Atomic Absorption Measurements Research Articles

Development of a Simple System for the Determination of Arsenic after Hydride Generation Atomic Absorption Spectrophotometry

A simple and inexpensive hydride generation system that uses a pyrex boiling tube as a reduction vessel to hold the acidified sample into which 2cm3 of 100-300mg sodium tetrahydroborate (III) solution isinjected such that the excess molecular hydrogen evolved carries the generated arsine directly through the atomic absorption spectrophotometer nebuliser to a nitrogen-hydrogen entrained air flame for atomic absorption measurement is described. The average absorption by arsenic atoms generated from the total arsine evolved was measured by integrating the absorbance for 16 seconds. The use of the absorption signal integration mode was found to free the technique from most kinetic interferences, while the stripping of the arsine from solution reduces the potential for chemical interferences in the solution phase. Gas flow rates affected sensitivity markedly, but theoptimal flow rates for nitrogen and hydrogen were standardised on 90cm3s-1 and 30cm3s-1 respectively as a compromise between lower flow-rates giving longer arsenic residence times and higher sensitivity, and higher flowrates giving a stiffer, less draught-sensitive flame. An optimum flame height of 6mm above the burner producedsufficient atomization and low background absorption. Generally, sample volumes between 5-20cm3 could be used in different acidic media within the concentration range 10% (v/v) . 50% (v/v). The proposed system produced a significantly improved atomic absorption sensitivity of 25ng and a detection limit of (95% confidence) of 5.2ng forarsenic. Both performance characteristics were found to be better by a factor . 12 and . 27 respectively than achieved with air-acetylene flames. The method is highly reproducible at trace levels having an overall precision of 1% for 0.5ƒÊg of arsenic. The upper limit of linearity of the response for atomic absorption measurements is about 0.7ƒÊg. In use, the apparatus is fast and convenient to operate, enabling about forty determinations per hour

Synthesis and characterization of polyacrylamides containing meso‐2,3‐dimercaptosuccinic acid end groups

AbstractBy using meso‐2,3‐dimercaptosuccinic acid‐cerium(IV) sulfate and meso‐2,3‐dimercaptosuccinic acid‐potassium permanganate redox systems, the polymerization reaction of acrylamide (AAm) monomer was examined in aqueous acidic medium at low temperatures. Water‐soluble polyacrylamides bearing meso‐2,3‐dimercaptosuccinic acid end groups were synthesized using meso‐2,3‐dimercaptosuccinic acid as a reducing agent. The effects of parameters such as the molar ratio of acrylamide to initiator, temperature, polymerization time, and sulfuric acid concentration on the yields and molecular weights of polymers were investigated. The augmentation in initiator concentration resulted in a decrease in molecular weight but an increase in the yield of polymers. The increase in reaction temperature from 20 to 60°C led to a decrease in the yield from 56.80% to 20.58%. Ce(IV) and Mn(VII) ions are reduced to Ce(III) and Mn(II) ions in the polymerization reaction and the synthesized acrylamide polymers containing meso‐2,3‐dimercaptosuccinic acid end groups can absorb these ions at the end of the polymerization reaction. Ultraviolet‐visible and atomic absorption measurements of polymer solutions were performed to indicate complexation between polyacrylamide and Ce(III) ions or Mn(II) ions. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:45–53, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20180

Optimization of parameters of chemical spray pyrolysis technique to get n and p-type layers of SnS

SnS thin films were prepared using automated chemical spray pyrolysis (CSP) technique. Single-phase, p-type, stoichiometric, SnS films with direct band gap of 1.33 eV and having very high absorption coefficient (> 10 5/cm) were deposited at substrate temperature of 375 °C. The role of substrate temperature in determining the optoelectronic and structural properties of SnS films was established and concentration ratios of anionic and cationic precursor solutions were optimized. n-type SnS samples were also prepared using CSP technique at the same substrate temperature of 375 °C, which facilitates sequential deposition of SnS homojunction. A comprehensive analysis of both types of films was done using x-ray diffraction, energy dispersive x-ray analysis, scanning electron microscopy, atomic force microscopy, optical absorption and electrical measurements. Deposition temperatures required for growth of other binary sulfide phases of tin such as SnS 2, Sn 2S 3 were also determined.

