Solid-Phase Extraction with Slurry Injection of the Resin Into ETAAS for Trace Determination of Thallium in Natural Water

Thallium in natural water samples was determined by electrothermal atomic absorption spectrometry after 1000-fold enrichment by mini solid-phase extraction from a 100-mL sample solution. A Tl-pyrrolidine-1-carbodithioate complex formed in a sample solution of pH 1.6 was extracted on fine particles of a cellulose nitrate resin dispersed in the sample solution. The cellulose nitrate resin was then collected on a membrane filter (25mm^ø) by filtration under suction using a glass funnel with an effective filtration area of 0.64cm². As a result, a circular thin layer of the resin phase with a diameter of 9mm was obtained. Then the resin phase was carved out by an acrylate resin puncher with a 10-mm^ø hole to put it into a sample cup containing 100µL of 10mM HNO₃ containing 0.5mM NaCl. The resin phase was suspended in the solution by ultrasonication. 1000-fold enrichment was thus attained within 15min, and the suspension was delivered to electrothermal atomic absorption spectrometry. The linear calibration graph was obtained in the range of 0–4ng of Tl in 100mL of a sample solution. The detection limit obtained by 3 method was 0.19ng. The proposed method was applied to the determination of Tl in natural water samples. The results showed the concentration of Tl in seawater was 12.1±1.8pgmL^–1 for the calibration graph method and 12.6±1.4pgmL^–1 for the standard addition method. A snowmelt sample contained 20.7±1.0pgmL^–1 of Tl.     

Voltammetric Determination of Trace Amounts of Fenitrothion on a Novel Nano-TiO2 Polymer Film Electrode

A novel nano-TiO₂ polymer modified glassy carbon (GC) electrode was developed for the determination of an organophosphorous pesticide, fenitrothion (-NO₂), in citrate buffer solution. The electrochemical behavior of fenitrothion was characterized by using cyclic voltammetry. An irreversible form, -NO₂, was transformed into a reversible redox couple (-NHOH/-NO), and it can be used to determine trace fenitrothion by square wave voltammetry. The experimental parameters, such as film thickness, pH value, accumulation potential and time were optimized. Interestingly, a cyclic voltammetric scan was observed to be more effective than a constant potential for the accumulation of fenitrothion. A linear response over a fenitrothion concentration of 2.5×10^–8 to 1.0×10^–5M was exhibited, with a detection limit of 1.0×10^–8M (S/N=3). The high sensitivity and selectivity of this film electrode was demonstrated by its practical application to the determination of trace amounts of fenitrothion in lake water and apple samples.     

Synthesis,Structure, and Magnetic Properties of the Silicides <Emphasis Type="BoldItalic">RE</Emphasis>IrSi (<Emphasis Type="Italic">RE</Emphasis> = Ce,Pr, Er,Tm, Lu) and SmIr<Subscript>0.266(8)</Subscript>Si<Subscript>1.734(8)</Subscript>

Summary. The equiatomic rare earth metal–iridium–silicides REIrSi (RE=Ce, Pr, Er, Tm, Lu) were prepared by arc-melting of the elements and subsequent annealing. All silicides were characterized through their X-ray powder patterns. The structures of CeIrSi, ErIrSi, and LuIrSi were refined from X-ray single crystal diffractometer data: LaIrSi type, P2₁3, a=629.15(2)pm, wR2=0.1232, 280F² values, and 11 variable parameters for CeIrSi; TiNiSi type, Pnma, a=673.4(1), b=416.07(5), c=744.88(9)pm, wR2=0.0705, 339F² values, and 20 variable parameters for ErIrSi, and a=664.0(3), b=412.9(1), c=742.6(1)pm, wR2=0.0398, 496F² values, and 20 variable parameters for LuIrSi. The iridium and silicon atoms in CeIrSi, ErIrSi, and LuIrSi build three-dimensional [IrSi] networks where the iridium atoms have three (CeIrSi, Ir–Si 229pm) and four (ErIrSi, Ir–Si 247–258pm; LuIrSi, Ir–Si 245–256pm) silicon neighbors. The [IrSi] networks leave larger channels in which the cerium, erbium, and lutetium atoms are located. Temperature dependent susceptibility data for LuIrSi indicate Pauli paramagnetism. CeIrSi shows Curie-Weiss paramagnetism above 100K with an experimental magnetic moment of 2.56(2)_B/Ce atom. With samarium as rare earth metal component the silicide SmIr_0.266(8)Si_1.734(8) with -ThSi₂ type structure was obtained: I4₁/amd, a=409.3(1), c=1397.2(5)pm, wR2=0.0575, 161F² values, and 9 variable parameters. Within the three-dimensional [Ir_0.266Si_1.734] network the Ir/Si–Ir/Si distances range from 230 to 237pm.     

