La matrice eau de mer et le signal du cuivre en spectrometrie d'absorption atomique sans flamme: Partie 2: Proposition d'un schéma explicatif des phénomènes observés pour une eau de mer

(Copper signals from seawater matrices in electrothermal atomic absorption spectrometry. Part 2: model for phenomena observed with sea water.)A model to explain the variations of copper signals in seawater is proposed on the basis of the results of Part 1 of this study and data obtained by ashing simulated seawaters under different conditions. The model is confirmed by the results found with nitric of sulfuric acid as modifier. In this model, ashing at 800°C hydrolyses MgCl₂ to MgO, and the consequent formation of sodium sulfide from the matrix stabilizes the copper in the furnace. The addition of a small nitrate concentration (0.2 M) induces, when magnesium is present, a complementary decrease of the interference.     

Effects of various salts on the determination of arsenic by graphite furnace atomic absorption spectrometry. Direct determination in seawater

The effect of Na, Mg, Ca and Sr as their nitrate, chloride and sulfate salts and seasalt, with and without the use of palladium, on the determination of arsenic by electrothermal atomic absorption spectrometry was investigated. In the absence of any stabilizing agent, arsenic was partially lost as molecular species at low temperatures. The effect of salts on the shape of the atomization signal, the integrated absorbance and the stabilizing effect were highly dependent both on their nature and mass. By trapping arsenic, oxide species resulting from the decomposition of nitrate salts induced a high stabilization effect depending on their vaporization temperatures: MgO～CaO>SrO>Na₂O. The stabilization effect of chlorides occurred about 200?°C lower and depended on mass, volatility and hydrolytic properties: SrCl₂>CaCl₂>MgCl₂～NaCl. The effect of sulfates was mainly dependent on their decomposition/vaporization mechanisms, and in the presence of Na₂SO₄ or CaSO₄ a strong chemical interference effect was observed. Palladium stabilized arsenic in the presence of nitrates, chlorides or even sulfates, leading to a similar delaying effect, signal shape and integrated absorbance. Seasalt induced also important modifications to the atomization signal of As. Moreover, an interference effect was observed, which could probably be attributed to the simultaneous vaporization of sulfate in seasalt. In seawater, Pd suppressed this interference effect and permitted to use a high pyrolysis temperature up to 1400?°C to remove the major part of the seawater matrix before atomization. Under optimized conditions, the detection limit for As obtained in unmodified seawater in the presence of Pd was 0.34 μg L^–1 for a 10 μl sample.     

Essais interlaboratoires: dosage du cadmium,du cuivre et du plomb dans l'eau de mer par spectrometrie d'absorption atomique electrothermique: |en|An in terlaboratory study of the determination of cadmium,copper and lead in seawater by electrothermal atomic absorption spectrometry

An in terlaboratory study of the determination of cadmium, copper and lead in seawater by electrothermal atomic absorption spectrometry.The reproducibility of a selective extraction method on Chelex-100 resin in the Ca²⁺ form, described previously, was tested on seawater with and without addition of Cd, Cu and Pb. The metals extracted were determined by electrothermal atomic absorption spectrometry (a.a.s.). The results obtained by the three laboratories participating in these tests prove the validity of the method for the determination of cadmium and copper. The largest dispersion of results, observed for lead, is related to the poorest precision of electrothermal a.a.s. for this element.     

Zeolite ZSM-5 containing copper ions: The effect of the copper salt anion and NH<Subscript>4</Subscript>OH/Cu<Superscript>2+</Superscript> ratio on the state of the copper ions and on the reactivity of the zeolite in DeNO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