Zinc Binding Properties of Engineered RING Finger Domain of Arkadia E3 Ubiquitin Ligase

Human Arkadia is a nuclear protein consisted of 989 amino acid residues, with a characteristic RING domain in its C-terminus. The RING domain harbours the E3 ubiquitin ligase activity needed by Arkadia to ubiquitinate its substrates such as negative regulators of TGF-β signaling. The RING finger domain of Arkadia is a RING-H2 type and its structure and stability is strongly dependent on the presence of two bound Zn(II) ions attached to the protein frame through a defined Cys3-His2-Cys3 motif. In the present paper we transform the RING-H2 type of Arkadia finger domain to nonnative RING sequence, substituting the zinc-binding residues Cys955 or His960 to Arginine, through site-directed mutagenesis. The recombinant expression, in Escherichia coli, of the mutants C955R and H960R reveal significant lower yield in respect with the native polypeptide of Arkadia RING-H2 finger domain. In particular, only the C955R mutant exhibits expression yield sufficient for recombinant protein isolation and preliminary studies. Atomic absorption measurements and preliminary NMR data analysis reveal that the C955R point mutation in the RING Finger domain of Arkadia diminishes dramatically the zinc binding affinity, leading to the breakdown of the global structural integrity of the RING construct.

Búsqueda de Catalizadores Sólidos Básicos para la Producción de Biodiesel

This work aimed to find active and stable solid base catalysts for clean biodiesel production using heterogeneous reaction systems. Three types of catalysts were synthesized and evaluated in the transesterification of triacetin: CaO, γ-Al2O3 modified with Na and K, and MgO modified with Na, Li, Rb and Cs. The influence of the textural proprieties, the type and amount of alkali metal impregnated and the activation with N2 on the basicity and the catalytic behavior were analyzed. Stability of catalysts was analyzed using atomic absorption measurements and reuse reactions. Results showed that metal impregnation does not lead to the formation of stable solids, because they present lixiviation in the reaction system. The CaO maintained a high catalytic activity during five reaction cycles showing its high potential of its use in an industrial process.

Direct analysis of environmental and biological samples for total mercury with comparison of sequential atomic absorption and fluorescence measurements from a single combustion event

A Direct Mercury Analyzer (DMA) based on sample combustion, concentration of mercury by amalgamation with gold, and cold vapor atomic absorption spectrometry (CVAAS) was coupled to a mercury-specific cold vapor atomic fluorescence spectrometer (CVAFS). The purpose was to evaluate combustion-AFS, a technique which is not commercially available, for low-level analysis of mercury in environmental and biological samples. The experimental setup allowed for comparison of dual measurements of mercury (AAS followed by AFS) for a single combustion event. The AFS instrument control program was modified to properly time capture of mercury from the DMA, avoiding deleterious combustion products from reaching its gold traps. Calibration was carried out using both aqueous solutions and solid reference materials. The absolute detection limits for mercury were 0.002 ng for AFS and 0.016 ng for AAS. Recoveries for reference materials ranged from 89% to 111%, and the precision was generally found to be <10% relative standard deviation (RSD). The two methods produced similar results for samples of hair, finger nails, coal, soil, leaves and food stuffs. However, for samples with mercury near the AAS detection limit (e.g., filter paper spotted with whole blood and segments of tree rings) the signal was still quantifiable with AFS, demonstrating the lower detection limit and greater sensitivity of AFS. This study shows that combustion-AFS is feasible for the direct analysis of low levels of mercury in solid samples that would otherwise require time-consuming and contamination-prone digestion.

