Graphite-furnace atomization of phosphorus

The slopes of the ln (absorbance) vs. T^?1 dependences for platform/graphite furnace atomization of phosphorus in the presence of Ni²⁺ or La³⁺ modifiers are measured, and found to be similar to the theoretical slope calculated for isothermal atomization. It is concluded that in both cases the atomization mechanism is the same and is expressed by P_2(gas) ? 2P_(gas); P_(gas) ? P^*_(gas). The atomic absorption signal for phosphorus appears and reaches its maximum later when the atomization is carried out from the platform in the presence of modifiers. Hence atomization takes place under nearly isothermal conditions and is much more efficient, thus providing the best conditions for the determination of phosphorus. Treatment of a deteriorated graphite surface with ZrOCl₂ solution repairs any defects and improves the sensitivity of phosphorus determination.     

Use of an Impaction-Electrothermal Atomization Atomic Absorption Spectrometric System for the Direct Determination of Cadmium,Copper, and Manganese in the Laboratory Atmosphere

Abstract

Results on an impaction-electrothermal atomization atomic absorption spectrometric system for the direct, and on a nearly real-time basis, determination of cadmium, copper, and manganese in the laboratory atmosphere are presented. Background levels for cadmium were 3 ng m^?3, for copper were 100 ng m^?3, and for manganese were 30 ng m^?3 and were found to increase with activity in the vicinity of the system. Addition of a connecting faceplate to the impactor allowed a more convenient and accurate method of standardization to be achieved.     

Structural conversion of an oxazolidine ligand upon treatment with copper(I) and (II) halides; structural,spectral, theoretical and docking studies

Abstract

In this work, the 2-(2-(pyridin-2-yl)oxazolidin-3-yl)ethanol (AEPC) ligand was prepared under solvent free conditions using ultrasonic irradiation, before reaction with a Cu(NO₃)₂/KSCN mixture, CuCl₂ and CuI, the products of which were characterized by elemental analysis, UV-Vis, FT-IR spectroscopy and single-crystal X-ray diffraction. The X-ray analyses results revealed that AEPC, after reactions with the three copper(I/II) halides, gave structures ([Cu(DEA)Cl₂] (2), DEA?=?diethanolamine, [Cu(BHEG)₂] (3), BHEG?=?bis(2-hydroxyethyl)glycinato); however, it retains its structure on treatment with Cu(NO₃)₂/KSCN mixture ([Cu(AEPC)(NCS)₂] (1)). The geometrical parameters for the complexes were compared with the Cambridge Structural Database (CSD) and coordination modes for thiocyanate ion were extracted. In the crystal structure of 1, the copper ion has a distorted square-pyramidal geometry and a CuN^pyN₂^NCSN^tertO^alc environment in which the AEPC acts as NN'O-donor in a facial coordination mode. In the crystal structure of 2, the copper ion has a Cu(N^sec)(O^alc)₂Cl₂ environment and distorted square-pyramidal geometry in which the DEA ligand is coordinated as a mer-NO₂-donor. The copper ion in 3 has a CuN₂O₄ environment and distorted octahedral geometry. The ability of these compounds to interact with the nine biomacromolecules (BRAF kinase, CatB, DNA gyrase, HDAC7, rHA, RNR, TrxR, TS and Top II) was investigated by Docking calculations and compared with that of doxorubicin. The thermodynamic stability of 1 and its isomer and also charge distribution patterns were studied by DFT and NBO analysis, respectively.     

Determination of kinetic parameters for atom formation at constant temperature in graphite furnace atomic absorption spectroscopy

A new method for the simultaneous determination of the kinetic order and activation energy for atom release under isothermal condition in a graphite furnace has been developed. Tungsten wire probe atomization was employed to examine the validity of the present method. By means of this model, the kinetic parameters for the atomization of Bi, Ge, Pb and Mn at constant temperatures were successfully determined. The values of the kinetic order and activation energy were found to be 0.67 ± 0.01 and 302 ± 8 kJ mol⁻¹ for Bi, 1.01 ± 0.08 and 109 ± 2 kJ mol⁻¹ for Ge, 0.46 ± 0.01 and 159 ± 2 kJ mol⁻¹ for Pb and 0.97 ± 0.03 and 372 ± 5 kJ mol⁻¹ for Mn, respectively. The atomization mechanism for these four elements from the tungsten probe surface was also discussed.     

