Development of an ion-sensitive field effect transistor based on PVC membrane technology with improved long-term stability

An NH -ISFET sensor based on PVC membrane technology with improved long-term stability has been developed. As a new approach, the plasticizer (tetra-n-undecyl) 3,3′,4,4′ -benzhydroltetracarboxylate (ETH2112) was used in membrane preparation. Its lipophilic nature provides a restricted diffusion of the membrane components to the external solution and improves membrane adhesion to the gate area of the ISFET. The good performance of this plasticizer was confirmed by comparison with usual plasticizers applied in standard ISE technology. Moreover, the durability and stability of the sensor were enhanced by the application of a graphite-epoxy layer as an internal reference between the gate area and the PVC membrane. This composite layer permits the reduction of the optical sensitivity and improves the adherence of the PVC membrane to the ISFET surface. Furthermore, this composite layer acts as a plug, preventing the entrance of water upon the encapsulant-chip interface, thus protecting electrical connections from moisture. As a result, an NH -ISFET with a long-term stability of three months and a sensitivity of −58.7 ± 2.3 mV decade⁻¹ in a linear range of 10⁻⁵ −0.1 mol dm⁻³ has been developed. The application of this sensor to a continuous-flow system has confirmed the feasibility of the technological approach proposed.     

Extraction of pesticides from aqueous samples: A comparative study

Three different extraction procedures for eight pesticides (chlorfenvinphos, diazinon, ethyl parathion, ethiofencarb, fenitrothion, malathion, metalaxyl, pirimicarb) in water samples are compared. The extraction procedures are: liquid-liquid extraction (LLE), solid-phase extraction (SPE) and microextraction (ME). For each procedure the most suitable conditions were obtained experimentally, with special remarks on ME, in which the effects of different mixtures of Kaltron with other solvents were tested. A preconcentration factor (PF) was used to rank the methods; the best results were observed for ME, (PF 15–45, whereas PF < 10 for SPE, and PF 13 for LLE). In all cases, the determination was performed by gas chromatography, using a nitrogen phosphorus detector and the internal standard method (methyl parathion) as the quantification procedure.     

Tandem oxidation processes for the preparation of nitrogen-containing heteroaromatic and heterocyclic compounds

alpha-hydroxy ketones undergo manganese dioxide-mediated oxidation followed by in situ trapping with aromatic or aliphatic 1,2-diamines to give quinoxalines or dihydropyrazines, respectively, in a one-pot procedure which avoids the need to isolate the highly reactive dicarbonyl intermediates. The scope and limitations of these procedures are outlined and modifications to this procedure are discussed in which reduction is carried out in the same reaction vessel, generating piperazines, or oxidation, leading to pyrazines.     

Short chain acyclic crown ethers

A series of short chain acyclic crown ethers such as (1,2), (1,3), (1,4)-phenylenediethers and some symmetric or assymmetrico-substituted phenyl ethers were prepared. The complexation studies of these compounds were carried out by a) direct UV titration method, b) picrate extraction method and c) isolation of crystalline complex.Taken in part from the master's thesis ofMaria Cecilia Bastos Vieira de Souza, Instituto Militar de Engenharia, 1978.     

Molecular features of organic matter in diagnostic horizons from andosols as seen by analytical pyrolysis

Andosols are usually formed from volcanic substrates, with thick A horizons high in organic carbon mainly in the form of stabilized humic fractions. The peculiar properties of these soils are, to large extent, affected by poorly crystalline materials like allophanes, imogolite and other Fe and Al oxyhydroxides that induce intense organo-mineral interactions which are considered to play a relevant role in OM protection against biodegradation as regards other soils developed under similar climatic conditions. Little is known about the molecular composition of this stabilized OM in a soil scenario often considered as an efficient C-sink in terms of C sequestration processes.

Whole soil samples in addition to isolated humic and fulvic acids from organic A horizons of three soils with andic properties and one non-andic soil (Sodic Cambisol) from the island of Tenerife (Canary Islands, Spain) were analysed by double shot pyrolysis-gas chromatography–mass spectrometry (Py-GC/MS) in order to get some insight on the molecular composition of different structural domains of progressive structural stability.

Clear differences were found between soils, both in thermal desorption and pyrolysis behaviour of humic substances. In general the results suggest large yields of aliphatic (both alkyl and carbohydrate-derived pyrolysis compounds) pointing to high-performance processes of incorporation of aliphatic humic constituents in andosols probably favoured by interactions with amorphous minerals, whereas in non-andic soils the latter are comparatively less stabilized and are removed in early pyrolysis stages as if they occurred as loosely joined, thermoevaporation-released products.