Synthesis and Characterization of (Fe(II),Co(II),Ni(II) and Cu(II)) Complexes with Schiff Base derived from [benzoyl hydrazine] with [benzyl mono oxime

The reaction of [Benzoyl hydrazine] with [Diphenyl mono oxime] and Glacial acetic acid was carried out in methanol gave a new tridentate ligand [Benzoic acid (2-hydroxyimino- 1, 2-diphyneylethylidene) - hydrazide]. This ligand was reacted with some metal ions (Fe(II), Co(II), Ni(II), and Cu(II)) in methanol with (1:1) metal : ligand ratio to give a series of new complexes of the general formula [M(L)Cl2.H2O], where M= Fe(11), Co(11), Ni(11) and Cu(11). All compounds were characterized by spectroscopic methods (I.R, UV-Vis), elemental microanalysis (C.H.N), atomic absorption, magnetic susceptibility, and conductivity measurements. From the obtained data the proposed molecular structures were suggested for the complexes of Fe (II), Co (II), Ni (II) and Cu (II) are of geometric octahedral.

Synthesis and Characterization of (Fe(II),Co(II),Ni(II) and Cu(II)) Complexes with Schiff Base derived from [benzoyl hydrazine] with [benzyl mono oxime

The reaction of [Benzoyl hydrazine] with [Diphenyl mono oxime] and Glacial acetic acid was carried out in methanol gave a new tridentate ligand [Benzoic acid (2-hydroxyimino- 1, 2-diphyneylethylidene) - hydrazide]. This ligand was reacted with some metal ions (Fe(II), Co(II), Ni(II), and Cu(II)) in methanol with (1:1) metal : ligand ratio to give a series of new complexes of the general formula [M(L)Cl2.H2O], where M= Fe(11), Co(11), Ni(11) and Cu(11). All compounds were characterized by spectroscopic methods (I.R, UV-Vis), elemental microanalysis (C.H.N), atomic absorption, magnetic susceptibility, and conductivity measurements. From the obtained data the proposed molecular structures were suggested for the complexes of Fe (II), Co (II), Ni (II) and Cu (II) are of geometric octahedral.

A method for low volume and low Se concentration samples and application to paired cerebrospinal fluid and serum samples

The well-known beneficial health effects of Se have demanded the development of rapid and accurate methods for its analysis. A flow injection (FI) method with inductively coupled plasma mass spectrometry (ICP-MS) as a selenium-selective detector was optimized. Flow injection was carried out using a Knauer 1100 smartline inert series liquid chromatograph coupled with a Perkin Elmer DRC II ICP-mass spectrometer. For sample injection a Perkin Elmer electronic valve equipped with a 25 μL sample loop was employed. Before measurement, standards or samples were administered with 1 μg/L rhodium as internal standard for correction of changes in detector response according to changes in sample electrolyte concentration. The method characterization parameters are: LOD (3σ criterion): 26 ng/L, LOQ (10σ criterion): 86 ng/L, linearity: 0.05–>10 μg/L, r 2=0.9999, serial or day-to-day precision at 2 μg/L: 4.48% or 5.6%. Accuracy was determined by (a) recovery experiments (CSF spiked with 2 μg/L Se); (b) comparison of FI-ICP-MS measurement with graphite furnace atomic absorption (GFAAS) measurements of 1:10 diluted serum samples; (c) Se determination in urine and serum control materials. Recovery (a) was 101.4%, measurement comparison with GFAAS (b) showed 98.8% (5 serum samples, 1:10 diluted in the range of 0.5–1.3 μg/L, compared to GFAAS determination, which was set to 100%), and accuracy was 96.8% or 105.6% for the serum or urine control material. Analysis time per sample was short and typically below 2 min for the complete measurement, including sample introduction, sample-line purge and quadruplicate Se determination. This method was used to determine Se in cerebrospinal fluid (CSF) and plasma (here parallel to GFAAS) in 35 paired serum and CSF samples. Se determination gave values in the range of 42–130 μg/L for serum and 1.63–6.66 μg/L for CSF. The median for Se in 35 individual CSF samples was 3.28 μg/L, the mean (±SD) was 3.67 (1.35) μg/L, whilst for individual serum samples the median was 81 μg/L and the mean (±SD) was 85 (26) μg/L. When relating the paired Se concentrations of CSF samples to respective serum samples it turned out that Se-CSF (behind blood brain barrier (BBB)) is independent on Se-serum concentration (before BBB).

