Analysis of hydrogen peroxide and an organic hydroperoxide via the electrocatalytic Fenton reaction

A new concept for the electrochemical detection of hydrogen peroxide, and organic hydroperoxides is presented. One advantage of the significance of this technique is that it does not require chemical modification of the electrode or addition of enzymes. Direct electro-reduction of the peroxides was not observed on the carbon disk electrode as it is a kinetically slow process. Redox cycling of the iron complex is apparent as Fe^IIEDTA rapidly reduces the O-O bond of the peroxides (Fenton Reaction) upon its production by the kinetically facile electro-reduction of Fe^IIIEDTA. This provides an enhanced and steady-state reductive current as observed by cyclic voltammetry. These features are indicative of the electrocatalytic (EC′) mechanism. A calibration curve was constructed based on the chronoamperometric response at 32 s and a detection limit for H₂O₂ and t-butyl hydroperoxide was calculated to be 0.4 μM and 20 µM, respectively. This difference is attributable to the rate in which the iron(II) complex reduces the O-O bond, H₂O₂ (2.3 × 10⁵ M^− 1 s^− 1) being faster than for the organic peroxide (5.1 × 10⁴ M^− 1 s^− 1). The Fe^IIEDTA complex was observed to be unreactive toward dialkyl peroxides. This method may find use in the detection of peroxide-based explosives or in enzymatic assays as it is rapid, simple, inexpensive and should prove to be robust.     

The effect of spatial confinement of Nafion in porous membranes on macroscopic properties of the membrane

Polyelectrolytes were incorporated into porous reinforcing materials to study the properties of ionomers in confined spaces and to determine the effect of the porous material on the behaviour of the membranes. Nafion^® was imbibed into porous polypropylene (Celgard^®), ultra-high-molecular weight polyethylene (Daramic^®), and polytetrafluoroethylene (PTFE) films. Through the use of reinforcing materials, it is possible to prepare membranes that are thinner, but stronger than pure ionomer membranes. Thin reinforced membranes have advantages such as lower areal resistance (as low as 0.14 Ω cm² for 57 μm CG3501 + Nafion^® compared to 0.34 Ω cm² for 89 μm cast Nafion^®) and lower dimensional changes due to swelling (as low as a 4% change in length and width for WDM + Nafion^® compared to 13% for cast Nafion^®). Using reinforcing materials results in a reduction in important membrane properties compared to bulk Nafion^®, such as proton conductivity (as low as 0.016 S cm⁻¹ for CG3401 + Nafion^® compared to 0.076 S cm⁻¹ for cast Nafion^®), effective proton mobility (as low as 3.2 × 10⁻⁴ cm² V⁻¹ s⁻¹ CG3401 + Nafion^® compared to 7.6 × 10⁻⁴ cm² V⁻¹ s⁻¹ for cast Nafion^®), and water vapour permeance (as low as 0.036 g h⁻¹ Pa⁻¹ m⁻² for WDM + Nafion^® compared to 0.056 g h⁻¹ Pa⁻¹ m⁻² for cast Nafion^®). By normalizing the membrane properties with respect to ionomer content, it was possible to examine the properties of the Nafion^® inside the pores of the membranes. The proton conductivity (as low as 0.032 S cm⁻¹ for CG3401 + Nafion^®), effective proton mobility (as low as 3.6 × 10⁻⁴ cm² V⁻¹ s⁻¹ for CG3401 + Nafion^®), and water vapour permeability (as low as 2.7 × 10⁻⁶ g h⁻¹ Pa⁻¹ m⁻¹ for PTFE MP 0.1 + Nafion^®) of the ionomer in the membrane are also diminished compared to bulk Nafion^® due to decreased connectivity of the ionomer and a restriction in macromolecular motions caused by the pore walls. A series of porous materials with increasing pore were also examined. As the pore size of the PTFE MP materials increased from 0.1 μm to 10 μm, the proton conductivity (0.022 S cm⁻¹ to 0.041 S cm⁻¹), effective proton mobility ((4.1 to 5.6) × 10⁻⁴ cm² V⁻¹ s⁻¹), and water vapour permeability ((2.4 to 4.3) × 10⁻⁶ g h⁻¹ Pa⁻¹ m⁻¹) of the reinforced membranes improved with increasing pore size and the properties of the ionomer inside the membranes approached the value of bulk Nafion^®.     