Studies of artificial hydrolytic metalloenzymes: The catalyzed carboxyester hydrolysis by copper(II), zinc(II) and cobalt(II) complexes of the tripod ligand tris(2-benzimidazylmethyl)amine

The hydrolysis kinetics of p-nitrophenyl acetate (NA) catalyzed by Cu^II, Zn^II and Co^II complexes of tris(2-benzimidazylmethyl)amine (NBT) have been studied. The hydrolysis rate is first-order in both metal(II) complex and NA. The second-order rate constants, k_cat are 0.083, 0.241 and 0.285mol^–1Ls^–1 (298K, I = 0.10molL^–1 KNO₃, 0.02molL^–1 tris buffer, 40% MeCN aqueous solution) for Zn–NBT, Co–NBT and Cu–NBT complexes, respectively. The result indicates that the hydrolytic metalloenzyme activity of different metal complexes increases with the electrophilicity of the metal ions and that the complexes, in this paper, constitute that most efficient hydrolytic metalloenzyme models reported to date. An increase in MeCN content in the solution greatly reduces the hydrolytic activity of the nucleophiles.     

Determination of Attogram Quantities of Silver via Quenching of the Solid Substrate Room-Temperature Phosphorescence of Rhodamine B Based on the Catalysis of its Oxidation by Potassium Persulfate

A new method of SS-RTP for the determination of trace silver has been established. This method is based on the fact that Ag⁺, when activated by ,-bipyridyl (bipy) in a media of HAc–NaAc (pH=4.9), can catalyze the reaction of Rhodamine B (RhoB) oxidized by K₂S₂O₈, thus causing the Solid Substrate Room-Temperature Phosphorescence (SS-RTP) of RhoB to be quenched. The activating efficiency of bipy is 6.7 times higher than that of o-phenanthroline (phen). The reduction of the phosphorescence intensity (I_p) of RhoB is directly proportional to the concentration of Ag⁺ ions in the range of 1.6016.0agspot^–1 (0.40µLspot^–1). The regression equation of the working curve can be expressed as I_p=18.78+5.100m_Ag+ (agspot^–1) (r=0.9994, n=6), the detection limit is 0.28agspot^–1. This rapid, accurate and sensitive method has been successfully applied to the determination of trace silver in tea and human hair samples, and the results agree well with the Atomic Absorption Spectroscopy (AAS) method. The mechanism of the catalyzing reaction is also discussed.     

Theoretical Study of Chemical Binding of Noble Gas Atom and Transition Metal Complexes: Ng–NiCO, Ng–NiN2, Ng–CoCO (Ng = He–Xe)

