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Two novel crown ether compounds, N,N`-bis(2-hydroxy-5-nitrobenzyl)-4, 13-diazadibenzo-18-crown-6 (CCE) and N, N`-bis(7-hydroxy-4-methylcoumarin-8-methylene)-4, 13-diazadibenzo-18-crown-6 (FCE), have been synthesized as potential reagents for the selective extraction and determination of heavy metal ions. Characterizations of the acid-base reactivity and the heavy metal ion extraction capabilities are reported. Both CCE and FCE undergo four-step ionization processes with associated tautomeric transformations and form stable complexes with divalent metal cations that can be extracted into 1,2-dichloroethane. Extraction constants for Ba(II), Ca(II), Cd(II), Cu(II), Hg(II), Pb(II), and Sr(II) have been determined for both reagents. For CCE, the extraction order is Hg(II) > Pb(II) > Cu(II) > Cd(II) > Ca(II) > Sr(II) > Ba(II), whereas the order for FCE is Hg(II) > Cu(II) > Pb(II) > Cd(II) > Ca(II) > Sr(II) > Ba(II). The selectivity of CCE for Hg(II) over the next-best-extracted cation, Pb(II), is nearly 2 x 10{sup 7} and that of FCE for Hg(II) over next-best-extracted cation, Cu(II), is nearly 5 x 10{sup 6}. Potential applications to chemical analysis, based on the unprecedented selectivity of both reagents for Hg(II), are briefly examined. 54 refs., 7 figs., 3 tabs.

A miniaturized piezoelectric mass sensor has been developed that displays a very high mass sensitivity, S{sub m}. The sensor is based upon thin film resonator (TFR) technology, which is used to produce a gold-coated thin film (5.5 {mu}m) resonator (TFR) of piezoelectric aluminum nitride in the shape of 400-{mu}m squares. At this thickness, the TFRs support a standing bulk acoustic wave in a longitudinal mode at frequencies of {approximately} 1 GHz. Coatings of poly(methyl methacrylate) and spontaneously adsorbed monolayers from alkanethiols (CH{sub 3}-(CH{sub 2}){sub n}SH, n = 3,17) were used for the evaluation of S{sub m}. Results indicated that the S{sub m} ({approximately} -550 cm{sup 2}/g) of the TFRs rivals those of the most sensitive mass sensors currently available, while offering such performance in a markedly smaller device. Coatings were also used to sorb a gaseous analyte (i.e. methanol) at the TFRs to test their potential as gas-phase sensors. Tests conducted using monolayers formed by the chemisorption of a fluorinated thiol (CF{sub 3}(CF{sub 2}){sub 7}(CH{sub 2}){sub 2}-SH) and an acid-terminated thiol (HO{sub 2}C(CH{sub 2}){sub 15}SH) at the gold electrodes demonstrated both the performance of the TFRs and a primitive manipulation of the sorption selectivity of the interfacial structure. Possible applicationsmore » of the TFRs as mass sensors are examined based upon their high mass sensitivity and compatibility for device integration using semiconductor processing technology. 51 refs., 4 figs., 2 tabs.« less

This paper describes some of our results in developing high performance hydrogen gas sensors using piezoelectric devices (i.e., Quartz Crystal Microbalances (QCMs) and Thin Film Resonators (TFRs)) coated with a PdNi (90/10) alloy. A sensor array has been built by coating quartz crystals with various PdNi thicknesses and tested via exposure to H/sub 2/ in N/sub 2/ in the concentration range from 20 to 500 ppm. The performance of the sensor array has been also characterized in the presence of various potential interference gases and vapors, such as carbon dioxide, nitrous oxide, water, toluene, acetone, acetonitrile, hexane, methyl isobutylketone, methylene chloride, and ethanol. Using the unique chemistry of Pd-H/sub 2/ system, we have developed an relatively straightforward method to compensate for contributions from the mentioned potential interference gases.

