Caffeine in your drink: natural or synthetic?

Owing to possible adulteration and health concerns, it is important to discriminate between natural and synthetic food ingredients. A new method for compound-specific isotope analysis (CSIA) by coupling high-temperature reversed-phase liquid chromatography to isotope ratio mass spectrometry (HT-RPLC/IRMS) was developed for discrimination of natural and synthetic caffeine contained in all types of drinks. The analytical parameters such as stationary phase, column inner diameter, and column temperature were optimized for the separation of caffeine directly from drinks (without extraction). On the basis of the carbon isotope analysis of 42 natural caffeine samples including coffee beans, tea leaves, guaraná powder, and maté leaves, and 20 synthetic caffeine samples from different sources by high-temperature reversed-phase liquid chromatography coupled to isotope ratio mass spectrometry, it is concluded that there are two distinguishable groups of caffeine δ(13)C-values: one between -25 and -32‰ for natural caffeine, and the other between -33 and -38‰ for synthetic caffeine. Isotope analysis by HT-RPLC/IRMS has been applied to identify the caffeine source in 38 drinks. Four mislabeled products were detected due to added but nonlabeled synthetic caffeine with δ(13)C-values lower than -33‰. This work is the first application of HT-RPLC/IRMS to real-world food samples, which showed several advantages: simple sample preparation (only dilution), high throughput, long-term column stability, and high precision of δ(13)C-value. Thus, HT-RPLC/IRMS can be a very promising tool in stable isotope analysis of nonvolatile compounds.     

Supported membrane nanodevices

Supported membrane nanodevices are based on natural or artificial ion channels embedded in a lipid membrane deposited on a chip wafer. Membrane conductance is modulated by biorecognitive events, with the use of intrinsic binding sites of the ion channel or via artificial sites fused to the channel protein. Artificial ion gates are constructed by coupling a specific ligand for the analyte near the channel entrance or a site important to triggering channel conformation. The binding event leads to the closure of the ion channel or induces a conformational change of the channel, reducing the ion flux. The signal transduced from the device is the decrease in the ion flux-induced electron current at a silver-silver chloride electrode at ultimate single-molecule sensitivity. Among the natural ion channels, gramicidin A, a transport antibiotic, was found to be most suitable, and thus was used by AMBRI, Australia, to set up prototypes of membrane biochips, using self-association of the dimer. Covalent dimerization-based devices, developed by the Vienna group, make use of the down-regulation of the permanently open membrane-spanning bisgramicidine ion channel. The reactive group at the C-terminus, a hydroxy group, allows precise coupling of the analyte-binding moiety in gramicidin as well as bisgramicidin. The device is set up with bilayer membranes deposited on apertures of a hydrophobic frame structure produced via microlithography, facing an aqueous or hydro-gel micro-environment on both sides, constructing black lipid membranes or patch-clamp devices "on chip." The setup of the device needs gel membrane supports that allow membrane formation and contribute to the stability of the bilayer by exposure of functional groups that promote electrostatic interaction and formation of hydrogen bridges and enable the introduction of covalent spacers and anchors. Photo-cross-linked polyvinylpyrrolidone and polyacrylamide, electropolymerized polydiaminobenzene and coated agarose, as well as various chemical modifications of these polymers, were employed as membrane supports. With optimized assemblies, the membrane support did allow the formation of stable bilayer membranes, proved by "gigaseal" (electrical sealing with giga-ohm resistance) to be free of any point defects in the lipid assembly. Supports with and without hydrophilic and hydrophobic anchors were studied with reference to promoting the formation of a self-assembled membrane, to their electric resistance, and to the capability to insert functional ionophores. All components, including novel chemically engineered ion channels, novel amphiphilic lipids, a microlithographically designed chip, isolating polymer frames, and a hydrogel membrane support, are combined in the new bionanodevice. Sensitivity and specificity were proved, for example, with the use of an antibody-antigen couple down-regulating the ion flux through the membrane channel. Single ion channels incorporated in the supported lipid bilayer gave stable signals at an operational stability of several hours, which is already sufficient to test and screen for membrane receptors but still insufficient to use this device as a sensor for off-site application. Further optimization to increase operational and storage stability is done by a number of groups to allow a broad application of these devices.     