选择性响应Cu~(2+)、Ag~+及阴离子的菲咯啉-水杨醛荧光探针

在乙酸酐中用2,9-二甲基-1,10-菲咯啉与水杨醛缩合反应得到2,2′-(1E,1′E)-2,2′-(1,10-菲咯啉-2,9-二基)双(乙烯-2,1-二基)双(2,1-亚苯基)二乙酸酯(探针1);再将其进一步水解得到2,2′-(1E,1′E)-2,2′-(1,10-菲咯啉-2,9-二基)双(乙烯-2,1-二基)二苯酚(探针2)。经1H NMR、13C NMR、IR、MS表征,探针化合物为大共轭结构,发光性能良好。两种探针分别表现出对Cu2+、Ag+不同的荧光猝灭作用,探针2还能识别阴离子F-和AcO-,具有双功能离子检测性能。光谱滴定、等温滴定量热及质谱等测定了配合物组成、作用常数及热力学参数,探针与金属离子的配合为放热反应,作用比为2∶1。     

选择性响应Cu2+、Ag+及阴离子的菲咯啉-水杨醛荧光探针

在乙酸酐中用2,9-二甲基-1,10-菲咯啉与水杨醛缩合反应得到2,2’-（1E,1’E）-2,2’-（1,10-菲咯啉-2,9-二基）双（乙烯-2,1-二基）双（2,1-亚苯基）二乙酸酯（探针1）;再将其进一步水解得到2,2’-（1E,1’E）-2,2’-（1,10-菲咯啉-2,9-二基）双（乙烯-2,1-二基）二苯酚（探针2）。经¹H NMR、¹³C NMR、IR、MS表征,探针化合物为大共轭结构,发光性能良好。两种探针分别表现出对Cu²⁺、Ag⁺不同的荧光猝灭作用,探针2还能识别阴离子F^-和AcO^-,具有双功能离子检测性能。光谱滴定、等温滴定量热及质谱等测定了配合物组成、作用常数及热力学参数,探针与金属离子的配合为放热反应,作用比为2：1。     

A new atomization cell for trace metal determinations by tungsten coil atomic spectrometry

A new metallic atomization cell is used for trace metal determinations by tungsten coil atomic absorption spectrometry and tungsten coil atomic emission spectrometry. Different protecting gas mixtures are evaluated to improve atomic emission signals. Ar, N₂, CO₂ and He are used as solvents, and H₂ and C₂H₂ as solutes. A H₂/Ar mixture provided the best results. Parameters such as protecting gas flow rate and atomization current are also optimized. The optimal conditions are used to determine the figures of merit for both methods and the results are compared with values found in the literature. The new cell provides a better control of the radiation reaching the detector and a small, more isothermal environment around the atomizer. A more concentrated atomic cloud and a smaller background signal result in lower limits of detection using both methods. Cu (324.7 nm), Cd (228.8 nm) and Sn (286.3 nm) determined by tungsten coil atomic absorption spectrometry presented limits of detection as low as 0.6, 0.1, and 2.2 μg L⁻¹, respectively. For Cr (425.4 nm), Eu (459.4 nm) and Sr (460.7 nm) determined by tungsten coil atomic emission spectrometry, limits of detection of 4.5, 2.5, and 0.1 μg L⁻¹ were calculated. The method is used to determine Cu, Cd, Cr and Sr in a water standard reference material. Results for Cu, Cd and Cr presented no significant difference from reported values in a 95% confidence level. For Sr, a 113% recovery was obtained.     

Preparation and adsorption properties of crosslinked polystyrene-supported low-generation diethanolamine-typed dendrimer for metal ions

Two novel chelating resins, polystyrene supported G1.0 diethanolamine-typed dendrimer (PS-DEA) and G2.0 diethanolamine-typed dendrimer (PS-(DEA)₂), were prepared by anchoring low-generations diethanolamine-typed dendrimer into crosslinked polystyrene in this paper. Fourier transform-infrared spectra (FTIR), scanning electron microscopy (SEM) and elemental analysis were employed to character their structures. The results of adsorption for metal ions showed that the resins had good adsorption capacities for Cu²⁺, Ag⁺ and Hg²⁺, especially PS-DEA for Cu²⁺. The adsorption kinetics and adsorption isotherms of PS-DEA for Cu²⁺ and PS-(DEA)₂ for Hg²⁺ were studied. The results showed that the adsorption kinetics of the two resins can be modeled by pseudo second-order rate equation wonderfully and Langmuir and Freundlich equations could well interpret the adsorption of PS-(DEA)₂ for Hg²⁺ and PS-DEA for Cu²⁺, respectively. The adsorption mechanism of the resins for Cu²⁺ was confirmed by X-ray photoelectron spectroscopy (XPS).     