Objective: This study was undertaken to assess frequencies of the methylenetetrahydrofolate reductase gene mutations cytosine-to-thymine substitution at base 677 (C677T) and adenine-to-cytosine substitution at base 1298 (A1298C) and their interactions with homocysteine and vitamin levels among Dutch women with preeclampsia. Study Design: Mutations were studied in the following 5 groups: 47 consecutive women with preeclampsia, 49 women with preeclampsia and with hyperhomocysteinemia, 36 women with preeclampsia but without hyperhomocysteinemia, 127 women with familial preeclampsia (typed for C677T mutations only), and 120 control subjects. Plasma levels of homocysteine, folate, and vitamin B 12 were measured. Results: Although 10.6% of the consecutive women with preeclampsia had strictly defined hyperhomocysteinemia (values >97.5th percentile), neither mutation was found in excess relative to the control group. Women with preeclampsia who had mild hyperhomocysteinemia (values >75th percentile) had a significant excess of the TT genotype (homozygosity for C677T mutation) relative to the women with preeclampsia who did not have hyperhomocysteinemia (odds ratio, 8.2; 95% confidence interval, 1.8-39). They also had significantly lower vitamin levels. Conclusion: Hyperhomocysteinemia in women with preeclampsia was associated with mutations in the gene for methylenetetrahydrofolate reductase, but the high frequency of hyperhomocysteinemia itself cannot be explained by these mutations alone. (Am J Obstet Gynecol 2001;184:394-402.)

The U.S. Department of Energy (DOE) is proceeding with plans for the ultimate disposal of approximately 380,000 m3 (∼100 million gallons) of high-level radioactive waste created as a byproduct of plutonium production and the processing of spent nuclear fuels. Critical to the successful disposal of this waste, which is kept in underground storage tanks, is the assessment of the volume and the constituents of the waste that remains at the tank sites after removal of the bulk of the material. The design of a system to characterize any waste which may have entered the vadose zone surrounding the underground storage tanks through leakage is the topic of this manuscript.

This paper focuses on the design, construction, preliminary testing, and potential applications of three forms of miniaturized analytical instrumentation. The first is an optical fiber instrument for monitoring pH and other cations in aqueous solutions. The instrument couples chemically selective indicators that were immobilized at porous polymeric films with a hardware package that provides the excitation light source, required optical components, and detection and data processing hardware. The second is a new form of a piezoelectric mass sensor. The sensor was fabricated by the deposition of a thin (5.5 micron) film of piezoelectric aluminum nitride (AIN). The completed deposition process yields a thin film resonator (TFR) that is shaped as a 400 micron square and supports a standing bulk acoustic wave in a longitudinal mode at frequencies of approx. 1 GHz. Various deposition and vapor sorption studies indicate that the mass sensitivity of the TFR's rival those of the most sensitive mass sensors currently available, though offering such performance in a markedly smaller device. The third couples a novel form of liquid chromatography with microlithographic miniaturization techniques. The status of the miniaturization effort, the goal of which is to achieve chip-scale separations, is briefly discussed.

The spatial dependence of spectral and matrix interference effects known to affect ICP emission spectrometry has been studied. The emissions of atoms, ions, and molecules were resolved on both a vertical and radial basis. Interference and sample volatility effects were found to be limited to specific spatial regions. Molecular background emission was dominated by the entrainment of air and was limited primarily to the outer radial regions of the plasma. In contrast, the radial displacement of analyte molecular emission from more slowly atomized samples varied with height. In the case of the easily ionized element interference on Ca atomic/ionic emission, evidence was found indicating at least two different mechanisms of interaction. The ability to attain radial resolution was instrumental in assigning causes to interference effects.