Summary. Ab initio multireference and coupled cluster methods (MR-SDCI(+Q), CASPT2, CCSD(T)) and density functional theory methods (B3LYP, MPWPW91) have been applied to examine geometrical structures and vibrational frequencies of noble gas (Ng) – transition metal compounds, Ng–NiCO, Ng–NiN₂, and Ng–CoCO (Ng = He, Ne, Ar, Kr, Xe). It is shown that the respective compounds can have a larger binding energy than a typical van der Waals interaction energy. The binding mechanism is explained by a partial electron transfer from a noble gas atom to the low-lying 4s and 3d vacant orbitals of the transition metal atom. Theoretical calculations show that the binding of noble gas atom results in a large shift of the bending frequency: 361.1cm^–1 (NiCO) to 403.5cm^–1 (Ar–NiCO); 308.5cm^–1 (NiN₂) to 354.8cm^–1 (Ar–NiN₂); 373.0cm^–1 (CoCO) to 422.6cm^–1 (Ar–CoCO). The corresponding experimental frequencies determined in solid argon are 409.1cm^–1 (NiCO), 357.0cm^–1 (NiN₂), and 424.9cm^–1 (CoCO), which are much closer to the corresponding frequency of Ar–NiCO, Ar–NiN₂, and Ar–CoCO, respectively.     

Determination of Heavy Metal Ions in Chinese Herbal Medicine by Microwave Digestion and RP-HPLC with UV-Vis Detection

A new method for the simultaneous determination of heavy metal ions in Chinese herbal medicine by microwave digestion and reversed-phase high-performance liquid chromatography (RP-HPLC) has been developed. The Chinese herbal medicine samples were digested by microwave digestion. Lead, cadmium, mercury, nickel, copper, zinc, and tin ions in the digested samples were pre-column derivatized with tetra-(4-chlorophenyl)-porphyrin (T₄-CPP) to form the colored chelates which were then enriched by solid phase extraction with C₁₈ cartridge and eluted from the cartridge with tetrahydrofuran (THF). The chelates were separated on a Waters Xterra RP₁₈ column by gradient elution with methanol (containing 0.05molL^–1 pyrrolidine-acetic acid buffer salt, pH=10.0) and THF (containing 0.05molL^–1 pyrrolidine-acetic acid buffer salt, pH=10.0) as mobile phase at a flow rate of 0.5mLmin^–1 and detected with a photodiode array detector in the range of 350–600nm. In the original samples the detection limits of lead, cadmium, mercury, nickel, copper, zinc and tin are 4ngL^–1, 3ngL^–1, 6ngL^–1, 5ngL^–1, 2ngL^–1, 6ngL^–1, and 4ngL^–1, respectively. This method was applied to the determination of lead, cadmium, mercury, nickel, copper, zinc and tin in Chinese herbal medicine samples with good results.     

Novel Coated-Wire Membrane Sensor Based on Bis(Acetylacetonato) Cadmium(II) for the Determination of Chromate Ions

A new electrode based on a complex of chromate ions with bis(acetylacetonato) cadmium(II) as a carrier was developed for detection of chromate in aqueous solution. The electrode exhibited linear response with Nernstian slopes of –28.8±0.5mVper decade for chromate within the concentration range of 2.5×10^–6–0.1M. The limit of detection as determined from the intersection of the extrapolated linear segments of the calibration plots was almost 1.0×10^–6M. The electrodes exhibited good selectivities for chromate. The response time of the electrode was <25s over the entire concentration range. The electrode can be used in the pH range 8.0–12.0 for chromate. It was used as an indicator electrode in titration with Pb(NO₃)₂ and for the determination of chromate ion in wastewater samples.     

Determination of Lead Using a New Chromogenic Reagent 2-(2-Sulfo-4-acetylphenylazo)-7-(2,4,6-trichlorophenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic Acid

