Figures of merit of pneumatic and ultrasonic sample introduction systems in inductively coupled plasma–multichannel-based emission spectrometry in an ultra-clean environment

Conventional figures of merit such as limits of detection, signal to background ratio or repeatability, are used to determine the performance of pneumatic and ultrasonic sample introduction systems in an ultra-clean environment with an axially viewed inductively coupled plasma-atomic emission spectrometry and multichannel detection. We observed that the ultrasonic nebuliser offered a large improvement of signal intensity (10-133 greater) compared to a cyclone chamber coupled with a pneumatic Meinhard nebuliser. This improvement is associated with an average increase of signal to background ratio by a factor 86 and an average decrease of detection limits by a factor 6. The improvement factors generally depend on the element and for the same element on spectral lines. Typically, the observed values of detection limits in this work are lower than those published and obtained in non-ultra-clean conditions. The results emphasize that the environmental conditions of cleaning and analysis are essential to avoid and control cross contamination of the samples and hence to obtain low detection limits.     

Preparation and properties of polyurethane networks based on α,ω-difunctional poly(hexafluoropropylene oxide)

Poly(hexafluoropropylene oxide), poly(HFPO), networks were prepared from functional polymers by end linking via urethane groups. The prepolymers were characterized by NMR spectroscopy and GPC. The networks were characterized by determination of the number of network chains from the shear modulus, and were snown to contain both trifunctional crosslinks and difunctional links. The properties of the networks were investigated by a range of techniques. Compared with fully-fluorinated networks formed via triazine cross-links, investigated previously, the urethane-linked networks were more readily prepared but were poorer elastomers, were less thermally stable, and were less resistant to swelling by common polar solvents. © 1995 John Wiley & Sons, Inc.     

Esters of 5-carboxyl-5-methyl-1-pyrroline N-oxide: a family of spin traps for superoxide

Apparent rate constants, at acidic pH and neutral pH for the reaction of a family of ester-containing 5-carboxyl-5-methyl-1-pyrroline N-oxides with superoxide (O2*-) were estimated, using ferricytochrome c as a competitive inhibitor. It was of interest to note that the rate constants were similar among the different nitrones and not that significantly different from that found for 5-(diethoxyphosphoryl)-5-dimethyl-1-pyrroline N-oxide. At acidic pH, the rate constant for spin trapping O2*- was 3-fold greater than that at physiological pH. Subsequent experiments determined the half-life of aminoxyls, derived from the reaction of these nitrones with O2*-. The EPR spectra were modeled by using a global analysis method. The results clearly demonstrated that EPR spectra of all the aminoxyls were inconsistent with a model that included a single gamma-hydrogen splitting. A better interpretation modeled them as two diastereomers with identical nitrogen splittings and slightly different beta-hydrogen splittings. Detailed line width analyses slightly favored an equal line width-unequal population ratio for the two diastereomers.     

2-Mercaptobenzimidazole (2-benzimidazolethiol) as a colorimetric reagent for palladium

Summary A spectrophotometric method for the determination of palladium using 2-mercaptobenzimidazole is described. The orange-yellow colour developed in aqueous medium atph 1.0–2.6 by the addition of an alcoholic solution of the reagent, is measured at 380 m. The system is found to obey Beer's law. The interference limits of diverse ions are also given.     

Crystal structure oftrans-ethyl(1,5,6-trimethylbenzimidazole)-bis(dimethylglyoximato)cobalt(III). Relationships between structural and spectroscopic properties in compounds of the general formulae [Co(dmgH)2(R)(1,5,6-Me3Bzm)]

Summary The synthesis and x-ray crystal structure oftrans-[Co(dmgH)₂(Et)(1,5,6-Me₃Bzm)] where dmgH=dimethylglyoximate(–1), and 1,5,6-Me₃Bzm=1,5,6-trimethylbenzimidazole, is reported. The compound C₁₉H₂₆N₆O₄Co is monoclinic, space group P2₁/n;a=11.700(4);b=24.205(6);c=8.500(3) Å and =101.63(3)°. D(calcd) 1.299 g cm^–3; Z=4 and R=0.066 for 2359 independent reflections. Comparison of Co-N(axial ligand) bond lengths for compounds of general formulaetrans-[Co(dmgH)₂(R)(L)], with L=pyridine or 1,5,6-trimethylbenzimidazole and R=CH(CN)Cl, CH₂NO₂, Me, Et,i-Pr, cyclo-hexyl or adamantyl is made. The Co–N(1,5,6-Me₃Bzm) bond lengths of the trimethylbenzimidazole derivatives show a fairly linear relationship with the electronic parameter of the axial R group, derived from the¹³C-n.m.r. spectra of their pyridine analogues. The influence of steric effects on the properties of these Co^III compounds is discussed.     