Thermodynamic of LiF dissolution in alkylcarbonates and some of their mixtures with water

The solubility of lithium fluoride has so far never been studied in alkylcarbonate solvents. These data is essential to understand the behavior of this salt in solution, in particular in the field of lithium-ion batteries. The solubility of lithium fluoride (LiF) was measured at various temperatures in propylene carbonate (PC), ethylene carbonate (EC) and dimethyl carbonate (DMC) by atomic absorption spectroscopy. The LiF free enthalpy, enthalpy and entropy of dissolution in these solvents were deduced from the results. The solubility of LiF differs significantly with the nature of the solvent, EC being by far the most solubilizing media. The high solubilizing power of EC towards LiF cannot be explain by any of the physico-chemical properties of the solvent, but by an entropy-driven phenomenon. The solubilities of LiF in water–alkylcarbonates mixtures were determined by conductimetry at several temperatures leading to the corresponding LiF thermodynamic properties in these media. Results are discussed and compared to those obtained by atomic absorption measurements. Finally, a scheme representing the different stages for the dissolution of LiF in alkylcarbonates is proposed.

Trace vanadium analysis by catalytic adsorptive stripping voltammetry using mercury-coated micro-wire and polystyrene-coated bismuth film electrodes

An electrochemical technique has been developed for ultra-trace (ng L −1) vanadium (V) measurement. Catalytic adsorptive stripping voltammetry for V analysis was developed at mercury-coated gold micro-wire electrodes (MWEs, 100 μm) in the presence of gallic acid (GA) and bromate ion. A potential of −0.275 V (vs Ag/AgCl) was used to accumulate the complex in acetate buffer (pH 5.0) at the electrode surface followed by a differential pulse voltammetric scan. Parameters affecting the electrochemical response, including pH, concentration of GA and bromate, deposition potential and time have been optimized. Linear response was obtained in the 0–1000 ng L −1 range (2 min deposition), with a detection limit of 0.88 ng L −1. The method was validated by comparison of results for an unknown solution of V by atomic absorption measurement. The protocol was evaluated in a real sample by measuring the amount of V in river water samples. Thick bismuth film electrodes with protective polystyrene films have also been made and evaluated as a mercury free alternative. However, ng L −1 level detection was only attainable with extended (10 min) deposition times. The proposed use of MWEs for the detection of V is sensitive enough for future use to test V concentration in biological fluids treated by the advanced oxidation process (AOP).

Room temperature synthesis of nanostructured mixed-ordered-vacancy compounds (OVCs) and chalcopyrite CuInSe2 (CIS) thin films in alkaline chemical bath

Room temperature synthesis of ordered-vacancy-compounds (OVCs) and copper indium diselenide (CuInSe2, CIS) by cation and anion exchange reactions of solid CdS thin films with CIS ionic solution in an alkaline chemical bath is reported. The growth parameters such as pH, deposition time and concentration of the solutions were optimized to achieve uniform thin films. Nanostructured CdS thin films (150 nm thick) prepared by chemical bath deposition are used for the deposition of OVC and CIS thin films. The ion exchange reaction between the CdS thin film and the CIS ionic solutions transforms the yellow colour CdS film into faint black, indicating the formation of OVC and CIS film. The resultant films were annealed in air at 200 °C for 1 h and further subjected to characterization using the x-ray diffraction, transmission electron microscopy, energy dispersive x-ray analysis, x-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, optical absorption and electrical measurement techniques. The OVC and CuIn3Se5 nanodomains are observed in chalcopyrite CIS thin films and these films have nanostructured morphology onto amorphous/nanocrystalline phase of CdS. The OVC–CIS films are p-type with a band gap energy of 1.453 eV.

New Functionalised C,C-pyridylpyrazoles: Synthesis and Cation Binding Properties

The synthesis of two new C,C-pyridylpyrazole isomers with a functionalised arm is described. The complexation capabilities of these ligands compared to their homologues towards bivalent metals (Hg2+, Cd2+, Pb2+, Cu2+, Zn2+) and alkali metal ions (K+, Na+, Li+) were investigated using a liquid–liquid extraction process. The percentage limits of extraction were determined by atomic absorption measurements.

