Atomization Characteristic of Chromium on a Molybdenum Tube Atomizer by Electrothermal Atomic Absorption Spectrometry and Determination of Chromium in Biological Materials

Atomization characteristics of chromium have been studied by electrothermal atomic absorption spectrometry with a molybdenum tube atomizer. The appearance temperature (T_app) of chromium nitrate was 1300°C. TheT_appwas independent of the heating rate of atomizer, but the temperature at the peak of the Cr AA signal increased with the heating rate. A sensitive absorption chromium signal was obtained in pure argon purge gas. The chromium signal decreased as the ratio of hydrogen in the purge gas increased. The optimal gas flow rate was Ar 480 ml min⁻¹+ H₂20 ml min⁻¹because of the avoidance of oxidation of the atomizer. The absolute characteristic mass (the mass of element giving 0.0044 abs.) of chromium by the atomizer was 0.35 pg and the detection limit was 23 pg ml⁻¹(3S/N). The interferences caused by large amounts of interferents were evaluated. The addition of thiourea served to eliminate the severe interferences. The accuracies of the recommended method were considered almost satisfactory for the determination of chromium in biological materials, compared with the certified values of NIST materials. The recovery of spiked chromium in biological materials was in the range from 93.5 to 102%.     

Matrix modification by Cu(NO3)2 for the determination of gold by electrothermal atomic absorption spectrometry with a molybdenum tube atomizer

Matrix modification by copper nitrate in electrothermal atomic absorption Spectrometry (ETAAS) of gold with a molybdenum tube atomizer has been investigated. The addition of copper nitrate served to eliminate the interferences from 10⁴–10⁵-fold concentrations of foreign elements at the 890 °C pyrolysis temperature. The absolute characteristic mass (giving 0.0044 absorbance) of gold in the presence of copper nitrate with the Mo atomizer was 0.26 pg and the detection limit was 38 pg/ml. These values were several times better than those obtained with graphite atomizers. The recovery of spiked gold in biological materials was in the range 96–106%. A sensitive and accurate ETAAS method was developed for complex matrix samples.     

Determination of bismuth in geological materials by automated hydride generation and electrothermal atomic absorption spectrometry

The rapid and precise determination of bismuth (>5 μg kg^?1 in geological materials is described. The sample is decomposed with a HClO₄/HNO₃/HF mixture; interferences are eliminated by addition of aluminium chloride, ascorbic acid and thiourea. Bismuth hydride is introduced into a quartz cell atomizer.     

Determination of gold in biological materials by electrothermal atomic absorption spectrometry with a molybdenum tube atomizer

Electrothermal atomic absorption spectrometry (ETA-ASS) of gold with a molybdenum tube atomizer has been investigated. A sensitive ETA-AAS method was developed. The gold absorption signal became higher with the heating rate of the tube atomizer and as the ratio of hydrogen in the argon purge gas decreased. The optimal heating rate and the optimal gas flow rate were 5.5 C/msec and Ar 480 ml/min + H(2) 20 ml/min, respectively. The absolute characteristic mass (the mass of element giving 0.0044 abs.) of gold by the atomizer was 1.8 pg and the detection limit was 130 pg/ml (3S/N). These values were > 10 times better than those obtained with graphite atomizers, ICP and ICP-MS. The interferences caused by large amounts of interferents were evaluated. The addition of thiourea served to eliminate severe interferences. The recovery of spiked gold in biological materials was in the range of 101-106%.     

