The contact angle of nanofluids as thermophysical property.

Droplet volume and temperature affect contact angle significantly. Phase change heat transfer processes of nanofluids - suspensions containing nanometre-sized particles - can only be modelled properly by understanding these effects. The approach proposed here considers the limiting contact angle of a droplet asymptotically approaching zero-volume as a thermophysical property to characterise nanofluids positioned on a certain substrate under a certain atmosphere. Graphene oxide, alumina, and gold nanoparticles are suspended in deionised water. Within the framework of a round robin test carried out by nine independent European institutes the contact angle of these suspensions on a stainless steel solid substrate is measured with high accuracy. No dependence of nanofluids contact angle of sessile droplets on the measurement device is found. However, the measurements reveal clear differences of the contact angle of nanofluids compared to the pure base fluid. Physically founded correlations of the contact angle in dependency of droplet temperature and volume are obtained from the data. Extrapolating these functions to zero droplet volume delivers the searched limiting contact angle depending only on the temperature. It is for the first time, that this specific parameter, is understood as a characteristic material property of nanofluid droplets placed on a certain substrate under a certain atmosphere. Together with the surface tension it provides the foundation of proper modelling phase change heat transfer processes of nanofluids.

Covalently immobilized enzymes on biocompatible polymers for amperometric sensor applications.

Glucose oxidase or choline oxidase were covalently immobilized on the surface of 2-hydroxyethyl and glycidyl methacrylate copolymer membranes. The polymerization was induced by gamma irradiation at low temperature. The enzyme modified polymers were applied on Clark-type or platinum electrodes to form amperometric sensors based on the electrochemical measurements of oxygen or hydrogen peroxide. Glucose and choline content in standard solutions were measured and linear calibration curves were determined. The sensors studied showed a response time of less than 2 min and the observed linear ranges were increased with respect to usual biosensors owing to the diffusion-limiting effects of the membranes used. The influence of the copolymer composition on the electrochemical response and on the retained enzyme activity were explored for verifying the optimum analytical performance. The immobilized enzyme membranes stored in suitable buffers were very stable and showed a decrease up to 20% in the electrode response after 3 months of constant use.

High-energy collisional spectroscopy in qualitative and quantitative analysis of diesel particulates.

High-energy collisional spectroscopy provides a powerful analytical method for the characterization of polynuclear aromatic hydrocarbons present in diesel particulates. The absence of any need for extraction procedures and the large amount of information available from collisional spectra makes this technique of great interest. In particular, 3-methylcholanthrene can be determined from the daughter spectra of its molecular ion, with methylene iodide as internal standard.

Amperometric biosensor with physically immobilized glucose oxidase on a PVA cryogel membrane.

A new method of physically immobilizing a biomolecule of analytical interest in poly(vinyl alcohol) cryogels was developed to obtain suitable biosensors. An amperometric glucose sensor was constructed using glucose oxidase immobilized on membranes obtained by a freezing-thawing cyclic process. No chemical cross-linking agent was used. Sensor behaviour was evaluated electrochemically with a hydrogen peroxide electrode. The glucose content in standard solutions was determined and linear calibration curves in the 5 x 10(-5)-3 x 10(-3) mol 1(-1) range were obtained. Temperature and pH effects on the electrochemical response were described and kinetic parameters in the immobilized system were evaluated.

PEG-modified glucose oxidase immobilized on a PVA cryogel membrane for amperometric biosensor applications.

Poly(ethylene glycol)-modified glucose oxidase was immobilized in a poly(vinyl alcohol) cryogel membrane, obtained by a freezing-thawing cyclic process, to obtain a suitable amperometric glucose sensor. The covalent linkage between PEG and GOD molecule improved the physical immobilization of enzyme in the polymeric matrix, by decreasing its loss in time. Sensor behaviour was evaluated electrochemically with a hydrogen peroxide electrode. The glucose content in standard solutions was determined and linear calibration curves in the 5x10(-5)-5x10(-3) mol l(-1) range were obtained. The kinetic parameters in the immobilized system were evaluated and analytical characteristics of sensor, including stability and influence of pH and temperature, were determined.

