Solid-phase extraction of trace Cu(II) Fe(III) and Zn(II) with silica gel modified with curcumin from biological and natural water samples by ICP-OES

Silica gel was firstly functionalized with aminopropyltrimethoxysilane obtaining the aminopropylsilica gel (APSG). The APSG was reacted subsequently with curcumin yielding curcumin-bonded silica gel (curcumin-APSG). This new bonded silica gel was used for separation, pre-concentration and determination of Cu(II), Fe(III), Zn(II) in biological and natural water samples by inductively coupled plasma optical emission spectrometry (ICP-OES). Experimental conditions for effective adsorption of trace levels of metal ions were optimized with respect to different experimental parameters using batch and column procedures in detail. The optimum pH value for the separation of metal ions simultaneously on the newly sorbent was 4.0. Complete elution of the adsorbed metal ions from the sorbent surface was carried out using 2.0 mL of 0.1 mol L^− 1 of HCl. Common coexisting ions did not interfere with the separation and determination at pH 4.0. The maximum static adsorption capacity of the sorbent at optimum conditions was found to be 0.63, 0.46 and 0.37 mmol g^− 1 for Cu(II), Fe(III) and Zn(II) respectively. The time for 95% sorption for Cu(II) Fe(III) and Zn(II) was less than 2 min. The detection limits of the method defined by IUPAC was found to be 0.12, 0.15 and 0.40 ng mL^− 1 for Cu(II), Fe(III) and Zn(II), respectively. The relative standard deviation (RSD) of the method under optimum conditions was lower 3.0% (n = 5). The procedure was validated by analyzing the certified reference river sediment material (GBW 08301, China), the results obtained were in good agreement with standard values. This sorbent was successfully employed in the separation and pre-concentration of trace Cu(II), Fe(III) and Zn(II) from the biological and natural water samples yielding 75-fold concentration factor.     

Modeling of iron adsorption on HTTA-loaded polyurethane foam using Freundlich,Langmuir and D-R isotherm expressions

The sorption of Fe(III) at low pH range from 1 to 4.5 on open cell polyether type HTTA-loaded polyurethane foam has been carried out using batch technique. The optimum shaking time for 2.5· 10^–4M solution of Fe(III) was found to be 30 minutes. The concept of macropore and micropore nature of polyurethane foam sorbent offers unique advantages of adsorption. Freundlich and Langmuir adsorption isotherms are followed at low concentration range from 1·10^–4 to 3·10^–4M solution of Fe(III). The Freundlich constant (1/n=0.46±0.013 andK=9.16±1.39 mg·g^–1) and Langmuir isotherm constants(M=21.78 mg·g^–1 andb=88.41±9.731·g^–1) were established. The sorption mean free energyE=12.22±0.09 kJ·mol^–1 and loading capacityC _m =145.21±6.1 mg·g^–1 were evaluated using Dubinin-Radushkevich isotherm, which suggested that the adsorption mechanism was chemisorption.     

Synthesis, EPR spectrum and X-ray structure of tetra-n-butylammonium bis(benzene-1,2-dithiolato(2−)-κS,S′)platinate(III)

The new salt, tetra-n-butylammonium bis(benzene-1,2-dithiolato(2−)-κ²S,S′)platinate(III), [NBu₄][Pt(C₆H₄S₂)₂] (1), has been synthesized in ethanol/water, and fully characterized by single crystal X-ray structure determination. The central platinum in the complex ion [Pt(bdt)₂]⁻ is tetracoordinated by the S atoms of the bdt²⁻ ligands (bdt²⁻ is benzene-1,2-dithiolate) in a square-planar geometry. The well-resolved frozen solution EPR spectrum exhibits rhombic symmetry. The room temperature effective magnetic moment (μ_eff = 1.80 Bohr magneton) is in line with this spectrum and strongly supports the Pt(III) oxidation state in 1. This observation is in excellent agreement with previous results reported on closely related Ni(III), Pd(III) and Pt(III) species.     