Isotherms of copper cation sorption by H-ZSM-5 zeolite from aqueous and aqueous ammonia solutions of copper acetate, chloride, nitrate, and sulfate are considered in terms of Langmuir’s monomolecular adsorption model. Using UV-Vis diffuse reflectance spectroscopy, IR spectroscopy, and temperatureprogrammed reduction with hydrogen and carbon monoxide, it has been demonstrated that the electronic state of the copper ions is determined by the ion exchange and heat treatment conditions. The state of the copper ions has an effect on the redox properties and reactivity of the Cu-ZSM-5 catalysts in the selective catalytic reduction (SCR) of NO with propane and in N₂O decomposition. The amount of Cu²⁺ that is sorbed by zeolite H-ZSM-5 from aqueous solution and is stabilized as isolated Cu²⁺ cations in cationexchange sites of the zeolite depends largely on the copper salt anion. The quantity of Cu(II) cations sorbed from aqueous solutions of copper salts of strong acids is smaller than the quantity of the same cations sorbed from the copper acetate solution. When copper chloride or sulfate is used, the zeolite is modified by the chloride or sulfate anion. Because of the presence of these anions, the redox properties and nitrogen oxides removal (DeNO _x ) efficiency of the Cu-ZSM-5 catalysts prepared using the copper salts of strong acids are worse than the same characteristics of the sample prepared using the copper acetate solution. The addition of ammonia to the aqueous solutions of copper salts diminishes the copper salt anion effect on the amount of Cu(II) sorbed from these solutions and hampers the nonspecific sorption of anions on the zeolite surface. As a consequence, the redox and DeNO _x properties of Cu-ZSM-5 depend considerably on the NH₄OH/Cu²⁺ ratio in the solution used in ion exchange. The aqueous ammonia solutions of the copper salts with NH₄OH/Cu²⁺ = 6–10 stabilize, in the Cu-ZSM-5 structure, Cu²⁺ ions bonded with extraframework oxygen, which are more active in DeNO _x than isolated Cu²⁺ ions (which form at NH4OH/Cu2+ = 30) or nanosized CuO particles (which form at NH₄OH/Cu²⁺ = 3).     

Effects of various salts on the determination of arsenic by graphite furnace atomic absorption spectrometry. Direct determination in seawater

The effect of Na, Mg, Ca and Sr as their nitrate, chloride and sulfate salts and seasalt, with and without the use of palladium, on the determination of arsenic by electrothermal atomic absorption spectrometry was investigated. In the absence of any stabilizing agent, arsenic was partially lost as molecular species at low temperatures. The effect of salts on the shape of the atomization signal, the integrated absorbance and the stabilizing effect were highly dependent both on their nature and mass. By trapping arsenic, oxide species resulting from the decomposition of nitrate salts induced a high stabilization effect depending on their vaporization temperatures: MgO approximately CaO>SrO>Na2O. The stabilization effect of chlorides occurred about 200 degrees C lower and depended on mass, volatility and hydrolytic properties: SrCl2>CaCl2>MgCl2 approximately NaCl. The effect of sulfates was mainly dependent on their decomposition/vaporization mechanisms, and in the presence of Na2SO4 or CaSO4 a strong chemical interference effect was observed. Palladium stabilized arsenic in the presence of nitrates, chlorides or even sulfates, leading to a similar delaying effect, signal shape and integrated absorbance. Seasalt induced also important modifications to the atomization signal of As. Moreover, an interference effect was observed, which could probably be attributed to the simultaneous vaporization of sulfate in seasalt. In seawater, Pd suppressed this interference effect and permitted to use a high pyrolysis temperature up to 1400 C to remove the major part of the seawater matrix before atomization. Under optimized conditions, the detection limit for As obtained in unmodified seawater in the presence of Pd was 0.34 microg L(-1) for a 10 microl sample.     

Determination of selenium in seawater by Zeeman GFAAS using nickel plus NH4NO3 modifier

The effectiveness of nickel plus NH₄NO₃ as a chemical modifier for the determination of selenium in seawater by Zeeman electrothermal atomic absorption spectrometry has been evaluated. The effect of changing the modifier mass and pyrolysis hold time on the integrated absorbance of selenium and the background absorbance has been investigated. Nickel and NH₄NO₃ allow the quantitative stabilization of selenium in the seawater matrix up to 1300° C as compared with 600° C without modifier. The modifier further reduces the background absorbance caused by seawater. The tolerable amounts of various inteferences such as chloride, sulphate and phosphorus in the presence of nickel plus NH₄NO₃ are evaluated for the determination of selenium in seawater. Received: 31 August 1995 / Revised: 21 December 1995 / Accepted: 6 January 1996     

The use of thermal analysis in the study of Ca<Subscript>3</Subscript>Al<Subscript>2</Subscript>O<Subscript>6</Subscript> formation by the polymeric precursor method