An unusual and persistent contamination of drinking water by cutting oil.

Drinking water contamination by materials, such as cutting oil, used to set up pipelines is an uncommon but possible event. This paper describes the analytical procedures used to identify the components of that contaminant in drinking water. Volatile and semi-volatile chemical species, responsible for an unpleasant taste and odour, were recognised by solid phase microextraction and GC/MS techniques. Among the volatile compounds, the presence of xylenes, bornyl acetate and diphenyl ether was confirmed by certificate standards and quantified in the most contaminated samples.

Investigation of used synthetic lubricants by computerized gas chromatography/mass spectrometry.

The chemical fractions of a used, synthetic lubricating oil for petrol engines were separated by flash chromatography on a silica gel column using variable mixtures of hexane/chloroform as eluents. The products extracted in the most polar fraction were separated by gas chromatography and then analyzed by computerized mass spectrometry. The analytical method used allowed the identification, among the various compounds, of a family of tetrahydropyran homologues with an aminic chain, phthalates, thiophene and pyridine derivatives. The presence of these structures, some of which are of toxicological interest, was also shown by infrared spectra.

Chemical evidence and risks associated with soybean and rapeseed meal fermentation.

The storage and transport of cereals and foodstuffs present recurrent problems. They may be attacked by insects or, under certain conditions, they may undergo spontaneous fermentation. Insect attack is normally avoided by fumigants, while fermentation, which depends on parameters such as temperature and humidity, is more difficult to stop and can produce chemical compounds which irremediably modify the nutritional and compositional properties of foodstuff. This paper describes the main chemical compounds produced by fermentation and self-ignition of soybean and rapeseed meal. Reported cases occurred in a storage site and during transport by ship, respectively.

Glucose sensors based on enzyme immobilization onto biocompatible membranes obtained by radiation-induced polymerization.

Amperometric glucose biosensors based on glucose oxidase immobilized onto poly(2-hydroxyethylmethacrylate) membranes obtained by gamma radiation-induced polymerization were constructed. In a three-electrode configuration, smooth or platinized platinum electrodes with different shapes were used, in order to detect the amount of hydrogen peroxide produced in the glucose oxidation. A saturated calomel electrode and a platinum foil were used as a reference and counterelectrode, respectively. The biocompatible obtained sensors were characterized as regards the temperature effect, the response, and lifetime. The determination of glucose in standard solutions was carried out, and linear calibration curves were obtained. Depending on the electrode configuration, the sensor had a response time of 1-4 min, and the measuring range extended from 5 x 10(-5) to 4 x 10(-3) M.

The influence of color, age, and sex on the content of zinc, copper, nickel, manganese, and lead in human hair.

The hair of 132 healthy subjects between 6 and 40 yr old living in the Veneto region in Italy was analyzed by means of HPLC method in order to determine the presence of zinc, copper, nickel, manganese, and lead. The collected samples were subdivided on the basis of age (6-11 and 19-40 yr), and sex and color (black, red, brown, and blond). From the data some evident differences were emphasized. In female hair the content of metals was higher than in male hair independently of color. Blond hair gave the lowest concentration values of the elements studied independently of sex. The maximum amount of the metals was found generally in black hair, followed by red and brown hair. Age seems to have a different influence, with the copper element decreasing appreciably in brown and blond female hair as the age of the subjects increased.

Covalently immobilized choline oxidase and cholinesterases on a methacrylate copolymer for disposable membrane biosensors.

Bienzymatic sensors for the determination of esters of choline were prepared by covalent co-immobilization of cholinesterases and choline oxidase on polymer membranes, obtained by radiation-induced copolymerization of 2-hydroxyethyl methacrylate and glycidyl methacrylate at low temperature. Optimization of the covalent attachment of choline oxidase and acetyl- or butyrylcholinesterase to copolymer was explored. The enzyme-modified polymers were applied on platinum electrodes to form amperometric sensors, based on the electrochemical detection of enzymatically developed hydrogen peroxide. Acetyl-, acetylthio-, butyryl-, and butyrylthiocholine contents in standard solutions were measured, and linear calibration curves were determined. Temperature and pH effects on the electrochemical response are described.