Sensitive spectrofluorimetric determination of ruthenium at nanotrace levels using 2-(α-pyridyl) thioquinaldinamide [PTQA]

A new spectrofluorimetric method for the determination of ruthenium with nonfluorescent 2-(α-pyridyl) thioquinaldinamide (PTQA) is described. The oxidative reaction of Ru(III) upon PTQA gives oxidised fluorescent product (λ_ex(max)=347 nm; λ_em(max)=486 nm). The sensitivity of the fluorescence reaction between ruthenium and PTQA is greatly increased in the presence of Fe (III). The reaction is carried out in the acidity range 0.01–0.075 M H₂SO₄. The influence of reaction variables is discussed. The range of linearity is 1–400 μg l⁻¹ Ru(III). The standard deviation and relative standard deviation of the developed method are ±1.210 μg l⁻¹ Ru (III) and 2.4%, respectively (for 11 replicate determinations of 50 μg l⁻¹ Ru (III)). The effect of interferences from other metal ions, anions and complexing agents was studied; the masking action is discussed. The developed method has been successfully tested over synthetic mixtures of various base metals and platinum group metals, synthetic mixtures corresponding to osmiridium, certified reference materials in spiked conditions and rock samples.     

On-line separation and preconcentration of inorganic arsenic and selenium species in natural water samples with CTAB-modified alkyl silica microcolumn and determination by inductively coupled plasma-optical emission spectrometry

A new, simple, and selective method has been presented for the separation and preconcentration of inorganic arsenic (As(III)/As(V)) and selenium (Se(IV)/Se(VI)) species by a microcolumn on-line coupled with inductively coupled plasma-optical emission spectrometry (ICP-OES). Trace amounts of As(V) and Se(VI) species were separated and preconcentrated from total As and Se at desired pH values by a conical microcolumn packed with cetyltrimethylammonium bromide (CTAB)-modified alkyl silica sorbent in the absence of chelating reagent. The species adsorbed by CTAB-modified alkyl silica sorbent were quantitatively desorbed with 0.10 ml of 1.0 mol l⁻¹ HNO₃. Total inorganic arsenic and selenium were similarly extracted after oxidation of As(III) and Se(IV) to As(V) and Se(VI) with KMnO₄ (50.0 μmol l⁻¹). The assay of As(III) and Se(IV) were based on subtracting As(V) and Se(VI) from total As and total Se, respectively. All parameters affecting the separation/preconcentration of As(V) and Se(VI) including pH, sample flow rate and volume, eluent solution and volume have been studied. With a sample volume of 3.0 ml, the sample throughput was 24 h⁻¹ and the enrichment factors for As(V) and Se(VI) were 26.7 and 27.6, respectively. The limits of detection (LODs) were 0.15 μg l⁻¹ for As(V) and 0.10 μg l⁻¹ for Se(VI). The relative standard deviations (RSDs) for nine replicate determinations at 5.0 μg l⁻¹ level of As(V) and Se(VI) were 4.0% and 3.6%, respectively. The calibration graphs of the method for As(V) and Se(VI) were linear in the range of 0.5–1000.0 μg l⁻¹ with a correlation coefficient of 0.9936 and 0.9992, respectively. The developed method was successfully applied to the speciation analysis of inorganic arsenic and selenium in natural water samples with satisfactory results.     

