Scanning Kelvin Microscope: a new method for surface investigations

Based on the well known Kelvin probe for work function measurements a new microstructure analysis system - the Scanning Kelvin Microscope - has been developed. It allows to measure simultaneously with high lateral resolution the distribution of the contact potential difference (CPD) between a conductive sample and a reference probe together with the topographical structure of the sample surface. The measurement is contact free and non-destructive and can be carried out in natural environments. At present the lateral resolution of the measurement approaches 5 microm. The results can be displayed on a computer in three dimensional colour pictures.     

Quantitative ultratrace distribution analysis of tantalum wires with SIMS

Summary The potential of SIMS for multielement ultratrace bulk analysis in refractory metals has already been shown in previous publications [1, 2]. In this paper it will be demonstrated, that the high sensitivity of SIMS can be used advantageously for high resolution distribution analysis. Due to the high useful yield (0.5 to 10^–5) it is possible to perform distribution analysis in the ng/g range with a sample consumption of about 1 pg per data point. A good lateral resolution of about 1 m and the variability of the sputtering rate over 3 orders of magnitude allow an optimization of the measurement parameters with respect to the sample geometry. This is of special importance in our work, because small lateral dimensions, high total sputtering depth (300 m) and crooked surfaces have to be considered. In this paper also the technical significance of sensitive high resolution distribution analysis of tantalum wires, which are used for microelectronic applications, will be discussed.

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Quantitative Ultraspuren-Verteilungsanalyse von Tantaldrähten mit Hilfe von SIMS

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Dedicated to Prof. Dr. G. Tölg on the occasion of his 60th birthday     

A sensitive fluorimetric assay for cationic surfactants

Summary A new fluorimetric assay for cationic surfactants is based on their capability of quenching the fluorescence of 8-octadecyloxypyrene-1,3,6-trisulfonate (PTS-18). It is specific for cationic surfactants which can be determined in the 40–400 g concentration range. The method is considered to be advantageous over former methods in that it only requires addition of the sample solution to the fluorophore solution, followed by measurement of fluorescence intensity of the probe. This is in contrast to existing methods where the detergent/dye ion pair has to be extracted before measurement.     

Rapid determination of halogens in milk by instrumental neutron activation analysis

The absolute concentrations of iodine, bromine and chlorine in milk, have been determined by epithermal neutron activation followed by high resolution gamma-ray spectrometry. Two kinds of milk commonly consumed in Israel have been investigated. The concentration of iodine, bromine and chlorine were found to be 0.18–0.30 g/ml, 2.02–2.85 g/ml and 0.65 mg/ml, respectively. The method is fast, selective, accurate and highly sensitive.     

Spectrophotometric determination of osmium with ethylisobutrazine hydrochloride

The sheath flow cuvette is used for refractive index determinations of neat solutions within picoliter probe volumes. In this detector, a sample stream is injected as a narrow stream into the center of a flowing sheath stream under laminar flow conditions. The sample stream retains its identity as a thin cylinder through the center of a 250-m square flow chamber. The propagation properties of a focused helium-neon laser are perturbed by interaction with the sample stream. Detection limits of RI=3×10^–6 were obtained within a 20 micrometer radius sample stream, corresponding to about a 400 picoliter probe volume. For analyte with refractive index significantly different than the solvent, detection limits are possible which correspond to a few picograms of analyte within the probe volume.     

Titrimetric determinations of cryptands and cryptates

Summary Using bromocresol green as a visual endpoint indicator solutions of the cryptands [2.2.1] and [2.2.2] can be determined by titration with HCl in the concentration range of 10^–1–10^–3 M with relative standard deviations of 0.2–0.4 %. If both cryptand and cryptate are present in one solution, then the sum of them can be determined titrimetrically in the same way. It is also possible to determine the contents of [2.2.1] and [2.2.2] by using a calcium or barium standard solution and the unknown cryptand solution as a titrant. By evaluation of the pH-curve thus obtained, the endpoint of the titration can be determined. In the concentration range of 10^–1–10^–2 M relative standard deviations of about 0.5% are obtained. [2.2.1] cryptand solutions are determined by using the standard addition technique of Gran with a calcium chloride solution. An ion-selective electrode is used as a probe for calcium ions. If this method is applied, the relative standard deviation in the range of 10^–2–10^–4 M solutions is approximately 3%. With this technique cryptand can be analysed even when cryptate is present in the solution.We wish to thank the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie for their financial support.     

