Showing papers in "Mikrochimica Acta in 2000"

High Resolution Surface Analysis by TOF-SIMS

Abstract: Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has developed into a mature technique meanwhile applied in many industrial laboratories for elemental and molecular surface characterization. Not only spectroscopic information but also information on the lateral distribution of surface species can be obtained (TOF-SIMS Imaging). The lateral resolution for the detection of elements is well beyond 100 nm using modern liquid metal ion guns. For molecular species, however, the achievable lateral resolution not only depends on the performance of the instruments but also on sample parameters like obtainable secondary ion yield and the area disturbed on the sample by impact of a single primary ion. Whereas for larger molecules the achievable resolution can be several micron, imaging with sub-μm resolution is possible if one monitors characteristic fragment ions.

Light Element Analysis of Individual Microparticles Using Thin-Window EPMA

Abstract: The determination of the concentration of light elements, such as carbon, nitrogen and oxygen, in e.g. atmospheric aerosol particles is important to study the chemical behaviour of atmospheric pollution. The knowledge of low-Z element concentrations gives us information on the speciation of nutrients (species having nutritional value for plants) and toxic heavy metals in the particles. The capability of the conventional energy-dispersive EPMA is strongly limited for the analysis of low-Z elements, mainly because the Be window in the EDX detector hinders the detection of characteristic X-rays of light elements such as C, N, O and Na. WDS is suitable for analysis of light elements, but the measurement of beam sensitive microparticles requires the minimisation of the beam current and the measurement time. A semi-quantitative analytical method based on EPMA using an ultra-thin window EDX detector was developed. It was found that the matrix and geometric effects that are important for low-energy X-rays can be reliably evaluated by Monte Carlo calculations. Therefore, the quantification part of the method contains reverse Monte Carlo calculation done by iterative simulations. The method was standardised and tested by measurements on single particles with known chemical compositions. Beam-sensitive particles such as ammonium-sulphate and ammonium-nitrate were analysed using a liquid nitrogen cooled sample stage. The shape and size of the particles, which are important for the simulations, were determined using a high-magnification secondary electron image. Individual marine aerosol particles collected over the North Sea by a nine-stage Berner cascade impactor were analysed using this new method. Preliminary results on five samples and 4500 particles show that the method can be used to study the modification of sea-salt particles in the troposphere.

Deposition and characterization of metastable Cu3N layers for applications in optical data storage

Abstract: Cu3N films for optical data storage were deposited on Si(100) wafers and 0.6 mm thick polycarbonate DVD base material discs at a temperature of 50 °C by reactive magnetron sputtering. A copper target was sputtered in rf mode in a nitrogen plasma. For basic investigations concerning the composition and structure of Cu3N, Si wafers were used as substrate material. To study the suitability of Cu3N as an optical data storage medium under technical conditions, Cu3N/Al bilayers were deposited on polycarbonate discs. The composition and structure of the films were investigated by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD).

Structural Analysis of Electroplated Amorphous-Nanocrystalline Ni-W

Abstract: Ductile nickel-tungsten (Ni-W) alloys containing about 20–21 at.%W were electroplated onto copper substrates. The development of the amorphous/nanocrystalline microstructure towards a complete crystallization by isochronal heat treatments in vacuum was monitored by different methods. For medium annealing temperatures a solid-solution of W in the fcc-Ni lattice was achieved resulting in an increased hardness. For temperatures of 600 °C and upward recrystallization started and thermodynamically stable intermetallic compounds like Ni4W and NiW were formed. A third phase, containing more than 80 at.%W was also detected but could not be identified so far. Only by combination of different methods and especially by use of analytical TEM structural analysis and phase identification in these amorphous-nanocrystalline Ni-W alloys were successful.

Preparation of Cr2O3-Al2O3 solid solutions by reactive magnetron sputtering

Abstract: (Al,Cr)2O3 layers were deposited on cemented carbide insert tips at a substrate temperature of 500 °C by means of reactive magnetron sputtering. An Al target was sputtered in RF mode and a Cr target in DC mode simultaneously in an oxygen/argon plasma. The influence of the Al and Cr sputter power and of the oxygen partial pressure on composition and structure of the (Al,Cr)2O3 layers as well as on the binding states of their components were investigated. Special attention was paid to the interpretation of the O ls and O-KLL fine structure and peak shifts. For the binary phases γ-Al2O3 and Cr2O3, a good agreement with literature values was observed in each case. In case of the ternary phases a continuous shift of the energetic position of the O1s peak, the O-KL23L23 transition and the modified Auger parameter α ′ of oxygen between the two binary phases γ-Al2O3 and Cr2O3 could be detected, indicating a wide range of solid solubility between Al2O3 and Cr2O3. As revealed by grazing incidence X-ray diffraction, the crystallinity of the ternary phases is less pronounced as compared to the binaries and increases with increasing oxygen flow rate.