Nanometer SiO2 modified with 5-sulfosalicylic acid as selective solid-phase extractant for Fe(III) determination by ICP-AES from biological and natural water samples

A new modified nanometer SiO₂ using 5-sulfosalicylic acid (SSA) as a solid-phase extractant was used for separation, preconcentration and determination of Fe(III) in aqueous solutions by inductively coupled plasma atomic emission spectrometry (ICP-AES). Its adsorption and preconcentration behaviour for Fe(III) in aqueous solutions was investigated using static procedures in detail. The optimum pH value for the separation of Fe(III) on the newly designed sorbent was 3.5. Complete elution of the adsorbed Fe(III) from the nanometer SiO₂-SSA was carried out using 2.0 mL of 0.01 mol L^− 1 of HCl. The time of 90% sorption was less than 2 min for Fe(III) at pH 3.5. Common coexisting ions did not interfere with the separation and determination of Fe(III) at pH 3.5. The maximum static adsorption capacity of the sorbent at optimum conditions was found to be 44.01 mg of Fe(III) per gram of sorbent. The relative standard deviation (RSD) of the method under optimum conditions was 3% (n = 5). The procedure was validated by analyzing three certified reference materials (GBW 08301, GBW 08504, GBW 08511), the results obtained were in good agreement with standard values. The nanometer SiO₂-SSA was successfully employed in the separation and preconcentration of the investigated Fe(III) from the biological and natural water samples yielding 100-folds concentration factor.     

Investigation of the spectral properties of a squarylium near-infrared dye and its complexation with Fe(III) and Co(II) ions

The spectral features of the squarylium near-infrared (NIR) dye NN525 in different solutions and its complexation with several metal ions were investigated. The absorbance maximum of the dye is λ=663 nm in methanol. This value matches the output of a commercially available laser diode (650 nm), thus making use of such a source practical for excitation. The emission wavelength of the dye in methanol is λ_em=670 nm. The addition of either Fe(III) ion or Co(II) ion resulted in fluorescence quenching of the dye. The Stern–Volmer quenching constant, K_SV, was calculated from the Stern–Volmer plot to be K_SV=2.70×10⁷ M⁻¹ for Co(II) ion. The K_SV value for Fe(III) ion could not be established due to the non-linearity of the Stern–Volmer plot and the modified Stern–Volmer plot for this ion. The detection limit is 6.24×10⁻⁸ M for Fe(III) ion and 1.55×10⁻⁵ M for Co(III) ion. The molar ratio of the metal to the dye was established to be 1:1 for both metal ions. The stability constant, K_S, of the metal–dye complex was calculated to be 3.14×10⁶ M⁻¹ for the Fe–dye complex and 2.64×10⁵ M⁻¹ for the Co–dye complex.     

Evaluation of a chloramine-T-selective electrode for catalytic titration of silver and mercury(II) based on iodide-catalyzed chloramine-T reactions

Semiautomatic methods are described for the catalytic titrimetric determination of microamounts of silver and mercury(II) using a chloramine-T-selective electrode as monitor. The methods are based on the inhibitory effect of Ag(I) and Hg(II) on the iodide-catalyzed chloramine-T-arsenite and chloramine-T-H₂O₂ reactions. Microamounts of silver in the range 0.2–200 μg (1 × 10⁻⁷−1 × 10⁻⁴ M) and of mercury(II) in the range 0.1–200 μg (2.5 × 10⁻⁸−5 × 10⁻⁵ M) were determined using the chloramine-T-As(III) indicator reaction. Mercury(II) in the range 4–2000 μg (1 × 10⁻⁶−5 × 10⁻⁴ M) was also determined using the chloramine-T-H₂O₂ indicator reaction. The accuracy and precision were in the range 0.1–1%.     

Solid-phase extraction of iron(III) with an ion-imprinted functionalized silica gel sorbent prepared by a surface imprinting technique

A new Fe(III)-imprinted amino-functionalized silica gel sorbent was prepared by a surface imprinting technique for selective solid-phase extraction (SPE) of Fe(III) prior to its determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). Compared with non-imprinted polymer particles, the ion-imprinted polymers (IIPs) had higher selectivity and adsorption capacity for Fe(III). The maximum static adsorption capacity of the ion-imprinted and non-imprinted sorbent for Fe(III) was 25.21 and 5.10 mg g⁻¹, respectively. The largest selectivity coefficient of the Fe(III)-imprinted sorbent for Fe(III) in the presence of Cr(III) was over 450. The relatively selective factor (α_r) values of Fe(III)/Cr(III) were 49.9 and 42.4, which were greater than 1. The distribution ratio (D) values of Fe(III)-imprinted polymers for Fe(III) were greatly larger than that for Cr(III). The detection limit (3σ) was 0.34 μg L⁻¹. The relative standard deviation of the method was 1.50% for eight replicate determinations. The method was validated by analyzing two certified reference materials (GBW 08301 and GBW 08303), the results obtained is in good agreement with standard values. The developed method was also successfully applied to the determination of trace iron in plants and water samples with satisfactory results.     

