-assisted laser desorption/ionization (MALDI) is advantageous for mass spectrometry applications where throughput is important. However, quantitative analysis is essentially problematic for MALDI-MS whose results depend on the intrinsically stochastic microcrystalline state of the matrix. High-throughput screening (HTS) of drug candidates is a typical example that requires high throughput. The application of MALDI-MS to HTS, which is quantitative analysis, imposes restrictions on designing an experimental system. Surface-assisted laser desorption/ionization (SALDI) methods, which do not depend on matrix crystal formation, are expected to be applied to quantitative analyses such as HTS. A recently developed one type of SALDI methods, desorption ionization using through hole alumina membrane (DIUTHAME), possesses a distinct feature that the surface microstructure effective for ionization is formed by through holes. In this study, the quantitative analysis capability of DIUTHAME was verified by applying DIUTHAME to enzyme-catalyzed reaction measurements, which are also used for HTS. Quantitative DIUTHAME-MS was conducted on various conditions of acetylcholinesterase-catalyzed reaction solutions containing cow milk as a substitute of biological media. Even for the enzyme-catalyzed reaction solutions containing complex additives that make the quantitative analysis extremely difficult, DIUTHAME based on the through hole structure enables quantitative measurements of the analytes by applying the reaction solutions to the back side of the laser exposed surface. In comparison with those obtained by MALDI-MS, the results obtained by DIUTHAME-MS showed less variability of data and delivered a better linearity of the Lineweaver-Burk plots and a more reasonable value of the Michaelis constant. Accordingly, it was demonstrated that DIUTHAME-MS possesses the quantitative analysis capability much better than that of MALDI-MS.

Structure determination of beta-glucans from Ganoderma lucidum with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry

A novel method that uses matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to analyze molecular weight and sequencing of glucan in Ganoderma lucidum is presented. Thus, β-glucan, which was isolated from fruiting bodies of G. lucidum, was measured in a direct and fast way using MALDI mass spectrometry. In addition, tandem mass spectrometry of permethylated glucans of G. lucidum, dextran, curdlan and maltohexaose were also pursued and different fragment patterns were obtained. The G. lucidum glucan structure was determined and this method for linkage analysis of permethylated glucan has been proven feasible.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update covering the period 1999-2000

This review describes the use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the analysis of carbohydrates and glycoconjugates and continues coverage of the field from the previous review published in 1999 (D. J. Harvey, Matrix-assisted laser desorption/ionization mass spectrometry of carbohydrates, 1999, Mass Spectrom Rev, 18:349-451) for the period 1999-2000. As MALDI mass spectrometry is acquiring the status of a mature technique in this field, there has been a greater emphasis on applications rather than to method development as opposed to the previous review. The present review covers applications to plant-derived carbohydrates, N- and O-linked glycans from glycoproteins, glycated proteins, mucins, glycosaminoglycans, bacterial glycolipids, glycosphingolipids, glycoglycerolipids and related compounds, and glycosides. Applications of MALDI mass spectrometry to the study of enzymes acting on carbohydrates (glycosyltransferases and glycosidases) and to the synthesis of carbohydrates, are also covered.

Determination of molecular weight profile for a bioactive β-(1→3) polysaccharides (Curdlan)

This paper focuses on the development of methodology based on MALDI-TOF mass spectrometry for evaluation of molecular weight profile of the water-insoluble portion of an extracellular polysaccharide, i.e. Curdlan. As previously demonstrated, MALDI analysis of water-insoluble Curdlan fraction gave number-average (M(n)) and weight-average (M(w)) molecular weights of 8000 and 8700 Da, respectively [T.W.D. Chan, K.Y. Tang, Rapid Commun. Mass Spectrom. 17 (2003) 887]. To validate the MALDI determined molecular weight information, several additional analytical schemes were used to analysis the water-insoluble Curdlan fraction. In all cases, the water-insoluble Curdlan sample was fractionated by gel permeation chromatography (GPC) using Sephadex G-75 column. The M (n) of low-mass and narrow distributed polysaccharide fractions were obtained by MALDI-MS. Good linearity was found in the calibration plot constructed from the measured M (n)-values and the corresponding elution time/volume. The relative quantity of various fractionated samples was then measured using three different approaches. These include (a) direct refractometric analysis; (b) UV-vis absorption analysis of the Aniline Blue stained sample; and (c) GC-MS analysis of the hydrolyzed and TMS-derivatized sample. Using results obtained from theses quantification methods and the correlation function between the GPC retention time and M (n), the MW and MWD of water-insoluble Curdlan were obtained. Our results demonstrated that the previous use of MALDI methods for measuring M(n), M(w) and polydispersity (PD) of water-insoluble Curdlan (with and without GPC fractionation) were unreliable. However, by standardizing the narrow distributed polysaccharides using MALDI-MS method, reliable molecular weight information for dispersed polysaccharides could be obtained. The M (n),M (w) and PD of the water-insoluble Curdlan were found to be 22,000, 31,500 Da and 1.40, respectively.