Ab-initio study on low-lying states of the TiSi molecule

 The electronic structure of the TiSi molecule was examined using two types of multireference single and double excitation configuration interactions with highly extended basis sets, one including valence correlation and the other including valence and core–valence correlation. A multireference coupled-pair approximation (MRCPA) was further applied to the latter. The calculations suggest a ⁵Δ ground state, and the lowest excited state is ³Π and is only slightly (0.12 eV as estimated by MRCPA) above the ground state. The spectroscopic constants of the low-lying ¹Δ, ³Δ, ¹Π, ⁵Π, and ⁷Σ⁺ states as well as the ⁵Δ ground state and the ³Π excited states were evaluated, and we found that the molecule has only a weak σ bond and that six of the eight valence electrons essentially do not contribute to the bonding. The bonding nature of TiSi in these states is discussed in comparison with the TiC molecule. Received: 7 October 2000 / Accepted: 8 January 2001 / Published online: 3 May 2001     

A novel method for determination of peroxynitrite based on hemoglobin catalyzed reaction

A novel spectrofluorimetric method for the determination of peroxynitrite is proposed. The method is based on a mimetic enzyme catalyzed reaction with hemoglobin as the catalyst and l-tyrosine as the substrate. A new fluorescent substance is produced that might probably be the coupled dimmer of tyrosine, which, instead of nitryl-tyrosine, is likely to be a new marking substance of ONOO⁻ injury in vivo. Kinetics of the reaction is studied and the possible reaction mechanism is also recommended. The proposed method is simple and highly sensitive with a detection limit of 5.00 × 10⁻⁸ mol L⁻¹ of peroxynitrite. A liner calibration graph is obtained over the peroxynitrite concentration range 5.60 × 10⁻⁷ to 2.10 × 10⁻⁵ mol L⁻¹, with a correlation coefficient of 0.9983. Interferences from some amino acids and metal ions normally seen in biological samples, and also some anions structurally similar to ONOO⁻ are studied.     

Resonance light-scattering method for the determination of BSA and HSA with sodium dodecyl benzene sulfonate or sodium lauryl sulfate

A new resonance light-scattering (RLS) assay of proteins such as bovine serum albumin (BSA) and human serum albumin (HSA) is presented. In the medium of phosphoric acid (pH=2.6), the weak RLS of sodium dodecyl benzene sulfonate (SDBS) or sodium lauryl sulfate (SLS) can be greatly enhanced by proteins, owing to interaction between the protein and the anionic surfactant and formation of an associate. The RLS intensity of the SDBS–protein system is stronger than that of the SLS–protein system under same experimental conditions. It is considered that the synergistic resonance caused by the absorption of both protein and SDBS could produce strong RLS, while absorption of protein only in the SLS system could cause relatively weak RLS. The enhanced intensity of RLS is proportional to the concentration of the protein. If SDBS is used as the probe the linear range is 7.5×10^–9–1.5×10^–5 g mL^–1 for BSA and 1.0×10^–8–1.0×10^–5 g mL^–1 for HSA. The detection limits are 1.8 and 2.8 ng mL^–1, respectively. When SLS is used as the probe the linear range is 2.0×10^–8–1.0×10^–5 g mL^–1 and 2.5×10^–8–1.0×10^–5 g mL^–1 for BSA and HSA, respectively, and the detection limits are 12.8 and 21.6 ng mL^–1, respectively. The biological mimics samples are synthetic concoctions of BSA and HSA with some interferents. In these samples, the concentration of interferents is higher than the concentration normally existing in organisms. The samples were determined satisfactorily.     