Oxidative degradation of non-ionic surfactant (TritonX-100) by chromium(VI)

Degradation of polyoxyethylene chain of non-ionic surfactant (TritonX-100) by chromium(VI) has been studied spectrophotometrically under different experimental conditions. The reaction rate bears a first-order dependence on the [Cr(VI)] under pseudo-first-order conditions, [TritonX-100]  [Cr(VI)] in presence of 1.16 mol dm⁻³ perchloric acid. The observed rate constant (k_obs) was 3.3 × 10⁻⁴ to 3.5 × 10⁻⁴ s⁻¹ and the half-life (t_1/2) was 33–35 min for chromium(VI). The effects of total [TritonX-100] and [H⁺] on the reaction rate were determined. Reducing nature of non-ionic TritonX-100 surfactant is found to be due to the presence of –OH group in the polyoxyethylene chain. It was observed that monomeric and non-ionic micelles of TritonX-100 were oxidized by chromium(VI). When [TritonX-100] was less than its critical micelle concentration (cmc) the k_obs values increased from 0.76 × 10⁻⁴ to 1.5 × 10⁻⁴ s⁻¹. As the [TritonX-100] was greater than the cmc, the k_obs values increases from 2.1 × 10⁻⁴ to 8.2 × 10⁻⁴ s⁻¹ in presence of constant [HClO₄] (1.16 mol dm⁻³) at 40 °C. A comparison was made of the oxidative degradation rates of TritonX-100 with different metal ion oxidants. The order of the effectiveness of different oxidants was as follows: permanganate > diperiodatoargentate(III) > chromium(VI) > cerium(IV).     

Pd(OAc)2/M(NO3)n (M = Cu(II), Fe(III); n = 2, 3): Kinetic investigations of an alternative Wacker system for the oxidation of natural olefins

Pd-catalyzed oxidative coupling of camphene by dioxygen afforded mainly a diene, which subsequently underwent oxidation to a ring-expanded β,γ-unsaturated ketone with LiNO₃ as reoxidant. However, the instability of LiNO₃ results to the decomposition of NO₃⁻ ions which subsequently deactivates the catalyst. The present investigation describes the oxidation of terpenes catalyzed by Pd(OAc)₂/M(NO₃)_n (M = Cu(II), Fe(III); n = 2 or 3), using dioxygen as final oxidant. Fe(III) and Cu(II) effectively stabilize the nitrate reoxidant as determined by the significant increase of both catalytic activity and stability of the system. Turnover frequency suggests that Fe(III) is the most efficient co-catalyst. Moreover, it is established that the co-catalysts NO₃⁻, Cu(II) and especially Fe(III) ions, change the product distribution (diene/ketone) remarkably. Their involvement in the rate-determining step was investigated and the results of the kinetic investigations clarified important aspects of Pd(II)-catalyzed oxidation reactions. The described protocol offers an alternative to the traditional Wacker system which uses CuCl₂ as co-catalyst and is not effective in promoting the oxidation of bicycle olefins.     