Electrothermal atomization of silver in graphite furnaces. Part 2. Effects of copper,ascorbic acid and Triton X-100

The effects of copper, ascorbic acid and Triton X-100 on the atomization process of Ag are presented as a function of the initial mass of analyte and the heating rate of atomization. In general, a double pulse structure is detected, at a heating rate of 300 K s⁻¹, in the absorbance profile and its time derivative. This behavior shows up in the Arrhenius plots as two temperature regions of atomization. In the presence of Cu and Triton X-100, a low atomization energy E_a is obtained in the low temperature region and a high value of E_a, which approaches the heat of vaporization of Ag, is obtained in the high temperature region. However, in the presence of ascorbic acid, two low desorption energies are obtained in both temperature regions, suggesting a higher dispersion of particles owing to the presence of a higher number of active sites. At a heating rate of 700 K s⁻¹, a single atomization step with an atomization energy of 233 kJ mol⁻¹ and a first kinetic order of release is detected in the presence of Cu. However, in the presence of ascorbic acid and Triton X-100, two temperature regions of atomization are obtained from the Arrhenius plots, even though the absorbance profiles look continuous. In these cases, a mass dependent E_a is obtained in the low temperature region, and a low E_a with a first kinetic order of release is obtained in the high temperature region. In summary, the low value of E_a indicates vaporization from disperse particles, whereas the mass dependent, higher value of E_a indicates atomization from small clusters, the size and energy of which increase as the initial mass of Ag increases.The structure of the absorbance profiles and their time derivatives, and also the behavior of the Arrhenius plots, correlate well with those predicted by the two-precursor atomization model proposed in our previous work [1].     

Thermal electron capture by some halopropanes

Thermal electron attachment rate constants for CF₃CHClCH₃, CF₂ClCFClCF₃ and CBrF₂CH₂CH₂Br have been measured with electron swarm method. Corresponding rate constants are equal to 7.6×10⁻¹¹, 5.5×10⁻⁹ and 1.5×10⁻⁸ cm³ molecule⁻¹ s⁻¹, respectively. The dissociative electron attachment (DEA) spectra for nine haloalkanes have been determined using negative ion mass spectrometry. The correlation between rate constants, position of the DEA peaks and vertical attachment energy (VAE) available in literature has been demonstrated.     

Determination of Rhodium in Biological Materials by Electrothermal Atomic Absorption Spectrometry with a Tungsten Tube Atomizer

Abstract

Electrothermal atomic absorption spectrometry (ETAAS) of rhodium with a tungsten tube atomizer has been investigated under optimum conditions (atomization temperature; 2230 C, purge gas; Ar 480 ml min^?1 + H₂ 20 ml min^?1, and pyrolysis temperature; 590 C). The absolute characteristic mass (the mass of element giving 0.0044 abs.) of rhodium by the atomizer was 86.5 pg and the detection limit was 16.5 ng ml^?1 (3S/N). The interferences caused by large amounts of interferents were evaluated. Al, Ca, Cu, Fe, K, Mg, Na, Pb and Zn severely interfered in the AA signal of rhodium. Ammonium phosphate, ascorbic acid, palladium nitrate, copper nitrate, lanthanum nitrate, thiocyanate and thiourea, well known as matrix modifiers were tested to eliminate the severe interferences. However, by the addition of these compounds, the rhodium signal was not recovered. The standard addition method was adapted for the determination of rhodium in biological materials. The recovery of spiked-rhodium in biological materials was in the range of 97.4 to 107%.     