Synthesis and characterization of novel silica gel supported N-pyrazole ligand for selective elimination of Hg(II)

The polar organic molecule N-(2-hydroxyethyl)-3,5-dimethylpyrazole reacted with a 3-glycidoxypropyltrimethoxysilane silylant agent, previously anchored on a silica surface in a heterogeneous way to yield the product SiPz. The epoxide group was opened yielding chelating pendant group bonded to the inorganic surface. The product was characterized through elemental analysis, infrared spectroscopy, 13C NMR, surface area and thermogravimetry. The binding and adsorption abilities of SiPz was investigated for Hg 2+, Cd 2+, Pb 2+, Cu 2+, Zn 2+, K +, Na + and Li + cations and compared to results of classical liquid–liquid extraction with the unbound N-pyrazole compound. The grafting at the surface of silica does not affect complexing properties of the ligand and the SiPz exhibits a high selectivity toward Hg 2+ ion with no complexation being observed towards Zinc and alkali metals. The extracted and the complexing cation percentage were determined by atomic absorption measurements.

Biosynthetic origin of medicarpin in elicited fenugreek (Trigonella foenum-graecum L.) seedlings

Medicarpin (M), an isoflavonoid phytoalexin with antioxidant [1] and antifungal properties [2], is produced by leguminous plants mainly in response to biotic or abiotic elicitation [3]. The difference in the biosynthetic origin of copper-induced accumulation between tissues of the same or related species prompted the systematic investigation on the accumulation of M and its 3-O-glucoside-6'-O-malonate (MGM) in intact seedlings, as well as their exudation in the culture media. Methanolic extracts of roots and shoots from 6-days old seedlings, treated hydroponically with CuCl2 (0.01, 0.05, 0.1, 0.5 and 1mM) for 24h, were analysed by RP-HPLC. At low [Cu] concentrations, roots produced high amounts of M, most of which exuded in the culture medium, while there was no significant decrease of MGM. Increase of [Cu] caused a progressive reduction of MGM to form free M, the excretion of which was significantly reduced. In contrast, M accumulation increased in shoots with increasing [Cu] concentration, while there were no significant changes in MGM. Atomic absorption measurements showed that [Cu] accumulated more in roots, than in shoots, which may explain the difference in the response of the two tissues, suggesting that mild [Cu] stress induces the biosynthesis of M, while severe stress conditions trigger the hydrolysis of MGM in order to form free M. The de novo synthesis of M in roots and shoots induced by copper elicitation was implied by the copper-induced increase of phenylalanine ammonia lyase enzyme activity, as well as the up-regulation of the M pathway genes, chalcone synthase and vestitone reductase, as monitored using RT-PCR.

Visualizing the Solute Vaporization Interference in Flame Atomic Absorption Spectroscopy

Every day, tens of thousands of chemists use analytical atomic spectroscopy in their work, often without knowledge of possible interferences. We present a unique approach to study these interferences by using modern response surface methods to visualize an interference in which aluminum depresses the calcium atomic absorption signal. Calcium atomic absorption measurements are performed on solutions that contain calcium only, calcium plus aluminum, and calcium plus aluminum with lanthanum added as a releasing agent. The interferences are known to be affected by flame temperature, so measurements were made under conditions of varied flame stoichiometry and observation height. Results are displayed using response surfaces generated by regression analysis of the results of a factorial design in which burner height and fuel ratios are varied. Response surface methods allow students to recognize the tradeoffs required to optimize instrumental parameters. The user can chose to optimize operating conditions based on minimizing the solute vaporization interference, maximizing the absorbance, optimizing signal-to-noise ratio, or any combination of these three diagnostic parameters. The conditions needed for stable, reproducible chemical analyses were substantially different from those that produce the maximum signal.