Cobalt(II) and nickel(II) complexes of a cyclam derivative as carriers in iodide-selective electrodes

The ligand 1,4,8-tri(n-octyl)-1,4,8,11-tetraazacyclotetradecane (L¹) containing pendant octyl groups has been synthesised. L¹ is a tetraazamacrocycle derived from the well-known cyclam unit, and the Ni²⁺ and Co²⁺ complexes, [Ni(L¹)]²⁺ and [Co(L¹)]²⁺, have been isolated and characterised. The ability of the nickel(II) and cobalt(II) complexes to act as anion receptors has been studied by using them as ionophores in membrane-based ion-selective electrodes (ISEs). The PVC membrane containing the complex [Ni(L¹)]²⁺ and 2-nitrophenyloctylether as plasticizer shows a Nernstian response against iodide in a concentration range from 1×10⁻¹ to 4×10⁻⁵ M I⁻ with a detection limit of 1.6×10⁻⁵ M I⁻ and a slope of 58.6 mV/pI⁻ at pH 7 (25 °C). In comparison, the electrode containing [Co(L¹)]²⁺ as ionophore gave a sub-Nernstian slope and a low lifetime. A comparison between the iodide-selective electrode containing [Ni(L¹)]²⁺ and other reported iodide-selective electrodes is also reported.     

Determination of Zirconium (IV) and Aluminium (III) in Waste Water

 Zirconium (IV) was determined spectrophotometrically by reaction with quercetin as primary ligand and oxalate as secondary ligand. Polyvinylpyrrolidone (PVP) was used as protective colloid to solubilize the formed zirconium quercetin oxalate ternary complex. The molar absorptivity of the 1:3:1 (zirconium–quercetin–oxalate) complex is 7.31 × 10⁴ L·mol⁻¹ cm⁻¹ at 430 nm with a stability constant of 8.2 × 10²⁰ and its detection limit is 0.16 mg/L. Beer’s law is rectilinear up to 1.46 mg/L of zirconium (IV). The sensitivity index is 1.25 ng cm⁻². The reaction of aluminium (III) with quercetin in presence of PVP as a surfactant has been studied spectrophotometrically. The molar absorptivity of the 1:3 (aluminium–quercetin) complex is 8.09 × 10⁴ × L·mol⁻¹·cm⁻¹ at 433 nm, its stability constant is 2.6 × 10¹³ with sensitivity index of 0.33 ng·cm⁻² and its detection limit is 0.08 mg/L. The optimal conditions for the quantitative determination of zirconium and aluminium were studied. The proposed methods are examined by statistical analysis of the experimental data. The methods are free from interference of most cations and anions. The proposed methods have been used to determine zirconium and aluminium in industrial waste water. Received May 30, 2001; accepted November 2, 2001; published online July 15, 2002     

Synchronous fluorescence measurement of enrofloxacin in the pharmaceutical formulation and its residue in milks based on the yttrium (III)-perturbed luminescence

A simple, rapid and sensitive synchronous fluorescence method is put forward for the determination of enrofloxacin (ENRO) in the pharmaceutical formulation and its residue in milk based on the yttrium (III)-perturbed luminescence. When Y³⁺ is added into the ENRO solution, the fluorescence of ENRO is significantly enhanced. The synchronous fluorescence technology is employed in the method to determine trace amount of ENRO residue in milks. The synchronous fluorescence intensity of the system is measured in a 1-cm quartz cell with excitation wavelength of 328 nm, Δλ = 80 nm. A good linear relationship between the fluorescence intensity and the ENRO concentration is obtained in the range of 1.0 × 10⁻⁹ to 2.0 × 10⁻⁶ mol L⁻¹ (r² = 0.9992). The limit of detection (LOD) of this method attains as low as 3.0 × 10⁻¹⁰ mol L⁻¹ (S/N = 3). The selectivity of this method is also very good. Common metal ions, rare-earth ions and some pharmaceuticals, which are usually used together with ENRO, do not interfere with the determination of ENRO under the actual conditions. The proposed method can be applied to determine ENRO residue in milks, and limit of quantification (LOQ) determined in the spiked milk is estimated to be 2.8 × 10⁻⁸ mol L⁻¹ (10 μg L⁻¹). Moreover, this method can be used as a rapid screening for judging whether the ENRO residues in milks exceed Minimal Risk Levels (MRLs) or not. In addition, the mechanism of the fluorescence enhancement is also discussed in detail.     