Determination of Platinum-Group Elements and Gold in Silicates by Gamma Activation Autoradiography and Instrumental Gamma Activation Analysis

The potential of the gamma activation determination of platinum-group elements and gold both by instrumental gamma activation analysis (bulk analysis) and by monitoring their distribution using autoradiography (local analysis) is studied. It is shown that platinum-group elements and gold can be determined by direct gamma-ray spectrometry in silicate samples with a detection limit of 10^–3–10^–5%. In contact gamma activation autoradiography, the detection limit for these elements is about 10 ng with a spatial resolution of 10–20 m.     

EPMA analysis of float glass surfaces

This work concentrates on the setting-up of conditions for the quantitative analysis of the composition profiles of major and minor components of float glass surfaces with an electron probe micro-analyser. Since surfaces are modified for depths of 10–50 m, they have been studied both in polished cross-section and perpendicularly to the electron beam by varying its energy to investigate the near-surface region (0–3m). The results demonstrate that combined use of the two methods supplies complete and continuous information on the quantitative distribution from large depths to the first layers of the float surfaces. The experimental conditions, sample preparation, in-depth and lateral resolutions, precision and accuracy of the methods are also investigated.     

Indirect determination of arsenic by flotation spectrophotometry

An indirect method of arsenic determination in the submicrogram range via the determination of molybdenum is presented here. High sensitivity is achieved by combination of the chemical amplification during formation of dodecamolybdoarsenic acid (arsenic: molybdenum ratio 1 12) with multiplication due to the formation of ion-association complexes during flotation-spectrophotometric molybdenum determination with crystal violet (molar ratio 1 2). Thus, the amplification factor relating to arsenic is 24.Dodecamolybdoarsenic acid is formed in a weakly acidic medium and is quantitatively extracted byn-butanol. Back extraction of the heteropoly acid to the aqueous phase and its simultaneous destruction provides the basis for the reaction of released molybdate ions with thiocyanate ions. The molybdenum-thiocyanate complex forms a sparingly soluble ion-association complex with crystal violet which can be floated with toluene on the phase boundary (film flotation). After separation of the aqueous phase the floated molybdenum compound is dissolved in acetone and the resulting free crystal violet ions are subjected to photometric determination at 590 nm as equivalent of the concentration of arsenic. The molar absorptivity of crystal violet is 3.2 · 10⁵1 · mol^–1 · cm^–1. Beer's law is obeyed in a concentration range from 0.01 to 1 g Mo · ml^–1 (0.001–0.1 g As · ml^–1). The resulting detection limit for arsenic is 1 ng · ml^–1.     

Electrosurface and Ion-Selective Properties of Track-Etched Nanofilters: The Effect of Polyvalent Metal Adsorption

The effect of polyvalent metal adsorption on the performance and ion selectivity of poly(ethylene terephthalate) track-etched membranes with pores of 10 nm in diameter was studied. Membrane samples were prepared from the track-etched membranes with pores of 20 nm in diameter by thermal shrinkage. It was shown that an effective pore diameter decreases and selectivity of track-etched membranes increases upon filtration of Al(NO₃)₃ and Cr(NO₃)₃ solutions. The results obtained are explained by ion adsorption leading to the formation of complexes between polyvalent metals and carboxyl groups on the pore surface that is confirmed by IR spectroscopy data. The study of electrosurface properties of modified membranes and the dependence of ion selectivity of track-etched membranes on the concentration of Al³⁺ ions in 10^–2 M KCl solution indicates the decrease of membrane negative surface charge resulted from Al³⁺ adsorption and membrane charge reversal at Al³⁺ concentration in a solution higher than 10^–6 M. The dependences of the ion selectivity on pH and Al³⁺ concentration C _Al in a solution are similar. At pH < 3 and C _Al > 10^–6 M, the _1–2 > _1–1 > _2–1 ion selectivity series characteristic of the initial negatively charged membranes for the 1–1, 1–2, and 2–1 electrolyte solutions is reversed into the _2–1 > _1–1 > _1–2 series characteristic of positively charged membranes.     