In fact, compared to Cambisol, humic and fulvic acids from andic soils led to comparatively richer pyrograms and compound assemblages. The lack of similar amounts of these loosely joined, mainly aliphatic structures after thermal desorption of the whole andic soils indicate an origin for humic substances based on rapid sequestration of C-forms of recent (litter or microbial) origin.     

STUDIES ON THE in vitro O2-DEPENDENT INACTIVATION OF NADH-GLUTAMATE SYNTHASE FROM Chlamydomonas reinhardii STIMULATED BY FLAVINS

The NADH-glutamate synthase (EC 1.4.1.14) complex from Chlamydomonas reinhardii may experience in vitro two kinds of 0₂-dependent inactivation stimulated by flavins.
A peroxide-mediated inactivation of enzyme, which affects the NADH- and MVt-glutamate synthase activities of the complex, but not the NADH-dehydrogenase activity, can be obtained by aerobic incubation of the enzyme with NAD(P)H plus flavin. This inactivation of enzyme seems to be due to a permanent modification of sulfhydryl groups near the active site for L-glutamine or 2-oxoglutarate. The addition of 10 mM dithioerythritol to inactive NADH-glutamate synthase produces a significant, but not complete, reactivation of the enzyme.
On the other hand, the NADH-glutamate synthase is highly susceptible to a photodynamic inactivation caused by singlet 0₂. Aerobic incubation of the active enzyme with flavin under illumination leads to the irreversible inactivation of all the activities associated with the enzymatic complex.     

A model of the annealing and activation of dissolution sites in magnetite exposed to (γ + n) radiation

The influence of gamma and reactor (n + γ) preirradiation on the dissolution of magnetite microcrystals synthetized by a low-temperature wet method was studied. Two opposite effects affect the dissolution rate: the annealing due to the gamma radiation and the generation of new imperfect coordination polyhedra. A model for the kinetic processes was proposed and the kinetic parameters were calculated.     

Full-wave analysis of stripping chronopotentiograms at scanned deposition potential (SSCP) as a tool for heavy metal speciation: Theoretical development and application to Cd(II)-phthalate and Cd(II)-iodide systems

A new mathematical treatment has been developed and implemented in an EXCEL spreadsheet in order to determine average equilibrium functions from the full set of data measured by scanning stripping chronopotentiometry (SSCP) in solutions containing different proportions of heavy metal ions and small-sized ligands. It has been applied to the experimental systems Cd(II)-phthalate and Cd(II)-iodide as models of complexation in the absence and in the presence of electrodic adsorption, respectively. The good agreement between the complexation parameters determined in this way, those predicted from literature data and those obtained using a cadmium ion selective electrode (ISE) confirms the validity of the proposed methodology and encourages its further refining for the analysis of macromolecular and heterogeneous systems.     

Recent progress in DNA analysis by capillary electrophoresis

A number of recent developments in DNA analysis by capillary electrophoresis are here reviewed. They include capillary arrays for fast, parallel DNA sequencing as well as microfabricated capillary arrays. Microfluidic chips for DNA sizing and quantitation are also covered, as well as microdevices containing arrays of regular obstacles acting as size-separators during DNA migration. Screening of DNA point mutations by two much improved techniques is also reported: in one case, such mutations are detected (but only on relative short, ca. 60-70 base-long fragments) by free electrophoresis in rather acidic (pH ca. 3) buffers; in the case of single-strand chain polymorphism, an improved technique is described based on near-neutral pH buffers with mixtures of Tris/MES cations/zwitterions. When studying the behavior of inorganic and organic cations in the Debye-Hückel layer of DNA, it was found that the latter (especially a large number of Good's buffers and other zwitterions, such as His) would bind to the DNA filament not only via charge interaction, but also via additional bonds, notably hydrogen bonds, thus altering the electrophoretic (and possibly the biological) behavior of DNA molecules. However, whether or not borate ions would bind to DNA remains still an unsettled question. Finally, capillary electrophoresis was found to be instrumental in measuring fine physicochemical parameters pertaining to DNA polyelectrolytes, such as their free mobility and their translational diffusion coefficients.     

Infinite dilution activity coefficents of hydrocarbons in tetra-n-alkyltin solvents between 40 and 60°C measured by gas-liquid chromatography

Infinite dilution activity coefficients for twenty-three hydrocarbons in tetra-n-amyltin (TAT) and in tetra-n-lauryltin (TLT) at several temperatures between 40 and 60°C were measured by gas liquid chromatography. The results, together with those obtained in an earlier paper in tetra-n-octyltin (TOT), are compared and discussed in terms of the equation of state theory of Flory and of the lattice fluid theory of Sanchez and Lacombe.