MALDI-TOF mass spectrometry of oligomeric food polyphenols

The structural heterogeneity of polyphenols from cranberries, grape seed extracts, sorghum and pomegranate was characterized by MALDI-TOF MS. Polyphenolics were isolated by liquid chromatography and subjected to MALDI-TOF MS using trans-3-indoleacrylic acid as the matrix. Spectrometric analysis gave information on degree of polymerization, monomeric substitution, and the nature of intermolecular bonds. Cranberry polyflavan-3-ols had variation in interflavan bonds (A- and B-types) and contained polyflavan-3-ols linked to anthocyanins through a CH3-CH bridge. Polygalloyl-polyflavan-3-ols in grape seed extract had large variation in the degree of galloyl substitution. Sorghum polyflavans had structural heterogeneity in glycosylation and hydroxylation. Pomegranate hydrolyzable tannins that correspond to previously described structures were detected, such as punicalagin, but others that correspond to oligomeric ellgitannins in which two to five core glucose units are cross-linked by dehydrodigalloyl and or valoneoyl units were also observed. Results demonstrate that large heterogeneity occurs in degree of polymerization, intermolecular bonds, pattern of hydroxylation, and substitution with monosaccharides and gallic acid.

Different behavior of dextrans in positive-ion and negative-ion mass spectrometry

A mass spectrometric (MS) comparative study of dextran samples using two different ionization techniques (matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI)) in both positive- and negative-ion modes is reported. The experiments were carried out with two polydisperse dextrans (1000 and 8800 Da) and isomaltotriose. In the positive-ion mode, the expected alkali metal ion adducts of dextrans were observed in both techniques. In contrast, the expected preferential formation of deprotonated molecules [M - H](-) was not confirmed in negative mode MALDI time-of-flight (TOF) MS, where the series of ions [M(x)- H +42](-) or [M(x+1)- H - 120](-), coming either from some addition or fragmentation, were observed. In both ionization techniques, these ions formed the main distributions of dextrans in the negative-ion mode. It seems that the negative molecular ions formed from the alpha1 --> 6 linkage of polyglucose oligomers easily decompose, and the product ions [M - H - 120](-) markedly dominate. The fragmentation experiments and especially the investigation of the fundamental role of the nozzle-skimmer potential in ESI-MS supported our explanation of the observed behavior because its higher values caused higher fragmentation. The experiments with isomaltotriose excluded any addition of 42 Da during the MS procedures, which is not distinguishable from the loss of 120 Da in the case of polydisperse dextrans. MALDI-TOFMS was found to be more sensitive for the detection of higher oligosaccharides and ESI-MS more useful for structural studies.

Sample preparation effects in matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry of partially depolymerised carboxymethyl cellulose

Sample preparation effects in matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) of partially depolymerised carboxymethyl cellulose (CMC) have been investigated. The depolymerisation was either enzymatic or acidic. Fractions of enzymatically depolymerised CMC were collected from size-exclusion chromatography (SEC) and further investigated by MALDI-TOFMS. 2,5-Dihydroxybenzoic acid was used as matrix, dissolved in H(2)O due to the poor solubility of CMC in suitable organic solvents. The samples were dried by two methods, in ambient atmosphere and at reduced pressure. Under reduced pressure the sample spot homogeneity increased. This drying method, however, produced additional adduct peaks in the mass spectra originating from ion exchange on the CMC oligomers. Analysis of CMC could be performed in both negative and positive ion modes. Mass discrimination and variation in ionisation efficiency were demonstrated by comparing mass spectra with SEC data. Measurements of the degree of substitution (DS) were performed on three CMCs with different DS values, which were depolymerised in trifluoroacetic acid. The three CMCs were easily distinguished from one another, but the obtained DS values deviated from the values supplied by the manufacturer.

Analysis of a bioactive beta-(1 --> 3) polysaccharide (Curdlan) using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

This paper focuses on the development of MALDI sample preparation protocols for the analysis of a bioactive beta-(1 --> 3) polysaccharide, i.e. Curdlan. The crude Curdlan sample was first separated into a low molecular weight water-soluble portion and a high molecular weight water-insoluble portion. The water-soluble portion was analyzed using a standard MALDI sample preparation method developed for dextran analysis. Two low-mass (<4000 Da) polysaccharide distributions differing by 16 Da were observed. For the analysis of the water-insoluble portion, several sample preparation protocols were evaluated using GPC-fractionated samples. A sample preparation method based on the deposition of the analyte solution with a mixture of 2,5-dihydroxybenzoic acid (DHB) and 3-aminoquinoline (3AQ) matrices in dimethyl sulfoxide (DMSO) at elevated temperature of 70 degrees C was found to reliably produce good MALDI spectra. MALDI analysis of the water-insoluble Curdlan portion gave number-average (Mn) and weight-average (Mw) molecular weights and polydispersity of 8000 Da, 8700 Da, and 1.10, respectively.