Method for determining content of phenolic compounds in Aloe arborescens

A spectrophotometric method for quantitative determination of total content of phenolic compounds in leaves of Aloe arborescens Mill. (Liliaceae) calculated as aloenin was developed. Statistical analysis showed that the relative uncertainty of the determination method was less than 2%. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 578–580, November–December, 2008.     

In-line pressurized-fluid extraction-solid-phase extraction for determining phenolic compounds in grapes

A procedure to determine 3-alkyl-2-methoxypyrazines in wines is described. It is based on the headspace solid-phase microextraction (HS-SPME) technique after a clean-up of the sample by distillation (previously acidified to pH 0.5) to remove ethanol and other volatile compounds that can interfere in the SPME. Determination is performed by means of capillary gas chromatography using a nitrogen-phosphorus detector. The method allows quantification of 3-isobutyl-2-methoxypyrazine, 3-sec-butyl-2-methoxypyrazine and 3-isopropyl-2-methoxypyrazine at their natural concentration levels and below their sensory thresholds in Cabernet Sauvignon and Merlot wines. The method was successfully applied to experimental red wines and the evolution of their pyrazine contents during the winemaking process was monitored. Pyrazine content increased during the first maceration day but did not change significantly during alcoholic and malolactic fermentation. Final contents in wines were 12-27 ng/l of 3-isobutyl-2-methoxypyrazine and 5-10 ng/l of 3-sec-butyl-2-methoxypyrazine.     

Improvement of on-line solid-phase extraction for determining phenolic compounds in water

Summary Modifying the most common design for the on-line coupling of a precolumn to reversed phase LC with diode array detection has resulted in reduction of the broadening of the peaks which results when the compounds of interest are strongly retained by a highly hydrophobic sorbent. The modification consists of the desorption of the analytes trapped on the precolumn solely by the organic solvent used to modify the solvent strength of the mobile phase. Results obtained using this design were compared with those obtained with the conventional design, with C₁₈ and PLRP-S precolumns. The performance of the system was also tested with a highly cross-linked styrene-divinylbenzene copolymer (ENVI-chrom P) precolumn for the determination of phenolic compounds in real samples. The advantages and disadvantages are discussed. Ion-pair solid phase extraction is used in order to increase the breakthrough volumes of more polar compounds, mainly phenol. The use of the new design enables phenolic compounds to be determined at the low μg L⁻¹ level with limits of detection ranging between 0.1 and 2 μg L⁻¹ in tap water when a 10 mL sample was analyzed.     

Crystal-optical method for determining the structures of complex compounds

Summary The crystal-optical method for determining the structures of complex compounds has beest extended to compounds of quadrivalent platinum. The structure bas been determined, for the first,of a compound, K₄P₁(NO₂)₄Cl₂. recently synthesized by A. V. Babaevas. It has been shown to be the cis isomer.     

Chemical sensors based on metal-electrolyte-insulator-semiconductor structures for determining carbon dioxide in air

Separation of iron(III) and palladium(III) in recovery from binary hydrochloric solutions with liquid membranes containing diphenylthiocarbamide in 1,2-dichloroethane was studied under galvanostatic electrodialysis conditions. The effect of the current density, process duration, and compositions of the receiving solution and liquid membrane on the iron(III) recovery rate was examined.     

Detection of phenolic compounds by thick film sensors based on Pseudomonas putida

Amperometric biosensors using bacterial cells were developed for the determination of phenolic compounds and the measurement was based on the respiratory activity of the cells. For this purpose, Pseudomonas putida DSM 50026 which is one of the well-known phenol degrading organisms, was used as a biological component. The cells were grown in the presence of phenol as the sole source of organic carbon. As well as phenol adapted cells, the bacterium which used the glucose as the major carbon source, was also used to obtain another type of biosensor for the comparison of the responses and specificities towards different xenobiotics. The commercial oxygen electrode was used as a transducer to test the sensor responses for both induced and non-induced cells. Our results showed that the adaptation step enable us to obtain biosensor devices with different substrate specificity. Moreover, P. putida was immobilized on the surface of thick film working electrodes made of gold by using gelatin membrane cross-linked with glutaraldehyde. The biosensors were calibrated for different phenolic substances. Furthermore, phenol detection was performed in synthetic wastewater samples.     

