Quenched Instationary Polymerization Systems, 6. The Direct Determination of Axial Dispersion in Size Exclusion Chromatography by Comparison of Theoretical and Ideal Peak Widths

For the direct determination of axial dispersion in size exclusion chromatography a simple method is presented which makes use of the measured and ideal peak widths. The peak width can be defined in two ways: either absolute as the difference of successive points of inflection or relative as the ratio of these points. If the absolute peak width is invariant for the number, molar mass and hyper distribution then this distribution can unambiguously be classified as Poissonian. The relative peak width for such distributions is strictly determined by the experimental parameters. It is demonstrated that axial dispersion only leads to an additive increase in the peak variances for peaks with a relative peak width smaller than 1.25. Thus, it is possible to determine directly the axial dispersion of an experimental size exclusion chromatography set‐up by the use of Poisson distributions prepared by quenched instationary polymerization techniques or any other technique leading to ideal Poisson distributions.     

Bis(O‐ethyl di­thio­carbonato‐κ2S,S′)­palladium(II)

The Pd atom in the title compound, [Pd(C₃H₅OS₂)₂], lies on an inversion center and adopts a square‐planar coordination geometry defined by the four S atoms of the two di­thio­carbonate (xanthate) ligands. In the solid state, the mol­ecules aggregate into layers in which the rows of mol­ecules alternate their orientation to allow each Pd atom to interact with two symmetry‐equivalent S atoms of the xanthate ligands of adjacent mol­ecules, generating a pseudo‐octahedral environment around each Pd atom. This weak interaction of 3.3579 (7) Å can be classified as a closed‐shell electrostatic intermolecular interaction.     

Ultrasound-Assisted Extraction and Characterization of Polyphenols from Apple Pomace,Functional Ingredients for Beef Burger Fortification

Currently, there is an increasing interest to valorise agri-food waste containing bioactive compounds with potential health benefits. In this paper, the recovery of functional molecules from apple pomace, the most abundant by-product of the apple processing industry, was carried out by ultrasound-assisted extraction (UAE) on fresh and freeze-dried samples. UAE extract, obtained by double extraction of freeze-dried apple pomace, was subjected to chromatographic and spectrophotometric characterization. It showed good levels of total phenol content, high antioxidant activity, and interesting antioxidant compounds (quercetin derivatives, chlorogenic acid, phloridzin). Subsequently, freeze-dried apple pomace, containing 40.19% of dietary fibre, was used as a fortifying agent for beef burgers (4% and 8%). The results concerning colour and sensory analysis of the fortified products were graded even better than the control (0%). The improved fibre and phenol content, together with the neutral flavour, represent the most interesting characteristics of fortified burgers. The results confirm that UAE was a successful technique for extracting phenol compounds and that the addition of apple pomace represents a valid approach to increase the health properties and palatability of beef burgers, including for consumers who do not like meat.     

Validation of a Microwave-Assisted Derivatization Gas Chromatography-Mass Spectrometry Method for the Quantification of 2-Hydroxybutyrate in Human Serum as an Early Marker of Diabetes Mellitus

Circulating levels of 2-hydroxybutyrate (2HB) are highly related to glycemic status in different metabolomic studies. According to recent evidence, 2HB is an early biomarker of the future development of dysglycemia and type 2 diabetes mellitus and may be causally related to the progression of normal subjects to impaired fasting glucose or insulin resistance. In the present study, we developed and validated a simple, specific and sensitive gas chromatography-mass spectrometry (GC-MS) method specifically intended to quantify serum levels of 2HB. Liquid–liquid extraction with ethyl acetate was followed by 2 min of microwave-assisted derivatization. The method presented acceptable accuracy, precision and recovery, and the limit of quantification was 5 µM. Levels of 2HB were found to be stable in serum after three freeze-thaw cycles, and at ambient temperature and at a temperature of 4 °C for up to 24 h. Extracts derivatized under microwave irradiation were stable for up to 96 h. No differences were found in 2HB concentrations measured in serum or plasma EDTA samples. In summary, the method is useful for a rapid, precise and accurate quantification of 2HB in serum samples assessed for the evaluation of dysglycemia and diabetes mellitus.     

Can the trilinear Higgs self-coupling be measured at future linear colliders?

We assess the possibility of measuring the trilinear self-coupling of the Standard Model Higgs boson at future electron-positron linear colliders with centre-of-mass energies between 500 and 1500 GeV. We consider rather light Higgs scalars, with mass below the threshold, produced in the double Higgs-strahlung channel and decaying via the dominant mode . Assuming ideal vertex tagging of the heavy-quark jets and mass reconstruction of the Z boson produced in association with the Higgs pair, we compare the yield of the above process to those of all irreducible electroweak and strong backgrounds proceeding through a intermediate state. Total cross sections and differential spectra of phenomenological relevance to the selection and analysis of the signal are given and discussed. Received: 20 September 1999 / Published online: 6 March 2000     

Comparison of Electrolytic Conductivity Theories: Performance of Classical and New Theories

Conductivity equations, based on the mean spherical approximation (MSA), haverecently been derived. We compare their performance with that of classicalequations at the level of experimental uncertainty using conductivity data forsome typical electrolyte solutions. For symmetrical electrolytes, the pictureisconsistent showing a better performance for the classical equations. The Leeand Wheaton equation also shows advantages at moderate concentrations. Forunsymmetrical electrolytes, the differences between MSA and classical equationsis larger. There is, however, an inherent inconsistency with the equilibriuminformation, which cannot be resolved at present.