Determination of arsenate in natural pH seawater using a manganese-coated gold microwire electrode

Direct electrochemical determination of arsenate (As^V) in neutral pH waters is considered impossible due to electro-inactivity of As^V. As^III on the other hand is readily plated as As⁰ on a gold electrode and quantified by anodic stripping voltammetry (ASV). We found that the reduction of As^V to As^III was mediated by elemental Mn on the electrode surface in a novel redox couple in which 2 electrons are exchanged causing the Mn to be oxidised to Mn^II. Advantage is taken of this redox couple to enable for the first time the electrochemical determination of As^V in natural waters of neutral pH including seawater by ASV using a manganese-coated gold microwire electrode. Thereto Mn is added to excess (∼1 μM Mn) to the water leading to a Mn coating during the deposition of As on the electrode at a deposition potential of −1.3 V. Deposition of As⁰ from dissolved As^V caused elemental Mn to be re-oxidised to Mn^II in a 1:1 molar ratio providing evidence for the reaction mechanism. The deposited As^V is subsequently quantified using an ASV scan. As^III interferes and should be quantified separately at a more positive deposition potential of −0.9 V. Combined inorganic As is quantified after oxidation of As^III to As^V using hypochlorite. The microwire electrode was vibrated during the deposition step to improve the sensitivity. The detection limit was 0.2 nM As^V using a deposition time of 180 s.     

Determination of Pb in natural waters with 2-mercaptobenzimidazole-5-sulfonate (MBIS)chemically modified gold electrode

The preparation, characterization and analytical applications of gold electrodes modified with ω-mercapto alkyl/aryl sulfonates are described. The devices resulted effective for the determination of free and labile Pb(II) in water samples by anodic stripping voltammetry (E_dep = −600 mV) and in particular 2-mercaptobenzimidazole-5-sulfonate (MBIS) offered the best performances with detection limit of 0.4 μg L⁻¹.Quantitative stripping of Pb from the electrode surface during the anodic scan, is obtained using sodium citrate buffer (pH = 9.0) as supporting electrolyte. Natural waters were analysed by standard addition method with good recoveries (mean percentage = 97%); no fouling effects due to humic acids or other organic constituents were observed in the reported conditions.     

Ba3MIIITiMVO9 (MIII = Fe,Ga, Y,Lu; MV = Nb,Ta, Sb) perovskite oxides: Synthesis,structure and dielectric properties

We describe the synthesis, structures and dielectric properties of new perovskite oxides of the formula, Ba₃M^IIITiM^VO₉, for M^III = Fe, Ga, Y, Lu and M^V = Nb, Ta, Sb. While M^V = Nb and Ta oxides adopt disordered/partially ordered 3C perovskite structures where M^III/Ti/M^V metal-oxygen octahedra are corner-connected, the M^V = Sb oxides show a distinct preference for the 6H structure, where Sb^V/Ti^IV metal-oxygen octahedra share a common face forming (Sb,Ti)O₉ dimers that are corner-connected to the M^IIIO₆ octahedra. The preference of antimony oxides (Sb^V:4d¹⁰) for the 6H structure – which arises from a special Sb^V–O chemical bonding that tends to avoid linear Sb–O–Sb linkages unlike Nb^V/Ta^V:d⁰ atoms which prefer ～180° Nb/Ta–O–Nb/Ta linkages – is consistent with the crystal chemistry of M^V–O oxides in general. The dielectric properties reveal a significant difference among M^III members. All the oxides with the 3C structure excepting those with M^III = Fe show a normal low loss dielectric behaviour with ε = 20–60 in the temperature range 50–400 °C; the M^III = Fe members with this structure (M^V = Nb, Ta) display a relaxor-like ferroelectric behaviour with large ε values at frequencies ≤1 MHz (50–500 °C).     

