Optimization and validation of an LC-fLD method for biotin in infant formula, infant cereals, cocoa-malt beverages, and clinical nutrition products

A fast and simple chromatographic method to determine biotin in foods is presented. Biotin is extracted using papain (60 degrees C, 1 h). After pH adjustment and filtration, biotin is determined by LC with fluorescence detection using postcolumn reagent avidin-FITC (avidin labeled with fluorescein isothiocyanate). The method has been validated in a large range of products: milk- and soy-based infant formulas, cereals, cocoa-malt beverages, and clinical nutrition products. The method showed recovery rates of 98.1 +/- 5.7% (average +/- SD) in a large range of concentrations. Biotin concentrations determined in infant formula standard reference materials 1846 and 1849 were in agreement with reference values. RSD of repeatability (RSDr) varied from 2.0 to 4.5%, and intermediate reproducibility (RSD(iR)) from 5.8 to 9.4%. LOD and LOQ were 3.0 and 5.0 microg/100 g, respectively. The proposed method is suitable for routine analysis of biotin in fortified foods (infant formulas, infant cereals, cocoa-malt beverages, and clinical nutrition products). It can be used as a faster, more selective, and precise alternative to the classical microbiological determination, and is easily transferable among laboratories.     

New mixing rules in simple equations of state for representing vapour-liquid equilibria of strongly non-ideal mixtures

Huron, M.-J. and Vidal, J., 1979. New mixing rules in simple equations of state for representing vapour-liquid equilibria of strongly non-ideal mixtures. Fluid Phase Equilibria, 3: 255-271.Good correlations of vapour-liquid equilibria can be achieved by applying the same two-parameter cubic equation of state to both phases. The results primarily depend on the method used for calculating parameters and, for mixtures, on the mixing rule. True parameters are the covolume b and the energy parameter a/b. For this latter one, deviations from a linear weighting rule are closely connected to the excess free energy at infinite pressure. Thus any mixing rule gives a model for the excess free energy, or any accepted models for this property can be used as mixing rules.From the above, an empirical polynomial mixing rule is used for data smoothing and evaluation, while for practical work a local composition model is used. The mixing rule thus obtained can be reduced to the classical quadratic rule for some easily predicted values of the interaction energies. For highly polar systems, it includes three adjustable parameters. Using literature data, the new mixing rule is applied, in the low and high pressure range, to binary mixtures with one or two polar compounds, giving good data correlation and sometimes avoiding false liquid-liquid immiscibility.     

When conflict induces the expression of incomplete preferences

Multicriteria conflict arises in pairwise comparisons, where each alternative outperforms the other one on some criterion, which imposes a trade-off. Comparing two alternatives can be difficult if their respective advantages are of high magnitude (the attribute spread is large). In this paper, we investigate to which extent conflict in a comparison situation can lead decision makers to express incomplete preferences, that is, to refuse to compare the two alternatives, or to be unable to compare them with confidence. We report on an experiment in which subjects expressed preferences on pairs of alternatives involving varying conflicts. Results show that depending on whether the participants are allowed to express incomplete preferences or not, attribute spread has a different effect: a large attribute spread increases the frequency of incomparability statements, when available, while it increases the use of indifference statements when only indifference and preference answers are permitted. These results lead us to derive some implications for preference elicitation methods involving comparison tasks.     

Vapour-liquid equilibrium and critical locus curve calculations with the soave equation for hydrocarbon systems with carbon dioxide and hydrogen sulphide

Huron, M.-J., Dufour, G.-N. and Vidal, J., 1978. Vapour-liquid equilibrium and critical locus curve calculations with the Soave equation for hydrocarbon systems with carbon dioxide and hydrogen sulphide. Fluid Phase Equilibria, 1: 247–265The aim of this work is to test the value of the Soave-Redlich-Kwong equation of state for predicting phase behaviour of mixtures. Special attention is paid to systems containing hydrogen sulphide or carbon dioxide with hydrocarbons. The properties analysed are critical loci and liquid vapour equilibria, with calculations of standard deviations for pressures and compositions. Optimum values of binary interaction parameters are proposed for these mixtures. Calculation methods to avoid trivial solutions in phase equilibria calculations and for finding critical loci with temperature extrema are described.     