A novel chromogenic reagent, 2-(2-sulfo-4-acetylphenylazo)-7-(2,4,6-trichlorophenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic acid 1, was prepared by diazo coupling of 4-acetylaniline-2-sulfonic acid and 2,4,6-trichloroaniline to chromotropic acid through –N=N– groups. Based on this reagent, a simple, sensitive and selective spectrophotometric method was developed for the determination of lead. In 0.20M phosphoric acid medium, lead reacts with 1 to form a 1:2 blue complex with an absorption maximum of 654nm. Beers law is obeyed in the range of 0–0.6mgL^–1 of lead. The apparent molar absorptivity is 1.25×10⁵Lmol^–1cm^–1. The detection limit and quantification limit were found to be 0.63µgL^–1 and 2.1µgL^–1, respectively. The relative standard deviation for eleven replicate measurements was of 2.6%. The interference of foreign ions was also investigated. All the other foreign ions studied did not interfere with lead determination except for Ca(II) and Ba(II). The interference caused by Ca(II) and Ba(II) can be eliminated by prior extraction of lead with potassium iodide-methylisobutylketone (KI-MIBK). The proposed method was applied to the determination of lead in certified samples with satisfactory results.     

2,3-Dihydroxypyridine Loaded Amberlite XAD-2 (AXAD-2-DHP): Preparation, Sorption–Desorption Equilibria with Metal Ions, and Applications in Quantitative Metal Ion Enrichment from Water, Milk and Vitamin Samples

2,3-Dihydroxypyridine loaded (via –N=N–linker) Amberlite XAD-2 (AXAD-2-DHP) was prepared and characterized by elemental analyses, TGA and FT-IR spectra. It (1g packed in a column of 1cm diameter; surface area 135.5m²g^–1) was found to be an effective solid phase sorbent for enriching Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Co²⁺ at pH 3.5 to 7.0 using flow rates between 1.0–5.0mLmin^–1. For desorption (recovery 97.0–99.8%) of the metal ions, 8 to 10mL of 2.0molL^–1 HCl or 1.5molL^–1 HNO₃ at a flow rate of between 2.0 and 4.0mLmin^–1 were found most suitable. The t_1/2 (time for 50% sorption) is between 2 and 10min when a 50mL solution (containing a total amount of metal of 2mg) was equilibrated with 0.5g of resin. Sorption of all metal ions except Pb²⁺ follows the Langmuir model, whereas for Pb the data fits with the Freundlich model. The sorption capacity is between 60.7 (for Cd) and 406.7 (for Cu) µmolg^–1. The resin can withstand an acid concentration of 6molL^–1 and can be reused for thirty cycles of sorption–desorption. The preconcentration factor varies between 100 and 300. For Cd, Ni and Cu the sorption capacity of 2,3-dihydroxypyridine loaded cellulose is lower than that of the present resin. The tolerance limits of electrolytes, humic acid, complexing agents, Ca²⁺ and Mg²⁺ in the enrichment of all metal ions are reported. The limits of detection are 3.88, 5.37, 8.72, 13.88, 4.71, 1.24, 0.59 and 0.30µgL^–1 for Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Co²⁺, respectively. The calibration curves for flame AAS determination were linear in the ranges 0.018–1.0, 0.067–5.0, 0.2–5.0, 0.9–20, 0.028–2.0, 0.077–5.0, 0.19–10 and 0.1–3.5µgmL^–1, respectively. All the eight metal ions in river and synthetic water samples, Co in vitamin tablets and Zn in milk samples have been quantitatively enriched with Amberlite XAD-2-DHP and determined by flame atomic absorption spectrometry.     

Determination of Iron in Tap and Waste Water Using Liquid–Liquid Extraction in a Flow-Injection System

A flow-injection procedure for the determination of iron(III) in water is described. The procedure is based on the formation of an ion pair between the tetraphenylarsonium (Ph₄As⁺) (TPA) or tetrabutylammonium (But₄N⁺) (TBA) cations and the tetrathiocyanatoferrate(III) complex (TTF). This ion pair is extracted with chloroform, and the absorbance of the organic phase is measured at 503nm (for Ph₄As⁺) or 475nm (for But₄N⁺). Iron concentrations higher than 0.9×10^–6molL^–1 (50µgL^–1) can be detected in the first case, with a relative standard deviation of 1.9% (n=12), a linear application rangeof between 1.34 and 54.0×10^–6molL^–1 (75–3015µgL^–1), and a sampling frequency of 30h^–1. For the ion pair with But₄N⁺, the detection limit is 0.52×10^–6molL^–1 (29µgL^–1), with a relative standard deviation of 1.6% and a linear application range between 0.73 and 54.0×10^–6molL^–1. Under the proposed working conditions, only Pd(IV), Cu(II) and Bi(III) interfere. With the application of the merging zones technique, considerable amounts of organic reagent can be saved. The TBA method was applied to the analysis of iron(III) in tap and industrial waste waters.     