Mercury(II) Biosorption Using <Emphasis Type="Italic">Lessonia</Emphasis> sp. Kelp

Lessonia nigrescens and Lessonia trabeculata kelps have been tested for the sorption of mercury from aqueous solutions. A pretreatment (using CaCl₂) allowed stabilizing the biomass that was very efficient for removing Hg(II) at pH 6–7. Sorption isotherms were described by the Langmuir equation with sorption capacities close to 240–270 mg Hg g⁻¹ at pH 6. The temperature had a negligible effect on the distribution of the metal at equilibrium. The presence of chloride anions had a more marked limiting impact than sulfate and nitrate anions. The uptake kinetics were modeled using the pseudo-second-order equation that fitted better experimental data than the pseudo-first-order equation. The particle size hardly influenced sorption isotherms and uptake kinetics, indicating that sorption occurs in the whole mass of the biosorbent and that intraparticle mass transfer resistance was not the limiting rate. Varying the sorbent dosage and the initial metal concentration influenced the equilibrium, but the kinetic parameters were not drastically modified. Metal can be eluted with hydrochloric acid, citric acid, or acidic KI solutions.     

Antiferromagnetic complexes involving metal---metal bonds IV. Synthesis, molecular structure and magnetic properties of the heterotrinuclear cluster, (C5H5Cr)2(μ-SCMe3)(μ-S)2Fe(CO)3, with direct and indirect exchange between Cr and Fe centers

The photochemical reaction between the antiferromagnetic complex (C₅H₅-CrSCMe₃)₂S (I) (containing a Cr---Cr bond 2.689 Å long) and Fe(CO)₅ results in the elimination of two carbonyl groups and one tert-butyl radical to give (C₅H₅Cr)₂(μ²-SCMe₃)(μ³-S)₂ · Fe(CO)₃ (III). As determined by X-ray diffraction, III contains a Cr---Cr bond of almost the same length as in I (2.707 Å), together with one thiolate and two sulphide bridges. The latter are also linked with the Fe atom of the Fe(CO)₃ moiety (average Fe---S bond length 2.300 Å). Fe also forms a direct bond, 2.726 Å long, with one of the Cr atoms, whereas its distance from the other Cr atom (3.110 Å) is characteristic for non-bonded interactions. Complex III is antiferromagnetic, the exchange parameter, −2J, values for Cr---Cr, Cr(1)---Fe and Cr(2)…Fe are 380, 2600 and 170 cm⁻¹, respectively. The magnetic properties of III are discussed in terms of the “exchange channel model”. The contributions from indirect interactions through bridging ligands are shown to be insignificant compared with direct exchange involving metal---metal bonds. The effects of steric factors and of the nature of the M(CO)_n fragments on the chemical transformations of (C₅H₅CrSCMe₃)₂S · M(CO)_n are discussed.     

Flow through FTIR sensor based on solid phase spectroscopy (SPS) on conventional octadecyl (C18) silica

The concept of a novel FTIR flow through sensor based on rigid silica C18 particles placed in a mid-IR flow cell is presented applied to the example of caffeine determination in soft drinks. The system is based on a standard flow cell equipped with two polyethylene spacers of different size that yield a gap inside the assembled flow cell. Particles of appropriate size (<25 μm diameter) suspended in methanol are pumped into the assembled flow cell where the particles are retained at the gap formed by the two spacers. Using an automated sequential injection system, pre-conditioning, sample–sensor interaction and sorbent regeneration can be performed in a highly reproducible way. The characterization and validation results clearly demonstrate the capability of the developed flow through FTIR sensor to determine non-polar molecules, such as caffeine, at the parts per million level, with a linear range from 1.8 to 115 mg L⁻¹, a precision expressed as R.S.D. of 4.1% and a sample throughput of approximately 10 samples/h. Furthermore, the sensor has the potential to be easily adapted to the analysis of polar, non-polar, cationic and anionic molecules by changing the solid support, providing interesting possibilities for the development of new applications in the trace analysis of organic molecules.     

