Study of migration of active components of phosphorescent oxygen sensors for food packaging applications

A study of migration of the active components of oxygen sensors into food is presented. Six types of sensors, based on different oxygen sensitive dyes (two metalloporphyrins and one ruthenium dye), polymers (polystyrene and polysulfone) and support materials, were exposed to a number of standard ‘food simulants’ recommended by FDA/EU guidelines and then assayed for migration or sensor components and changes in oxygen calibration. Both metalloporphyrin sensor dyes leached only in olive oil and in 95% ethanol (used as a positive control), at maximum levels of 19.22 μg/dm² for PtOEPK and 113.96 μg/dm² for PtTFPP. The RuDPP dye showed maximum leaching in 95% ethanol (25.19 μg/dm²) while also migrating in an acidic aqueous simulant. Planar supports such as polyester tended to enhance the stability of the sensor. Migration of the styrene monomer from the polystyrene encapsulation medium was concluded to be low enough to be insignificant. Migration of sensor components was shown to correlate with the changes in sensor response to oxygen. Based on these results, sensor combinations were ranked on the basis of their resistance to leaching and their general stability, safety and suitability for use on a large scale in packaged foods and related food applications was proven.     

Solid-phase microextraction for qualitative and quantitative determination of migrated degradation products of antioxidants in an organic aqueous solution

Low molecular weight aromatic substances may migrate out from plastic packaging to their contents, especially if they consist of organic aqueous solutions or oils. It is, therefore, extremely important to be able to identify and quantify any migrated substances in such solutions, even at very low concentrations. We have in this work investigated and evaluated the use of solid-phase microextraction for the specific task of extraction from an organic aqueous solution such as a simulated pharmaceutical solution consisting of 10 vol.% ethanol in water. The goal was furthermore to investigate the possibility of simultaneously identifying and quantifying the substances in spite of differences in their chemical structures. Methods were developed and evaluated for extraction both with direct sampling and with headspace sampling. Difficulties appeared due to the ethanol in the solution and the minute amounts of substances present. We have shown that a simultaneous quantification of migrated low molecular weight degradation products of antioxidants using only one fibre is possible if the extraction method and temperature are adjusted in relation to the concentration levels of the analytes. Comparions were made with solid-phase extraction.     

Molecular orbital study for Na, Mg, and Al adsorption on the Si (111) surface

We investigated the interactions between the Si(111) surface and the Na, Mg, and Al atoms using cluster model calculations. Calculations were performed at levels of complete-active-space self-consistent-field (CASSCF) and multi-reference singly and doubly excited configuration interaction (MRSDCI) calculations using the model core potential method. Our calculations revealed that the most favorable sites of Na, Mg, and Al adsorption on Si(111) are on top (T₁), bridge (B₂), and 3-fold filled (T₄) sites, respectively. The nature of chemical bonds between these metal atoms and the dangling bonds of the surface Si atoms are found to be essentially covalent.     

A rapid HPIC method for the quantitative determination of tetramethylammonium chloride in some aqueous solutions used as food simulants

Summary The present paper reports a rapid HPIC method for the determination of tetramethylammonium chloride in aqueous matrices which are used as food simulants in migration tests. These simulants were: bidistilled water, an aqueous solution of 3% acetic acid, an aqueous solution of 15% ethyl alcohol, a mixed aqueous solution of 3% acetic acid and 15% ethyl alcohol. The method, as developed, has been applied to the determination of unreacted tetramethylammonium chloride residues which are able to migrate from finished epoxy resins which are used as food packaging materials.Research partially supported by National Research Council of Italy, Special Project RAISA, sub-project 4, Paper N^o 695.     

Analysis of tinuvin 1577 polymer additive in edible oils using on-line coupled HPLC-GC

An application of automated on-line HPLC-HRGC is described for direct analysis of edible oils for migrated polymer additives. The sample preparation, separating the additive from the oil triglycerides, is carried out using normal phase HPLC. The fraction of the eluent containing the additive is automatically transferred to a HRGC where a second and final separation of the additive from minor oil components takes place. The method compares well with off-line separation methods. Migration data for Tinuvin 1577 from PET and PC polymers as well as an unspecified experimental polymer is given. The advantages and disadvantages of using different edible oils as food simulants are discussed.     

Computer-assisted choice of discrete spacers for anionic isotachophoresis separations

In isotachophoresis (ITP), the sample constituents migrate, depending on their concentrations in the loaded sample, either in fully developed zones or in the boundary layers between the zones of constituents of the corresponding effective mobilities. The latter (spike) migration mode is analytically beneficial in selective detections of trace analytes, especially, when appropriately chosen discrete spacers minimize detection interferences due to matrix constituents. To facilitate a search for suitable mixtures of discrete spacers, a two-step calculation procedure was developed in this work. Using a pool of discrete spacers consisting of 42 anionic and zwitterionic constituents, this procedure was shown effective in the anionic ITP separations performed at pH = 6.5-10.0. Besides the predictions of the migration orders, it was helpful in identifying the spacing constituents that could cause resolution problems due to an uncertainty with which pH of the leading electrolyte solution is known. The ionic mobility and pKa data, taken for the spacing constituents from the literature and the ones obtained from the ITP experiments carried out in this work, were used in the calculations performed in a context with the choice of spacers. Although the data obtained from the ITP experiments provided better results, small uncertainties with which they were acquired (attributable to fluctuations in the experimental conditions) set practical limits in the calculation based choice of multi-component mixtures of the spacing constituents.     