A dispersive liquid-liquid microextraction procedure for determination of boron in water after ultrasound-assisted conversion to tetrafluoroborate

A novel, simple and green procedure is presented for the determination of boron. The method is based on ultrasound-assisted conversion of boron to tetrafluoroborate anion and the formation of an ion pair between BF₄⁻ and Astra Phloxine reagent (R), followed by dispersive liquid-liquid microextraction of the ion pair formed and subsequent UV-vis spectrophotometric detection. The conversion of boron to tetrafluoroborate anion is performed in an acidic medium of 0.9 mol L⁻¹ H₂SO₄ in the presence of 0.1 mol L⁻¹ F^- by means of 10 min of ultrasonication. The extraction of the ion pair formed between BF₄⁻ and R (1 × 10⁻⁴ mol L⁻¹ R) is carried out by dispersive liquid-liquid microextraction using 0.5 mL of amyl acetate (as extraction solvent), tetrachloromethane (as auxiliary solvent) and acetonitrile (as dispersive solvent) in a ratio of 1:1:2. The absorbance of the coloured extracts obeys Beer's law in the range 0.22-18.7 mg L⁻¹ of B(III) at 553 nm wavelength. The limit of detection calculated from a blank test (n = 10) based on 3 s is 0.015 mg L⁻¹ of B(III). The method was applied to the determination of boron in mineral waters.     

Improved lifetime of PEM fuel cell catalysts through polymer stabilization

A novel approach to increase lifetime of Pt/C catalysts was demonstrated and shown that Nafion-stabilized Pt catalyst (denoted here as Nafion-Pt/C) synthesized by a colloid route gives rise to an enhanced durability as compared to a conventional Pt/C catalysts commonly used in PEM fuel cell. A high catalytic activity of the catalyst is also observed by both CV (cyclic voltammetry) and ORR (oxygen reduction reaction) measurements. This catalyst durability in comparison with conventional Pt/C is increased directly by electrochemically-accelerated durability test (ADT). The loss rate of electrochemical active area (ECA) for Nafion-Pt/C catalysts is only 0.004 m² g⁻¹ cycle⁻¹, compared to a value of 0.012 m² g⁻¹ cycle⁻¹ for Pt/C. This indicates the catalyst is three times higher durability than Pt/C.     

The interface behavior of hemoglobin at carbon nanotube and the detection for H(2)O(2)

Direct electrochemistry of hemoglobin (Hb) is observed at carbon nanotube (CNT) interface. The adsorbing Hb can transfer electron directly at CNT interface compared with common carbon material. The heterogeneous electron transfer rate constant k of Hb can be calculated as 0.062 s⁻¹, the transfer coefficient α is 0.21 and the average surface coverage of Hb on CNT surface is 3.58 × 10⁻⁹ ± 2.7 × 10⁻¹⁰ mol/cm². It is found that the adsorbing Hb still keeps its catalytic activity to H₂O₂. This sensor was used to detect H₂O₂. The apparent Michaelis-Menten constant is calculated as 6.75 × 10⁻⁴ mol L⁻¹.     

Heavy doping of H ion in 12CaO·7Al2O3

12CaO·7Al₂O₃ (C12A7, mayenite), which has a nanoscale porous structure that can accommodate extraframework species such as hydride (H⁻), oxide (O²⁻), hydroxide (OH⁻) ions, and electrons, has been doped with H⁻ ions to investigate its effects as dominant extraframework species. Chemical doping with CaH₂ enables the concentration of H⁻ ions to reach almost the theoretical maximum. The concentration of H⁻ ions is characterized by optical absorption intensity ascribed to photoionization of H⁻ ions, and ¹H magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. Persistent electron generation, which is accompanied by the formation of an F⁺ absorption band and electrical conductivity, by irradiation with ultraviolet light at room temperature increases as the H⁻ ion doping increases until it reaches half the theoretical maximum and then decreases as the H⁻ ion concentration increases further. This dependence indicates that both H⁻ and O²⁻ ions are necessary for the generation of persistent electrons.     