Energy Dispersive X-Ray Fluorescence Analysis and X-Ray Microanalysis of Medieval Silver Coins

Abstract: Austrian medieval silver/copper coins were investigated at their surfaces by energy dispersive X-ray fluorescence analysis (EDXRF) and at the cross-sections by X-ray microanalysis in the scanning electron microscope (SEM/EDX) in order to estimate the error occurring when corroded objects of art and archaeology are analyzed on the surface by non-destructive methods. Additionally, Ag/Cu-standards were treated in diluted sulphuric acid and the depletion of copper on the surface was measured by EDXRF. By calculating the ratio of the Ag-K/Ag-L intensity the process of blanching could be studied.

Mathematical Modelling of 3D Electron-Photon Transport in Microbeam Analysis

Abstract: In electron microbeam techniques, the particle beam is focused on the material to be analysed. When the electron beam enters the target, the electrons give rise to ionization processes producing secondary electrons and photons, the latter being used to characterize the material. As a consequence, a detailed description of the photon diffusion requires the solution of two coupled equations describing respectively electron and photon diffusion. The approach considering two transport equations, even if formally correct, is almost unaffordable because of the high mathematical complexity of the electron transport equation. In this article, an alternative approach is suggested which is based on the use of an approximate solution for the electron transport using the Fokker-Planck equation [5]. The resulting electron distribution, computed analytically as a solution of the above equation, is very similar to the ionization distribution and is used as the source term in the Boltzmann transport equation describing the photon diffusion in the material. The 3D photon transport equation for unpolarised photons with this source term is solved to obtain a detailed description of the photon fluorescence from a homogeneous slab.

Monte Carlo Simulation of Secondary Fluorescence in Small Particles and at Phase Boundaries

Abstract: Results from Monte Carlo simulations and experimental measurements of X-ray spectra of small Cu-particles in Fe-containing slags are presented. The analyzed Cu-particles remain suspended in flash smelting and Cu converter slags, which contain Fe up to about 33 wt%, and have diameters ranging from 5 up to 100 μm. Conventional standardless analysis of measured X-ray spectra gives an apparent Fe content of ∼ 1–5 wt%, depending on the particle diameter, which cannot be explained in terms of the thermodynamic solubility of Fe in solid Cu. In order to study the influence of the Fe-containing slag to the apparent Fe content in the particles, X-ray spectra have been computed by means of Monte Carlo simulation of the coupled electron and photon transport. The simulation code used is largely based on the general-purpose simulation package PENELOPE and it incorporates ionization cross sections evaluated from an optical-data model and bremsstrahlung cross sections that reproduce radiative stopping power derived from partial wave calculations. Simulated Fe k-ratios, for different experimental situations, have been found to be in satisfactory agreement with measurements. The apparent Fe content is explained in terms of secondary fluorescence of Fe Kα by Cu Kα X-rays.

Uncertainties in Determination of pH

Abstract: A statistical analysis of multi-point calibration procedure for practical measurement of pH under laboratory conditions is given. The procedure is shown to provide the necessary elements for simple assignment of an uncertainty to a pH measurement – an essential element of quality control. Performance of ordinary least squares regression for prediction of confidence limits is compared to orthogonal regression, inverse regression and Monte Carlo simulations. In case of pH measurement by multi-point calibration procedure, methods considering uncertainties in both axes are found to be statistically more satisfactory than ordinary least squares regression. By analysis of 50 pH calibration data, randomly selected from 250 5-point glass electrode calibrations, it is found that the practical differences, however, are of minor importance. The significance of uncertainty in pH is demonstrated for an example from metal ion speciation in aqueous solution.

High-Spatial-Resolution Low-Energy Electron Beam X-Ray Microanalysis

Abstract: Performing X-ray microanalysis at beam energies lower than those conventionally used (< 10 keV) is known to significantly improve the spatial resolution for compositional analysis. However, the reduction in the beam energy which reduces the X-ray interaction diameter also introduces analytical difficulties and constraints which can diminish the overall analytical performance. This paper critically assesses the capabilities and limitations of performing low beam energy, high spatial resolution X-ray microanalysis. The actual improvement in the spatial resolution and the reduction in the X-ray yield are explored as the beam energy is reduced. The consequences for spectral interpretation, quantitative analysis and imaging due to the lower X-ray yield and the increased occurrence of X-ray line overlaps are discussed in the context of currently available instrumentation.

