Development and Calibration of a Portable Air Sampler

This paper describes the development and calibration of a portable air sampler for detecting chemical vapors. The air sampler is equipped with a preconcentrator, a battery operated mini-pump, a three-way valve, capacitive sensors housed in a sensing chamber, and a data acquisition and control circuit board. The preconcentrator is used to adsorb trace level chemicals and to thermally desorb them into the sensing chamber. The air sampler was calibrated using known concentrations of ethylbenzene vapor generated by an Environics gas mixing system. The air sampler was also tested using low concentration toluene and ethanol vapors generated by diffusion based vapor generation device. The concentration factor of the preconcentrator was experimentally determined.     

Modal dispersion curves of an optical waveguide with a core cross-section partially bounded by one turn of an equiangular spiral under weak guidance approximation

In this paper, we present a theoretical analysis of propagation of electromagnetic waves through a fiber with a spiral shape core cross-section with two cases. In one case the remaining unbounded part closed by a straight line and in other case remaining part not bounded by well defined line. Using Goell's point matching method under weak guidance condition modal characteristic equations for the lowest order modes are derived. The comparison of dispersion curves for two cases is also shown and interpreted.     

Heat-resistant thermosetting polymers based on a novel tetrakisaminophenoxycyclotriphosphazene

Two heat-resistant thermosetting polymers ( IX and X ) have been developed based on a new cyclotriphosphazene containing tetrakisamine. These polymers were synthesized by the reaction of tetrakisamine ( IV ) with maleic anhydride followed by in situ cyclodehydration and polymerization of the maleimides ( VII and VIII ) at 235–240°C for 1.5 h and 290°C for 0.5 h. The thermogravimetric analyses (TGA) of the developed cyclotriphosphazene containing cyclomatrix polymers showed their thermal stability up to 350°C and char yield of 71% in nitrogen at 800°C and 65% in air at 700°C. The monomer, 2,2,4,4-tetrakis(4′-aminophenoxy) -6,6-diphenylcyclotriphosphazene ( IV ), useful for producing a variety of heat- and fire-resistant polymers, has been synthesized in good yield. Its syntheses involve Friedel-Crafts reaction of hexachlorocyclotriphosphazene ( I ) with benzene followed by the reaction of 2,2,4,4-tetrachloro-6,6-diphenylcyclotriphosphazene ( II ) with potassium 4-nitrophenoxide. The reduction of the obtained 2,2,4,4-tetrakis(4′-nitrophenoxy)-6,6-diphenylcyclotriphosphazene ( III ) with molecular hydrogen in presence of PtO₂ gave the tetrakisamine ( IV ). The structure of the synthesized monomer and intermediates were characterized by FT-IR, ¹H-NMR, ³¹P-NMR, mass spectroscopy, differential scanning calorimetry (DSC), and elemental analysis. These resins are potential candidates for the development of heat- and fire-resistant composites, laminates, and adhesives, useful for space, aerospace, and electronic application. © 1993 John Wiley & Sons, Inc.     

Hyperfine fields at implanted119Sn in Fe

Metastable FeSn systems produced by high dose implantation of¹¹⁹Sn into Fe foils are studied by conversion electron Mössbauer spectroscopy. The hyperfine field experienced by Sn implanted in Fe depends on the implantation dose. Clustering and precipitation of Sn take place at doses of 5x10¹⁶/cm² and beyond. Isochronal annealing of the implanted sample at 500 C causes the Sn atoms to move towards the surface, probably due to vacancy assisted migration, resulting in the precipitation of almost the entire implanted Sn on the Fe surface. This precipitate acts as a source for the in-diffusion of Sn into Fe at 600 C.     

Characterisation of nickel(II) complexes of a substituted 2-acetylpyridine thiosemicarbazone by electronic and n.m.r. spectral studies

Summary Ni^II complexes of 1H-hexahydroazepine-1-thiocarboxylic acid-2-[1-(2-pyridinyl)ethylidene] hydrazide (HL4A) of general formula [Ni(L4A)X] (X=Cl, Br, I or NCS) have been synthesized and characterised by physical and spectroscopic methods. The molar conductivities show that all of the complexes are non-electrolytes. The terdentate character of the ligand in all cases is inferred from i.r. spectra, while the electronic spectra suggest planar geometries.     

Efficient synthesis of xanthenedione derivatives using cesium salt of phosphotungstic acid as a heterogeneous and reusable catalyst in water

Cs_2.5H_0.5PW₁₂O₄₀ has been reported to be an efficient catalyst for the synthesis of 1,8-dioxo-octahydroxanthene from aldehydes and 1,3-cyclohexanedione/dimedone in water. This approach is environmentally benign with clean synthetic procedure, short reaction time, easy workup procedure, excellent yield, and regeneration of catalyst, which made this protocol efficient and safe.     