Evaluation of a Collision-Reaction Interface (CRI) for Carbon Effect Correction on Chromium Determination in Environmental Samples by ICP-MS

Spectral interferences in inductively coupled plasma quadrupole mass spectrometry (ICP-MS) may affect several trace element analyses. In this work, the performance of a collision-reaction interface (CRI) for correction of spectral interferences on chromium determination at m/z 52 affected by ⁴⁰Ar¹²C⁺ in a rich-carbon medium was evaluated. Hydrogen or He gases were introduced through sampler or skimmer cones of the CRI for promoting collisions and reactions. Background equivalent concentrations (BEC) and signal-background ratios (SBR) were the chosen parameters for evaluating CRI performance. It was observed that the introduction of both gases through the sampler cone was not effective considering the maximum gas flow rate evaluated at 140 mL min^?1. The best condition to reduce polyatomic interferences caused by carbon containing species was obtained while introducing 60 mL min^?1 of H₂ through the skimmer cone. The trueness of the developed procedure was checked by ⁵²Cr⁺ determination in certified reference materials. Sequential extractions in acetic acid and ammonium acetate (carbon sources) media, according to the Bureau Communautaire de Référence (BCR) of the Commission of the European Communities, was employed for BCR 701 (Lake Sediment) and microwave-assisted digestion was applied for Sewage Sludge from Industrial Origin (BCR 146 R). The feasibility of the CRI to overcome spectral interferences caused by molecular ions containing carbon on ⁵²Cr⁺ determined by ICP-MS was demonstrated.     

Dispersive Solid-Phase Extraction of Rhodium from Water,Street Dust,and Catalytic Converters Using a Cellulose–Graphite Oxide Composite

A cellulose–graphite oxide composite was synthesized and characterized as an adsorbent for dispersive solid-phase extraction of rhodium from various samples before atomic absorption detection. The pH, adsorbent volume, centrifugation time and rate, eluent concentration, volume and type, adsorption and elution contact time, sample volume, and matrix interferences were optimized. The developed method is simple, rapid, and inexpensive. The tolerance limits for rhodium were 10,000?mg?L^?1 sodium, 25,000?mg?L^?1 potassium, 10,000?mg?L^?1 magnesium, and 20,000?mg?L^?1 calcium. The recovery for rhodium exceeded 95%. Elution was performed with 10?mL of 2.5?mol?L^?1 H₂SO₄. The adsorption and elution contact times were 30 and 60?s, respectively. The detection limit of the method for rhodium was 5.4?µg?L^?1 and the precision as the relative standard deviation was 1.6%. A certified reference material 2556 (used auto catalyst pellets) and fortified samples were analyzed to evaluate the accuracy of the method. The optimized method was used for the preconcentration of rhodium from tap water, well water, wastewater, seawater, catalytic converters, and street dust.     

Determination of cadmium by suction-flow liquid-liquid extraction combined with inductively-coupled plasma atomic emission spectrometry

The flow manifold described permits suction-flow liquid-liquid extraction of cadmium in a discrete aqueous sample as its diethyldithiocarbamate into carbon tetrachloride. The organic extract is fed into the nebulizer of an inductively-coupled plasma atomic emission spectrometer by a peristatic pump. An increase in sensitivity of ca. 250-fold is achieved in comparison with direct aspiration of the aqueous solution. The sampling frequency is 20 h^?1 and the consumption of carbon tetrachloride and 5% (w/v) sodium diethyldithiocarbamate solution are each 0.6 ml min^?1. The 3σ detection limit is 0.4 ng ml^?1 cadmium, and the calibration is linear up to 300 ng ml^?1. The relative standard deviation for 10 replicate measurements is 1.5% for 50 ng ml^?1 cadmium. The flow interferences observed can be decreased or eliminated by the addition of citrate to the buffer solution. Results of analysis of some certified biological reference materials are given.     