Spectrophotometric Determination of Some Phenolic Antibiotics in Dosage Forms

Abstract: A simple and sensitive spectrophotometric method is described for the determination of some phenolic antibiotics namely: cefadroxil, amoxicillin and vancomycin. The method is based on the measurement of the orange yellow species produced when the drugs are coupled with diazotized benzocaine in triethylamine medium. The method is applicable over the range of 0.8–12 μg/ml for cefadroxil, 2–16 μg/ml for amoxicillin and 2–18 μg/ml for vancomycin. The formed compounds absorb at 455 nm for both cefadroxil and amoxicillin and at 442 nm for vancomycin. The proposed method has detection limits of 0.018 μg for cefadroxil, 0.0034 μg for amoxicillin and 0.0156 μg for vancomycin. The stoichiometric ratio for the studied compounds was found to be 1:1 and a proposal of the reaction pathway was made. The proposed method was applied for the analysis of the cited drugs in their pharmaceutical preparations. The results are in good agreement with those obtained by the official methods.

Distribution of Ion-Implanted Nitrogen in Iron Alloys Investigated by AES

Abstract: The depth distribution and the lateral distribution of nitrogen after implantation by means of plasma immersion ion implantation (PIII) in ferritic alloys with 03 wt-% Al and 36 wt-% Cr has been studied by scanning Auger electron spectrometry (AES) To get information about the chemical state of nitrogen and to improve the detection limit methods of data analysis (factor analysis, LLS) have been applied to depth and line profiles, respectively Thereby the detection limit for nitrogen was reduced from 6% to 1% The nitrogen distribution is laterally homogeneous in the near surface region only Depth profiles obtained at several points within the sputter crater showed that the in-depth distribution of nitrogen varies markedly between different points on the sample and from sample to sample The nitrogen concentration in the implantation maximum corresponds to Fe2N1−x (x ≈ 004 018) A remarkable feature are grains having a 10 μm wide seam rich in N and a nearly nitrogen-free grain’s interior The N/Fe ratio determined from line profiles show that the outer layer of the grains has almost the exact composition Fe4N and the transition to the nearly nitrogen-free grain's interior (cN ≤ 1%) occurs within 1 4 μm The same shape of the N(KLL) peak was found in depth profiles and line scans, respectively, and it corresponds to gasnitrided samples γ ′–Fe4N and ɛ–Fe2N1−x

Determination of Cd, Co, Cr, Cu, Fe, Ni and Pb in Milk, Cheese and Chocolate

Abstract: Combined analytical procedures consisting of wet digestion step followed by instrumental determination - differential pulse cathodic stripping voltammetry (DPCSV) or electrothermal atomic absorption spectrometry (ETAAS) - as well as a direct analysis method - slurry sampling ETAAS - for the determination of Cd, Co, Cr, Cu, Fe, Ni and Pb in milk, cheese and chocolate are described and compared. Wet digestion using a mixture of HNO3-HClO4-H2O2 is proposed for complete matrix decomposition prior to trace analyte determination by DPCSV or ETAAS. A mixture of HNO3-H2O2 is used for slurry preparation. Optimal instrumental parameters for trace analyte measurements are presented. The reliability of the procedures has been verified by analyzing standard reference materials. Results obtained are in good agreement with the certified values and the relative standard deviations (for these results) are in the range 5-10 % for wet digestion DPCSV or ETAAS and 3-9 % for slurry sampling ETAAS in the range of 2mg g ˇ1 (Cd) to 12mg g ˇ1 Fast, sensitive, accurate and precise analytical meth- ods are required for daily quality control of milk and milk products. The importance of elements such as Cu, Cr and Fe is related to lipid oxidation involved in storage and processing (1). Serious attention is paid to the toxicological effects of other heavy metals such as Cd, Co, Ni and Pb in view of the importance of milk and its by-products in the diet of infants and children (2-4).

Characterisation of Radioactive Particles by SIMS

Abstract: Secondary ion mass spectrometry (SIMS) was optimised for characterisation of uranium- and plutonium-containing particles in soils, swipes and forensic samples. This was done by analysing in-house produced spherical UO2-particles. Screening techniques as α-autoradiography together with SIMS analysis were employed to detect UO2-particles in a soil sample from Chernobyl.