SIMPLE EXPLANATION OF THE MISSES IN THE COOPERATION OF CHARGES IN PHOTOSYNTHETIC O2 EVOLUTION

Abstract —In the model of Forbush et at. (1971) the observed damping of the flash yield sequence of photosynthetic O₂ evolution was related to a certain percentage of ‘misses’ (α; i.e. centers not converted). The possibility of a miss was supposed to be equal for all states S_0.1,2,3. We propose a new model and a new recurrence law that gives better quantitative agreement with the O₂ yield oscillations observed in Chlorella during a sequence of flashes. We find a better fit with all experimental results by assuming very unequal misses; the misses occur nearly exclusively on S₂ (and also sometimes on S₃). In the simpler case of only one miss on one state, half of S₂ exists as an inactive form S₂₊^- because it is in apparent equilibrium with pool A. The active form of S₂ is converted to S₃ in a flash and the unchanged inactive form S₂₊^- explains the miss: S ₁ hv→S₂₊^-=S₂hv→S₃ (S₂₊^- is a transition state between S₁ to S₂ associated with Q^-). In the dark, the apparent equilibrium constant K_A between pool A and Q (i.e. S₀, S₁ in the dark) is very large; this explains why there is no miss on these states. In light, the experimental value of K_A between pool A and Q (i.e. S₂, S₃ in the light) is 1, and this explains why the misses are large for states S₂, S₃; i.e., S₂₊^-/S2- 1 and sometimes S₃₊^-/S₃?0–1. This new model predicts that the total number of active states ΣS_i=S₀+S₁+S₂+S₃ is an oscillating function of the flash number. This sum 2S, is also the number of trapping centers for excitons. As fluorescence is proportional to excitons that are not trapped, our model explains why the fluorescence oscillates as a function of the flash number. We find also that the initial rates of O₂ evolution after (n - 1) flashes vs the 02 yield of the n^th flash are not exactly on a straight line, which also favors our model.     

Iterative calculation by perturbation of the configuration interaction for fundamental state and first excited states of MgO

For the lowest energy states of the MgO molecule, zero-order multiconfigurational wavefunctions are constructed by an iterative process, the remaining configuration interaction being treated by a Rayleigh—Schrödinger second-order perturbation. The calculated energies compare well with the experimental spectrum. The ground state appears to be a¹Σ⁺ state built essentially from the closed-shell SCF determinant and a di-excited (6σ)² → (7σ)² determinant.     

Determination of vitamin B12 in food products by liquid chromatography/UV detection with immunoaffinity extraction: single-laboratory validation

A fast and simple method to determine vitamin B12 in foods is presented. The method allows, in addition to the determination of added cyanocobalamin, the determination of natural vitamin B12 forms, making it also applicable to nonfortified products, especially those that are milk-based. Vitamin B12 is extracted in sodium acetate buffer in the presence of sodium cyanide (100 degrees C, 30 min). After purification and concentration with an immunoaffinity column, vitamin B12 is determined by liquid chromatography with UV detection (361 nm). The method has been validated in analyses of a large range of products: milk- and soy-based infant formulas, cereals, cocoa beverages, health care products, and polyvitamin premixes. The method showed appropriate performance characteristics: linear response over a large range of concentrations, recovery rates of 100.8 +/- 7.5% (average +/- standard deviation), relative standard deviation of repeatability, RSDr, of 2.1%, and intermediate reproducibility, RSDiR, of 4.3%. Limits of detection and quantitation were 0.10 and 0.30 microg/100 g, respectively, and correlation with the reference microbiological assay was good (R2 = 0.9442). The proposed method is suitable for the routine determination of vitamin B12 in fortified foods, as well as in nonfortified dairy products. It can be used as a faster, more selective, and more precise alternative to the classical microbiological determination.     

The dielectric constant and solvent effect on the stabilities of copper(II) chloro complexes

Transition Metal Chemistry -