Single-phase Ca₃Al₂O₆ was prepared via polymeric precursor method. The influence of the reactants nature in the Ca₃Al₂O₆ synthesis was investigated. For this purpose, citric acid and soluble salts of calcium (nitrate, chloride, carbonate) and aluminium (nitrate, chloride, acetate) were used as starting materials, in the presence and, respectively, in the absence of ethylene glycol. Ca₃Al₂O₆ resulted as single-phase after annealing at 1050 °C for 1 h only starting from calcium nitrate or carbonate and aluminium nitrate or acetate as salts precursor for Ca²⁺ and Al³⁺ cations. The formation of Ca₃Al₂O₆ is not conditioned by the ethylene glycol presence in these mixtures. Using calcium and aluminium chlorides, the phases present at 1050 °C are Ca₁₂Al₁₄O₃₃ and unreacted CaO.     

Behavior of mercury(II) salts in electrothermal atomic absorption spectrometry : Application to the Determination of Thiosulfate

Mercury(II) salts have different decomposition temperatures in a graphite tube or tantalum coil used for electrothermal atomic absorption spectrometry. The nitrate, perchlorate and acetate were spontaneously reduced to mercury vapor at room temperature, but the thiosulfate, sulfide, cyanide and bromide were reduced only on heating. Chloride and thiocyanate in a graphite furnace and iodide in a tantalum coil did not give mercury absorbance on heating. Thiosulfate (1–10 × 10^?6 M) was determined by addition to mercury(II) nitrate in acetate buffer, removing the response from the excess mercury(II) nitrate by drying below 100° C in the graphite furnace, and measuring the mercury absorbance on heating, which was proportional to the thiosulfate concentration.     

The role of counter-anions in photocatalytic reduction of Ni(II) with a trace amount of titania nanoparticles

The reduction of Ni(II) ion, originated from nitrate or sulfate salts, was investigated based on photo-generated electrons in UV-irradiated TiO₂ aqueous suspensions. Design of experiments, modeling, and process optimization were performed using central composite design of response surface methodology. Influence of pH, temperature, and nickel concentration was investigated based on percentage of reduction efficiency (RE). Under operating conditions of pH = 9.3, T = 40 °C, [Ni(II)]_o = 5 mg L^?1, [TiO₂] = 100 mg L^?1 and after 90 min treatments, 64.8 and 76.1 % RE were achieved for nitrate and sulfate counter-anions, respectively. The higher efficiency obtained with sulfate anion was attributed to the more ionic strength and its interaction with titania nanoparticles. Rate of Ni(II) ions reduction, originated from both of the nickel salts, obeys pseudo-first-order kinetic model. As a relevant criterion, the electrical energy consumption and other criteria were evaluated and were compared with other previously reported processes.     

Increased rates of initiation of polymerization by 4-4′-dicyano-4-4′-azopentanoic acid in the presence of ferric salts

The initiation of the polymerization of acrylamide by 4-4′-dicyano-4-4′-azopentanoic acid in aqueous solution has been studied kinetically at 25°C. Ferric chloride and ferric sulfate were used to terminate polymerization so that rates of initiation could be calculated from the rates of production of ferrous iron. Velocity coefficients at 25°C. for the initiation reaction were found to be (25.7 ± 2.8) × 10^?7 sec.^?1 for the ferric chloride terminated reaction and (73.6 ± 0.6) × 10^?7 sec.^?1 for the ferric sulfate-terminated polymerization. The value reported for the initiation reaction when acrylamide is polymerized in the absence of metal salts is 1.29 × 10^?7 sec.^?1. Velocity coefficients for the termination reaction have been calculated from the overall rates of polymerization obtained with ferric salts present. In the case of the ferric chloride-terminated reaction, it has been shown that the rate of polymerization is reduced by increasing the total concentration of chloride ions. Termination velocity coefficients at 25°C. for the inner sphere complexes FeCl²⁺·5H₂O and FeSO₄⁺·4H₂O have been calculated to be 18.9 × 10⁴ and 7.98 × 10⁴ l./mole-sec., respectively. The dependence on the concentration of ferric chloride of the molecular weights of the polymers produced has also been considered.     