Differential-pulse polarographic determination of some N-substituted phenothiazine derivatives in dosage forms and urine through treatment with nitrous acid

Abstract: A highly sensitive differential-pulse (DPP) polarographic method is described for the determination of three N-substituted phenothiazine derivatives, chlorpromazine (CZ), promazine (PZ) and promethazine (PMZ). The method involves the use of nitrous acid as an oxidant. Polarographically-active sulphoxides with diffusion-current constants (Id) of 2.53, 3.05 and 3.37 were obtained for CZ, PZ and PMZ, respectively. The polarographic waves were characterized as being diffusion-controlled, irreversible and partly affected by adsorption phenomena. All parameters affecting the oxidation process and polarographic behaviour were optimized and incorporated into the procedure. The limiting current-concentration plots in the DPP mode were rectilinear over the range: 0.006–0.1 mM, 0.005–0.08 mM and 0.008–0.1 mM for CZ, PZ and PMZ, respectively, with minimum detectability (S/N=3) of 3 × 10−7 M for CZ and PZ, and 4 × 10−7 M for PMZ, respectively. The kinetic parameters of the electrode reaction, including rate constant, free energy of activation ΔG and effect of temperature on both parameters were studied. The proposed method was successfully applied to the determination of phenothiazines in dosage forms; the results obtained were in agreement with those given with the official methods. The method was further applied to the determination of promazine in spiked human urine. The percentage recovery was 96.86 ± 0.30. The advantages of the proposed method over other reported methods were discussed. A proposal of the electrode reaction was made.

SEM-EDS and XPS Studies of the High Temperature Oxidation Behaviour of Inconel 718

Abstract: The oxidation in air under isothermal conditions of Inconel 718 has been investigated at 900 °C. We have studied the firsts stages of the high temperature oxidation mechanism. The oxidised samples were examined using a number of surface analytical techniques including XPS and SEM-EDS. The results have shown that minor alloying elements strongly influence the oxidation behaviour of the alloy:

Investigations of the Growth of Self-Assembled Octadecylsiloxane Monolayers with Atomic Force Microscopy

Abstract: Self-assembled monolayers of octadecylsiloxane were prepared and characterized by atomic force microscopy and ellipsometry. Parameters, like the residual water concentration of the solvent and the solution age, that affect both the surface coverage and the order of the film were investigated. Besides ex-situ measurements, also in-situ atomic force microscopy was used to characterize the growth and the kinetics of the adsorption process. Furthermore, self-assembly of organic films was used as a model system for studying the influence of the measurement process on in-situ experiments in the AFM liquid cell.

Analysis of Slightly Rough Thin Films by Optical Methods and AFM

Abstract: In this paper the analysis of a family of rough silicon single crystal surfaces covered with native oxide layers is performed using a combined optical method based on a multisample treatment of the experimental data obtained using variable angle of spectroscopic ellipsometry and near normal spectroscopic reflectometry. Within this analysis the values of the thicknesses of the native oxide layers are determined together with the values of statistical parameters of roughness, i.e. with the rms values of the heights and the values of the autocorrelation lengths, for all the samples studied. For interpreting experimental data the perturbation Rayleigh–Rice theory and scalar diffraction theory are employed. By means of the results of the analysis achieved using both the theories limitations of the validity of these theories is discussed. The correctness of the values of the statistical parameters determined using the optical method is verified using AFM measurements.

Microanalysis of Glass Containing Alkali Ions

Abstract: The common problems connected with alkali ion migration during EPMA were studied on glasses containing nearly all possible alkali ions (Na, K, Rb, Cs). Binary silica glasses were prepared by melting from a very pure batch in Pt crucible. The glasses were carefully polished using alcohol to prevent surface corrosion by water and they were stored in vacuum. The specimens were coated with carbon layers approximately 30-nm thick and exposed to a 50- keV electron beam of 100 μm diameter. It was found that all alkali ions migrate under the electron beam, but the rate of the migration depends on the current density. The decay curves (characteristic X-ray intensity versus time) are similar in shape in all cases. The decay curve shows two transport regimes, the first being linear-like, the second being the exponential-like. The first transport regime busts into the rapid alkali migration after a time known as the incubation period. The period is in general longer for the larger-alkali ions size. It was found that even large rubidium and caesium ions migrate inside the glass with the same mechanism as sodium and potassium ions. While for K, Rb, and Cs ions the incubation periods were observed under the suitable experimental conditions, binary glass containing Na exhibits no observable incubation period. Except for the binary Na2O + SiO2 glass, the suitable experimental conditions for reliable quantitative EPMA can be found.

