Atomic Absorption Spectroscopy Measurements Research Articles

Interaction of resins and metal pigments in water‐borne printing inks

In aqueous alkaline ink media aluminium pigments react with the evolution of hydrogen, whereas the more noble copper and brass pigments react by the absorption of oxygen, which can be measured gas‐volumetrically. These different corrosion reactions can be inhibited with addition of certain binders for printing inks, such as styrene‐maleic acid resins, maleic resins and to some extent styrene‐acrylate resins. So, certain ink resins inhibit corrosion reactions of different noble metal pigments in a reducing hydrogen atmosphere (aluminium) as well as in an oxidizing oxygen atmosphere (copper and brass). The overall best resin is that with the lowest acid number. Atomic absorption spectroscopy measurements showed that a lower acid number pruduces a lower solubility of copper and zinc in the medium.

Influence of Clay Binders on the Performance of Pd/HZSM-5 Catalysts for the Hydroisomerization of n-Butane

The influence of the amount of two clay binders (montmorillonite and bentonite) on the acid properties and performance of Pd/HZSM-5 zeolite with different Si/Al ratios for the hydroisomerization of n-butane has been studied. Temperature-programmed desorption of ammonia, atomic absorption spectroscopy, chemisorption, and surface area measurements were used to characterize the catalysts. After agglomeration, some zeolite protons are neutralized by clay sodium and, consequently, a lower n-butane conversion is obtained. The product selectivity is also strongly influenced by the binder due to the fact that zeolite hydrogen transfer activity, metal/acid site balance, and diffusion of products are modified. If the appropriate binder is selected, the decrease in conversion will be compensated by a much higher isobutane selectivity. Thus, a catalyst based on Pd/HZSM-5, with a zeolite Si/Al ratio of 25, and agglomerated with bentonite in a zeolite/clay ratio of 35/65 wt/wt, showed not only an adequate mechanical resistance but also high isobutane selectivity and isobutane yield (87.1 and 23.9 mol %, respectively). It should be remarked that, under the same reaction conditions, the parent catalyst without binder showed worse isomerization activity (18.5 mol % isobutane yield with 47.3% isobutane selectivity).

Sequential injection standard addition for on-line measurement of mercury in the river Elbe

The improvement of reliability by a sequential injection procedure for on-line standard addition is described. This procedure is applied to a monitor for on-line determination of mercury in river water at concentrations from 20 to 1000 ng/l. The flow injection cold vapour atomic absorption spectrometry measurement include an on-line digestion by BrCl and UV-irradiation. The instrumental arrangement is controlled by the home-made software “FIMS-Master” (programmed based on LabView ®). During standard addition period, a selector valve is switched that alternately for 1 s standard (500 and 1000 ng/l, respectively) and for 9 s sample is transported to the injection valve. Standard and sample are mixed on the way to the injection valve by dispersion. The instrument has been tested at the German monitoring stations of Schnackenburg and Schmilka at 474.5 and 4.0 km from Czech border, respectively. Details are published at the web: http//www.rzbd.fh-hamburg.de/∼prmercol.

Synthesis and Characterization of Poly(N-isopropylacrylamide)-Coated Polystyrene Microspheres with Silver Nanoparticles on Their Surfaces

Dispersion copolymerization of styrene and a poly(N-isopropylacrylamide) macromonomer in ethanol−water media has been successfully carried out in the presence of AgNO3. Nearly monodisperse polystyrene microspheres with diameters ranging from 530 to 1250 nm were obtained. Nanoscopic silver particles were generated on their surfaces via in situ reduction of Ag+ by radicals generated from the initiator, 2,2‘-azobisisobutyronitrile (AIBN). The particle sizes of both polystyrene microspheres and silver nanoparticles were affected by the initial AIBN, AgNO3, and macromonomer concentrations. The diameters of the silvered microspheres and silver nanoparticles followed the relationships Dn ∝ [AIBN]0-0.107 [AgNO3]00.083[macromonomer]0-0.533 and dn ∝ [AIBN]00.027 [AgNO3]00.173 [macromonomer]0-0.137, respectively. Over 95.8% of the silver ions are converted into zerovalent metal and immobilized on the microspheres, according to atomic absorption spectroscopy measurements. The silvered microspheres were characterized by transmission electron microscopy, atomic force microscopy, and FTIR, UV−visible, and X-ray photoelectron spectroscopy. The surface-grafted PNIPAAm chains were found not only to serve as steric stabilizers to prevent the flocculation of the polystyrene particles but also to adsorb the Ag nanoparticles onto the surface of the microspheres. A mechanism for the formation of silvered polystyrene microspheres in dispersion copolymerization was presented.