Multielement XRF Semimicroanalysis of Pb(Zr,Ti)O3 Type Ferroelectric Ceramic Materials Doped with Pb(Nb,Mn)O3 and Bi2O3 by the Thin Layer Method

A method of wavelength-dispersive XRF analysis of Pb(Zr,Ti)O₃ type ferroelectric ceramics doped with Pb(Nb,Mn)O₃ and Bi₂O₃ is presented. The major elements Pb, Zr, Ti and minor elements Nb, Mn, Bi were determined. Matrix effects were minimized by using the thin layer method. Standards of the same chemical composition but varied masses were prepared to simplify calibration. To minimize errors resulting from inhomogeneity of a mass per unit area, the internal standard was used. Preparation of the sample consisted in digesting 25mg of the materials (with nickel as the internal standard) in sulfuric acid, evaporating to dryness and digesting in nitric acid and hydrogen peroxide, filling up to 25mL, and dropping 0.5mL of the solution onto a substrate. Standard samples were prepared by dropping different amounts of the multielement solution onto the substrate. The residual standard deviation for the reference sample of mass from 0.25mg to 0.7mg was within the range of 0.001–0.009mg (correlation coefficient 0.998–0.999) for major elements and within the range of 0.00003–0.0009mg (correlation coefficient 0.989–0.993) for minor elements. The detection limits for 0.5mg samples were within the range of 0.015%–0.35% for manganese and zirconium, respectively.     

Third-Order Nonlinear Optical Response of a New PVA Composite with PbS Nanocrystals

High third-order nonlinear optical susceptibility (⁽³⁾(;, –,)=3.4·10 ^–16 m²/V²) in the visible spectral range may be achieved in PVA composites with narrow-gap PbS semiconductor nanocrystals with a large exciton diameter.     

Depth profile studies of ZrTiN coatings by laser ablation inductively coupled plasma mass spectrometry

The feasibility of depth profiling was studied by using a 193-nm ArF* excimer laser ablation system (GeoLas, MicroLas, Goettingen, Germany) with a lens array-based beam homogenizer in combination with an ICP-QMS Agilent 7500. Two ablation cells (20 and 1.5 cm³) were compared at the laser repetition rate of 1 Hz, laser beam energy of 135 mJ and the carrier gas flow rate 1.5 L min^–1 He + 0.78 L min^–1 Ar. The ablation cell dimensions are important parameters for signal tailing; however, very small cell volumes (e.g. 1.5 cm³) may cause memory effects, which can be probably explained by dominant inertial losses of aerosol on cell walls with its delayed mobilization. The 20-cm³ ablation cell seems to be appropriate for depth profiling by continuous single-hole drilling. The study of the influence of the pit diameter magnitude on the waning and emerging signals under small crater depth/diameter aspect ratios, which range between 0.75 and 0.0375 for the 3-m-thick coatings and pit diameters 4–80 m, revealed that the steady-state signals of pure coating and pure substrate (out of interface) were obtained at crater diameters between 20 and 40 m. Depth resolution defined by means of slopes of tangents in the layer interface region depend on the pit diameter and has an optimum value between 20 and 40 m and gives 0.6 m for the 20-m pit. In-depth variation of concentration of coating constituent (Ti) was proved to be almost identical with two different laser/ICP systems.Viktor Kanický performed this work while on leave at ETH Zurich     

Nonempirical calculations of the potential-energy fields of the nucleophilic addition of H− and F− to acetylene and methylacetylene molecules

By using the basis 3–21 + G, the minimum-energy routes for the nucleophilic addition to the F^– ion to methylacetylene have been calculated within the framework of the Hartree-Fock-Roothaan method according to and against the Markovnikov rule with the formation of the 1-fluoropropenyl and 2-fluoropropenyl anions. The results have been compared with data from previous calculations of the nucleophilic addition of H^– and F^– to acetylene with the formation of vinyl and fluorovinyl anions, as well as of the nucleophilic addition of H^– to methylacetylene according to and against the Markovnikov rule with the formation of the 1-propenyl and 2-propenyl anions. It has been established that the reaction with H^– is exothermic, while the reaction with F^– is endothermic. The activation energies of the reactions with F^– are lower than the activation energies of the corresponding reactions with H^–. It is shown that the reactions with H^– have a relatively early transition state, while the reactions with F^– are characterized by a later transition state.Translated from Teoreticheskaya i Éxperimental'naya Khimiya, Vol. 28, No. 1, pp. 5–11, January–February, 1992.     

Analysis of the anisotropy of the rotation of spin probes according to saturation-transfer ESR spectra

Expressions for calculating the form of the second-harmonic ESR absorption spectra for the cases of discontinuous isotropic and uniaxial rotation of a spin probe around the principal axes of the magnetic tensors have been obtained. In the case of a macroscopically unoriented system, the form of the spectrum in the second harmonic shows little sensitivity to rotational anisotropy, which can be established on the basis of the spectroscopic parameters L/L, C/C, and H/H only in a restricted number of ceases. The relations between the correlation times determined from these parameters in the model of isotropic rotation and their relationship to the true values of in the case of uniaxial rotation of the probe have been analyzed. With respect to oriented sytems, the calculated spectra have been compared with the experimental spectra for a cholestane spin probe in phospholipid multilayers. Consideration of the inhomogeneous broadening of the line is necessary in order to achieve satisfactory agreement.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 22, No. 3, pp. 331–336, May–June, 1986.     