Denitrification of simulated nitrate-rich wastewater using sulfamic acid and zinc scrap

An enhanced chemical denitrification process was studied as an alternative treatment of nitrate-rich wastewater which cannot be easily treated using conventional biological methods. To accelerate denitrification and to reduce the conversion to ammonia, nitrite reductants were added. In a batch test with the initial nitrate concentration of 500 mg NO ₃ ^? -N per L, sulfamic acid and zinc were found to be the best nitrite and metal reductants, respectively. In a column test with the initial nitrate concentration of 500 mg NO ₃ ^? -N per L, optimum results were experimentally obtained over a zinc scrap column with a 1.0 molar ratio of [NH₂SO₃H]/[NO ₃ ^? -N] and the recirculating flow rate of 6 L min^?1 at pH 2.5. Approximately 98.8 % of nitrate anions were removed, and the observed reaction rate constant (k) was 0.135 min^?1. Zinc consumption was reduced to 46.6 % compared to the procedure without sulfamic acid, and sulfamic acid consumption was reduced to 40 % compared to the results of our previous study. Based on these experimental results, it was concluded that chemical nitrate denitrification using sulfamic acid and zinc scrap is an effective alternative treatment protocol for nitrate-rich wastewater.     

Amperometric Glucose Biosensor Based on Rhodium Dioxide‐Modified Carbon Ink

An amperometric method for the determination of glucose using a screen printed carbon electrode is reported. The electrode material was bulk modified with rhodium dioxide and the enzyme glucose oxidase immobilized in a Nafion‐film on the electrode surface and investigated for its ability to serve as a detector of glucose in flow injection analysis. The sensor exhibited a linear increase of the amperometric signal with the concentration of glucose in the range of 1–250 mg L^?1 with a detection limit (evaluated as 3σ) of 0.2 mg L^?1 under optimized flow rate of 0.4 mL min^?1 in 0.1 M phosphate buffer (pH 7.5) carrier. At the potential applied (?0.2 V vs. Ag/AgCl), interferences from redox species present in the sample matrix were negligible. The biosensor reported here retained its activity for more than 40 injections or 4 months of storage at 6 °C. The RSD was determined as 1.8% for a glucose concentration of 25 mg L^?1 (n=5) with a typical response time of about 28 s.     

Atomic absorption spectrometric determination of selenium with carbon furnace atomization

A Varian Techtron model 63 carbon rod atomizer is used for the atomic absorption spectrometric determination of nanogram quantities of selenium. The pronounced interferences from the matrices in biological digests can be obviated by isolating selenium from sample matrices by precipitation with ascorbic acid. The precision of the determination is improved by incorporating 5000 μg Ni ml^?1 in the analytical solutions. Selenium at μg g^?1 and sub-μg g^?1 levels in a variety of biological samples can be determined. The detection limit is 25 ng Se g^?1.     

Thermal Behavior and Non-isothermal Decomposition Reaction Kinetics of NEPE Propellant with Ammonium Dinitramide

Thermal decomposition behavior and non‐isothermal decomposition reaction kinetics of nitrate ester plasticized polyether NEPE propellant containing ammonium dinitramide (ADN), which is one of the most important high energetic materials, were investigated by DSC, TG and DTG at 0.1 MPa. The results show that there are four exothermic peaks on DTG curves and four mass loss stages on TG curves at a heating rate of 2.5 K·min^?1 under 0.1 MPa, and nitric ester evaporates and decomposes in the first stage, ADN decomposes in the second stage, nitrocellulose and cyclotrimethylenetrinitramine (RDX) decompose in the third stage, and ammonium perchlorate decomposes in the fourth stage. It was also found that the thermal decomposition processes of the NEPE propellant with ADN mainly have two mass loss stages with an increase in the heating rate, that is the result of the decomposition heats of the first two processes overlap each other and the mass content of ammonium perchlorate is very little which is not displayed in the fourth stage at the heating rate of 5, 10, and 20 K·min^?1 probably. It was to be found that the exothermal peak temperatures increased with an increase in the heating rate. The reaction mechanism was random nucleation and then growth, and the process can be classified as chemical reaction. The kinetic equations of the main exothermal decomposition reaction can be expressed as: dα/dt=10^12.77(3/2)(1?α)[?ln(1?α)]^1/3 e^{?1.723×104/T}. The critical temperatures of the thermal explosion (T_be and T_bp) obtained from the onset temperature (T_e) and the peak temperature (T_p) on the condition of β→0 are 461.41 and 458.02 K, respectively. Activation entropy (ΔS^≠), activation enthalpy (ΔH^≠), and Gibbs free energy (ΔG^≠) of the decomposition reaction are ?7.02 J·mol^?1·K^?1, 126.19 kJ·mol^?1, and 129.31 kJ·mol^?1, respectively.     