Do New Pennies Lose Their Shells? Hypothesis Testing in the Sophomore Analytical Chemistry Laboratory

Post-1982 pennies have a varying copper content that can be investigated in the introductory analytical chemistry lab. Groups of four students analyzed ten pennies sampled from the entire minting period to test the hypothesis that the copper shell wears out with time. The results of the flame atomic absorption spectrometry measurements disproved the hypothesis. Four groups observed an increase of 2 mg of copper per year of circulation, the opposite of the behavior expected if the hypothesis were true. Two groups reported a strong positive correlation between copper content and original penny mass. Only one group observed random variations in copper content. Copper-clad copper pennies have a dynamically changing copper content that could be the result of minting variability or changes accompanying the storage of pennies. Student reactions to these results are noted. Future experiments are suggested.

Sono-electroanalysis: Application to the detection of lead in wine

Abstract The quantitative detection of lead in wine is shown to be possible by anodic stripping voltammetry under conditions of insonation. An immersion horn probe is introduced into a thermostatted conventional three-electrode cell opposite a mercury plated platinum disc working electrode. Following acidification of the wine sample lead ions can be reduced at the Hg/Pt electrode surface at −1.0 V (vs SCE). The large mass transport associated with power ultrasound yields efficient pre-concentration of the lead before it is stripped by an anodic linear sweep of the potential. Insonation further offers the crucial benefits of first surface activation and cleaning, helping to prevent electrode fouling by the organic components in wine and second fully equilibrating “free” and “bound” Pb 2+ ions in the complex matrix. By use of standard microaddition of lead to the solution the system can be calibrated to give the total amount of lead present. Experiments using samples of a white Italian Chardonnay gave a total lead content of 22±6 μ g l −1 . This value was compared with those obtained by independent atomic absorption spectroscopy (AAS) measurements performed by two different laboratories. Quantitative agreement was found.

The role of biomineralization in microbiologically influenced corrosion.

Synthetic iron oxides (goethite, alpha-FeO.OH; hematite, Fe2O3; and ferrihydrite, Fe(OH)3) were used as model compounds to simulate the mineralogy of surface films on carbon steel. Dissolution of these oxides exposed to pure cultures of the metal-reducing bacterium, Shewanella putrefaciens, was followed by direct atomic absorption spectroscopy measurement of ferrous iron coupled with microscopic analyses using confocal laser scanning and environmental scanning electron microscopies. During an 8-day exposure the organism colonized mineral surfaces and reduced solid ferric oxides to soluble ferrous ions. Elemental composition, as monitored by energy dispersive x-ray spectroscopy, indicated mineral replacement reactions with both ferrihydrite and goethite as iron reduction occurred. When carbon steel electrodes were exposed to S. putrefaciens, microbiologically influenced corrosion was demonstrated electrochemically and microscopically.

Electric Current Density Imaging of Pedunculate Oak(Quercus RoburL.) Twigs by Magnetic Resonance Imaging

The use of Electric Current Density Imaging (CDI) technique to map spatial distribution of induced electric currents through two years old twigs of pedunculate oak (Quercus robur L.) is presented. Specifically, this magnetic resonance technique was implemented to image conductivity contrast in different tree tissues. Imaged electric conductivity distributions of pith, wood, and phloem together with cambial zone and undifferentiated xylem were compared with flame atomic absorption spectrometry measurements of potassium. Good correlation was observed. The undifferentiated xylem + cambial zone + complete phloem showed higher electrical conductivity and normalized potassium values than both differentiated xylem and pith. By a novel magnetic resonance imaging technique it is demonstrated that the path of least resistance to an electric current was along tissues of maximum free potassium concentration.