Optical sensors

Summary A fibre optic biosensor for ethanol was developed, which is based on the enzymatic oxidation of ethanol. The sensor layer contains an oxygen-sensitive fluorescing indicator which reports the decrease in the local oxygen partial pressure as the result of the enzymatic oxidation. The sensor measures in the 50–500 mmol/l ethanol range, with an accuracy of ± 4 mmol/l at 100 mmol/l. The detection limit is 10 mmol/l ethanol.

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Optische SensorenTeil 20. Ein faseroptischer Biosensor für Ethanol

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Presented in part at the Biosensor International Workshop 1987 at GBF, Braunschweig, June 1987     

Optical sensors for dissolved sulfur dioxide

Colorimetric sensing membranes for the determination of sulfur dioxide were developed and characterized. These films can be used for sensing trace amounts of sulfur dioxide both in the gas phase and in aqueous solutions. Lipophilic pH indicator ion pairs were immobilized in hydrophobic gas-permeable silicone and phenyl substituted ormosil. On exposure to SO₂ the films undergo a visually detectable color change from blue to yellow. No cross-sensitivity to pH and CO₂ was observed. Response times depend on the thickness of the sensing membranes, the indicator concentration in the film as well as on the respective SO₂ concentration. Membranes with response times of < 1 min (t₉₀) were developed. The sensitivity to sulfur dioxide depends on the pK_a of the indicator. An increase in the pK_a results in a lower detection limit. The new optical SO₂ sensors are chemically and mechanically stable and are easy to manufacture. The storage stability of the membranes is at least 7 months if stored in the dark. Received: 17 December 1997 / Revised: 12 June 1998 / Accepted: 15 June 1998     

Optical sensors for dissolved ionic chemical species

The sensing of ions in various media is a continuing problem that often requires new techniques as existing sensors may be inadequate for a particular example. Chemical sensors based on fibre optics have recently been the subject of considerable interest, as they have a number of advantages over conventional systems. This paper reviews those optical fibre chemical sensors that have been developed for the sensing of ionic chemical species in solution.     

Optical filtering technologies for integrated fluorescence sensors

Numerous approaches have been taken to miniaturizing fluorescence sensing, which is a key capability for micro-total-analysis systems. This critical, comprehensive review focuses on the optical hardware required to attenuate excitation light while transmitting fluorescence. It summarizes, evaluates, and compares the various technologies, including filtering approaches such as interference filters and absorption filters and filterless approaches such as multicolor sensors and light-guiding elements. It presents the physical principles behind the different architectures, the state-of-the-art micro-fluorometers and how they were microfabricated, and their performance metrics. Promising technologies that have not yet been integrated are also described. This information will permit the identification of methods that meet particular design requirements, from both performance and integration perspectives, and the recognition of the remaining technological challenges. Finally, a set of performance metrics are proposed for evaluating and reporting spectral discrimination characteristics of integrated devices in order to promote side-by-side comparisons among diverse technologies and, ultimately, to facilitate optimized designs of micro-fluorometers for specific applications.     

Optical fibre chemical sensors

Summary Optical fibre chemical sensors permit the determination of a wide range of anions, cations, gases and organic compounds in solution or gas phases. For in-line operation in complex or aggressive mixtures the requirements of selectivity, sensitivity, longevity and reproducible response impose great demands on the sensor reagents and protective membrane system. These demands will be alleviated by preceding the sensors with sample pretreatment and separation procedures and permit the best exploitation of their characteristics. For simpler analytical matrices, or those which are largely unchanging, tailored sensors provide a very useful means of specific determination. There is a clear need for high sensitivity and high selectivity of the reagent over as wide a range of conditions as possible — a demanding requirement.