Speciation of volatile antimony compounds in culture headspace gases of Cryptococcus humicolus using solid phase microextraction and gas chromatography–mass spectrometry

Direct analysis of the volatile antimony compounds stibine (SbH₃), monomethylantimony, dimethylantimony (Me₂Sb) and trimethylantimony (Me₃Sb) using solid phase microextraction (SPME) with polydimethylsiloxane fibres and gas chromatography–mass spectrometry (GC–MS) is described. The best analyte to background signal ratio was achieved using a 20 min extraction time. Antimony species were separated using a 3% phenylmethylsilicone capillary column operated at a column pressure of 70 kPa, a flow rate of 1.4 ml min^?1 and temperature ramping from 30 to 36 °C at 0.1 °C min^?1. Cryogenic focusing of desorbed species was required to achieve resolution of antimony species. The optimized SPME–GC–MS method was applied to the analysis of headspace gases from cultures of Cryptococcus humicolus incubated with inorganic antimony(III) and (V) substrates. The headspace gases from biphasic (aerobic–anaerobic) biomass‐concentrated culture incubations revealed the presence of SbH₃, Me₂Sb and Me₃Sb. Stibine was the major antimony species detected in cultures amended with inorganic antimony(V). Me₃Sb was the sole volatile antimony species detected when cultures were amended with antimony(III). Copyright © 2002 John Wiley & Sons, Ltd.     

Determination of Cobalt with a Tungsten Tube Atomizer by Electrothermal Atomic Absorption Spectrometry and its use for the Analysis of Biological Materials

 The determination of cobalt by electrothermal atomic absorption spectrometry with a tungsten tube atomizer has been investigated. The absolute characteristic mass (the mass of element giving 0.0044 abs.) of cobalt by the atomizer was 5.8 pg and the detection limit was 0.65 ng/ml (3S/N). The interferences caused by large amounts of interferents like Al, Ca, Cu, Fe, K, Mg, Na, Pb and Zn were evaluated and most of these elements were found to interfere with the cobalt signal. Ammonium thiocyanate as a chemical modifier was found to be efficient to eliminate the severest interferences. The accuracies of the recommended method were found to be almost satisfactory for the determination of cobalt in biological materials, as shown by a comparison with the reported values of NIST materials at the 0.02–0.4 μg/g level. Received August 24, 1998. Revision February 9, 1999.     

Investigation of interferences in the determination of thallium in marine sediment reference materials using high-resolution continuum-source atomic absorption spectrometry and electrothermal atomization

A high-resolution continuum-source atomic absorption spectrometer with a xenon short-arc lamp as the radiation source, a compact double echelle monochromator with a focal length of 302 mm and a spectral resolution of λ/Δλ≈110 000, and a UV-sensitive charged-coupled device (CCD) array detector was used to investigate the spectral interferences found with a conventional line-source atomic absorption spectrometer in the determination of thallium in marine sediment reference materials. A transversely heated graphite furnace was used as the atomizer unit, and the samples were introduced in the form of slurries. A strong iron absorption line at 276.752 nm, which was observed at atomization temperatures >2000 °C in the vicinity of the thallium resonance line at 276.787 nm, could be responsible for some of the interferences observed with low-resolution continuum-source background correction. The outstanding feature at atomization temperatures <2000 °C was the electron excitation spectrum of the gaseous SO₂ molecule that exhibited a pronounced rotational fine structure, and is for sure the main reason for the observed spectral interferences. The molecular structures could be removed completely by subtracting a model spectrum recorded during the atomization of KHSO₄, using a least squares algorithm. The same results, within experimental error, were obtained for thallium in a variety of marine sediment reference materials using ammonium nitrate as a modifier, ruthenium as a permanent modifier in addition to ammonium nitrate, and without a modifier, using aqueous standards for calibration, demonstrating the ruggedness of the method. A characteristic mass of 15–16 pg Tl was obtained, and a limit of detection of 0.02 μg g⁻¹ Tl was calculated from the standard deviation of five repetitive determinations of HISS-1, the sediment with the lowest thallium content.     