面心立方C60表面过程的计算机模拟

近年来发现的C60及其金属掺杂化合物形成一个新的材料族，其半导体性质、超导性质及非线性光学性质已受到广泛注意，但目前对这类材料的表面性质尚缺乏研究，我们曾采用参数化的Lenard－Jones6－12模型函数比较不同晶型C6o的相对稳定性　[1]，预测面心立方C60（FccC60）的声子散射频率和态密度[2]，并计算其表面能[3]，取得有意义的结果，表明这一简单模型势能函数是C60分子间有效范德华作用的一种合理抽提．本工作进一步将该势能函数应用于研究fccC60表面吸附分子的迁移机理，并用蒙特卡罗方法模拟fcC（110）及（100）晶面的熔化过程，…     

Loss of stability by migration and chemical reaction of Santonox R in branched polyethylene under anaerobic and aerobic conditions

Plaques of branched polyethylene stabilized with 0.1 wt.% 4,4′-thiobis(6-tert-butyl-3-methylphenol) [Santonox^® R] were aged at different temperatures between 75 and 95 °C in anaerobic (nitrogen or water) and aerobic (air or water saturated with air) media. Antioxidant concentration profiles were obtained by oxidation induction time (OIT) measurements using differential scanning calorimetry. Results obtained by high performance liquid chromatography of extracts confirmed that the gradual decrease in OIT with increasing ageing time was due to migration of antioxidant to the surrounding medium. The antioxidant concentration profiles along the plaque thickness direction were flat in the plaques aged in the non-aqueous media indicating that the migration of antioxidant to the surrounding medium was controlled by the low evaporation rate at the material boundary. Crystals of antioxidant were detected by optical microscopy on the samples exposed to nitrogen. The similarity of the antioxidant concentration profiles obtained after ageing in nitrogen and in air suggested that the fraction of the antioxidant oxidized is negligible in comparison with the loss of antioxidant by migration to the surrounding media. The antioxidant concentration profiles along the plaque thickness direction obtained after ageing in water were less flat, suggesting faster dissolution in the water phase than evaporation in the case of non-aqueous ageing. The antioxidant diffusivity could be determined from the aqueous experiments and was in reasonable agreement with data reported by Moisan. For the samples exposed to water, the loss of antioxidant was faster from the samples exposed to water saturated with air. This difference is attributed to a faster degradation of the antioxidant in the oxygen-containing water phase increasing the mass transport from the polymer phase boundary to the water phase.     

Identification of bioactive peptides in hypoallergenic infant milk formulas by CE‐TOF‐MS assisted by semiempirical model of electromigration behavior

Biologically active peptides derived from complex bovine milk protein hydrolysates are of particular interest in food science and nutrition because they have been shown to play different physiological roles, providing benefits in human health. In this study, we used CE‐TOF‐MS for separation and identification of bioactive peptides in three hypoallergenic infant milk formulas. An appropriate sample cleanup using a citrate buffer with DTT and urea followed by SPE with Sep‐Pack® C18 and StrataX^TM cartridges allowed the detection of a large number of low molecular mass bioactive peptides. This preliminary identification was solely based on the measured experimental monoisotopic molecular mass values (M_exp). Later, we evaluated the classical semiempirical relationships between electrophoretic mobility and charge‐to‐mass ratio (m_e vs. q/M^α, α = 1/2 for the classical polymer model) to describe their migration behavior. The assistance of migration prediction proved to be useful to improve reliability of the identification, avoiding misinterpretations and solving some identity conflicts. After revision, the identity of 24, 30, and 38 bioactive peptides was confirmed in each of the three infant milk formulas. A significant number of these peptides were reported as inhibitors of angiotensin‐converting enzyme, however, the presence of sequences with other biological activities such as antihypertensive, antithrombotic, hypocholesterolemic, immunomodulation, cytotoxicity, antioxidant, antimicrobial, antigenic, or opioid was also confirmed.     

高效液相色谱法检测食品接触产品中的三聚氰胺及其衍生物的迁移量

建立了高效液相色谱同时检测三聚氰胺(MEL)及其衍生物——三聚氰酸二酰胺(ANE)、三聚氰酸一酰胺(ADE)和三聚氰酸(CYA)单体迁移量的方法.样品分别采用水、4％乙酸、10％乙醇作为食品模拟物,在70℃浸泡4h,浸泡液过0.45μm微孔薄膜后进入色谱柱.色谱分离采用Luna NH2柱,柱温:30℃,流动相为V(乙腈...