Feasibility study for producing a carrot/potato matrix reference material for 11 selected pesticides at EU MRL level: Material processing, homogeneity and stability assessment

The feasibility for producing a matrix reference material for selected pesticides in a carrot/potato matrix was investigated. A commercially available baby food (carrot/potato-based mash) was spiked with 11 pesticides at the respective EU maximum residue limits (MRLs), and further processed by either freezing or freeze-drying. Batches of some 150 units were produced per material type. First, the materials were assessed for the relative amount of pesticide recovered after processing (ratio of pesticide concentration in the processed material to the initially spiked pesticide concentration). In addition, the materials’ homogeneity (bottle-to-bottle variation), and the short-term (1 month) and mid-term (5 months) stability at different temperatures were assessed. For this, an in-house validated GC-EI-MS method operated in the SIM mode with a sample preparation procedure based on the QuEChERS (“quick, easy, cheap, effective, rugged, and safe”) principle was applied. Measurements on the frozen material provided the most promising results (smallest analyte losses during production), and also freeze-drying proved to be a suitable alternative processing technique for most of the investigated pesticides. Both the frozen and the freeze-dried material showed to be sufficiently homogeneous for the intended use, and storage at −20 °C for 5 months did not reveal any detectable material degradation. The results constitute an important step towards the development of a pesticide matrix reference material.     

The behaviour of acetamide under ‘Galisol’ heat storage conditions

Acetamide, as a phase-change material for energy storage, is preferable to other organic materials because of its noncorrosive behaviour and the high storage capacity (264 MJ/m³). In the paper a possibility is offered for a considerable decrease of the supercooling tendency and for the prevention of the disturbing sublimation effects, by modifying the dynamic working function principle ‘Galisol’. For this purpose we have used a heat-transfer liquid with a partial solubility for acetamide. The study reviews solubility data, investigations of the thermal behaviour by the DTA method with large samples, cloud point investigations, equilibrium surface tensions and heat-storage investigations of combinations of acetamide and heat-transfer liquids. A phase diagram of the acetamide-trichloroethylene system is presented. The heat-storage behaviour of acetamide in its combination with trichloroethylene and a surface active material is very promising and offers a high heat-transfer power comparable to that of inorganic salt hydrates under ‘Galisol’ conditions. Nevertheless, the fact that water-free acetamide, which is very expensive, has to be used must be taken into consideration.     

Triacylglycerol profiling by using chromatographic techniques

Triacylglycerols (TGs) make up the major part of naturally occurring fats and oils. The composition and fine structure of TGs determine to a large extent the functionality of fats and oils as food ingredients and the physiological effects of fats and oils as component of the human diet. Analysis of intact TGs is usually performed by chromatographic methods. In this article the application of gas‐liquid chromatography, high‐performance chromatography in normal and reversed phase mode, thin‐layer chromatography and supercritical fluid chromatography for the qualitative and quantitative determination of TGs is reviewed. Emphasis is put on those factors that are decisive for obtaining reliable quantitative data. Furthermore, techniques for the stereospecific analysis of the fatty acid distribution along the glycerol backbone of TGs are presented briefly.     

Dissection of Nod factor signalling in legumes: cell biology, mutants and pharmacological approaches

Nodulation factors (NFs) are lipochito‐oligosaccharide signal molecules excreted by soil‐living rhizobia. These molecules elicit a range of responses in the legume roots, with which the bacteria can live in symbiosis. In this review we focus on the genetic, pharmacological and cell biological approaches that have been, and are being, undertaken to decipher the signalling pathways that lead to the symbiotic responses in the plant.     

Aflatoxin M1 in milk powders: Processing, homogeneity and stability testing of certified reference materials

As part of the certification campaign of three candidate reference materials for the determination of aflatoxin M₁ (AfM₁) in whole milk powders, homogeneity, short- and long-term stability tests of naturally contaminated milk powders have been performed. The homogeneity of two AfM₁-contaminated milk powders was studied by taking samples at regular intervals of the filling sequences and analysing in triplicate for their AfM₁ contents by liquid chromatography with fluorescence detection (LC-FLD) using random stratified sampling schemes. The homogeneity testing of an AfM₁ 'blank' milk powder material was performed by determining the nitrogen content because AfM₁ levels were below the limit of detection of the most sensitive determination method. The short-term stability of AfM₁-contaminated milk powders was evaluated at three different storage temperatures (4, 18 and 40°C). After storage times of 0, 1, 2 and 4 weeks, samples were investigated using LC-FLD. The long-term stability study comprised of measurements after 0, 6, 12 and 18 months after storage at -20 and 4°C. Analyses were done by LC-FLD. Based on the homogeneity tests, the materials were sufficiently homogenous to serve as certified reference materials. Corresponding uncertainty contributions of 0.23-0.89% were calculated for the homogeneity. The stability measurements showed no significant trends for both short- and long-term stability studies. The long-term stability uncertainties of the AfM₁-contaminated milk powders were 7.4 and 6.3%, respectively, for a shelf-life of 6 years and storage at -20°C. Supplementary stability monitoring schemes over a long period of several years are currently ongoing.     

The cytoskeleton in plant and fungal cell tip growth

Tip-growing cells have a particular lifestyle that is characterized by the following features: (1) the cells grow in one direction, forming a cylindrical tube; (2) tip-growing cells are able to penetrate their growth environment, thus having to withstand considerable external forces; (3) the growth velocity of tip-growing cells is among the fastest in biological systems. Tip-growing cells therefore appear to be a system well suited to investigating growth processes. The cytoskeleton plays an important role in cell growth in general, which is why tip-growing cells provide an excellent model system for studying this aspect. The cytoskeletal system comprises structural elements, such as actin filaments and microtubules, as well as proteins that link these elements, control their configuration or are responsible for transport processes using the structural elements as tracks. Common aspects as well as differences in configuration and function of the cytoskeleton in various types of tip-growing cells reveal the general principles that govern the relationship between the cytoskeleton and cell growth.     