A high temperature and high sensitivity micro-thermobalance

A thermobalance which ensures a sensivity of 1 × 10^?6 g and an excellent stability up to 1500 C has been developed. A sample, which is suspended from one end of the beam of the balance, is heated in a compact furnace with a small heat capacity. Temperature is measured by a Pt-PtRh (10%) thermocouple placed close to the sample. Use of an alumina mantle ensures easy control of atmosphere: at room temperature, the evacuation can be done to 1 × 10^?4 Torr, and stable operation can be done up to 1500 C in air inert gas at a flow-rate smaller than 50 ml min^?1. It is also possible to use a corrosive gas as atmosphere. In a blank test with platinum cell support (6.5 mm diam. and 0.1 mm thick) suspended in an air stream of 50 ml min^?1 and heated up to 1500 C at 10 C min^?1, the drift was smaller than 20 × 10^?6 g and the reproducibility was better than 10×10^?6 g. This paper refers to the construction of the thermobalance, and its performances. And some examples of high temperature thermogravimetry through the results of analyses of CaCO₃, quick lime and byproduct lime are also reported.     

Rapid Analysis of Nitrate and Nitrite by Ion-Interaction Chromatography on a Monolithic Column

Ion-interaction chromatography with direct conductivity detection has been used for analysis of nitrate and nitrite. Chromatographic separation was performed on a monolithic silica-based C₁₈ column dynamically modified with tetrabutylammonium (TBA⁺). Using the optimized mobile phase, containing 2.0 mmol L^?1 TBA⁺ and 0.8 mmol L^?1 citrate (pH 6.0), delivered at a flow rate of 6.0 mL min^?1, separation of five anions (chloride, nitrite, bromide, nitrate, and sulfate) was achieved in only 40 s at a column temperature of 30 °C. The detection limits for nitrate and nitrite were 0.74 and 0.92 mg L^?1, respectively. The relative standard deviation (RSD, n = 5) of the retention times of nitrate and nitrite was 0.1% and RSD of chromatographic peak areas were 0.4 and 0.2%, respectively. The method was successfully used for analysis of the anions in groundwater. Recovery of nitrate and nitrite was 99.1 and 105%, respectively.     

Flow-injection spectrophotometric determination of silicate,phosphate and arsenate with on-line column separation

The simultaneous determination of silicate, phosphate and arsenate by using flow-injection analysis with on-line column separation is described. Determinations are based on measurement of the absorbance at 810 nm of the heteropoly blue formed with ascorbic acid as reducing reagent. Effects of flow rates, temperature of reaction coils and sample injection volumes are reported; optimum conditions are 0.25 ml min^?1 for the ascorbic acid stream, 95°C for the reaction coils and 300 μl for the injection volume. With the anion-exchange column (TSK-gel SAX), the optimal flow rate of the eluent is 0.75 ml min^?1. Relative retention times depend on the concentration of the KCl/NH₃/EDTA eluting solution; separation and simultaneous determination of the three ions are satisfactory at around 10^?4 mol l^?1 concentrations of the three ions.     