The consequences of using N2 as a nebulizer gas during operation of a direct current plasma were evaluated with respect to its utility as a practical analytical procedure. Performance of the N2 system vs. that of an all-Ar plasma was compared on the basis of background plasma emission, atomization efficiency, detection limits, sensitivity, plasma electron density, and immunity from the easily ionized matrix element interference effect. Observations with regard to the mechanism of the EIE effect were also made. It was concluded in many cases that the use of N2 as a nebulizer gas does not significantly degrade analytical performance. An exception to this conclusion was the finding that refractory samples did not atomize as efficiently in the N2 plasma system.

The observation of molecular fluorescence caused by high-power pulsed laser excitation has been found to be an accurate technique for the determination of relative OH radical concentrations on a spatially resolved basis in a circular air-acetylene flame. It was found that the high power of radiational excitation used allowed fluorescence saturation to be approached. Theory then predicts fluorescence intensities to be independent of temperature and collisional quenching effects. However accurate estimates of relative concentrations can not be obtained unless corrections are made for incomplete saturation and postfilter effects. Procedures for conveniently applying such corrections are reported.

La methode decrite, est basee sur la mesure des legeres modifications de masse, a la surface d'un cristal de quartz piezoelectrique, dues a l'adsorption d'un immunogene sur une surface specialement modifiee. Resultats d'une etude faite avec de l'IgG antihumaine de chaire, immobilisee a la surface de cristaux de quartz piezoelectriques, a l'aide de trimethoxyorganosilane. Les cristaux ont ete places dans le circuit d'un oscillateur electronique et testes pour la detection de l'antigene complementaire humain. Les modifications de masse se traduisent par des changements dans les frequences de resonnance des cristaux

Spatially resolved flame temperatures are spectroscopically measured using the slope method, over small (≃0.7 μl), relatively homogenous volumes of flame gases. The spatial resolution is uniquely obtained by introducing Co as a thermometric species into isolated volumes via the use of a droplet injection technique. By this method the emission of light is restricted to a limited volume, whose position in the flame can be accurately determined and controlled. Vertical resolution is determined by the width of the entrance slit of the monochromator employed (100 μm in this study), and horizontal resolution is limited by the width of the emission cloud formed by the injected droplets (1 to 3 mm). The possibility of self-absorption effects are greatly reduced because of the short radiation path length involved. The performance of the method is illustrated by its application to the spatial temperature mapping of the secondary reaction zone of a cylindrical air-acetylene flame. The effects of N2 as a sheathing gas and flame stoichiometry on the radial and vertical temperature distribution of the flame are also investigated. It is determined that a large, virtually isothermal, central zone exists in the flame.

The measurement of electron temperature and electron density from line and continuum radiation in Ar plasmas used for spectroscopic purposes is discussed. The correct equations for the calculation of these parameters from experimentally observable quantities are identified. Such expressions yield the theoretical spectral irradiance expected from line and continuum radiation. To aid calculations, grouped constants from these equations are calculated using SI units of measure. The sources of accurate values for the parameters and correction factors appearing in the irradiance equations are listed. In addition the approximations made in order to simplify electron temperature and electron density determinations are reviewed. Practical aspects of making accurate measurements of these parameters in Ar plasmas are considered. Theoretical plots of line to continuum emission ratio vs electron temperature and of continuum irradiance vs electron density are presented as an illustration using parameters appropriate for Ar emission at 430 nm and the spectrally adjacent continuum.

A direct reading emission spectrometer system is described which permits dynamic background correction measurements at each analytical wavelength. The system utilizes a refractor plate mounted on a tuning fork as a rapid means for square-wave shifting the spectral band pass from each analytical wavelength to the adjacent background wavelength position. A laboratory computer controls the system, receives the data, and performs the background subtraction. Evaluation of the system has shown that photon counting statistics are applicable and that reliable background corrections are obtained. Comparisons of this correction approach with others that have been used have further demonstrated its advantages for multielement analysis by emission spectrometry.

Description d'un dispositif permettant la speciation de composes mineraux solides. Exemples d'analyses qualitatives et quantitatives de melanges binaires et tertiaires de composes contenant V, Pb, Hg et Cd