Production of reference materials for the detection and size determination of silica nanoparticles in tomato soup

A set of four reference materials for the detection and quantification of silica nanoparticles (NPs) in food was produced as a proof of principle exercise. Neat silica suspensions were ampouled, tested for homogeneity and stability, and characterized for total silica content as well as particle diameter by dynamic light scattering (DLS), electron microscopy (EM), gas-phase electrophoretic molecular mobility analysis (GEMMA), and field-flow fractionation coupled with an inductively coupled mass spectrometer (FFF-ICPMS). Tomato soup was prepared from ingredients free of engineered nanoparticles and was spiked at two concentration levels with the silica NP suspension. Homogeneity of these materials was found sufficient to act as reference materials and the materials are sufficiently stable to allow long-term storage and distribution at ambient temperature, providing proof of principle of the feasibility of producing liquid food reference materials for the detection of nanoparticles. The spiked soups were characterized for particle diameter by EM and FFF-ICPMS (one material only), as well as for the total silica content. Although questions regarding the trueness of the results from EM and FFF-ICPMS procedures remain, the data obtained indicate that even assigning values should eventually be feasible. The materials can therefore be regarded as the first step towards certified reference materials for silica nanoparticles in a food matrix.     

STUDIES ON TEXTILE DETERGENCY AT LOW TEMPERATURE

Detergent efficiency of nonionic surfactant solutions with and without electrolyte as a function of temperature has been determined. In these experiments hexadecane was chosen as a model oily soil and polyester/cotton fabrics as solid substrate. It was found that the evolution of detergent efficiency with temperature in systems containing electrolyte followed the same trends as those of systems without electrolyte: As the temperature increases detergent efficiency also increases and an optimum is reached, then a pronounced decrease is observed. However there is a shift in the temperature at which the optimum is obtained toward lower temperatures as electrolyte concentration increases. This shift has been attributed to the effect of salting-out electrolytes on the HLB-temperature of ternary water/nonionic surfactant/oil systems.     

The Relation Between Phase Behavior and Formation of Narrow Size Distribution W/O Emulsions

Water-in-oil (W/O) emulsions of the water/C₁₂E₅/isooctanol/isooctane system have been prepared at 25° C. Phase behavior studies of the system with constant (2.5 and 6 wt.%) isooctanol concentration showed that the surfactant becomes more lipophilic with the increase in the alkanol concentration. Emulsification was carried out using four low-energy emulsification methods using the slow addition of one or various components to the rest of them, with gentle agitation. Emulsions with low-polydis-persity were obtained when the emulsification process started with a single lamellar liquid crystalline phase. If in addition to a lamellar liquid crystalline phase, other phases, such as excess water phase, were initially present, emulsions with intermediate polydispersity were produced. When a lamellar liquid crystalline phase was not involved and the spontaneous natural curvature of the surfactant was not changed during emulsification, highly polydisperse emulsions were obtained.     

Tungstotellurates of the imidazolium and 4-methylimidazolium cations

Tungstotellurates of the organic imidazolium and 4-methyl-imidazolium cations have been prepared and characterized by X-ray diffraction and i.r. spectroscopy. The [TeW₆O₂₄]^6– anion is formed by close packing of oxygen atoms with Te and W atoms in distorted octahedral voids. In both compounds the organic cations are involved in hydrogen bonds, to the [TeW₆O₂₄]^6– anion in [H₂imz]₆[TeW₆O₂₄] · 2(Himz) (1) and to Te(OH)₆ units in [4-H₂-methyl-imz]₆[TeW₆O₂₄] · Te(OH)₆ (2). Solution studies of (1) and (2) by ¹H-, ¹⁸³W- and ¹²⁵Te-n.m.r. have been carried out. Thermogravimetric (t.g.) and calorimetric (d.s.c.) analyses were performed for both compounds.     

Analysis of ofloxacin in plasma samples by high-performance liquid chromatography

Summary A sensitive HPLC method has been developed for determination of ofloxacin (OFL) in biological fluids. Sample preparation was performed by adding phosphate buffer (pH 7.4, 0.1m) then extraction with trichloromethane. OFL and the internal standard, sarafloxacin (SAR), were separated on a reversed-phase column with aqueous phosphate solution-acetonitrile, 80∶20, as mobile phase. The fluorescence of the column effluent was monitored at λ_ex 338 and λ_em 425 nm. The retention times were 2.66 and 4.24 min for OFL and SAR, respectively, and the detection and quantitation limits were 8 and 15 ng mL⁻¹, respectively. Plots of response against ofloxacin concentration were linear in the range 8 to 2000 ng mL⁻¹. Recovery was 92.9% for OFL.     

Formation of polymeric nano-emulsions by a low-energy method and their use for nanoparticle preparation

Formation of polymeric O/W nano-emulsions has been studied in the water/polyoxyethylene 4 sorbitan monolaurate/ethylcellulose solution system by the phase inversion composition (PIC) method. These nano-emulsions were used for the preparation of nanoparticles by solvent evaporation. Composition variables such as O/S ratio or final water content as well as emulsification path have been found to play a key role in the formation of stable, nanometer sized emulsions. Nano-emulsions with a constant water content of 90 wt.% and O/S ratios from 50/50 to 70/30 showed an average droplet size of about 200 nm as assessed by dynamic light scattering. Mean nanoparticle diameters, as determined by transmission electron microscopy image analysis, were of the order of 50 nm and showed a slight increase as well as a broader size distribution at increasing O/S ratios. The findings verify that the low-energy emulsification methods are not only valid for aliphatic and semipolar oils, but also for a highly polar solvent such as ethylacetate containing a preformed polymer.     

Isomeric distribution and catalyzed isomerization of cobalt(III) complexes with pentadentate macrocyclic ligands. importance of hydrogen bonding

We have investigated the isomeric distribution and rearrangement of complexes of the type [CoXLn]2+,3+ (where X = Cl-, OH-, H2O, and Ln represents a pentadentate 13-, 14-, and 15-membered tetra-aza or diaza-dithia (N4 or N2S2) macrocycle bearing a pendant primary amine). The preparative procedures for chloro complexes produced almost exclusively kinetically preferred cis isomers (where the pendant primary amine is cis to the chloro ligand) that can be separated by careful cation-exchange chromatography. For L13 and L14 the so-called cis-V isomer is isolated as the kinetic product, and for L15 the cis-VI form (an N-based diastereomer) is the preferred, while for the L14(S) complex both cis-V and trans-I forms are obtained. All these complexes rearrange to form stable trans isomers in which the pendent primary amine is trans to the monodentate aqua or hydroxo ligand, depending on pH and the workup procedure. In total 11 different complexes have been studied. From these, two different trans isomers of [CoClL14(S)]2+ have been characterized crystallographically for the first time in addition to a new structure of cis-V-[CoClL14(S)]2+; all were isolated as their chloride perchlorate salts. Two additional isomers have been identified and characterized by NMR as reaction intermediates. The remaining seven forms correspond to the complexes already known, produced in preparative procedures. The kinetic, thermal, and baric activation parameters for all the isomerization reactions have been determined and involve large activation enthalpies and positive volumes of activation. Activation entropies indicate a very important degree of hydrogen bonding in the reactivity of the complexes, confirmed by density functional theory studies on the stability of the different isomeric forms. The isomerization processes are not simple and even some unstable intermediates have been detected and characterized as part of the above-mentioned 11 forms of the complexes. A common reaction mechanism for the isomerization reactions has been proposed for all the complexes derived from the observed kinetic and solution behavior.