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.     

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.     

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 -     

Pure component vapour pressure from a Carnahan-Starling equation of state: theoretically based temperature law for the attractive parameter

The proposed equation of state associates the Carnahan-Starling hard-sphere repulsion term with an attraction term of the Redlich-Kwong type containing a temperature function α(T_r). It is applied for calculating the vapour pressures of 14 pure hydrocarbon and non-hydrocarbon components. For α(T_r), three empirical laws and one law deduced from the Clausius-Clapeyron equation are investigated. This last one gives the best results, and its two adjustable parameters may be generalized as a function of the acentric factor.