Functional Dendritic Macromolecules: Preparation and Optical Properties

Repetitive coupling reactions of branched azobenzene derivatives resulted in dendritic macromolecules, or “wedges” and “dendrimers”. These molecules were designed to incorporate aliphatic and polar units in order to prepare Langmuir-Blodgett (LB) films. Atomic force microscopy (AFM), absorption spectroscopy, and second harmonic generation (SHG) measurements revealed structural properties of the LB films in terms of size, aggregation, and orientation. AFM measurements revealed that growth of the branches increased as a function of the generation. In absorption spectroscopy and SHG measurements, results showed that wedges had an unsymmetric orientation in the LB films, while dendrimers had a symmetrically functionalized structure.

Extension of the dynamic range of flame atomic absorption spectrometry using flow injection analysis with variable-volume dilution chambers

A simple and inexpensive procedure is proposed for the extension of the dynamic range of flame atomic absorption spectrometry measurements using on-line dilution. The proposed methodology is based on the use of a manifold with two coupled dilution chambers and a zone injection system. The samples are prediluted in a closed system which includes a variable-volume mixing chamber (10–120 ml) and two injection valves. The samples are injected through one of these valves, and the other is employed to take 100 μl of prediluted samples which are then passed through a new dilution chamber (volume 1–10 ml) and aspirated by the nebulizer of the instrument. A third injection valve mounted in the last part of the manifold is used for the direct injection of diluted standard solutions. Various dilution factors are obtained, ranging from 2 to 130 000 times, thus extending the analytical range of copper determination to more than 100 000 mg l −1.

A photo‐cured calcium ion‐selective electrode for use in flow injection potentiometry that tolerates high perchlorate levels

AbstractAn improved photo‐cured membrane selective to calcium was developed based on the calcium bis[4‐(l, 1,3,3‐tetramethylbutyl)phenyl] phosphate ionophore and incorporates the lipophilic additive, potassium tetrakis(p‐chloropheny1)borate. The calcium electrode exhibited a hyper‐Nernstian response of 31.0 mV change per activity decade and a log‐linear range between 1 × 10−5 to 0.1 M in pure calcium chloride solution, in steady‐state mode. The calcium electrode was fast responding, reaching 90% of steady‐state value in 5s making it ideal for flow injection measurements. The photo‐cured electrode can measure calcium in a high perchlorate background, and was used to determine the total calcium level in full cream milk that was digested by a nitric/perchloric acid mixture. The results obtained were in good agreement with atomic absorption spectroscopy measurements.

Synthesis and characterization of Schiff Base Chelates of Tetramic Acids as NMR Contrast Agents for micro imaging

Novel Cu(II) complexes derived from N,N′ P-ethylene-bis-(1′,5′,5′-trimethyltetramic acid-3′-acetiminato)copper(II) aCu [1] were evaluated as contrast agents for NMR microscopy and therefore tested for penetration into living cells (Xenopus laevis oocytes). By in vitro1H NMR relaxation (T1) and atomic absorption spectroscopy measurements (AAS) we confirmed, that independent of the complex isomers (Z/Z, Z/E, E/E, E/Z) compounds with alkyl substituents in R1 – R5 exclusively were able to penetrate the plasma membranes. It is noteworthy that compounds containing the tetramic acid moieties from both a penetrating and a non-penetrating complex most likely were accumulated in the plasma membrane and/or plasma membrane-associated vesicles, which was concluded from in vitro NMR measurements combined with AAS trace analyses. In this context the crystal and molecular structure of the ‘chimerical’ C17H22N4O4Cu · 3H2O kCu · 3H2O were determined by x-ray analysis. The x-ray structural parameters are discussed in detail.

Effect of Cu(2+)-ions on semiconductor properties of synthetic DOPA melanin polymer.