Crystal and Species Engineering with Semi‐Flexible Nitrogen Containing Organic Cations: Generation of [H13O6]+ Ions with the Unfavoured Unbranched Topology by Enclosing Hydrochloric Acid in a Porous Inorganic‐Organic Hybrid Material

The reaction of rhodium(III) chloride trihydrate with 1, 4‐diazacycloheptane in concentrated hydrochloric acid results in the formation of tris(1, 4‐diazoniacycloheptane) hexaaquahydrogen(1+) bis(hexachlororhodate(III)) chloride, [C₅H₁₄N₂]₃[H₁₃O₆][RhCl₆]₂Cl ( 1 ). Dark red crystals of 1 are obtained by diffusion‐controlled crystallization at room temperature. Slow evaporation of the mother liquor over a period of several days yields a few tiny crystals of the bis(1, 4‐diazoniacycloheptane) hexachlororhodate(III) chloride hydrate, [C₅H₁₄N₂]₂[RhCl₆]Cl ˙ 1.75 H₂O ( 2 ), as red thin squared plates. In the context of crystal engineering, compounds 1 and 2 are inorganic‐organic hybrid materials built up from octahedral [RhCl₆]^3‐, simple Cl^‐ and semi‐flexible heterocyclic 1, 4‐diazoniacycloheptane ions, incorporating either the [H₁₃O₆]⁺ and further Cl^‐ ions or portions of simple water molecules. Both compounds crystallize in the space group type P2₁/c. Compound 1 contains isolated [H₁₃O₆]⁺ ions with a linear chain‐like configuration enclosed in the cavities of the inorganic‐organic framework. The presence of a strong central O···H···O hydrogen bond within the [H₁₃O₆]⁺ ions in 1 is confirmed by the short O···O separation of 2.47Å and by characteristic IR absorption bands at 1626 (s), ～ 1250 (m) and 668 (m) cm^‐1. During the thermal decomposition, compound 1 looses at first five equivalents of water and one equivalent of hydrochloric acid in a two‐step process at 37 °C and 67 °C. This is followed by the decomposition of the 1, 4‐diazoniacycloheptane cations and the hexachlororhodate(III) anions, starting at 190 °C and proceeding intensified at 240 °C.     

Constantes d'acidite de l'acide pyrophosphorique et constantes de stabilite des complexes avec le potassium et le sodium: en|The acidity constants of pyrophosphoric acid and the stability constants of complexes with potassium and sodium ions

(The acidity constants of pyrophosphoric acid and the stability constants of complexes with potassium and sodium ions)The effect of potassium and sodium ions on the acidity constants of pyrophosphoric acid is studied by potentiometry at 25°C and at an ionic strength of 0.5 mol l^-1. Comparison of the results obtained in potassium chloride or sodium chloride medium with those found in tetramethylammonium chloride medium provides evidence of the formation of potassium and sodium complexes of the type MHP₂O^2-₇ and MP₂O^3-₇. Stability constants of these complexes are calculated and distribution diagrams of the species as a function of pH are given for the three different media utilized.     

Synthesis,Characterization of a Novel 1,2,4‐Thiotriazine Derivative (CAMTTO), and Copper(I) and Silver(I) Complexes thereof (CAMTTO = {(4‐[(4‐Chlorobenzylidene)‐amino]‐6‐methyl‐3‐thioxo‐[1,2,4]‐triazin‐3,4‐dihydro(2H)‐5‐one)}