Atmospheric deposition of V,Cr, and Ni since the late glacial: effects of climatic cycles,human impacts,and comparison with crustal abundances

Vanadium, Cr, and Ni accumulating in a Swiss peat bog since 12 370 14C yr B.P. have been measured using inductively coupled plasma-mass spectrometry (ICP-MS) after acid dissolution in a microwave autoclave. Strict quality control schemes were applied to guarantee the accuracy of the applied analytical methodology. The concentration gradients in the peat column and comparison with Pb indicate that V, Cr, and Ni are effectively immobile in the ombrotrophic section of the peat profile but that Ni is added to the minerotrophic peat layers by chemical weathering of the underlying sediments. The lowest metal concentrations were found during the Holocene climate optimum (5320-8230 14C yr B.P.) when "natural background" values averaged 0.55 +/- 0.13 microg g(-1) V, 0.76 +/- 0.17 microg g(-1) Cr, and 0.46 +/- 0.09 microg g(-1) Ni (n = 18); given the average bulk density (0.05 g/cm3) and accumulation rate (0.05 cm/ yr) of peat in this zone, the corresponding atmospheric fluxes are approximately 14, 19, and 12 microg m(-2) yr(-1) for V, Cr, and Ni, respectively. The highest concentrations of V, Cr, and Ni were found during the Younger Dryas cold climate event (centered at 10 590 14C yr B.P.) when background values were exceeded by about 40 times. Elevated concentrations and accumulation rates were also found at 8230 and 5320 14C yr B.P., which are consistent with the elevated dust fluxes recorded by Greenland ice cores. By far the greatest contribution of the three elements to the peat inventory is atmospheric soil dust, and the metal fluxes vary not only with climate change but also land-use history (especially the beginning of forest clearing for agriculture ca. 6 millennia ago). The V/Sc, Cr/Sc, and Ni/ Sc ratios were remarkably similar to their corresponding ratios in the earth's crust until the onset of the Industrial Revolution (240 14C yr B.P.), which largely validates the use of crustal concentrations for calculating enrichment factors (EF) for these elements. In modern samples, the EFs of V, Cr, and Ni reach maximum values between 2.4 and 4.1, relative to background; anthropogenic emissions are a more likely explanation of the elevated EFs than either plant uptake or chemical diagenesis. This study demonstrates the usefulness of peat bogs as archives of atmospheric metal deposition and underpins the potential of peat cores to help distinguish between lithogenic and anthropogenic metal sources.     

The application of glauber salt in a new type of a latent heat storage unit

The application of Glauber salt as a latent heat storage material is a difficult technical problem owing to the separation of the coexisting phases (stratification) during melting. In order to avoid stratification and to improve the heat transfer in the course of the charge and discharge, a new storage type called ‘GLS’ was developed, in which the heat is transferred in a closed container to the latent heat storage material by means of the vapour of a heat transfer liquid. Surface-active materials which were added to the storage materials produce optimum conditions for the heat transfer and material transport during the heat transfer processes. Under the conditions of the GLS storage unit on application of Glauber salt, constant storable amounts of energy were found which are in good agreement with the theoretical values. The heat storage can be performed with high energy densities in narrow temperature differences and with high power of the transferred heat.     

Properties of high density polyethylene and its behaviour under ‘Galisol’ heat storage conditions

High density polyethylene (HDPE), crosslinked by electron beams in air, is presented as a latent heat storage material for energy storage applications at a temperature level of about 120°C. The study includes thermal investigations before and after the irradiation, investigations of the form stability, gel content determinations and microscopic investigations of HDPE. An electron energy of 0.4 MeV and a radiation dosage of 200 kGy were found to be the optimum conditions for the irradiation of the investigated HDPE in air. The pellets obtained were form-stable owing to the formation of a thin crosslinked surface layer (about 0.5 mm thickness). In spite of the presence of oxygen during irradiation, the melting enthalpy of the initial state was retained almost quantitatively. Apart from that, a quasicomplete irradiation of the pellets in volume in air, with a higher electron energy, is also possible. In this case about 95% of the initial melting enthalpy is obtained, providing a maximum gel content of 50%. Moreover, the paper offers a possibility of overcoming the low heat transfer power of HDPE by applying it in form of modified pellets in a ‘Galisol’ model storage unit with water as the heat transfer liquid. Owing to the large heat transfer area connected to boiling and condensation of water, excellent values of heat transfer power of 100–114 W/kg HDPE (ΔT=16 K) are obtained. These are comparable to those of salt hydrates, provided there is sufficient form stability. The significant influence of somewhat lower form stability on the heat output is shown.     

Method of determination of the cycle stability of ‘Galisol’ latent heat storage unit substance combinations. Its application to the investigation of the glauber salt storage unit

The evidence of the cycle stability of a latent heat storage unit is an important requirement of its technical application. In this paper an apparatus for investigation of Galisol (GLS) latent heat storage substance combinations is described. The stored heat and the heat transfer power are determined with an uncertainty of ± 5 per cent by means of the applied calibration. The results of the cycle stability of the Glauber salt in its substance combination confirm the stability behaviour of this salt hydrate under the dynamic conditions of the GLS storage unit.