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Faseroptische chemische Sensoren

Zusammenfassung Faseroptische chemische Sensoren erlauben die Bestimmung einer großen Zahl von Anionen, Kationen, Gasen und organischen Verbindungen in Lösung oder Gasphasen. Für den direkten Einsatz in Komplexen oder aggressiven Mischungen stellen die Ansprüche hinsichtlich Selektivität, Empfindlichkeit, Langlebigkeit und Reproduzierbarkeit hohe Anforderungen an die Sensorreagentien und das schützende Membransystem. Diese Anforderungen werden dadurch gemildert, daß Probenvorbereitung und Trennverfahren vorausgeschickt werden, was die beste Ausnutzung der Sensoreigenschaften ermöglicht. Für einfachere Matrices oder solche, die im wesentlichen unveränderlich bleiben, stellen maßgeschneiderte Sensoren ein nützliches Mittel für die spezifische Bestimmung dar.Die Notwendigkeit liegt auf der Hand, daß die Reagentien über einen möglichst großen Bereich von Einsatzbedingungen hohe Empfindlichkeit und hohe Selektivität aufweisen — eine wichtige Anforderung.

     

Optical fibre SERS sensors

Surface-enhanced Raman scattering (SERS) has established itself as an important analytical technique. However, efforts to transfer the technology from the laboratory to the production line, clinic or field have been frustrated by the lack of robust affordable substrates and the complexity of interfacing between sample and spectrometer. Prompted by the success of optical fibre systems for implementing normal Raman scattering spectroscopy in remote locations and biomedical applications, attention has now shifted to the development of SERS-active optical fibres. Other workers have attempted to develop SERS probes with extended interaction lengths and both far-field and near-field SERS imaging techniques for high-resolution chemical mapping of surfaces. This review discusses the development of these technologies and presents the current state of the art. Although recent developments show great promise, some outstanding challenges and opportunities remain to be addressed.     

Planar sensors for determination of polyoxyethylated compounds

For determination of nonionic surface-active substances (NSAS), in particular, polyoxyethylated nonylphenols, in aqueous solutions, the planar sensors are developed based on various carbon materials (graphite, carbon nanotubes). The effect of the nature and concentration of electroactive compounds (EAC), carbonaceous materials, plasticizers on the electroanalytical and performance characteristics of planar NSAS sensors is observed. It is shown that the planar electrodes can be used in determination of individual homologues of polyoxyethylated nonylphenols in the concentration interval from 1 × 10^–5 to 1 × 10^–2 М at pH 4–10 in model solutions, in small-volume samples, for determination of the content of surfactants in technological preparations, domestic chemistry products, and also in environmental monitoring of natural waters.     

HPLC法同时测定松果菊属中4种酚类化合物

松果菊属(Echinacea Moenck.)是原产于美洲的一类菊科野生花卉,也称“紫锥菊”。该属植物共有8种及数个变种,均为多年生草本,其中已开发为药品者主要为淡紫松果菊(E.palli-a)、狭叶松果菊(E.angustifolia)及紫花松果菊(E.purpurea)[1]。松果菊属植物主要用于促进机体的免疫功能     

Optical biochemical sensor for determining hydroperoxides in nonpolar organic liquids as archetype for sensors consisting of amphiphilic conetworks as immobilisation matrices