Weathering phenomena on naturally weathered potash-lime-silica-glass with medieval composition studied by secondary electron microscopy and energy dispersive microanalysis

Abstract: Samples of two model glasses with chemical compositions similar to medieval stained glass were exposed to the natural environment at 23 test sites for a period of 6 months, 1 and 2 years within an exposure programme of the “Working Group of Effects on Materials, Including Historic and Cultural Monuments” of the Economic Commission for Europe of the United Nations. During the exposure the environmental data were measured and collected at each test site in order to enable a correlation between the pollutant load in the ambient atmosphere and the weathering phenomena of the glass samples. After the exposure, which was performed in a sheltered as well as in an unsheltered mode for gaining information about the influence of dry and wet deposition of air pollutants, the glass samples were analysed in the scanning electron microscope with energy dispersive microanalysis (SEM/EDX). Model glass M1 – a potassium rich glass – was covered to a high amount with crystalline weathering products (above all syngenite), whereas glass M3 – a glass with a higher Ca and Si content – turned out to be more stable against weathering. This glass was covered with gypsum and arcanite crystals but in total to a less extent than glass M1.

Environmetrical treatment of water quality survey data from Yantra River, Bulgaria

Abstract: The environmetrical analysis carried out has indicated that the short-term water quality survey may give a very important information on the latent factors influencing the water quality of Yantra river basin. The principal components analysis carried out reveals that at least four principal components are necessary for multivariate statistical modeling of the water quality – combination of natural and anthropogenic influences (“mixed” factor) reflecting parameters such as water hardness, marine influence, organic pollution; typical anthropogenic influences (“anthropogenic” factor) explaining the metal contamination of the river water; everyday wastes, usually N-containing pollutants such as nitrates, nitrites or ammonia, form the “N-containing wastes” factor and a “temperature” factor formed by typical physical parameters such as water and air temperature.

X-Ray Microanalysis in the Environmental SEM: A Challenge or a Contradiction?

Abstract: In this paper, the application of X-ray energy dispersive spectroscopy in the environmental scanning electron microscope is reviewed. Various techniques that have been used to remove the effects of the beam spreading in the gaseous environment are discussed, specifically the pressure variation techniques and the beam-stop method. The results of the application of modified versions, developed at the University of Michigan, are also presented. It is shown that quantitative analysis in the environmental SEM, operating at 30 kV, is possible at short working distances (6 mm to 7.2 mm, gas path length 1.2 mm to 2.2 mm) in the 70 to 350 Pa range.

Localised Electrochemical Desorption of Gold Alkanethiolate Monolayers by Means of Scanning Electrochemical Microscopy (SECM)

Abstract: Lateral structures of bare gold within self-assembled monolayers (SAMs) of gold alkanethiolates were created by electrochemical desorption in the direct mode of the scanning electrochemical microscope (SECM). The ultramicroelectrode (UME) of the SECM was positioned 10-20 μm above the surface and used as the auxiliary electrode in a three electrode cell with the SAM-coated Au electrode as working electrode. The microscopic auxiliary electrode causes an inhomogeneous electric field above the macroscopic gold electrode and limits the total current. As a consequence only thiols located directly beneath the UME are affected by the desorption procedure. Sample regions from which the SAM had been removed were imaged in the SECM feedback mode or, after galvanic Cu deposition, by scanning electron microscopy (SEM) and optical microscopy (after sulfidisation of Cu). The influence of hydrocarbon chain length, protection of the SAM by an additional layer of n-octanol and the use of alternating current were investigated in order to decrease the size of the bare surface areas and to enhance their edge definition. In particular the use of alternating current led to feature sizes of 1.2 times the UME diameter which represents an advance with regard to 2-3 UME diameters reported earlier.

Two-Phase Aqueous Extraction of Chromium and its Application to Speciation Analysis of Chromium in Plasma

Abstract: This work proposes a new extraction method for chromium based on the two-phase aqueous system isopropyl alcohol-ammonium sulfate-ammonium thiocyanate (i-PrOH-(NH4)2SO4-NH4SCN), and the related experimental conditions are optimized. The results show that chromium (III) can be quantitatively extracted under the selected conditions: 4 mL of i-PrOH, 200 μL of 2 mol/L sulfuric acid, 1 mL of 4 mol/L NH4SCN and 3 mL of saturated (NH4)2SO4 solution (Vtotal=10 mL). Application of the proposed method to speciation analysis of plasma chromium was also investigated and satisfactory results were obtained.