Simple and selective determination of arsenite and arsenate by electrospray ionization mass spectrometry

Arsenic pollution of public water supplies has been reported in various regions of the world. Recently, some cancer patients are treated with arsenite (As^III); most Japanese people consume seafoods containing large amounts of negligibly toxic arsenic compounds. Some of these arsenic species are metabolized, but some remain intact. For the determination of toxic As^III, a simple, rapid and sensitive method has been developed using electrospray ionization mass spectrometry (ESI-MS). As^III was reacted with a chelating agent, pyrrolidinedithiocarbamate (PDC, C₄H₈NCSS^-) and tripyrrolidinedithiocarbamate-arsine, As(PDC)₃, extracted with methyl isobutyl ketone (MIBK). A 1 μL aliquot of MIBK layer was directly injected into ESI-MS instrument without chromatographic separation, and was detected within 1 min. Arsenate (As^V) was reduced to As^III with thiosulfate, and then the total inorganic As was quantified as As^III. This method was validated for the analysis of urine samples. The limit of detection of As was 0.22 μg L⁻¹ using 10 μL of sample solution, and it is far below the permissible limit of As in drinking water, 10 μg L⁻¹, recommended by the WHO. Results were obtained in < 10 min with a linear calibration range of 1-100 μg L⁻¹. Several organic arsenic compounds in urine did not interfere with As^III detection, and the inorganic As in the reference materials SRM 2670a and 1643e were quantified after the reduction of As^V to As^III.     

Synthesis,Characterization, and Singlet Oxygen Sensitization by Antimony (III/V) Corrole Complexes

The synthesis, structural, spectroscopic characterization, and DFT/TD-DFT calculations of antimony corroles are reported herein. The studied complexes can be described as [(Corr)Sb^III] and [(Corr)(oxo)Sb^V]₂, where Corr is the trianion of corrole. All these complexes are diamagnetic in nature as is evident from sharp peaks with normal chemical shifts in the ¹H NMR spectra. Single crystal XRD analysis reveals that the antimony(V) corrole complex is the bis-μ-oxo-bridged dinuclear antimony(V). Both the tetra and hexa-coordinated [(Corr)Sb^III] and [(Corr)(oxo)Sb^V]₂ antimony complexes adopt domed-structure with weak d-π electron coupling. The Sb−O bond distances in the co-facial dimer of [(Corr)(oxo)Sb^V]₂ are 1.9802(16) Å (DFT: 2.0141 Å ) (for Sb1−O1), and 1.9639(17) Å (DFT: 1.9957 Å ) (for Sb2−O2) respectively. We observed that even though iodosobenzene is frequently used to oxidize [(Corr)Sb^III] species, the oxidation of [(Corr)Sb^III] is indeed very facile in nature and it even occurred in the air-equilibrated CHCl₃ solution while storing for few days. Excitation of these antimony (III/V) corrole complexes in DCM/MeOH (1 : 1) at 77 K results in red emission with maxima at 640–720 nm. The singlet oxygen production of [(Corr)(oxo)Sb^V]₂ has a quantum yield of 69 % and is two times higher than the analogous [(Corr)Sb^III] derivatives.     

The lanthanoid polyantimonides with the ideal compositions Pr5Sb12 and Nd5Sb12 crystallizing with a new structure type and Ho2Sb5 with Dy2Sb5-type structure

The title compounds were isolated in well-crystallized form from samples with a substantial excess of antimony, annealed at temperatures slightly below the melting point of that element. Their crystal structures were determined from single-crystal diffractometer data. Pr_9-xSb_21-y and Nd_9-xSb_21-y crystallize with a new monoclinic structure type, Pearson symbol mS(62-5.4), space group Cm, Z=2 with a=2859.1(4) pm, b=426.3(1) pm, c=1356.1(2) pm, β=95.52(1)°, R=0.034 for 4351 structure factors and 188 variable parameters for Pr_9-xSb_21-y and a=2845(2) pm, b=424.7(8) pm, c=1345.9(9) pm, β=95.42(7)°, R=0.069 for 2928 F values and 188 variables for Nd_9-xSb_21-y. Of the 30 atomic sites, three show fractional occupancy corresponding to the compositions Pr_8.303(5)Sb_20.03(1) and Nd_8.30(2)Sb_19.98(9), respectively. A model for the order of occupied atomic sites with a tripled b-axis is proposed resulting in the ideal compositions Pr₅Sb₁₂ and Nd₅Sb₁₂. The holmium compound Ho₂Sb₅ has a Dy₂Sb₅-type structure: mP28, P2₁/m, a=1301.8(3) pm, b=414.9(1) pm, c=1451.1(2) pm, β=102.14(1)°, R=0.028 for 2573 F values and 86 variables. In both structure types most rare earth atoms have nine antimony neighbors forming tricapped trigonal prisms. The coordination polyhedra of the antimony atoms show a great variety, with a trigonal prism of rare earth atoms as one extreme case. The other extreme coordination of an antimony atom is a distorted octahedron formed by six antimony atoms. The differences and similarities of both structures are discussed. Chemical bonding within the antimony polyanions is analyzed on the basis of an extended Zintl-Klemm concept using bond-length-bond-strength relationships.     