The purpose of the present study was to examine semiconductor properties of synthetic DOPA melanin, which are basic for future biological applications. DC conductivity, electron spin resonance (ESR), and atomic absorption spectroscopy (AAS) measurements have been performed to investigate the effect of Cu(2+)-ions on the semiconductor properties of melanin polymer synthesized from DOPA (3,4-dihydroxyphenylalanine). DOPA melanin - Cu2+ complexes examined show the decrease of both thermal activation energy delta Ea and pre-exponential factor sigma o values upon doping. At the same time no substantial changes in conductivity at 293 K have been observed. Formation of bipolaron states due to chelation of copper ions by melanin orthosemiquinones has been postulated. The Meyer-Neldel rule with a characteristic temperature T0 equal to 298 K and possible physiological implication of this fact are discussed. These data suggest, that DOPA melanin polymer could be useful as a type of culture substratum.

Separation and determination of uranium(VI) with calixarene hydroxamic acids

A new calixarene hydroxamic acid, 5,11,17,23-tetra-(N-p-chlorophenyl hydroxamate c-phenyl-25,26,27,28-tetrahydroxycalix[4]arene (CPCHA) was synthesized and used for the extraction and spectrophotometric determination of uranium(VI). The molar absorptivity of the uranium(VI)-CPCHA-thiocyanate complex was 9.9·103 1·mol−1·cm−1 at 436 nm. The system obeyed Beer's law in the range of 1.78–23.1 ppm of uranium. The uranium(VI)-hydroxamate-ethyl acetate complex was directly aspirated for graphite furnace atomic absorption spectrometry measurements (GFAAS) which increased the sensitivity by about a factor of fifty. Uranium was determined in various standard and environmental samples.

Comparison of theoretical and experimental spectroscopic constants in atomic absorption spectroscopy with electrothermal atomization

The Lambert-Beer law applied to atomic absorption spectroscopy measurements with line sources contains a spectroscopic constant that can be theoretically derived. Its value can also be obtained in many ways from the experimental data. In this paper the two sets of data are compared to see when and at what level an agreement can be found.

Hydrogen-atom assisted CVD of copper at low temperatures and in-situ gas-phase spectroscopy studies

A novel low-temperature chemical vapour deposition (CVD) process has been developed by using hydrogen-atom reactions with metal compounds to produce copper thin films for ULSI applications. High-purity copper films, with low resistivity, good step coverage and strong adhesion to various substrates were obtained by using hydrogen-atom assisted CVD with CuCl at 200 °C, and with β-diketonate copper (II) complexes Cu(fod) 2 and Cu(hfa) 2 at 100–150 °C. Gas-phase Cu atoms (10 10–10 11 cm −3) and concentration as a function of time were measured in-situ by atomic absorption spectroscopy during deposition. The diatomic molecule CuF was measured by atomic emission spectroscopy using oxygen-atom reactions with β-diketonate copper (II) complexes Cu(fod) 2 and Cu(hfa) 2. Thermodynamic calculations of enthalpy, ΔH 0 showed that these reactions were exothermic and spontaneous at room temperature. The spectroscopy measurements of Cu atoms and CuF diatomic molecules in the reaction were studied as a means to develop insight into the gas-phase reaction. The reaction mechanisms were evaluated on the basis of atomic absorption spectroscopy measurements.

Hot gas desulfurization with vanadium-promoted zinc ferrite sorbents

The performance of zinc ferrite promoted with V 2 O 5 was investigated as a hot gas desulfurization sorbent. The sorbents were prepared by the incipient impregnation technique, and the vanadium loading and the calcination temperature were varied. The sorbents were tested in a packed-bed microreactor set-up for five sulfidation-regeneration cycles to investigate their breakthrough behaviour. Sulfidation was performed at 873–973 K with H 2 S-H 2 -H 2 O-N 2 mixtures, while regeneration was carried out at 923–973 K with O 2 -N 2 mixtures. The fresh, sulfided, and regenerated sorbents were characterized by atomic absorption spectroscopy, X-ray diffraction, surface area and porosity measurements. The results of the investigation indicated that the sorbents exhibited a more stable cyclic performance with higher vanadium loading, all vanadium-promoted sorbents reduced the H 2 S content of the gas to levels below the equilibrium level for zinc oxide, some H 2 S was chemisorbed by vanadium, and two-step calcination imparted structural stability to the sorbents.