TOF-SIMS imaging of halide/thiocyanate anions and hydrogen sulfide in mouse kidney sections using silver-deposited plates

In vivo imaging of reactive small molecule metabolites with high spatial resolution and specificity could give clues to understanding pathophysiology of various diseases. We herein applied time of flight-secondary ion mass spectrometry (TOF-SIMS) to newly developed silver-deposited plates that were stamped on mouse tissues, and succeeded in visualization of halide (Cl⁻, Br⁻, and I⁻) and pseudohalide thiocyanate (SCN⁻) anions, a class of substrates for neutrophils/eosinophil peroxidases to produce hypohalous acids (HOX/OX⁻ mixture; X: (pseudo)halides), as well as hydrogen sulfide (H₂S). Forty-micrometer frozen mouse kidney sections on cover glasses were attached to 37 °C preheated silver-deposited plates and incubated at −10 °C for 1 h. After sputter cleaning to remove surface contaminants, the plates were analyzed by TOF-SIMS to identify distribution of Br⁻, AgBr₂⁻, I⁻, AgI₂⁻, SCN⁻, as well as S²⁻ and AgS⁻ as products of tissue-derived H₂S. Br⁻, AgBr₂⁻, I⁻, and SCN⁻ anions were mainly distributed in core regions including the inner medulla and inner stripe of the outer medulla (except for I⁻), rather than outer regions such as the cortex and outer stripe of the outer medulla. AgI₂⁻ anion was spread over the whole kidney, although its levels were relatively low. In contrast, S²⁻ and AgS⁻ anions were mainly present in the outer regions. To our knowledge, this is the first imaging study to reveal the distribution of (pseudo)halides and H₂S in animal tissue sections.     

Simultaneous determination of uranium carbide dissolution products by capillary zone electrophoresis

Separation and simultaneous determination of a number of organic acid anions (oxalate, mellitate, trimellitate and benzoate) and U(VI) with direct UV detection is developed for analysis of uranium carbide (UC) dissolution products by capillary zone electrophoresis (CZE). Reverse polarity mode is used. It is found that complex formation of U(VI) with carbonate, used as a carrier electrolyte, allows U(VI) to be determined, as negatively charged species, in a single run with organic acid anions. Some parameters such as pH value, composition of electrolyte and detection wavelength are optimized. Under the chosen conditions (carbonate buffer (ionic strength of 100 mM), pH 9.8, 0.15 mM tetradecyltrimethylammonium bromide (TTAB)) a complete separation is achieved. Calibration plots are linear in two ranges of concentration for U(VI) (∼1 × 10⁻⁵ to 1 × 10⁻³), mellitate and trimellitate (∼5 × 10⁻⁶ to 5 × 10⁻⁴), and about one range (∼1 × 10⁻⁴ to 5 × 10⁻³) for oxalate and benzoate. Accuracy of the procedure is checked by the “added-found” method in standard mixture solutions. Relative standard deviation is within the range of 2–10% and the recovery is in the range of 90–110%. This method is applied for the analysis of real UC dissolution samples.     