This paper reports the successful design of a prototype of an optical biochemical sensor for the determination of hydroperoxides in nonpolar organic liquids. The sensor consists of a matrix of an amphiphilic polymer conetwork (APCN), a novel class of very promising polymeric materials for easy preparation of biochemical sensor matrices. APCNs are characterised by nanoscopic phase separation between the hydrophilic and the hydrophobic phases. For medium ratios of conetwork composition, the domains of both phases are interconnected both on the surface of the conetworks and throughout the bulk. The APCNs have peculiar swelling properties—the hydrophilic phase swells in hydrophilic media and the hydrophobic phase swells in hydrophobic media. In both types of media dissolved reagents can diffuse from the solution into the swollen phase of the polymeric conetwork. This enables loading of the hydrophilic phase of the APCNs with enzymes and indicator reagents by simple impregnation. Hydrophobic analytes can diffuse into the polymeric conetwork via its hydrophobic phase and react with indicator reagents immobilised in the hydrophilic phase at the huge internal interface between the two opposite phases. To prepare the described hydroperoxide-sensitive biosensors, we used APCN films consisting of 58% (w/w) poly(2-hydroxyethyl acrylate) (PHEA) as hydrophilic chains and 42% (w/w) polydimethylsiloxane (PDMS) as hydrophobic linkers. Horseradish peroxidase (HRP) and diammonium 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) as indicator reagent were co-immobilised in this optically clear and transparent matrix. In this feasibility study the conditions investigated were principally those relevant to characterisation of the innovative matrix material and the disposable biosensor produced from it; the biosensor was not optimised. Sensitivity toward tert-butylhydroperoxide (tBuOOH) dissolved in n-heptane was acceptable, between approximately 1 and at least 50 mmol L⁻¹, even in the dry state. The response time was 1.7 to 5.0 min. No leaching of immobilised reagents was observed during a period of at least one hour. Pre-swelling the sensors with water increased the reaction rate and the total turnover number of the enzyme. In a dry atmosphere at 4 °C the sensors were found to be stable for at least two weeks.     

Optical and electrochemical sol-gel sensors for inorganic species

The use of sol-gels as a sensing matrix for the development of unique sensing strategies is discussed. Sol-gels offer almost limitless possibilities for sensing substrates due to the variety of physical properties that can be obtained by altering a number of discussed fabrication conditions and techniques. By careful consideration of the sensing requirements, novel detection methods have been developed for a variety of analytes and applications. Here, sol-gels have been used to monitor pH at the extreme ends of the scale ([H⁺] = 1–11 M and [OH⁻] = 1–10 M) and in mixed solvent/solute systems using dual sensing approaches. The use of ligand-grafted sol-gel monoliths for optical determination of metal ion species is also discussed. The electrochemical determination of Cr(VI) by electrodeposited sol-gel modified electrodes is also presented.     

无机物的光学和电化学传感器

本文讨论将溶胶凝胶作为一种基质来发展独特的传感策略．溶胶凝胶为传感基质的制备和发展提供了无限空间,这种空间得益于基质物理性质的多样性,可以通过改变一些传感器已知的制备条件和合成技术来实现．我们在对传感需求的认真考虑和研究的基础上,开发出了用于一些分析物的新的检测方法,同时发展了它们的应用．溶胶凝胶被用来监测浓强酸（[H^＋]=1～11M）,浓强碱（[OH^-]：1～10M）及采用双传感方法来测定混合溶剂／溶质系统．本文还讨论了使用配体嫁接的块状溶胶凝胶对金属离子进行光学测定．最后介绍了用电化学法和溶胶凝胶修饰的电极来测定六价铬的方法．     

Optical sensors: An ion-selective optrode for potassium

A new type of sensor (called ion-selective optrode) for the continuous determination of electrolytes is presented that can be exploited in optical and fibre-optic sensors. It is based on the ability of certain fluorescent dyes to respond to an electrical potential at the interface between a lipid phase and an aqueous phase. The potential is created by addition of a neutral ion-carrier, and its magnitude is measured with an appropriate potential-sensitive dye. An opto-sensor for potassium is described. A lipid bilayer is formed on a glass support by applying the Langmuir-Blodgett film technique. A lipid-soluble rhodamine dye is incorporated into this layer together with valinomycin as the ion-carrier. When exposed to potassium ion solutions in the 0.01–100 mM range, fluorescence intensity is continuously diminished. It is shown that two kinds of response towards potassium solutions occur: one is selective for this ion, but the other is unselective, being evident with other metal ions. the unselective response can be compensated for by a reference optrode. The signal change of the ion-selective optrode depends on the nature of the layer and the concentration of dye and valinomycin. The relationship between ΔI/I (i.e., the reduction in intensity relative to the total signal) and the logarithmic analyte concentration is linear over a wide range, typically 0.01–10 mM. The selectively factor over sodium varies from 2.5 to 5.