Determination of Arsenic in Orange Juice by Dry Ashing Hydride Generation Atomic Absorption Spectrometry

A procedure suitable for routine analysis of arsenic in orange juice using instrumentation available in most control laboratories was developed. Organic matter is destroyed by the dry ashing technique, the ash is dissolved in HCl, and hydrides of arsenic are generated by the addition of sodium borohydride prior to atomization in a flame-heated quartz cell and atomic absorption spectroscopy measurement. Experimental conditions for the destruction of organic matter were established, and an interference study was carried out. Copper and iron do not interfere in arsenic determination at levels found in orange juice. The methodology developed has a detection limit in orange juice of 0.1 ng g−1, a relative standard deviation of 1%, and a recovery percentage of 98 ± 8. The accuracy of the proposed method was checked by analysis of a certified sample of tomato leaves, NIST SRM 1573 (certified 0.27 ± 0.05 μg/g; found 0.26 ± 0.03 μg/g). The arsenic content of orange juice products was determined. The extremely low arsenic levels found (0.3-4.4 ng g−1)do not present problems from a toxicological point of view.

Dissolution and scanning electron microscopic studies of Ca,P particle‐containing bioactive glasses

Calcium phosphate (Ca,P) precipitation behavior on the surface of two bioactive glasses and four bioactive glass composites--two with hydroxylapatite (Ca10(PO4)6 (OH)2) and two with rhenanite (CaNaPO4)--were studied in simulated body fluid (SBF) and in Tris-Buffer at 5, 8, 16, 24, 48, 72, and 144 h. The weight loss of the materials was measured and the amount of precipitation was estimated using scanning electron microscopy with electrochemical detection (SEM-EDX) analysis. The test was repeated for one glass and its respective rhenanite composite every 3 h until 60 h and thereafter every 10 h until 150 h in SBF. Atomic absorption spectroscopy, spectrophotometry, SEM-EDX analysis, and pH measurements were performed on these samples. It is shown that in vitro the composite materials have a higher capacity for Ca,P precipitation than the glasses. Weight losses of the materials correlate well with their composition. Both the glass and Ca,P phases influence the precipitation mechanism and rate. Precipitation begins preferably from the glass phase. Ca,P particles clearly influence the time of onset and rate of precipitation. Cross-sectional EDX analysis of the samples revealed an absence of a clear Si-rich layer in glass A0B0 (SiO2 53.9 mol %, Na2O 27.5, CaO 12.4, P2O5 6.2, Al2O3 0.0 and B2O3 0.0) composites. This was attributed to the presence of extra calcium and phosphate ions on the surface of the material. The ion-concentration and pH change curves offered insight into the mechanism of precipitation. A connection was established between SEM-EDX results and the release curves. Formation of an Si,Ca,Na film was observed that seemed to initiate the Ca,P precipitation.(ABSTRACT TRUNCATED AT 250 WORDS)

Atomic resonance absorption spectroscopy measurements on high-temperature CO dissociation kinetics

The dissociation rate coefficient of CO was measured behind reflected shock waves in the temperature range 5500 < J<9000 K. By the use of the atomic resonance absorption spectroscopy (ARAS), the time-dependent formation of C and O atoms could be directly observed in the postshock reaction zone. The experiments were performed in mixtures of CO highly diluted in argon at pressures between 0.5 and 1.3 bar. The initial CO concentrations varied from 100 to 10,000 ppm. Assuming vibrational equilibrium, the data for the thermal decomposition of CO, (CO + Ar ^ C + O + Ar), can be represented by the following modified Arrhenius expression: k = 4.3 X1027 J-3-1 exp(-129,000 K/J) cn^mol-^-1 ±50%. Computer simulations based on a two-temperature model were not able to explain observed reaction induction times. Vibrational relaxation alone seems to have a negligible influence under the present conditions. The effect of impurities was minimized by keeping background pressure in the shock tube below 5xlO~ 7 mbar.