Preparation of PSSS‐grafted polysulfone microfiltration membrane and its rejection and removal properties towards heavy metal ions

3‐Hydroxy‐N,N‐diethylaniline (HDEA) as a tertiary aromatic amine was introduced onto the surface of chloromethylated polysulfone (CMPSF) microfiltration membrane through modification reaction, resulting in the modified membrane PSF‐DEA. A redox surface‐initiating system (DEA/APS) was constituted by the bonded tertiary aromatic amine group DEA and ammonium persulfate (APS) in aqueous solution, and so, the free radicals formed on the membrane initiated sodium p‐styrenesulfonate (SSS) as an anionic monomer to produce graft polymerization, getting the grafting‐type composite microfiltration membrane, PSF‐g‐PSSS membrane. Subsequently, the adsorption property of PSF‐g‐PSSS membrane for three heavy metal ions, Pb²⁺, Zn²⁺, and Hg²⁺ ions, was fully examined, and the rejection performance of PSF‐g‐PSSS membrane towards the three heavy metal ions was emphatically evaluated via permeation experiments. The experimental results show that by the initiating of the surface‐initiating system of DEA/APS, the graft polymerization can smoothly be carried out under mild conditions. PSF‐g‐PSSS membrane as a functional microfiltration membrane has strong adsorption ability for heavy metal ions by right of strong electrostatic interaction (or ion exchange action) between the anionic sulfonate ions on the membrane and heavy metal ions. The order of adsorption capacity is Pb²⁺ > Zn²⁺ > Hg²⁺, and the adsorption capacity of Pb²⁺ ion gets up to 2.18 μmol/cm². As the volume of permeation solutions, in which the concentrations of the three metal ions are 0.2 mmol/L, are in a range of 50 to 70 mL, the rejection rate of PSF‐g‐PSSS membrane for the three heavy metal ions can reach a level of 95%, displaying a fine rejection and removing performance towards heavy metal ions.     

The Determination Of Thallium In Human Hair By Graphite Furnace Atomic Absorption Spectrophotometry

Abstract

An atomic absorption spectrophotometric procedure is des-scribed for the rapid determination of thallium in human hair. Samples of 500 μg are dissolved in nitric acid and treated with hydrogen peroxide. Aliquots of 10 μL are then analyzed using electrothermal atomization in a graphite tube furnace. The characteristic concentration for the method is 1 mg Tl kg^?1 which is adequate for forensic investigation. The relative standard deviation for a series of signals from a hair sample spiked to contain 32 mg Tl^?1 kg was 3 per cent.     

Superhydrogels of Nanotubes Capable of Capturing Heavy‐Metal Ions

Self‐assembly regulated by hydrogen bonds was successfully achieved in the system of lithocholic acid (LCA) mixed with three organic amines, ethanolamine (EA), diethanolamine (DEA), and triethanolamine (TEA), in aqueous solutions. The mixtures of DEA/LCA exhibit supergelation capability and the hydrogels consist of plenty of network nanotubes with uniform diameters of about 60 nm determined by cryogenic TEM. Interestingly, the sample with the same concentration in a system of EA and LCA is a birefringent solution, in which spherical vesicles and can be transformed into nanotubes as the amount of LCA increases. The formation of hydrogels could be driven by the delicate balance of diverse noncovalent interactions, including electrostatic interactions, hydrophobic interactions, steric effects, van der Waals forces, and mainly hydrogen bonds. The mechanism of self‐assembly from spherical bilayer vesicles into nanotubes was proposed. The dried hydrogels with nanotubes were explored to exhibit the excellent capability for capturing heavy‐metal ions, for example, Cu²⁺, Co²⁺, Ni²⁺, Pb²⁺, and Hg²⁺. The superhydrogels of nanotubes from the self‐assembly of low‐molecular‐weight gelators mainly regulated by hydrogen bonds used for the removal of heavy‐metal ions is simple, green, and high efficiency, and provide a strategic approach to removing heavy‐metal ions from industrial sewage.     

Etilefrine Plastic Membrane Electrodes Based on Individual and Mixed Ion-exchangers of Etilefrinium Phosphotungstate and Tetraphenylborate.

Abstract

Etilefrine hydrochloride (EfCl) selective PVC membrane electrodes based on Etilefrinium phosphotungstate (I), Etilefrinium tetraphenylborate (II) and a mixture of both (III) were prepared, The electrodes exhibited near Nernstian response over the concentration ranges 5.0 × 10^?6 - 1.0 × 10^?1, 6.3 × 10^?6 - 1.0 × 10^?1 and 6.3 × 10^?5 - 1.0 × 10^?1 M EfCl for electrodes I, II and III, respectively. The working pH ranges of electrodes I, II and III were 10 - 8.0, 10 - 7.5 and 10 - 7.5 and their isothermal coefficients were 0.00150, 0.00088 and 0.00072 V/°C, respectively. The electrodes showed good selectivity to EfCl with respect to many inorganic cations, sugars and amino acids. The standard additions method was used to determine EfCl in pure solutions and in pharmaceutical preparations.     