Pyrolysis of Eucalyptus wood in a fluidized-bed reactor

Eucalyptus wood can be utilized as a biomass feedstock for conversion to bio-oil using a pyrolysis process. Eucalyptus wood samples were initially pyrolyzed on a laboratory-scale pyrolysis system at different values in the ranges of 300–800 °C and 0.050–0.300 L min^?1 to determine the effects of operation temperature and N₂ flow rate, respectively, on the yields of products. Then, the bio-oil in the highest yield (wB = 44.37 %), which was obtained at pyrolysis final temperature (450 °C), heating rate (35 °C min^?1), particle size (850 μm), and sweeping flow rate (0.200 L min^?1), was characterized by Fourier transform infra-red spectroscopy, gas chromatography/mass spectrometry and column chromatography. Subsequently, it was shown that the operating temperature and N₂ gas flow rate parameters affected the product yields. Also, some important physico-chemical properties of the pyrolytic oil obtained in high yield were determined as a calorific value of 37.85 MJ kg^?1, an empirical formula of CH_1.651O_0.105N_0.042S_0.001, a rich chemical content containing many different chemical groups, a density of 981.48 kg m^?3, and a viscosity of 61.24 mm² s^?1. Based on the determined properties of the pyrolytic oil, it was concluded that the use of pyrolytic oil derived from Eucalyptus wood may be useful for the production of alternative liquid fuels and fine chemicals after the necessary improvements.     

On-line coupling of electrochemical preconcentration in tungsten coil electrothermal atomic absorption spectrometry for determination of lead in natural waters

A flow injection system was coupled to a tungsten coil electrothermal atomizer (150 W) for on-line separation and preconcentration of lead based on its electrochemical reduction on the atomizer surface. The electrochemical cell is built up inside the furnace by using a Pt flow-through anode and the atomizer itself as the flow-through cathode. The manifold and the tungsten coil power supply were controlled by a computer running a program written in Visual Basic, which was utilized in synchronism with the original software of the atomic absorption spectrometer. The flow-through anode (50 mm long, 0.7 mm i.d.) was inserted in tip of the autosampler arm by replacing the last section of the PTFE sample delivering tube. The tungsten coil atomizer and the counter electrode were easily connected to a d.c. power supply. An enrichment factor of 25 was obtained for lead after a 120-s electrodeposition for a sample flowing at 1.0 ml min⁻¹. The method detection limit was 0.2 μg l⁻¹ Pb and the R.S.D.<5% (n=10 for 5 μg l⁻¹ Pb). Up to 2% m/v NaCl or KCl and 5% m/v CaCl₂ or MgCl₂ did not interfere on the separation and atomization of 5 μg l⁻¹ Pb.     

Colorimetric Sensing of Nitroaromatic Energetic Materials Using Surfactant-Stabilized and Dithiocarbamate-Functionalized Gold Nanoparticles

Abstract

There is an increasing need for sensitive/selective determination of explosive traces in soil and post-blast debris for environmental and criminal investigations. A colorimetric sensor was developed to detect and quantify trinitrotoluene (TNT) and tetryl by the use of surfactant-stabilized and dithiocarbamate-functionalized gold nanoparticles (AuNPs). The sensor was manufactured by modifying the nanoparticles with the cationic surfactant cetyl trimethyl ammonium bromide and incorporating diethyldithiocarbamate (DDTC) in the AuNPs synthesis. DDTC firmly bound to AuNPs may show charge-transfer interactions with the —NO₂ groups of the analytes, and a color change proportional to analyte concentration accompanied the agglomeration of nanoparticles, at which the absorbances were recorded at 534?nm and 458?nm for TNT and tetryl, respectively. Although the limit of detection was 8?mgL^?1 (3.52?×?10^?5?molL^?1) for TNT and 0.8?mgL^?1 (2.78?×?10^?6?molL^?1) for tetryl, providing moderate sensitivity, the cost was greatly reduced compared to those of other thiol-functionalized AuNPs sensors. Possible interferences of other energetic substances in synthetic mixtures, of camouflage materials used in passenger belongings (e.g., detergent, sugar, caffeine, and paracetamol) and common soil ions were also examined. The method was statistically validated against a reference gas chromatography/mass spectrometry method. This sensor may pave the way for the manufacture of novel low-cost nitroaromatic explosive sensors made of DDTC-based pesticides.