When other separation techniques fail: compound-specific carbon isotope ratio analysis of sulfonamide containing pharmaceuticals by high-temperature-liquid chromatography-isotope ratio mass spectrometry

Compound-specific isotope analysis (CISA) of nonvolatile analytes has been enabled by the introduction of the first commercial interface to hyphenate liquid chromatography with an isotope ratio mass spectrometer (LC-IRMS) in 2004, yet carbon isotope analysis of unpolar and moderately polar compounds is still a challenging task since only water as the eluent and no organic modifiers can be used to drive the separation in LC. The only way to increase the elution strength of aqueous eluents in reversed phase LC is the application of high temperatures to the mobile and stationary phases (HT-LC-IRMS). In this context we present the first method to determine carbon isotope ratios of pharmaceuticals that cannot be separated by already existing separation techniques for LC-IRMS, such as reversed phase chromatography at normal temperatures, ion-chromatography, and mixed mode chomatography. The pharmaceutical group of sulfonamides, which is generally mixed with trimethoprim in pharmaceutical products, has been chosen as probe compounds. Substance amounts as low as 0.3 μg are sufficient to perform a precise analysis. The successful applicability and reproducibility of this method is shown by the analysis of real pharmaceutical samples. The method provides the first tool to study the pharmaceutical authenticity as well as degradation and mobility of such substances in the environment by using the stable isotopic signature of these compounds.     

Liquid PMMA: A High Resolution Polymethylmethacrylate Negative Photoresist as Enabling Material for Direct Printing of Microfluidic Chips

Polymethymethacrylate (PMMA) is one of the most important thermoplasts and a commonly used material in microsystem fabrication, for example, microfluidics owning mainly to its optical transparency, biocompatibility, low autofluorescence, and low cost. However, being a thermoplastic material PMMA is typically structured using industrial replication techniques making PMMA unsuitable for rapid prototyping. The fact that neither material nor processing technique can be directly transferred from laboratory to industrial state makes the research‐to‐business conversion often extremely difficult in microfluidics since material properties have a major impact on the final system behavior. This paper presents “Liquid PMMA,” a fast curing viscous PMMA prepolymer which can be used as a negative photoresist and directly structured using ultraviolet or visible light with tens of micron resolution and smooth surfaces. Using this technique microfluidic chips in PMMA can be fabricated within minutes. The cured Liquid PMMA parts show the same high optical transparency, low autofluorescence, and surface properties like commercial PMMA. In this way, microfluidic chips can be rapidly developed and optimized on the laboratory scale in the same material which is later on used on the industrial scale.

     

Large-scale patterning of gold nanopillars in a porous anodic alumina template by replicating gold structures on a titanium barrier

Gold nanopillars are grown in patterns inside a porous anodic alumina template. On selected positions, defined by a gold "seed" pattern, gold is electroplated into the pores, while a barrier layer underneath the porous template blocks the deposition on the rest of the surface. Large-scale arrays of free-standing nanopillar islands are obtained after selective etching of the alumina template.     

Gas chromatographic triglyceride profiling of milk fat; comparison of packed and short metal capillary columns

 The quantitative aspects of triglyceride profiling of milk fat by capillary column gas chromatography (GC) were investigated. Fifty samples of pure Austrian milk fat were tested as described in Annex III of the European Community (EC) Commission regulation no. 454/95 by using a packed as well as a short metal capillary column. Capillary GC was equivalent to the packed column in terms of analytical precision (relative standard deviation of repeated injections). All samples tested fulfilled the purity criteria (S-values), irrespective of the chromatographic technique used. Nevertheless, the S-values obtained by capillary GC deviated to some extent from those of the packed column. The differences exceeded the value for reproducibility laid down in Annex III, EC regulation no. 454/95 in 18 of 50 cases. As a consequence, the equivalency of capillary GC for determining the purity of milk fat according to EC regulation no. 454/95 should be re-assessed. Received: 4 April 1997 / Revised version: 26 June 1997     

Low-intensity Husbandry as a Cost-efficient Way to Preserve Dry Grasslands

Abstract

Dry grasslands represent unique ecosystems that are known for high biodiversity. Land use changes have led to a decline in Europe. Shrub encroachment is a major problem in incorrectly or unmanaged areas, and affects not only flora and fauna but also leads to changes in the appearance of the landscape. Our study was conducted on the island of Hiddensee, north-east Germany, where today dry grasslands are endangered by shrub encroachment. We analysed the current land use under consideration of farming costs as well as current agricultural subsidies. Our results show that revenues of low-intensity cattle husbandry only account for 61% of total costs and that farming becomes profitable only with subsidies. Our study illustrates that goats can be a cost-efficient solution for areas with high shrub cover in contrast to manual clearing. The maintenance of dry grasslands is therefore more cost-efficient with grazing animals than with technical-manual labour.     

Locating New Stops in a Railway Network

Given a railway network together with information on the population and their use of the railway infrastructure, we are considering the effects of introducing new train stops in the existing railway network. One effect concerns the accessibility of the railway infrastructure to the population, measured in how far people live from their nearest train stop. The second effect we study is the change in travel time for the railway customers that is induced by new train stops. Based on these two models, we introduce two combinatorial optimization problems and give NP-hardness results for them. We suggest an algorithmic approach for the model based on travel time and present a real-world application with its first experimental results.