The relaxation oscillator as a resonance photon detector

A commercially available neon indicator lamp in a Relaxation Oscillator (RO) configuration has been demonstrated to be capable of detecting light intensities of the order of nanowatts under ambient light conditions with a subpicometer spectral resolution. The RO has also been shown as capable of acting as a wireless light switch with light intensities of the order of 1 µW. Temporal excitation studies have also shown the predominant mechanism describing the observed frequency changes in the RO to be a result of laser perturbation of the neon lamp when it is in the Townsend-discharge region and not in the abnormal glow.     

The role of oxygen in the reduction of tetrazolium salts with nadh mediated by 5-methyl phenazonium methyl sulfate. An EPR and voltammetric study

The reduction of tetrazolium salts (namely INT, MTT and BNT) with NADH in the presence of catalytic amounts of PMS (5-methylphenazonium methylsulfate) was studied, and the influence of oxygen on the system was considered. The redox potentials of all the investigated compounds, the kinetic measurements, as well as the application of the Marcus theory confirmed that PMS and tetrazolium ions are reduced by NADH through an inner-sphere mechanism. The EPR investigations led to the detection of all possible radical species coming from PMS and tetrazolium ions and are in agreement with a mechanism which excludes any role of oxygen in the system NADH/PMS/tetrazolium for the formation of formazan.     

Flame atomic absorption and ICP-atomic emission spectroscopic determination of Cu, Zn and Cd in solid suspensions of biological samples

Summary A method, based on slurrying of solids, is described for the direct, routine flame atomic absorption (flame AAS) and inductively-coupled plasma atomic emission (ICP-AES) spectroscopic trace determination of Cu, Zn and Cd in solid biological samples. The sample powder (particles < 20 m) — between 40 and 100 mg — is firstly wetted with a 0.5% sodium hexametaphosphate solution and is then dispersed in a 5.6% v/v nitric acid solution. Both magnetic and ultrasonic stirring were evaluated. The latter proved to be the more effective especially when dealing with the higher concentration suspensions. The suspension is then aspirated directly into the spectrometer. Direct comparison with aqueous calibration standards can be used in all cases.All samples were analyzed with an accuracy of ±10% and a precision (relative standard deviation) of better than 7%. The limits of detection were as low as 2.0×10^–2 g/g for zinc. Sensitivities, reported as concentration required to give a 0.0044 absorbance signal, were as low as 2.4×10^–2 g/g for zinc. The advantages of this method are its simplicity, low cost, speed of analysis and simple and rapid calibration.

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Bestimmung von Cu, Zn und Cd in festen Suspensionen biologischer Proben durch Flammen-AAS und ICP-AES

Zusammenfassung Zur Spurenbestimmung von Cu, Zn und Cd in biologischen Proben durch Flammen-AAS und ICPAES wird eine Aufschlämmung von Festteilchen benutzt. Die pulverisierte Probe (mit Teilchengrössen < 20 um, 40–100 mg) wird zunächst mit 0,5%iger Natriumhexametaphosphatlösung benetzt und dann in 5,6%iger Salpetersäurelösung dispergiert. Besonderes bei höheren Konzentrationen hat sich Ultraschall-Rühren besser bewährt als magnetische Methoden. Die Suspension wird direkt in das Gerät eingeführt. In allen Fällen wurde der Vergleich mit wässrigen Standardlösungen durchgeführt. Die Richtigkeit betrug 10%, die Präzision (relative Standardabweichung) war besser als 7%. Die Nachweisgrenze lag für Zink bei 2×10^–2 g/g, die Empfindlichkeit (Extinktion 0,0044) bei 1,8×10^–2 g/g. Die Vorteile des Verfahrens sind: Einfachheit, niedrige Kosten, Schnelligkeit und einfache sowie rasche Eichung.

     

Development of an analytical method for monitoring worker populations exposed to platinum-group elements

The increasing industrial use of platinum-group elements (PGEs), namely Ir, Pd, Pt and Rh, and related allergies such as rhinitis, conjunctivitis, asthma, urticaria and contact dermatitis, have led to a growing need to monitor selected populations of exposed workers. In this study, the levels of PGEs were measured in indoor airborne particulate matter and in biological samples taken from employees of a plant where car catalytic converters are produced and precious metals are recovered from spent carbon catalysts. The development of an analytical procedure based on quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) for the analysis of PGEs in airborne particulate matter and on sector field inductively coupled plasma mass spectrometry (SF-ICP-MS) for the analysis of PGEs in blood, serum, urine and hair is described. For airborne particulate matter deposited on filters, the limits of detection (LoDs) were found to be 0.006 ng m⁻³, 0.020 ng m⁻³, 0.018 ng m⁻³ and 0.006 ng m⁻³ for Ir, Pd, Pt and Rh, respectively. Repeatability of measurements ranged from 1.8 to 8.5%, while recovery was in the range from 92 to 102%. For biological samples LoDs in blood, serum, urine and hair ranged from (in ng l⁻¹) 0.2–0.6 for Ir, 5–10 for Pd, 1–3 for Pt and 2–3 for Rh. For all biological materials, the repeatability varied from 1.1 to 12% for the four elements. Recovery data for the determination of PGEs in biological matrices were found to range from 84.0 to 107.8%. The method was applied to the determination of either total or respirable airborne PGEs collected from five different work areas in the plant. The difference between areas with high and low exposure correlates closely with metal levels in hair, blood and urine. The correlation coefficients between Pt in airborne particulate matter and Pt in biological materials was 0.994, 0.991 and 0.970 for blood, hair and urine, respectively.     

Phosphine-substituted ruthenium carbonyl carboxylates

The behaviour of the [Ru₂(CO)₄(CH₃COO)₂]_n/tributylphosphine/acetic acid system has been investigated as a function of reaction conditions and molar ratios of reactants. Tricyclohexylphosphine and triethylphosphite were also used as ligands and investigation was extended to the related oxalic, malonic, succinic, glutaric and adipic acid derivatives. These derivatives were isolated and characterized in view of their possible role as catalysts in the homogeneous hydrogenation of carboxylic acids in the presence of phosphine- or phosphite-substituted ruthenium carbonyl derivatives.     

Use of a standard system to evaluate the matrix effect on the treatment of a solution from atrazine contaminated soils

The influence of humic substances on the electrochemical treatment of solutions resulting from the remediation of atrazine contaminated soil has been investigated. In particular the effect on the hydrogen peroxide production stage and the effect on the hydroxyl radical oxidation treatment have been separately studied. In order to quickly assess the possible inhibition of the removal, an inorganic system has been adopted as a standard system. The results confirm the validity of electrochemical technologies also for the treatment of a real effluent where a matrix effect is expected since the organic matter content affects only the hydrogen peroxide production.     

Molecular dynamics and the structure of macrocycles —Solvent acetonitrile interactions

Microwave complex permittivities,* = -J, are reported in the 1–90 GHz frequency range for the macrocycles 18-crown-6 (18C6) and 15C5 added to acetonitrile in stoichiometric proportions, in the solvent CCl₄ at 25°C. Digitized infrared spectra of the CN stretch ₂ vibration of acetonitrile for the same systems are reported in the 2300–2200 cm^–1 spectral region. The macrocycle 12C4 added to CH₃CN has also been investigated in the infrared. Both the dielectric relaxation and infrared results are interpreted in terms of macrocycle-acetonitrile interactions, probably involving a methyl-hydrogen to ethereal-oxygen interaction. These interactions with CH₃CN diminish in strength according to the sequence: 18C6 > 15C5 > 12C4.This paper is dedicated to the memory of the late Dr C. J. Pedersen.