Improving sensitivity of a small angle x-ray scattering camera with pinhole collimation using separated optical elements

International audienceWe show that a significant improvement in the sensitivity of a Huxley–Holmes design for a small angle x-ray scattering camera is obtained by separating the mirror and the monochromator. The design of the camera involves a long x-ray mirror close to a point x-ray source associated with a curved focusing crystal located close to the sample. The sample area is located at half the distance between the source and detector planes. Diffuse scattering produced by the mirror is not incident on the focusing crystal, thus reducing the background signal. Complete elimination of hard x rays allows precise calibration and hence absolute determination of sample cross section by means of a semitransparent beam stop. In pinhole geometry, the flux corresponds to a ;107 photons/s through the sample, collimated to 1022 Å21 in q range. This allows determination of scattered intensities on the order of 1023 cm21, corresponding to the scattering related to isothermal compressibility of less than 0.1 mm of pure water. As a reference sample, the widely used Lupolen™, a semicrystalline polymer, is calibrated. The high-q limit (q'4.5 nm21) of a porous calcite sample can be used as a secondary standard for specific area determination of solid/solid or solid–liquid dispersions

Report of the interlaboratory comparison organised by the EU Reference for Laboratory Food Contact Material - ILC02 2009- Bisphenol A in 50% aqueous ethanol (milk simulant): Laboratory performance and precision criteria of a harmonised method

The Institute for Health and Consumer Protection (IHCP) of the European Commission¿s Directorate-General Joint Research Centre hosts the Community Reference Laboratory for Food Contact Materials (EURL-FCM). One of its core tasks is to organize interlaboratory comparisons (ILCs) among appointed National Reference Laboratories (NRLs). This report presents the results of the second ILC exercise of the EURL-FCM for the year 2009, which focused on the determination of Bisphenol A (BPA) in 50% aqueous ethanol as a food simulant for milk. The general aim was to develop and perform the validation of a method for the analysis of Bisphenol A as model substance for a polycarbonate (PC), since it is a material that has typically been used as baby bottles and therefore typically in contact with mostly milk-type products. The strategy rose from the implementation of the new milk simulant 50% Ethanol (EtOH) in Commission Directive 2007/19/EC that current CEN standards for specific migration have not addressed yet. Four 50% ethanol solutions containing different concentrations of Bisphenol A were provided for analysis encompassing concentrations of relevance to exposure determination and compliance determination. The homogeneity and stability studies were performed by the EURL-FCM laboratory. Standard operating procedures (SOPs) for the two approaches were also written. There were 31 participants from twenty-five countries to whom samples were dispatched and 26 of which submitted results. The results of analyses were received and statistically interpreted. The assigned values were obtained as a consensus values after applying the robust statistics to the results obtained from the participants. Laboratory results were rated with z-scores in accordance with ISO 13528 [1]. Standard deviations for ILC comparison (also called target standard deviations) were set based on Horwitz equation and Horrat ratio 0.5. The results and preliminary report were discussed in the plenary of December 2009. The participation of the laboratories was regarded as satisfactory for the aim of the precision experiment with regards of the numbers of received results. As a conclusion of the precision exercise on the quantification of Bisphenol A in the new milk simulant 50% ethanol, this ILC showed that the validation of the method based on HPLC-FLD according to the description based mostly on the previous CEN standard TS 13130-13 was successful. The precision that can be suggested were of 15% reproducibility SD and 6% repeatability SD for the 0.0067 mg/kg level, 10% reproducibility SD and 4% repeatability SD for the 0.0.21 mg/kg level, 6% reproducibility SD and 2% repeatability SD for the 0.0.75 mg/kg level, 6% reproducibility SD and 0.2% repeatability SD for the 0.56 mg/kg level. With respect to the scarcity of data previously available in the validation performed as reported in the CEN standard TS 13130-13 (issued version of 2005), this validation also provides a great breadth of valuable detailed and traceable raw data, which should prove extremely relevant for the creation of an extension of the standard from CEN.JRC.DG.I.2-Chemical assessment and testin

Report of an interlaboratory comparison organised by the EU Reference Laboratory for Food Contact Materials - ILC01 2009 - DIDP in Oil Laboratory performance and precision criteria of a harmonised method