Simultaneous speciation of inorganic arsenic and antimony in natural waters by dimercaptosuccinic acid modified mesoporous titanium dioxide micro-column on-line separation and inductively coupled plasma optical emission spectrometry determination

A novel absorbent was prepared by dimercaptosuccinic acid chemically modifying mesoporous titanium dioxide and was employed as the micro-column packing material for simultaneous separation/preconcentration of inorganic arsenic and antimony species. It was found that both trivalent and pentavalent of inorganic As and Sb species could be adsorbed quantitatively on dimercaptosuccinic acid modified TiO₂ within a pH range of 4–7, and only As(III) and Sb(III) could be quantitatively retained on the micro-column within a pH range of 10–11 while As(V) and Sb(V) were passed through the micro-column without the retention. Based on this fact, a new method of flow injection on-line micro-column separation/preconcentration coupled to inductively coupled plasma optical emission spectrometry was developed for simultaneous speciation of trace inorganic arsenic and antimony in natural waters. Under the optimized conditions, an enrichment factor of 10 and sampling frequency of 10 h^− 1 were obtained with on-line mode. The detection limits of As(III), As(V), Sb(III), and Sb(V) are 0.53, 0.49, 0.77 and 0.71 ng mL^− 1 for on-line mode and as low as 0.11, 0.10, 0.15 and 0.13 ng mL^− 1 for off-line mode due to its higher enrichment factor (50), respectively. The relative standard deviations of two modes are less than 6.7% (C = 20 ng mL^− 1, n = 7). The concentration ratio of lower oxidation states/higher oxidation states changing from 1:10 to 10:1 has no obvious effect on the recoveries of As(III) and Sb(III). In order to validate the developed method, two certified reference materials of GSBZ5004-88 and GBW(E)080545 water sample were analyzed and the determined values are in good agreement with the certified values. The proposed method was successfully applied to the simultaneous speciation of inorganic arsenic and antimony in natural waters.     

Multielemental speciation of As, Se, Sb and Te by HPLC-ICP-MS

An anion exchange HPLC-ICP-MS procedure allowing the simultaneous multielemental speciation analysis of arsenic, selenium, antimony and tellurium has been developed. Four arsenic species (As^III, As^V, monomethylarsonic acid and dimethylarsinic acid), two selenium species (Se^IV and Se^VI) may be determined in a single run as well as one antimony (Sb^V) and one tellurium species (Te^VI). Alternatively Sb and/or Te may be used as internal standards for As and Se speciation studies. Optimisation of ICP-MS conditions led to satisfactory relative (0.01 (Sb^V) to 1.8 (Se^VI) ng ml⁻¹) and absolute detection limits (1–180 pg). Reproducibility ranged from 3.1 to 5.6% and the linearity was verified in the 0–200 ng ml⁻¹ range.     

Anodic stripping voltammetry of antimony using gold nanoparticle-modified carbon screen-printed electrodes

Carbon screen-printed electrodes (CSPE) modified with gold nanoparticles present an interesting alternative in the determination of antimony using differential pulse anodic stripping voltammetry. Metallic gold nanoparticles deposits have been obtained by direct electrochemical deposition. Scanning electron microscopy measurements show that the electrochemically synthesized gold nanoparticles are deposited in aggregated form. Any undue effects caused by the presence of foreign ions in the solution were also analyzed to ensure that common interferents in the determination of antimony by ASV. The detection limit for Sb(III) obtained was 9.44 × 10⁻¹⁰ M. In terms of reproducibility, the precision of the above mentioned method in %R.S.D. values was calculated at 2.69% (n = 10). The method was applied to determine levels of antimony in seawater samples and pharmaceutical preparations.     