Analysis of Alloy Nanoparticles

Abstract: Quantitative analysis of particles less than 10 nm in diameter requires a focused electron beam to isolate individual particles for X-ray emission spectrometry. Effects such as phase separation among particles and surface segregation within particles can only be determined by this technique. This analysis can be made quantitative with minimal use of the usual correction factors provided the small particles are supported on ceramic materials about the same thickness as the particles themselves. Two alloy nanoparticle systems are examined here: Pt-Rh and Pt-Re. In each case the catalytic properties resulting from various processing procedures have been correlated with the microstructure within and among individual particles.

Quantitative AES-Mapping and Depth Profiling

Abstract: Some aspects of the composition depth profiling of material below a solid surface are reviewed. The methods using ion bombardment and detection of secondary ions, Auger or photo-electrons and the interpretation of results using models for the processes involved are briefly discussed. Attention is then turned to quantitative Auger microscopy because this methodology requires the use of simultaneous detection of scattered radiation and electrons, via EDX, AES, backscattered and loss electrons, to assist with interpretation of the surface composition of inhomogeneous materials. It is proposed that a combination of Monte Carlo simulation and the measurement of the angular dependence of these signals may offer a means of non-destructive measurement of composition depth profiles.

Investigation of chemically treated basalt and glass fibres

Abstract: Basalt and E-glass fibres were treated in 0.1N and 2N NaOH up to 3 hours to evaluate their chemical durability in alkaline environments. For the fibres tensile strength and mass were determined before and after alkaline treatment. The morphology of fibre surfaces was investigated using SEM. Changes of chemical (surface) composition were characterised by EDX and infrared spectroscopy. The chemical durability studies carried out on basalt and E-glass fibres indicate a better alkaline resistance of basalt. In particular a higher tensile strength was determined and changes induced by alkaline attack are less pronounced in the infrared spectra of basalt. A higher mass loss of basalt is most likely due to the smaller diameter of basalt fibres.

Quantitative Trace Analysis by Wavelength-Dispersive EPMA

Abstract: “Trace” elements may be defined as elements whose concentrations are of a similar order to the detection limit. In WD analysis the detection limit is a function of the ‘figure of merit’ P2/B, where P is the pure-element peak intensity and B the background intensity. With normal analysis conditions detection limits of ∼100 ppm are typical, but substantial improvements can be achieved by using higher values of accelerating voltage and beam current. Long counting times are also advantageous, but should preferably be divided into relatively short alternating peak and background measurements to minimise the effect of instrumental drift. Using separate routines for trace and major element analysis is desirable owing to their different requirements. As the statistically defined detection limit is reduced, errors due to background nonlinearity and interferences (overlaps) from other elemental peaks become more probable. Spectrum simulation is useful for optimising background offsets and choice of crystal to minimise interferences, and estimating interference corrections when these are necessary. ‘Blank’ standards containing none of the trace elements of interest are also useful for quantifying background nonlinearity.

Kinetic Spectrophotometric Determination of Hydrazine with Neutral Red-Nitrite System

Abstract: A new kinetic spectrophotometric method for the determination of hydrazine is described. The method is based on the inhibitory effect of hydrazine on the reaction of neutral red with nitrite in acidic media and 28 °C. A product from the reaction of neutral red with nitrite was used to monitor the reaction spectrophotometrically at 352 nm. Hydrazine can be determined in the range 4.7×10−6∼3.1×10−5mol/L with a detection limit of 3.1×10−6mol/L. The method was applied to the determination of hydrazine in water samples.

Kinetic Spectrophotometric Determination of Oxalic Acid Based on the Catalytic Oxidation of Bromophenol Blue by Dichromate

Abstract: A sensitive catalytic method is developed for the spectrophotometric determination of oxalic acid. It is based on the catalytic action of oxalic acid on a new indicator reaction – the oxidation of Bromophenol Blue by dichromate in dilute sulfuric acid medium. The reaction rate is monitored spectrophotometrically by measuring the absorbance at 600 nm after quenching the reaction with sodium hydroxide. A calibration graph from 0.1 to 8.0 μg mL−1 of oxalic acid and a detection limit of 0.04 μg mL−1 was obtained. The applicability of this method was demonstrated by the determination of oxalic acid in water extracts from vegetables such as spinach, mushrooms and fresh kidney beans.