Structural and spectral investigations on some new Ni(II) complexes of di-2-pyridyl ketone N(4)-phenylthiosemicarbazone

Ni(II) complexes (1–5) of di-2-pyridyl ketone N(4)-phenylthiosemicarbazone (HL) have been synthesized and spectrochemically characterized. Elemental analyses revealed a NiL₂ · 2H₂O stoichiometry for compound 1. However, the single crystals isolated revealed a composition NiL₂ · 0.5(H₂O)0.5(DMF). The compound crystallizes into a monoclinic lattice with the space group P2₁/n. Complexes 2, 3 and 4 are observed to show a 1:1:1 ratio of metal:thiosemicarbazone:gegenion, with the general formula NiLX · yH₂O [X = NCS, y = 2 for 2; X = Cl, y = 3 for 3 and X = N₃, y = 4.5 for 4]. Compound 5 is a dimer with a metal:thiosemicarbazone:gegenion ratio of 2:2:1, with the formula [Ni₂L₂(SO₄)] · 4H₂O.     

Synthesis of mono- and binuclear dioxomolybdenum(VI) complexes derived from N(4)-substituted thiosemicarbazones: X-ray crystal structures of [(MoO2L)2], [MoO2Lpy] and [MoO2Lpy]

Four molybdenum(VI) thiosemicarbazonato complexes have been synthesized and characterized. The dinuclear complexes [(MoO₂L¹)₂] (1) and [(MoO₂L²)₂] (3) have been prepared by the reaction of [MoO₂(acac)₂] with 2-hydroxyacetophenone N(4)-cyclohexyl (H₂L¹) and N(4)-phenyl (H₂L²) thiosemicarbazones in alcoholic medium. Mononuclear dioxomolybdenum(VI) complexes of the type [MoO₂L¹py] (2) and [MoO₂L²py] (4) have been prepared by the reaction of 1 or 3 with pyridine (py) in alcoholic medium. In all the complexes, molybdenum is coordinated by two terminal oxo-oxygen atoms, (O_t), oxygen, nitrogen and sulfur atoms from the principal ligand and by an oxygen atom from the second unit in 1, and by a nitrogen atom from pyridine in complexes 2 and 4. All complexes have been spectroscopically characterized. The molecular structures of complexes 1, 2 and 4 have been determined by the single crystal X-ray diffraction method.     

Mercury(II) ion-selective electrodes based on heterocyclic systems

Mercury ion-selective electrodes (ISEs) were prepared with a polymeric membrane based on heterocyclic systems: 2-methylsulfanyl-4-(4-nitro-phenyl)-l-p-tolyl-1H-imidazole (I) and 2,4-diphenyl-l-p-tolyl-1H-imidazole (II) as the ionophores. Several ISEs were conditioned and tested for the selection of common ions. The electrodes based on these ionophores showed a good potentiometric response for Hg2+ ions over a wide concentration range of 5.0 x 10(5-) - 1.0 x 10(-1)M with near-Nernstian slopes. Stable potentiometric signals were obtained within a short time period of 20 s. The detection limits, the working pH range of the electrodes were 1.0 x 10(-5) M and 1.6-4.4 respectively. The electrodes showed better selectivity for Hg2+ ions over many of the alkali, alkaline-earth and heavy metal ions. Also sharp end points were obtained when these sensors were used as indicator electrodes for the potentiometric titration of Hg2+ ions with iodide ions.     

Six coordinate Ni(II) complexes of ONN donor aroylhydrazone ligands: synthesis,spectral studies,and crystal structures

A new ligand N′-(pyridin-2-ylmethylene)nicotinohydrazide (HL²) and two Ni(II) complexes of stoichiometry NiL¹·H₂O [L¹-2-benzoylpyridine nicotinoylhydrazone] and NiL²·H₂O have been synthesized and characterized by elemental analyses, IR and UV–Vis spectral studies. Structures of HL² and Ni(II) compounds have been determined by single crystal X-ray diffraction studies which reveal a distorted octahedral geometry around the two Ni(II) centers.

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Graphical abstract A new ligand N￠-(pyridin-2-ylmethylene)nicotinohydrazide (HL2) and two Ni(II) complexes of stoichiometry NiL1·H2O [L1-2-benzoylpyridine nicotinoylhydrazone] and NiL2·H2O have been synthesized and characterized by elemental analyses, IR, UV–Vis spectral studies and single crystal X-ray analysis.