Sensitive electrochemical detection of arsenic (III) using gold nanoparticle modified carbon nanotubes via anodic stripping voltammetry

Gold nanoparticles were deposited electrolessly on multiwalled carbon nanotubes (CNTs) via in situ reduction of HAuCl₄ by NaBH₄. The resulting gold covered nanotubes were immobilised onto the surface of a glassy carbon electrode via evaporation of a suspension in chloroform. Anodic stripping voltammetry was performed with the modified electrode in As(III) solutions. A limit of detection (LOD based on 3σ) of 0.1 μg L⁻¹ was obtained but more importantly a sensitivity of 1985 μA μM⁻¹ was obtained with square wave voltammetry (SWV) in an optimised system with a deposition time of 120 s. These values, particularly the high sensitivity compare favourably with previously reported methods in the area of electrochemical arsenic detection.     

Synthesis of MPTS-modified cobalt ferrite nanoparticles and their adsorption properties in relation to Au(III)

Cobalt ferrite magnetic nanoparticles (Co-MNP) were prepared by a co-precipitation method and subsequently coated with (3-mercaptopropyl)trimethoxysilane (MPTS) for the extraction and recovery of Au(III) from aqueous chloride solutions. Physical characterization of the MPTS-modified particles (Co-MPTS) was performed using FT-IR, TGA, and SEM. Results from FT-IR confirmed that MPTS was present on the surface of the magnetic nanoparticles. The amount of MPTS was 0.36 mmol g⁻¹ of Co-MPTS, obtained by elemental analysis. SEM images revealed aggregates composed of nanocrystalline Co-MPTS particles. The extraction efficiency as a function of the pH, contact time, and initial Au(III) concentration was evaluated. The modified particles showed maximum adsorption in the pH range from 1.0 to 4.0. The adsorption behavior of Co-MPTS toward Au(III) followed a Langmuir isotherm and the maximum adsorption capacity was found to be 120.5 mg g⁻¹. The stability of the modified materials was improved as compared to that of bare Co-MNP. The subsequent desorption of gold could be achieved by using acidified thiourea solution; the highest gold recovery reached 85%.     

Hydroformylation of oct-1-ene catalyzed by dinuclear gem-dithiolato-bridged rhodium(I) complexes and phosphorus donor ligands

The dinuclear gem-dithiolato bridged compounds [Rh₂(μ-S₂Cptn)(cod)₂] (1) (CptnS₂²⁻ = 1,1-cyclopentanedithiolato), [Rh₂(μ-S₂Chxn)(cod)₂] (2) (ChxnS₂²⁻ = 1,1-cyclohexanedithiolato), [Rh₂(μ-S₂CBn₂)(cod)₂] (3) (Bn₂CS₂²⁻ = 1,3-diphenyl-2,2-dithiolatopropane) and [Rh₂(μ-S₂CⁱPr₂)(cod)₂] (4) (ⁱPr₂CS₂²⁻ = 2,4-dimethyl-2,2-dithiolatopentane) dissolved in toluene in the presence of monodentate phosphine or phosphite P-donor ligands under carbon monoxide/hydrogen (1:1) atmosphere are efficient catalysts for the hydroformylation of oct-1-ene under mild conditions (6.8 atm of CO/H₂ and 80 °C). The influence of the gem-dithiolato ligand, the P-donor co-catalyst and the P/Rh ratio on the catalytic activity and selectivity has been explored. Aldehyde selectivities higher than 95% and turnover frequencies up to 245 h⁻¹ have been obtained using P(OMe)₃ as modifying ligand. Similar activity figures have been obtained using P(OPh)₃ although the selectivities are lower. Regioselectivities toward linear aldehyde are in the range 75–85%. The performance of the catalytic systems [Rh₂(μ-S₂CR₂)(CO)₂(PPh₃)₂]/PPh₃ has been found to be comparable to the systems [Rh₂(μ-S₂CR₂)(cod)₂] at the same P/Rh ratio. The system [Rh₂(μ-S₂CBn₂)(cod)₂] (3)/P(OPh)₃ has been tested in the hydroformylation-isomerization of trans-oct-2-ene. Under optimized conditions up to 54% nonanal was obtained. Spectroscopic studies under pressure (HPNMR and HPIR) evidenced the formation of hydrido mononuclear species under catalytic conditions that are most probably responsible for the observed catalytic activity.     