Multi-walled carbon nanotubes and Ru(bpy)3/nano-Au nano-sphere as efficient matrixes for a novel solid-state electrochemiluminescence sensor

An effective method for immobilization of Ru(bpy)₃²⁺ on glassy carbon electrode surface (GCE) is developed for the preparation of a novel electrochemiluminescence sensor. First of all, the positively charged Ru(bpy)₃²⁺ is modified on the surface of negatively charged gold nanoparticles (nano-Au) via the electrostatic interactions to obtain the Ru(bpy)₃²⁺/nano-Au nano-sphere (abbreviate as Ru-AuNPs). Subsequently, the large amount of Ru-AuNPs are immobilized on the multi-wall carbon nanotubes (MWCNTs)-Nafion homogeneous composite coated GCE by dual interaction: firstly, the Nafion, a kind of typical cation-exchange membrane, can absorb the Ru-AuNPs as the enrichment of cation Ru(bpy)₃²⁺ on the Ru-AuNPs surface; secondly, the employment of carboxylic MWCNTs in the Nafion film can also chemosorb the Ru(bpy)₃²⁺ cation on the Ru-AuNPs surface to increase the carrier content. At the same time, the experiment confirms that the enhancement of the ECL intensity on the sensor is attributed to following reasons. One hand, the employment of MWCNTs in the Nafion film enlarged the electro-active surface areas to benefit the contact between the signal probe on the composite film and coreactant used as reinforcing agent. On the other hand, the nano-materials of MWCNTs and nano-Au also improve the conductivity of the assembled film to increase the quantity of excited state of Ru(bpy)₃²⁺ in the unit time under the electrochemical condition and finally cause better properties in luminescence. In the experiment, the influence of the coreactant tripropylamine (TPA) on proposed ECL sensor is investigated. The logarithm of ECL intensity is proportional to the logarithm of TPA concentration on the range of 4 × 10⁻¹⁰ M to 2.8 × 10⁻⁶ M and 2.8 × 10⁻⁶ M to 0.71 × 10⁻³ M. After optimizing these conditions, the ECL sensor with TPA as coreactant is employed to detect a kind of alkaloid medicine, Matrine, for evaluating the practical application in the medicine analysis. The present sensor with TPA as coreactant shows the good response to the medicine concentration of the Matrine from 2.0 × 10⁻⁶ M to 6.0 × 10⁻³ M, which is used to detect the Matrine concentration in the Matrine injection.     

A novel capillary microliter droplet sample injection-chemiluminescence detector and its application to the determination of benzoyl peroxide in wheat flour

A novel capillary microliter order droplet injection-chemiluminescence (CL) system is proposed. In this system, the liquid sample microdrops, automatically formed at the end of a capillary tip by the effect of the gravity and the gas pressure, repeatedly drop into the miniature reaction cell and reacts with CL reagent to generate CL signal. The phenomena of sample zone dilution and spreading are eliminated as the capillary is used as the sample channel and gas pressure is used as driving force without the liquid carrier stream. Therefore, a high sensitivity is obtained. To evaluate the applicability of the proposed method, a determination of benzoyl peroxide (BP) is examined. The system shows that the benzoyl peroxide is detected linearly in the concentration range from 5×10⁻¹⁰ to 1×10⁻⁶ g ml⁻¹. The detection limit (signal-to-noise ratio=3) is 1.4×10⁻¹⁰ g ml⁻¹ for benzoyl peroxide (mass concentration is 1.1 pg, i.e., 4.5 fmol), which is the best result reported so far. The relative standard deviation (n=11) is 1.5% for 2.0×10⁻⁸ g ml⁻¹ BP. The proposed detector for the detection of benzoyl peroxide offers the advantages of sensitivity, simplicity, rapidity, automation and miniaturization. The proposed method has been applied satisfactorily to the determination of benzoyl peroxide in wheat flour.     

Metal furnace heated by flame as a hydride atomizer for atomic absorption spectrometry: Sb determination in environmental and pharmaceutical samples

The present work describes a metallic hydride atomizer for atomic absorption spectrometry, by evaluating the performance of the Inconel 600^® tube. For this purpose, stibine was used as the model volatile compound and antimony determination in river and lake sediments and in pharmaceutical samples was carried out to assess the metal furnace performance. Some parameters are evaluated such as those referring to the generation and transport of the hydride (such as KBH₄ and acid concentrations, carrier gas flow rate, injected volume, etc.), as well as those referring to the metal furnace (such as tube hole area, flame composition, long-term stability, etc.). The method presents linear Sb concentration from 2 to 80 μg L⁻¹ range (r > 0.998; n = 3) and the analytical frequency of ca. 140 h⁻¹. The limit of detection (LOD) is 0.23 μg L⁻¹ and the precision, expressed as R.S.D., is less than 5% (40 μg L⁻¹; n = 10). The accuracy is evaluated through the reference materials, and the results are similar at 95% confidence level according to the t-test.     