The reaction of 4‐amino‐6‐methyl‐1,2,4‐triazin‐thione‐5‐one (H₂AMTTO, 1 ) with 4‐chlorobenzaldhyde led to the corresponding iminic compound {(4‐[(4‐chloro‐benzylidene)‐amino]‐6‐methyl‐3‐thioxo[1,2,4]‐triazin‐3,4‐dihydro(2H)‐5‐one), CAMTTO ( 2 ). Treatment of 2 with copper(I) chloride in chloroform gave the dimeric complex [{(CAMTTO)₂CuCl}₂]·2CHCl₃ ( 3 ). Treatment of 2 with copper(I) chloride and silver(I) nitrate in the presence of the co‐ligand triphenylphophane gave the complexes [(CAMTTO)CuCl(PPh₃)₂] ( 4 ) and [(CAMTTO)Ag(PPh₃)₂]NO₃·2CHCl₃ ( 5 ). All compounds have been characterized by elemental analyses, ¹H NMR spectroscopy, IR spectroscopy, and partly by mass spectrometry and X‐ray diffraction studies. In addition 4 and 5 have been characterized by ³¹P{¹H} NMR spectroscopy. Crystal data for 2 at ?80 °C: monoclinic, space group P2₁/c, a = 1370.3(1), b = 767.8(1), c = 1268.7(1) pm, β = 107.12(1)°, Z = 4, R₁ = 0.0379; for 3 at ?80 °C: monoclinic, space group P2₁/c, a = 1442.6(2), b = 878.8(1), c = 2558.7(3) pm, β = 95.31(1)°, Z = 2, R₁ = 0.0746; for 4 at ?80 °C: triclinic, space group , a = 1287.9(1), b = 1291.7(1), c = 1359.5(1) pm, α = 90.44(1)°, β = 94.81(1)°, γ = 107.54(1)°, Z = 2, R₁ = 0.0359 and for 5 at ?80 °C: triclinic, space group , a = 1060.5(1), b = 1578.2(2), c = 1689.6(2) pm, α = 87.70(1)°, β = 86.66(1)°, γ = 76.84(1)°, Z = 2, R₁ = 0.0487.     

[1‐Allylpyridinium][Cu2Cl3]: Synthesis,X‐ray Structure and the Regularity of Crystal Architecture of 1‐Allyl/(amino)‐pyridinium Copper(I) Chloride π‐Complexes

By alternating‐current electrochemical technique crystals of copper(I) π‐complex with 1‐allylpyridinium chloride of [C₅H₅N(C₃H₅)][Cu₂Cl₃] ( 1 ) composition have been obtained and structurally investigated. Compound 1 crystallizes in monoclinic system, space group C2/c a = 24.035(1) Å, b = 11.4870(9) Å, c = 7.8170(5) Å, β = 95.010(5)°, V = 2150.0(2) ų (at 100 K), Z = 8, R = 0.028, for 4836 independent reflections. In the structure 1 trigonal‐pyramidal environment of π‐coordinated copper(I) atom is formed by a lengthened to 1.376(2) Å C=C bond of allyl group and by three chlorine atoms. Other two copper atoms are tetrahedrally surrounded by chlorine atoms only. The coordination polyhedra are combined into an original infinite (Cu₄Cl₆^2—)_n fragment. Structural comparison of 1 and the recently studied copper(I) chloride π‐complexes with 3‐amino‐, 2‐amino‐, 4‐amino‐1‐allylpyridinium chlorides of respective [LCu₂Cl₃] ( 2 ), [L₂Cu₂Cl₄] ( 3 ), and [LCuCl₂] ( 4 ) compositions allowed us to reveal the trend of the inorganic fragment complication which depends on pKa (base) value of the corresponding initial heterocycle.     

Hydrogen‐bonding motifs and thermotropic polymorphism in redetermined halide salts of hexamethylenediamine

The redetermined crystal structures of hexane‐1,6‐diammonium dichloride, C₆H₁₈N₂²⁺·2Cl⁻, (I), hexane‐1,6‐diammonium dibromide, C₆H₁₈N₂²⁺·2Br⁻, (II), and hexane‐1,6‐diammonium diiodide, C₆H₁₈N₂²⁺·2I⁻, (III), are described, focusing on their hydrogen‐bonding motifs. The chloride and bromide salts are isomorphous, with both demonstrating a small deviation from planarity [173.89 (10) and 173.0 (2)°, respectively] in the central C—C—C—C torsion angle of the hydrocarbon backbone. The chloride and bromide salts also show marked similarities in their hydrogen‐bonding interactions, with subtle differences evident in the hydrogen‐bond lengths reported. Bifurcated interactions are exhibited between the N‐donor atoms and the halide acceptors in the chloride and bromide salts. The iodide salt is very different in molecular structure, packing and intermolecular interactions. The hydrocarbon chain of the iodide straddles an inversion centre and the ammonium groups on the diammonium cation of the iodide salt are offset from the planar hydrocarbon backbone by a torsion angle of 69.6 (4)°. All three salts exhibit thermotropic polymorphism, as is evident from differential scanning calorimetry analysis and variable‐temperature powder X‐ray diffraction studies.     