Spectrophotometric and Atomic Absorption Determination of Ramipril, Enalapril Maleate and Fosinopril through Ternary Complex Formation with Molybdenum (V)-Thiocyanate (Mo(V)-SCN)

Three different sensitive and accurate spectroscopic procedures were developed for the determination of three angiotensin-converting enzyme inhibitors, namely, ramipril, enalapril maleate and fosinopril. The first two spectrophotometric (extractive and non-extractive) procedures were based on ternary complex formation with molybdenum(V) thiocyanate. The formed complex can be determined by extraction with chloroform measured at lambdamax 517 nm Beer's law was obeyed in the concentration range from (10--90 microg ml(-1)) for ramipril and fosinopril and (4--36 microg ml(-1)) for enalapril maleate with molar absorptivity 1.2x10(4), 2x10(4) and 3.4x10(4) l mol(-1) cm(-1), respectively, or by direct measurement after addition of benzalkonium chloride as surfactant and measuring the formed ternary complex at lambdamax 545 nm with a linear relationship in the concentration range from (8-7-2 microg ml(-1)), (3--27 microg ml(-1)) and (8--72 microg ml(-1)) for ramipril, enalapril maleate and fosinopril with molar absorptivity 1.5x10(4), 5x10(4) and 2.1x10(4) l mol(-1) cm(-1), respectively. The third procedure is atomic absorption measurement through the quantitative determination of molybdenum content of the complex. These methods hold their accuracy and precision well when applied to the determination of ramipril, enalapril maleate and fosinopril in their dosage forms.

C,N‐Pyridylpyrazole‐Based Ligands: Synthesis and Preliminary Use in Metal Ion Extraction

The synthesis of new N‐donor pyridylpyrazole ligands with a functionalized arm is described. The complexation capabilities of these compounds towards bivalent metal ions (Hg2+, Cd2+, Pb2+, Cu2+, and Zn2+) and alkali metal ions (K+, Na+, and Li+) were investigated using the liquid‐liquid extraction process. The percentage limits of extraction were determined by atomic absorption measurements.

Water-soluble and highly fluorescent hybrids of multi-walled carbon nanotubes withuniformly arranged gold nanoparticles

Water-soluble hybrids of multi-walled carbon nanotubes (MWNTs) and gold nanoparticles(Au@MWNTs) were fabricated via the in situ solution method and characterized bytransmission electron microscopy (TEM), scanning electron microscopy (SEM), andenergy dispersive x-ray spectroscopy (EDS). An optoelectronic-active compound ofN,N′-bi(2-mercaptoethyl)-perylene-3,4,9,10-tetracarboxylic diimide (MEPTCDI) wasemployed as interlinker and stabilizer for the formation of the Au@MWNTs hybrids.The size of Au nanoparticles in the hybrids can be controlled and decreased to alimited small range with high stability via this in situ fabrication approach. Thehybrid formation mechanism was proposed by making comparison with otherhybrids, employing various organic or organic groups as interlinkers, and wasfurther demonstrated by TEM, ultraviolet–visible (UV–vis), and atomic absorptionmeasurements. The optical properties of the Au@MWNTs hybrids were studied, and itwas found that the hybrid exhibited strong visible luminescence under UV lampirradiation, which might extend its potential applications to biological labeling,etc.

Spray deposition of highly transparent fluorine doped cadmium oxide thin films

The cadmium oxide (CdO) and F:CdO films have been deposited by spray pyrolysis method using cadmium acetate and ammonium fluoride as precursors for Cd and F ions, respectively. The effect of temperature and F doping on the structural, morphological, optical and Hall effect properties of sprayed CdO thin films was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), optical absorption and electrical measurement techniques. TGA and DTA studies, indicates the formation of CdO by decomposition of cadmium acetate after 250 °C. XRD patterns reveal that samples are polycrystalline with cubic structure and exhibits (2 0 0) preferential orientation. Considerable broading of (2 0 0) peak, simultaneous shifting of corresponding Bragg's angle have been observed with respect to F doping level. SEM and AFM show the heterogeneous distribution of cubical grains all over the substrate, which are randomly distributed. F doping shifts the optical gap along with the increase in the transparency of CdO films. The Hall effect measurement indicates that the resistivity and mobility decrease up to 4% F doping.