Polyfluorocycloalkenes. Part XVIII. Aryl adducts of decafluorocyclohexene

Decafluorocyclohexene reacted slowly with aniline to give 1-phenylamino- 3-phenyliminoheptafluorocyclohex-2-ene, which was hydrolysed by hydrochloric acid to 3-phenylaminoheptafluorocyclohex-2-enone. Decafluorocyclohexene reacted stepwise with phenyl lithium, giving 1-phenylnonafluorocyclohexene and thence 1,2-diphenyloctafluorocyclohexene: the former product was attacked slowly by pentafluorophenyl lithium at ?40°C affording 1-pentafluorophenyl- 1-phenyloctafluorocyclohexene. Phenyl lithium reacted sluggishly with bis(pentafluorophenyl)octafluorocyclohexene to give 1-pentafluorophenyl-2-(2′,3′,5′,6′-tetrafluoro-1′-biphenylyl)octafluorocyclohexene and 1,2-bis(2′,3′,5′,6′-tetrafluoro-1′-biphenylyl)octafluorocyclohexene. 1,2-Diphenyloctafluorocyclohexene and 1,2-bis(pentafluorophenyl) octafluorocyclohexene were fluorinated by cobalt(III) fluoride to give the olefin, 1,2-bis(undecafluorocyclohexyl)octafluorocyclohexene.     

Development and validation of an analytical method for detection of estrogens in water

An analytical procedure enabling routine analysis of four environmental estrogens at concentrations below 1 ng L^–1 in estuarine water samples has been developed and validated. The method includes extraction of water samples using solid-phase extraction discs and detection by gas chromatography (GC) with tandem mass spectrometry (MS–MS) in electron-impact (EI) mode. The targeted estrogens included 17- and 17-estradiol (aE2, bE2), estrone (E1), and 17-ethinylestradiol (EE2), all known environmental endocrine disruptors. Method performance characteristics, for example trueness, recovery, calibration, precision, accuracy, limit of quantification (LOQ), and the stability of the compounds are presented for each of the selected estrogens. Application of the procedure to water samples from the Scheldt estuary (Belgium – The Netherlands), a polluted estuary with reported incidences of environmental endocrine disruption, revealed that E1 was detected most frequently at concentrations up to 7 ng L^–1. aE2 was detected once only and concentrations of bE2 and EE2 were below the LOQ.Presented at the 9th FECS Conference on Chemistry and the Environment, Bordeaux, France, 29 August–1 September 2004     

UV index experimental values during the years 2000 and 2001 from the Spanish broadband UV-B radiometric network

An analysis is made of experimental ultraviolet erythemal solar radiation data measured during the years 2000 and 2001 by the Spanish UV-B radiation evaluation and prediction network. This network consists of 16 Robertson-Berger type pyranometers for evaluating solar erythemal radiation and five Brewer spectroradiometers for evaluating the stratospheric ozone. On the basis of these data the Ultraviolet Index (UVI) was evaluated for the measuring stations that are located either in coastal regions or in the more densely populated regions inland on the Iberian Peninsula. It has been checked that in most cases the maximum irradiance values corresponded to solar noon, although there were exceptions that could be explained by cloudiness. The maximum experimental values of the UVI were around 9 during the summer, though frequently passing this value at the inland measurement stations. The annual accumulated dose of irradiation on a horizontal plane has also been studied, as well as the evolution through the year in units of energy, standard erythemal doses and minimum erythemal doses, according to different phototypes.     

Regioselective cyclomanganation of Schiff bases. An unexpected effect of chloro substituents

In this paper we describe the synthesis of new metallacycles by the cyclomanganation reaction of benzyl-benzylidene-amines by using [MnMe(CO)₅] as metallating agent. These ligands can undergo metallation on different aromatic carbon atoms but no important differences have been found in the regioselectivity of the process, that can be related to the electronic effect of the substituents, and in all the cases studied the endo-cyclomanganated complexes of para-substituted imines have been obtained. The corresponding exo-metallacycles were obtained by reaction of [MnMe(CO)₅] on the imine 2,6-Cl₂C₆H₃CHNCH₂Ph and 2,4,6-Me₃C₆H₂CHNCH₂Ph, derived from 2,6-dichlorobenzaldehyde and 2,4,6-trimethylbenzaldehyde, respectively.The results described suggest that the mechanism of the cyclomanganation is similar to that of cyclopalladation and it can be proposed that cyclomanganation takes place by the formation of a four-centered transition state, involving the C-H and Mn-C_acetyl bonds, in the acetyl coordination complex formed in the first step of the reaction.     

Effects of chain length and heat treatment on the nanotribology of alkylsilane monolayers self-assembled on a rough aluminum surface

The conformational order of alkylsilane monolayers self-assembled on a rough aluminum surface is affected by the molecular chain length and the thermal history of the sample. These monolayers have been characterized by grazing angle FTIR spectroscopy. Tribological mechanisms were explored using initial molecular conformation order, sliding distance, normal load, and substrate compliance as experimental variables. Results indicate that the initial conformational disorder of the molecules determines the level of friction at the commencement of sliding. Adverse changes in dynamic friction and monolayer life during sliding are not thermally induced but are related to substrate roughness and local plasticity. Plastic deformation reduces the spatial density of the alkylsilane monolayer and is accentuated by an increase in the normal load.