Electrothermal atomization of palladium stabilized selenium in the presence of phosphate

The interference caused by phosphate (as Na₂HPO₄) in the electrothermal atomic absorption determination of selenium was investigated for reduced and unreduced palladium nitrate modifiers. An increase of the amount of phosphate in the sample was accompanied with increasing losses of selenium. Kinetic parameters of the selenium atomization were calculated for various amounts of phosphate interference. These results were compared with previous findings for palladium stabilized selenium and the sulfate interference observed for this system. The increasing chemical interference is due to phosphorous replacing the selenium bound by palladium. The phosphorus thus makes the palladium surface unavailable for the stabilization of selenium.     

Thermal Behavior of d‐Ribose Adsorbed on Silica: Effect of Inorganic Salt Coadsorption and Significance for Prebiotic Chemistry

Understanding ribose reactivity is a crucial step in the “RNA world” scenario because this molecule is a component of all extant nucleotides that make up RNA. In solution, ribose is unstable and susceptible to thermal destruction. We examined how ribose behaves upon thermal activation when adsorbed on silica, either alone or with the coadsorption of inorganic salts (MgCl₂, CaCl₂, SrCl₂, CuCl₂, FeCl₂, FeCl₃, ZnCl₂). A combination of ¹³C NMR, in situ IR, and TGA analyses revealed a variety of phenomena. When adsorbed alone, ribose remains stable up to 150 °C, at which point ring opening is observed, together with minor oxidation to a lactone. All the metal salts studied showed specific interactions with ribose after dehydration, resulting in the formation of polydentate metal ion complexes. Anomeric equilibria were affected, generally favoring ribofuranoses. Zn²⁺ stabilized ribose up to higher temperatures than bare silica (180 to 200 °C). Most other cations had an adverse effect on ribose stability, with ring opening already upon drying at 70 °C. In addition, alkaline earth cations catalyzed the dehydration of ribose to furfural and, to variable degrees, its further decarbonylation to furan. Transition‐metal ions with open d‐shells took part in redox reactions with ribose, either as reagents or as catalysts. These results allow the likelihood of prebiotic chemistry scenarios to be evaluated, and may also be of interest for the valorization of biomass‐derived carbohydrates by heterogeneous catalysis.     

A 2‐D 3d–4f Heterometallic Compound: Hydrothermal Synthesis,Structure and Magnetic Properties

A novel two‐dimensional 3d–4f heterometallic inorganic compound with the formula [Cu^II₃Gd^III(μ₃‐OH)₆(μ₃‐SH)(SO₄)(H₂O)₃] ( 1 ) was synthesized by treating gadolinium nitrate, copper chloride and DTSA under hydrothermal conditions. The structure was determined by X‐ray crystallography. The crystal is of orthorhombic, space group P2₁2₁2₁ with a = 6.63090(1) Å, b = 11.3145(3) Å, c = 15.7869(3) Å, Cu₃GdH₁₃O₁₃S₂, M = 633.09, Z =4, V = 1184.42(4) ų, F(000) = 1200, R₁ = 0.0244 and ωR = 0.0522. The solid‐state dc magnetic susceptibility measurements revealed antiferromagnetic interactions between the paramagnetic metal center ions.     

Determination of Metals in Olive Oil by Electrothermal Atomic Absorption Spectrometry: Validation and Uncertainty Measurements

The determination of trace metals in organic matrices is still highly demanding despite improvements in analytical instrumentation. The present study was undertaken in order to evaluate electrothermal atomic absorption spectrometry for the determination of cadmium, copper, iron, lead, and nickel in olive oil. A variety of approaches were used. The most suitable digestion procedure was heating the samples at 300°C for 24 hours and ashing in a muffle furnace at 450°C for 16 hours. The validation data were detection limits of 0.2–153 ng g^?1; mean trueness on certified reference materials of 81–94%; mean recovery on spikes of 90–120%; and repeatability of 12–53%. The combined relative uncertainty was 0.298–0.766. Oils processed by pressing had higher copper, iron, and lead concentrations than oils processed by centrifugation. The reported method provides an efficient way for monitoring trace metal content during olive oil production.