Determination of 99Tc in urine by liquid scintillation counting to evaluate internal contamination.

A practical method is described which allows the radiochemical determination of 99Tc in urine. The radionuclide is recovered as tetraphenylarsonium pertechnetate by coprecipitation with tetraphenylarsonium perchlorate and its activity is counted by the liquid scintillation technique. The lower limit of detection, assumed equal to three standard deviations of the blank activity, is about 2 pCi in 50 ml of urine and permits an evaluation of an internal contamination of one investigation level even four months after intake. The urinary excretion function of 99Tc is calculated from experimental data reported in the literature for 99mTc and is used to establish derived investigation levels on the basis of annual limits on intake recommended by the International Commission on Radiological Protection. The illustrated method is sensitive enough to perform accurate evaluations every three months, a frequency suitable for radiological protection of workers.

Cryptic chemical identification as a crime intelligence aid.

A dead body was found near the sea and a commercial port in north-east Italy. The man had been shot and then burnt, by using a large volume of fire accelerant. The chemical composition of the flammable mixture had to be determined in order to aid police investigations. GC-MS analysis of residual cloth and soil identified a common gasoline, together with some unrelated compounds deriving from the container used to carry the inflammable liquid. A reconstruction of the event, an examination of the surroundings where the crime took place and the cryptic chemicals found, enabled the investigators to restrict and intensify their enquiries within a specific area.

Amperometric biosensor involving covalent immobilization of choline oxidase and butyrylcholinesterase on a methacrylate-vinylene carbonate co-polymer.

A two-enzyme sensor for the determination of choline esters was prepared by the covalent co-immobilization of choline oxidase and butyrylcholinesterase on polymer membranes, obtained by radiation-induced co-polymerization of 2-hydroxyethylmethacrylate and vinylene carbonate at low temperature. The enzyme-modified membrane was applied to a platinum electrode and the determination of substrates was based on the electrochemical detection of enzymically generated H2O2. The analytical characteristics of this sensor, including the optimization of immobilization procedures, calibration curves for different substrates, pH and temperature effects and stability, are described.

High-performance liquid chromatographic determination of urinary 2,5-hexanedione as mono-2,4-dinitrophenylhydrazone using ultraviolet detection.

The good correlation between exposure to n-hexane and 2,5-hexanedione urinary excretion confers on this diketone an important toxicological meaning. this paper proposes a reversed-phase HPLC method which includes, after acid hydrolysis, a derivatization step of 2,5-hexanedione with 2,4-dinitrophenylhydrazine at 70 degrees C for 20 min. The reaction conditions, such as temperature, reagent concentration and time, are optimized so as to allow the condensation of a single carbonyl group. A linear response was obtained in the 0.19-20.0 mg/l range with a detection limit of 0.03 mg/l, corresponding to a signal-to-noise ratio of 3. A phosphate buffer (pH 3.3)-acetonitrile mixture (50:50) as the eluent and UV detection at 334 nm were used.

Acetylcholine biosensor involving entrapment of acetylcholinesterase and poly(ethylene glycol)-modified choline oxidase in a poly(vinyl alcohol) cryogel membrane.

A bienzymatic sensor for the determination of acetylcholine was prepared by physical coimmobilization of acetylcholinesterase and poly(ethylene glycol)-modified choline oxidase in a poly(vinyl alcohol) cryogel membrane obtained by a cyclic freezing-thawing process. The enzyme-modified polymer was applied on a platinum electrode to form an amperometric sensor, based on the electrochemical detection of enzymatically developed hydrogen peroxide. The analytical characteristics of this sensor, including calibration curves for choline and acetylcholine, pH, and temperature effects, and stability are described.