Crystal and electronic structure of the red semiconductor Ba4LaSbGe3Se13 comprising the complex anion [Ge2Se7-Sb2Se4-Ge2Se7]

Ba₄LaGe₃SbSe₁₃ was prepared by reacting the elements under exclusion of air at 700°C, followed by slow cooling to room temperature. It crystallizes in a new type of the monoclinic space group P2₁/c, with lattice dimensions of a=1633.30(9) pm, b=1251.15(7) pm, c=1303.21(7) pm, β=103.457(2)°, V=2590.0(2) 10⁶ pm³ (Z=4). The structure contains isolated GeSe₄ as well as Ge₂Se₇ digermanate units. Two of the latter are interconnected via an Sb₂Se₄ bridge yielding an almost linear complex anion [Ge₂Se₇-Sb₂Se₄-Ge₂Se₇]¹⁴⁻. The oxidation states are assigned to be Ba^II, La^III, Ge^IV, Sb^III, and Se^−II, in accord with an electronically saturated nonmetal. The lone pair of Sb^III reflects itself in highly irregular Se coordination. The red color of the material is indicative of semiconducting behavior with an activation energy of 2.0 eV. Electronic structure calculations based on the LMTO approximation point to a smaller gap, typical for this calculation method. We utilized the COHP tool to explore the bonding character of the different Sb-Se interactions.     

Speciation of arsenic in ground water samples: A comparative study of CE-UV, HG-AAS and LC-ICP-MS

The performance of capillary electrophoresis-ultraviolet detector (CE-UV), hydride generation-atomic absorption spectrometry (HG-AAS) and liquid chromatography-inductively coupled plasma mass spectrometry (LC-ICP-MS) have been compared for the speciation of arsenic (As) in groundwater samples. Two inorganic As species, arsenite (As^III), arsenate (As^V) and one organo species dimethyl arsenic acid (DMA) were mainly considered for this study as these are known to be predominant in water. Under optimal analytical conditions, limits of detection (LD) ranging from 0.10 (As^III, AsT) to 0.19 (DMA) μg/l for HG-AAS, 100 (As^III, DMA) to 500 (As^V) μg/l for CE-UV and 0.1 (DMA, MMA) to 0.2 (As^III, As^V) μg/l for LC-ICP-MS, allowed the determination of the above three species present in these samples. Results obtained by all the three methods are well correlated (r² = 0.996*** for total As) with the precision of <5% R.S.D. except CE-UV. The effect of interfering ions (e.g. Fe²⁺, Fe³⁺, SO₄²⁻ and Cl⁻) commonly found in ground water on separation and estimation of As species were studied and corrected for. Spike recovery was tested and found to be 80-110% at 0.5 μg/l As standard except CE-UV where only 50% of the analyte was recovered. Comparison of these results shows that LC-ICP-MS is the best choice for routine analysis of As species in ground water samples.     

Synthesis, crystal structures, magnetic and electric transport properties of Eu11InSb9 and Yb11InSb9

Two new rare-earth metal containing Zintl phases, Eu₁₁InSb₉ and Yb₁₁InSb₉ have been synthesized by reactions of the corresponding elements in molten In metal to serve as a self-flux. Their crystal structures have been determined by single crystal X-ray diffraction—both compounds are isostructural and crystallize in the orthorhombic space group Iba2 (No. 45), Z=4 with unit cell parameters a=12.224(2) Å, b=12.874(2) Å, c=17.315(3) Å for Eu₁₁InSb₉, and a=11.7886(11) Å, b=12.4151(12) Å, c=16.6743(15) Å for Yb₁₁InSb₉, respectively (Ca₁₁InSb₉-type, Pearson's code oI84). Both structures can be rationalized using the classic Zintl rules, and are best described in terms of discrete In-centered tetrahedra of Sb, [InSb₄]⁹⁻, isolated Sb dimers, [Sb₂]⁴⁻, and isolated Sb anions, Sb³⁻. These anionic species are separated by Eu²⁺ and Yb²⁺ cations, which occupy the empty space between them and counterbalance the formal charges. Temperature-dependent magnetic susceptibility and resistivity measurements corroborate such analysis and indicate divalent Eu and Yb, as well as poorly metallic behavior for both Eu₁₁InSb₉ and Yb₁₁InSb₉. The close relationships between these structures and those of the monoclinic α-Ca₂₁Mn₄Sb₁₈ and Ca₂₁Mn₄Bi₁₈ are also discussed.     