Synthesis of a Calix[4]crown‐6 Cone Conformer‐Based Oligomer and its Metal Cation Extraction Abilities

A new calixcrown‐6 oligomer 5 was synthesized by reacting a 1,3‐distal di‐amino derivative of cone p‐tert‐butylcalix[4]crown‐6 with malonyl dichloride. Extraction studies with precursor monomers 2 and 3 and oligomer 5 showed differences in their metal cation extraction behavior and selectivity. Precursors monomers 2 and 3 were selective for Hg²⁺; whereas, oligomer 5 showed high affinity towards both alkali (Li⁺, Na⁺, K⁺, and Cs⁺) and heavy metal cations (Cu²⁺, Cd²⁺, Hg²⁺ and Pb²⁺).     

Spectroscopic and Thermal Studies on 2,4,6-trinitro Toluene (TNT)

The kinetics and mechanism of the initial stage of thermal decomposition of 2,4,6-trinitro toluene (TNT), a widely used high explosive, have been studied, together with its morphology and evolved gaseous products using thermogravimetry (TG), differential thermal analysis (DTA), infrared spectroscopy (IR) and hot-stage microscopy. The kinetics of the thermolysis has been followed by IR after suppressing volatilisation by matrixing and by isothermal TG without suppressing volatilisation to simulate actual user conditions. The best linearity was obtained for Avrami-Erofeev equation for n=1 in isothermal IR and also in isothermal TG. The activation energy was found to be 135 kJ mol⁻¹, with logA (in s⁻¹) 12.5 by IR. The effect of additives on the initial thermolysis of TNT has also been studied. Evolved gas analysis by IR showed that CO₂, NO₂, NO and H₂O are more dominant than N₂O, HCN and CO. The decomposition involves the initial rupture of the C-NO₂ bond, weakened by hydrogen bonding with the labile hydrogen atom of the adjacent CH₃ group, followed by the abstraction of the hydrogen atom of the methyl group by NO₂, generated in the initial step. This revised version was published online in August 2006 with corrections to the Cover Date.     

Characterization of crystalline and amorphous content in pharmaceutical solids by dielectric thermal analysis

Morphological and thermodynamic transitions in drugs as well as their amorphous and crystalline content in the solid state have been distinguished by thermal analytical techniques, which include dielectric analysis (DEA), differential scanning calorimetry (DSC), and macro-photomicrography. These techniques were used successfully to establish a structure versus property relationship with the United States Pharmacopeia standard set of active pharmaceutical ingredient (API) drugs. A distinguishing method is the DSC determination of the amorphous and crystalline content which is based on the fusion properties of the specific drug and its recrystallization. The DSC technique to determine the crystalline and amorphous content is based on a series of heat and cool cycles to evaluate the drugs ability to recrystallize. To enhance the amorphous portion, the API is heated above its melting temperature and cooled with liquid nitrogen to ?120 °C (153 K). Alternatively a sample is program heated and cooled by DSC at a rate of 10 °C min^?1. DEA measures the crystalline solid and amorphous liquid API electrical ionic conductivity. The DEA ionic conductivity is repeatable and differentiates the solid crystalline drug with a low conductivity level (10^?2 pS cm^?1) and a high conductivity level associated with the amorphous liquid (10⁶ pS cm^?1). The DSC sets the analytical transition temperature range from melting to recrystallization. However, analysis of the DEA ionic conductivity cycle establishes the quantitative amorphous and crystalline content in the solid state at frequencies of 0.10–1.00 Hz and to greater than 30 °C below the melting transition as the peak melting temperature. This describes the “activation energy method.” An Arrhenius plot, log ionic conductivity versus reciprocal temperature (K^?1), of the pre-melt DEA transition yields frequency dependent activation energy (E _a, J mol^?1) for the complex charging in the solid state. The amorphous content is inversely proportional to the E _a where the E _a for the crystalline form is higher and lower for the amorphous form with a standard deviation of ±2%. There was a good agreement between the DSC crystalline melting, recrystallization, and the solid state DEA conductivity method with relevant microscopic evaluation. An alternate technique to determine amorphous and crystalline content has been established for the drugs of interest based on an obvious amorphous and crystalline state identified by macro-photomicrography and compared to the conductivity variations. This second “empirical method” correlates well with the “activation energy” method.