C carbide ligand in the trigonal prismatic environment of rheniums in [Re12CS17(CN)6] complexes

The electronic state of carbon in trigonal prismatic environment in [Re₁₂CS₁₇(CN)₆]ⁿ⁻ complexes with variable redox state n = 6 ↔ 8 was studied by molecular orbital method and electron localization function. The state is characterized by sp²-hybridisation and oxidation state −4. A weak long-distance interaction between μ₆-С and μ₂-S in the group [(μ₆-С)(μ₂-S)₃] was discovered for n = 6, the interaction disappears for n = 8.     

High-accuracy determination of iron in seawater by isotope dilution multiple collector inductively coupled plasma mass spectrometry (ID-MC-ICP-MS) using nitrilotriacetic acid chelating resin for pre-concentration and matrix separation

In the present paper we describe a robust and simple method to measure dissolved iron (DFe) concentrations in seawater down to <0.1 nmol L⁻¹ level, by isotope dilution multiple collector inductively coupled plasma mass spectrometry (ID-MC-ICP-MS) using a ⁵⁴Fe spike and measuring the ⁵⁷Fe/⁵⁴Fe ratio. The method provides for a pre-concentration step (100:1) by micro-columns filled with the resin NTA Superflow of 50 mL seawater samples acidified to pH 1.9. NTA Superflow is demonstrated to quantitatively extract Fe from acidified seawater samples at this pH. Blanks are kept low (grand mean 0.045 ± 0.020 nmol L⁻¹, n = 21, 3× S.D. limit of detection per session 0.020–0.069 nmol L⁻¹ range), as no buffer is required to adjust the sample pH for optimal extraction, and no other reagents are needed than ultrapure nitric acid, 12 mM H₂O₂, and acidified (pH 1.9) ultra-high purity (UHP) water. We measured SAFe (sampling and analysis of Fe) reference seawater samples Surface-1 (0.097 ± 0.043 nmol L⁻¹) and Deep-2 (0.91 ± 0.17 nmol L⁻¹) and obtained results that were in excellent agreement with their DFe consensus values: 0.118 ± 0.028 nmol L⁻¹ (n = 7) for Surface-1 and 0.932 ± 0.059 nmol L⁻¹ (n = 9) for Deep-2. We also present a vertical DFe profile from the western Weddell Sea collected during the Ice Station Polarstern (ISPOL) ice drift experiment (ANT XXII-2, RV Polarstern) in November 2004–January 2005. The profile shows near-surface DFe concentrations of 0.6 nmol L⁻¹ and bottom water enrichment up to 23 nmol L⁻¹ DFe.     

Kinetics and mechanisms of the catalyzed decomposition of hydrogen peroxide by ethylenebis(oxyethylenedinitrilo)tetracetate complex of iron(III)

The rate of decomposition of H₂O₂ in the presence of Fe(III)-y complex (y is ethylenebis(oxyethylenedinitrilo)tetraacetic acid (EGTA) anion) was investigated under variable conditions of pH and temperature, various water-miscible solvents, and different concentrations of H₂O₂, [Fe-y]⁻, and acetate ions. The following rate law holds: Rate = (k₁K₃K₄/[H⁺]) [Fe-y(OH)]²⁻ [H₂O₂] at pH less than 9.80, and Rate = (k₂K₅[H⁺]/K₃) [Fe-y(OH)₂]³⁻[OOH]⁻ at pH above 9.80. The values of k₁K₄and k₂K₅ at 25 °C were found to be 1523 and 0.747 M⁻¹ S⁻¹, respectively. Activation enthalpy and activation entropy for this reaction were determined from Arrhenius plots and found to be ΔH^* = 34.38 K J mol⁻¹ and ΔS^* = −167.2 J K⁻¹ mol⁻¹.