The Institute for Health and Consumer Protection (IHCP) of the European Commission¿s Directorate-General Joint Research Centre hosts the European Union Reference Laboratory for Food Contact Materials (EURL-FCM). One of its core tasks is to organize interlaboratory comparisons (ILCs) among appointed National Reference Laboratories (NRLs). This report presents the results of the second ILC of the EURL-FCM which focused on the determination of Di-isodecyl phthalate (DIDP) in an oil matrix. The aim was to develop and perform the validation of a method for the analysis of DIDP (as model substance for a technical mixture of phthalates) from oil (as simulant for fatty foods). This exercise was used both as proficiency testing and to validate a standard operating procedure (SOP) for the determination of DIDP in oil that was written by the EURL based on the most performant methods used by NRLs in the proficiency test of 2008. Participation of local laboratories under NRLs was encouraged (by producing 60 samples). There were 28 participants to whom samples were dispatched 24 of which submitted results. From the EURL-NRL network 23 laboratories out of 24 reported results. There were 2 guests from Germany that provided results as well. Participants were invited to report four replicates measurements under repeatability conditions. The ILC was closed permanently in the middle of October for statistical interpretation. Based on the results in this precision experiment the method performance was assessed through evaluation of the repeatability and reproducibility standard deviation (SD) according to the mechanism described in ISO 5725 [11,12]. The assigned value and its uncertainty were obtained as a consensus values after applying the robust statistics to the results obtained from the participants. Laboratory results were rated with z and z¿ scores in accordance with ISO 13528 [1]. Standard deviations for proficiency assessment (also called target standard deviations) were set based on Horwitz equation. The participation of the laboratories was regarded as satisfactory for the aim of the precision experiment with regards of the numbers of received results thanks to the proactive involvement of the NRLs-FCM. As a conclusion for participation and laboratory performance, this ILC showed: A noted increase in participation compared to the similar exercise of 2008. The number of laboratories submitting results for DIDP in oil rose from 17 to 25. This was due in part from the experience acquired in the previous year exercise as well as to the provision by the EURL of both the method description in a CEN like format as well as of the internal standard. A great increase in laboratory performance compared to 2008 with 76-92% of successful achievement of results from the participants within the tolerance limits (range 76-92% depended on concentration level considered) compared to 59% in 2008. In particular the performance at the concentration level of the SML was 80% compared to 59% for the same exercise in 2008. The harmonisation of the procedure and following a harmonised method for determination of DIDP in oil in 2009 resulted in a decrease more then 2.5 times in the reproducibility SD from 37% to 14 % for the concentration level around SML of 9 mg/kg while the repeatability SD remained almost the same ¿ 6.5%.JRC.DG.I.2-Chemical assessment and testin

Spherical Colloids: Effect of Discrete Macroion Charge Distribution and Counterion Valence

We report the coupled effects of macroion charge discretization and counterion valence in the primitive model for spherical colloids. Instead of considering a uniformly charged surface, as it is traditionally done, we consider a more realistic situation where \textit{discrete monovalent microscopic charges} are randomly distributed over the sphere. Monovalent or multivalent counterions ensure global electroneutrality. We use molecular dynamics simulations to study these effects at the ground state and for finite temperature. The ground state analysis concerns the counterion structure and \textit{charge inversion}. Results are discussed in terms of simple analytical models. For finite temperature, strong and weak Coulomb couplings are treated. In this situation of finite temperature, we considered and discussed the phenomena of ionic pairing (pinning) and unpairing (unpinning).Comment: 24 pages, 12 (main) figures (28 EPS files). To appear in Physica

A general method for the synthesis of nanostructured large-surface-area materials through the self-assembly of functionalized nanoparticles

A general synthetic method for the preparation of nanostructured materials with large surface area was developed by using nanoparticle building blocks. The preparation route involves the self-assembly of functionalized nanoparticles in a liquid-crystal phase. These nanoparticles are functionalized by using difunctional amino acid species to provide suitable interactions with the template. Optimum interactions for self-assembly of the nanoparticles in the liquid-crystal phase were achieved with one -NH2 group anchored to the nanoparticle surface per 25 Å2. To maximize the surface area of these materials, the wall thicknesses are adjusted so that they are composed of a monolayer of nanoparticles. To form such materials, numerous parameters have to be controlled such as the relative volume fraction of the nanoparticles and the template and size matching between the hydrophilic component of the copolymer and nanoparticles. The surface functionalization renders our synthetic route independent of the nanoparticles and allows us to prepare a variety of nanostructured composite materials that consist of a juxtaposition of different discrete oxide nanoparticles. Examples of such materials include CeO2, ZrO2, and CeO2–Al(OH)3 composites

The challenge of studying TiO2 nanoparticle bioaccumulation at environmental concentrations: Crucial use of a stable isotope tracer

International audienceThe ecotoxicity of nanoparticles (NPs) is a growing area of research with many challenges ahead. To be relevant, laboratory experiments must be performed with well-controlled and environmentally realistic (i.e. low) exposure doses. Moreover, when focusing on the intensively manufactured titanium dioxide (TiO2) NPs, sample preparations and chemical analysis are critical steps to meaningfully assay NP?s bioaccumulation. To deal with these imperatives, we synthesized for the first time TiO2 NPs labeled with the stable isotope 47Ti. Thanks to the 47Ti labeling, we could detect the bioaccumulation of NPs in zebra mussels (Dreissena polymorpha) exposed for 1h at environmental concentrations via water (7 - 120 µg/L of 47TiO2 NPs) and via their food (4 ? 830 µg/L of 47TiO2 NPs mixed with 1?106 cells/mL of cyanobacteria) despite the high natural Ti background, which varied in individual mussels. The assimilation efficiency (AE) of TiO2 NPs by mussels from their diet was very low (AE= 3.0±2.7%) suggesting that NPs are mainly captured in mussel gut, with little penetration in their internal organs. Thus, our methodology is particularly relevant in predicting NP?s bioaccumulation and investigating the factors influencing their toxicokinetics in conditions mimicking real environments