Analysis of high-molecular-weight oligosaccharides from human milk by liquid chromatography and MALDI-MS.

Pooled human milk oligosaccharides were fractionated by anion-exchange chromatography on AG 1-X2 and by an improved gel filtration procedure that allowed the separation of large oligosaccharides on Toyopearl HW 40 (S) and Bio-Gel P-6 columns, respectively. The analysis of the resulting nonderivatizated fractions by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) revealed several neutral and acidic high-molecular-weight oligosaccharides. So far unknown acidic oligosaccharides containing up to 20 monomers were detected in a molecular mass range of 2094-3626 Da. Furthermore, neutral structures containing up to 35 monosaccharides were identified after fractionation on Toyopearl HW 40 (S) and subsequent P-6 fractionation, demonstrating the suitability of the applied method for the preparation of oligosaccharides in this high-molecular-mass range. The composition of the detected oligosaccharides was found to be the same as those previously identified in oligosaccharides of lower masses. However, an enormous structural heterogeneity was observed when acidic and neutral fractions were characterized by high-pH anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). From our analysis we may conclude that each molecular mass identified by MALDI-MS corresponds to a variety of isomeric structures. The total number of oligosaccharides occurring in human milk may consequently be much higher than estimated before.     

Influence of pressure in the first pumping stage on analyte desolvation and fragmentation in nano-ESI MS.

In ESI MS, some classes of biomolecules are detected only with low signal intensities due to difficulties in achieving efficient analyte desolvation, either because an analyte tends to fragment already at gentle desolvation conditions (i.e., noncovalent protein complexes or nucleotides) or because an analyte requires very strong activation in order to remove solvent molecules (i.e., carbohydrates). Even though the pressure in the first pumping stage of the ESI instrument is known to have an influence on the desolvation conditions, it has never been the focus of a detailed investigation. The role of the pressure in the first pumping stage is systematically interrogated in this study for several model substances. Ion signal intensities and signal-to-noise ratios are significiantly enhanced if the pressure in the first pumping stage is increased and adjusted, and analyte fragmentation can be substantially reduced. Thus, besides thermal heating and the acceleration in the nozzle-skimmer region, which are usually optimized, the pressure in the first pumping stage is an additional important desolvation parameter.     

Method of testing stabilized stainless steels for resistance to intergranular corrosion

Relationships between the effective chromium and carbon contents and the parameter of resistance (k) are discussed in this paper in relation to their applicability to stabilized steels. The efficiency coefficients of stabilization in Ti-stabilized steels of four types, determined according to the completeness of chemical composition, were the basis for indicating the parameters of the resistance of these steels to intergranular corrosion. The comparison with low carbon steels, two of optimized chemical composition, one stabilized with niobium, reveals sufficient resistance to, and guarantee of this resistance to the intergranular corrosion for the 08Cr18Ni10Ti grade. The method of evaluating the resistance to intergranular attack based on calculating the minimum effective chromium content, the maximum effective carbon content and the resistance parameter k that issues therefrom, is suitable for practical application directly during the making of stainless steels.     

Effects of competing and complex responses on the reaction time of acute psychiatric groups.

Compared 8 acute nonparanoid schizophrenics to 12 depressed and 29 nonpsychotic psychiatric controls (age range = 18-41 yrs) to determine if schizophrenic deficit on 4 auditory reaction time tasks was a function of slower rate of processing information. The tasks varied along the dimensions of complexity (simple vs 2-choice) and competition (low vs high). It was hypothesized that slower processing rate implied slower reaction time on the simple tasks and greater slowing down on the complex tasks. Some Ss in each group were tested 2 times to determine the relative stability of the deficit. Essentially, for both testing sessions schizophrenics were slower than both control groups on all 4 tasks. However, they slowed down more than the nonpsychotic group only on the complex task with high competition. The depressed group, which performed like the nonpsychotic group on the 3 other tasks, also slowed down more than the nonpsychotic group on this task, but only on the 1st testing session. It is concluded that schizophrenic deficit was stable and did not arise primarily from slower rate of processing data, although interference might have augmented it. (17 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)