Isolation of a urease from watermelon seeds and the study of its properties

The enzyme urease has been isolated from the seeds of the watermelon of the Ogonek variety and has been characterized. The molecular weight of a rechromatographed sample of the enzyme has been determined as 480,000. The pH dependence of the activity of the urease and the kinetic parameters of the enzyme have been studied.All-Union Scientific-Research Institute of the Chemistry and Technology of Drugs, Khar'kov. Vitaminy Scientific-Production Amalgamation, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 624–628, September–October, 1983.     

Extraction and spectrophotometric determination of uranium(VI) withN-phenylcinnamohydroxamic acid

Uranium(VI) reacts withN-phenylcinnamohydroxamic acid to form an orange-yellow complex in the pH range 5.5–8.5. The orange-yellow complex, having the composition of 12 (metal:ligand), is quantitatively extractable into ethyl acetate. The spectrum of the complex exhibits a maximum absorption at 400 nm with a molar absorptivity of 6500 M^–1·cm^–1. The coloured system obeys Beer's law in the concentration range 2–40g·ml^–1 of uranium(VI). The photometric sensitivity of the colour reaction is 0.037 g·cm^–2 of uranium(VI). Most of the common ions do not interfere and the method has been found to be simple, precise, and free from the rigid control of experimental conditions. The method has been applied to the determination of uranium in synthetic matrices and potable water.     

The determination of tin in explosive materials by thermal neutron activation analysis

A method, based on the measurement of the -photopeak at 332 keV arising from a¹²⁴Sn(n, )^125mSn reaction, has been developed for the rapid measurement of Sn at concentrations of 20 g g^–1, present as the cross-linking agent, in explosive charges. The method is comparative, and has a limit of detection of 0.6 g g^–1 and a precision of 5% RSD. The method requires no sample preparation and is economical in effort.     

Determination of dextromethorphan and dextrorphan in urine by capillary zone electrophoresis: Application to the determination of debrisoquin-oxidation metabolic phenotype

Summary A capillary zone electrophoresis method has been developed for the determination of dextromethorphan and its metabolite, dextrorphan, in urine. A linear relationship was observed between the peak area and the concentration of both dextromethorphan and dextrorphan within the range of 490 ng mL^–1 to 500 g mL^–1 with a correlation coefficient of greater than 0.9999. The limit of detection was 80 ng mL^–1 for both compounds. The inter-day coefficients of variation for the concentrations of 2.5 g mL^–1 and 50 g mL^–1 were 6.2% and 4.1% for dextromethorphan, and 5.6% and 2.8% for dextrorphan (n=15). The method could be applied directly to the determination of dextromethorphan and dextrorphan in human urine without any sample pretreatment for the elimination of interfering compounds as is required in published highperformance liquid chromatography and gas chromatography methods. Using dextromethorphan as a probe of the debrisoquin-oxidation metabolic phenotype, the 44 healthy volunteers were phenotyped after oral administration of a 15 mg dose using both this capillary electrophoresis method and a high-performance liquid chromatography assay from the literature. Good agreement was found between the two methods.     

Inexpensive precision ph microcell for volumes of 50–200μl with replaceable glass membrane and diaphragm

Summary The development of an inexpensive microcell for pH measurement is described. The cell can be used for sample volumes of 50–200l. Its main advantages are the easy replacement of both the diaphragm and the pH glass membrane at low cost. The reproducibility with a conventional pH meter is ±0.01 pH unit, but can be improved to ±0.004 pH unit by differential measurement.

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Eine preisgünstige pH-Mikromezelle

Zusammenfassung Die Herstellung einer preisgünstigen pH-Mikromeßzelle wurde beschrieben. Sie kann für Probevolumina von 50–200l eingesetzt werden. Hauptvorteile sind das preisgünstige und einfache Auswechseln von Verschleißteilen, wie pH-Membran und Diaphragma. Thermostatierung der Probe und Mikrotitrationen in der Meßzelle sind möglich. Mit Hilfe einer differentiellen Meßmethode können pH-Messungen mit einer Reproduzierbarkeit besser als ±0,004 pH-Einheiten erzielt werden. Wird ein konventionelles pH-Meter verwendet, so liegt die Reproduzierbarkeit des Meßwertes bei ±0,01 pH.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.