Electrochemical Behavior of Irreversibly Adsorbed Sb on Au Electrode

The electrochemical processes of irreversibly adsorbed antimony (Sb_ad) on Au electrode were investigated by cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM). CV data showed that Sb_ad on Au electrode yielded oxidation and reduction features at about 0.15 V (vs saturated calomel electrode, SCE). EQCM data indicated that Sb_ad species were stable on Au electrode in the potential region from −0.25 to 0.18 V (vs SCE); the adsorption of Sb inhibited the adsorption of water and anion on Au electrode at low electrode potentials. Sb₂O₃ species was suggested to form on the Au electrode at 0.18 V. At a potential higher than 0.20 V the Sb₂O₃ species could be further oxidized to Sb(V) oxidation state and then desorbed from Au electrode.     

Achieving Near-unity Photoluminescence Quantum Yields in Organic-Inorganic Hybrid Antimony (III) Chlorides with the [SbCl5] Geometry

Hybrid organic–inorganic antimony halides have attracted increasing attention due to the non-toxicity, stability, and high photoluminescence quantum yield (PLQY). To shed light on the structural factors that contribute to the high PLQY, five pairs of antimony halides with general formula A₂SbCl₅ and A₂Sb₂Cl₈ are synthesized via two distinct methods and characterized. The A₂SbCl₅ type adopts square pyramidal [SbCl₅] geometry with near-unity PLQY, while the A₂Sb₂Cl₈ adopts seesaw dimmer [Sb₂Cl₈] geometry with PLQY≈0 %. Through combined data analysis with the literature, we have found that A₂SbCl₅ series with square pyramidal geometry generally has much longer Sb⋅⋅⋅Sb distances, leading to more expressed lone pairs of Sb^III. Additional factors including Sb−Cl distance and stability of antimony chlorides may also affect PLQY. Our targeted synthesis and correlated insights provide efficient tools to precisely form highly emissive materials for optoelectronic applications.     

Investigation of the kinetics of aquation of the 1:2 complex between Cr and nitrilotriacetic acid

Aquation of the 1:2 complex between Cr^III and nitrilotriacetic acid (NTA) was monitored using a combination of capillary electrophoresis (CE), ultraviolet–visible (UV–vis) spectrophotometry, and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. To our knowledge, this is the first published report of the use of either CE or ATR-FTIR to monitor the kinetics of ligand exchange reactions of Cr^III–aminocarboxylate complexes. The aquation products were identified as the 1:1 Cr^III complex with NTA and “free” NTA. The 1:1 complex dimerized to form a 2:2 complex in a slower subsequent reaction step. Rates of disappearance of the 1:2 complex were first-order under all experimental conditions. First-order rate constants for aquation, k_obs (h⁻¹), measured using all three techniques were similar at equivalent pH conditions, and with values reported previously in the literature. Measured k_obs values exhibited a complicated pH dependence with three distinct regions: (i) at pH < 6.5, k_obs values increased with decreasing pH, (ii) between pH 6.5 and 8.0, k_obs values were relatively constant, and (iii) at 8.0 < pH < 10.0, k_obs increased with increasing pH and then leveled off. A kinetic model incorporating five distinct aquation pathways was successfully employed to model the pH dependence of k_obs from 0.0 < pH < 10.0. These results show that CE and ATR-FTIR can be used as tools for better understanding ligand exchange processes occurring in aqueous solution.     

Ga-Ga bonding and tunnel framework in the new Zintl phase Ba3Ga4Sb5

A new Zintl phase Ba₃Ga₄Sb₅ was obtained from the reaction of Ba and Sb in excess Ga flux at 1000°C, and its structure was determined with single-crystal X-ray diffraction methods. It crystallizes in the orthorhombic space group Pnma (No. 62) with a=13.248(3) Å, b=4.5085(9) Å, c=24.374(5) Å and Z=4. Ba₃Ga₄Sb₅ has a three-dimensional [Ga₄Sb₅]⁶⁻ framework featuring large tunnels running along the b-axis and accommodating the Ba ions. The structure also has small tube-like tunnels of pentagonal and rhombic cross-sections. The structure contains ethane-like dimeric Sb₃Ga-GaSb₃ units and GaSb₄ tetrahedra that are connected to form 12- and 14-membered tunnels. Band structure calculations confirm that the material is a semiconductor and indicate that the structure is stabilized by strong Ga-Ga covalent bonding interactions.     