Simulated parametric optimization of the back-lit Si solar cell

The back-lit design is viable for the Si solar cell because Si is an indirect-gap semiconductor that requires a relatively long absorption depth. In this work, key parameters relating to the operation of the back-lit mono-crystalline Si solar cell are investigated by using the Medici device simulator. On the effect of the photon incident angle on the solar cell power, a reduction of as much as 16% is observed when the incident angle is reduced 3.8° from the vertical incidence. The ideal thickness of the p-type substrate that leads to the maximum cell power is found to be 70 μm or less. In the back-lit design, both the n-type collector contact and the p-type substrate contact are located on the front side. To the extent of the 10 μm-wide design investigated, it is found that the larger the n-type collector width, or the smaller the p-type substrate contact, the larger the cell power. In regards to the substrate and collector doping, the optimum doping concentrations leading to a maximum cell power of 2.28 × 10^?2 W cm^?2, or 22.8 mW cm^?2, are found to be 1 × 10¹⁶ cm^?3 and 1 × 10¹⁷ cm^?3 for the substrate and the collector, respectively. In terms of the wavelength of the incident light, the cell power is nearly steady up to 0.8 μm, but decreases rapidly above, as the photon energy falls to near or under the energy gap. All considered, the back-lit design, which simplifies fabrication by putting both the cathode and the anode on the front side, is found to produce a cell power as little as 15% less than that of a standard front-lit design.     

Indirect atomic absorption spectrometry (IAAS) as a tool for the determination of iodide in infant formulas by precipitation of AgI and redissolution with cyanide

A method to determine iodide in infant formula samples by indirect atomic absorption spectrometry (IAAS) was developed. The iodide in solution resulting from an alkaline digestion (Na₂CO₃–NaOH) of the sample is precipitated with silver; the precipitate is redissolved by adding cyanide solution, and this solution is subjected to GF-AAS. Temperatures of 1000 and 2100°C were selected for the ashing and atomization steps, respectively, using a mixture of Pd and Mg(NO₃)₂ as a matrix modifier (at concentrations of 36 and 16 μg ml⁻¹, respectively). The sensitivity, LOD, LOQ and characteristic mass obtained were, respectively, 1.12×10⁻² l μg⁻¹, 3.1 μg g⁻¹ and 10.4 μg g⁻¹ and 7.3 pg, referred to sample. The linear interval of concentrations extends up to 10 μg l⁻¹ of iodide, with no need to use the standard addition method; the mean R.S.D. of data within this range is 3.4%, with 2.9% over the whole procedure. No interfering effects were observed among the foreign ions studied, and 100.0% was the mean analytical recovery achieved within the linear range of concentrations. The application of the method to seven real samples gave a mean content of 12.8 μg g⁻¹ of iodide, as well as less than 3.1 μg g⁻¹ in eight other samples.     

A novel fluorescent method for determination of peroxynitrite using folic acid as a probe

A novel method for the determination of peroxynitrite using folic acid as a fluorescent probe is described. The method is based on the oxidation of the reduced, low-fluorescent folic acid by peroxynitrite to produce a high-fluorescent emission product. The fluorescence increase is linearly related to the concentration of peroxynitrite in the range of 3 × 10⁻⁸ to 5.0 × 10⁻⁶ mol L⁻¹ with a correlation coefficient of 0.998, and the detection limit is 1 × 10⁻⁸ mol L⁻¹. Interferences from some metal ions normally seen in biological samples, and also some anions structurally similar to peroxynitrite were studied. The optimal conditions for the detection of peroxynitrite were evaluated.