Eu7Ga6Sb8: A Zintl phase with Ga-Ga bonds and polymeric gallium antimonide chains

The Zintl phase Eu₇Ga₆Sb₈ was obtained from a direct element combination reaction at 900°C. It crystallizes in the orthorhombic space group Pbca (No. 61) with a=15.6470(17) Å, b=17.2876(19) Å, c=17.9200(19) Å, and Z=8. In Eu₇Ga₆Sb₈, the anionic framework forms infinite chains of [Ga₆Sb₈]¹⁴⁻ which are arranged side by side to make a sheet-like arrangement but without linking. The sheets of chains are separated by Eu²⁺ atoms and also within the sheet, Eu²⁺ atoms fill the spaces between two chains. The chain is made up of homoatomic tetramers (Ga₄)⁶⁺ and dimers (Ga₂)⁴⁺ connected by Sb atoms. The compound is a narrow band-gap semiconductor with E_g∼0.6 eV and satisfies the classical Zintl concept. Extended Hückel band structure calculations confirm that the material is a semiconductor and suggest that the structure is stabilized by strong Ga-Ga covalent bonding interactions. Magnetic susceptibility measurements for Eu₇Ga₆Sb₈ show that the Eu atoms are divalent and the compound has an antiferromagnetic transition at 9 K.     

Disposable screen-printed ring disk carbon electrode coupled with wall-jet electrogenerated iodine for flow injection analysis of arsenic(III)

We report here a wall-jet electrogenerated iodine approach for sensitive detection of arsenite (As^III) by using a disposable screen-printed ring disk carbon electrode. Iodide (I⁻) is first oxidized to iodine (I₂) at the disk electrode; the electrogenerated I₂ can be effectively reduced back to I⁻ in the presence of As^III. The inhibited reduction current of I₂ to I⁻ can thus be monitored at the ring electrode and used for As^III analysis. Various factors influencing the flow injection analysis (FIA) of As^III were thoroughly investigated in this study. Under the optimized conditions, a linear calibration plot up to 10 μM with a detection limit (S/N = 3) of 70 nM was obtained by using 50 μM KI as the mobile phase in FIA. Practical utility of the proposed method was demonstrated to detect As^III in “Blackfoot” disease endemic village groundwater from southwestern coast area of Taiwan (Pei-Men).     

Revision of iron(III)–citrate speciation in aqueous solution. Voltammetric and spectrophotometric studies

A detailed study of iron (III)–citrate speciation in aqueous solution (θ = 25 °C, I_c = 0.7 mol L⁻¹) was carried out by voltammetric and UV–vis spectrophotometric measurements and the obtained data were used for reconciled characterization of iron (III)–citrate complexes. Four different redox processes were registered in the voltammograms: at 0.1 V (pH = 5.5) which corresponded to the reduction of iron(III)–monocitrate species (Fe:cit = 1:1), at about −0.1 V (pH = 5.5) that was related to the reduction of FeL₂⁵⁻, FeL₂H⁴⁻ and FeL₂H₂³⁻ complexes, at −0.28 V (pH = 5.5) which corresponded to the reduction of polynuclear iron(III)–citrate complex(es), and at −0.4 V (pH = 7.5) which was probably a consequence of Fe(cit)₂(OH)_x species reduction. Reversible redox process at −0.1 V allowed for the determination of iron(III)–citrate species and their stability constants by analyzing E_p vs. pH and E_p vs. [L⁴⁻] dependence. The UV–vis spectra recorded at varied pH revealed four different spectrally active species: FeLH (log β = 25.69), FeL₂H₂³⁻ (log β = 48.06), FeL₂H⁴⁻ (log β = 44.60), and FeL₂⁵⁻ (log β = 38.85). The stability constants obtained by spectrophotometry were in agreement with those determined electrochemically. The UV–vis spectra recorded at various citrate concentrations (pH = 2.0) supported the results of spectrophotometric–potentiometric titration.