A kinetic study of the oxidation of 2-(2-hydroxyethyl)pyridine by chromium(VI) in strongly acidic aqueous solutions of HClO4

Oxidation of 2-(2-hydroxyethyl)pyridine (pyeol) to 2-pyridylacetaldehyde (pyeal) by Cr^VI has been studied in the 0.5–2.0M HClO₄ range at I=2.2M and in super acidic media within the 3–7M HClO₄ range. In all cases the reaction has been examined under pseudo-first order conditions keeping the alcohol and H⁺ _aq in excess. Cr^III-complexes formed during reduction of Cr^VI by pyeol at different molar ratios of the reactants, were isolated chromatographically and identified as [Cr(H₂O)₆]³⁺ and [Cr(pyeac)(H₂O)₄]²⁺ ions (pyeac=2-pyridylacetic acid). Free 2-pyridylacetaldehyde (pyeal) was separated and determined as its 2,4-dinitro-phenylhydrazone derivative. A dependence of the rate constants on [pyeol] and [H⁺] has been established at I=1.2M and I=2.2M. The apparent activation parameters at [H⁺]=1 and 2M have been determined. A rate law of the form d[Cr^VI]/dt= (k ₁[H ⁺]+k ₂[H ⁺]²)[pyeol][Cr^VI] is proposed. A linear dependence of log k _obs on H₀ in the super acidic media is obeyed. A rate decrease is observed if oxygen instead of argon is in the reaction cell. The reaction mechanism has been discussed.     

Electrochemical Behavior of Epinephrine at a Penicillamine Self-Assembled Gold Electrode,and its Analytical Application

The fabrication and electrochemical characteristics of a penicillamine (PCA) self-assembled monolayer modified gold electrode were investigated. The self-assembled electrode shows obvious electrocatalytic activity for the oxidation of epinephrine (EP). In phosphate buffer (pH 7.73), a sensitive oxidation peak was observed at 0.190V with the PCA modified Au electrode. The peak current is proportional to the concentration of EP in the range of 2.0×10^–56.0×10^–4molL^–1 and 5.0×10^–6 2.0×10^–4molL^–1 for cyclic voltammetry (CV) and differential pulse voltammetry (DPV) with the detection limits of 1.8×10^–7 and 1.3×10^–7molL^–1, respectively. The possible reaction mechanism is also discussed. The PCA self-assembled monolayer modified gold electrode is highly stable and can be applied to the determination of EP in practical injection samples. Application is simple, rapid and produces accurate results.     

Kinetics of formation,dissociation and equilibrium constants of pentacyanoaquoruthenate(II) with heterocycles

The kinetics of formation and dissociation reactions of [Ru(CN)₅L]^3– with a series of heterocyclic ligands were studied in aqueous media. In this presence of an excess of heterocycle, the observed second order rate constants were calculated from the k_obs versus [ligand] plot at =0.100m NaClO₄. Activation parameters for the formation reactions (H=28±7kJmol^–1 and S=140±35JK^–1mol^–1) are comparable for all systems, indicating a common mechanism. The kinetics of exchange of coordinated heterocycles for 1,3,5-triazine yielded a rate saturation typical of a limiting dissociative mechanism. Activation parameters of the limiting first order specific rate of dissociation reactions were H=85±7kJmol^–1 and S=18±4JK^–1mol^–1. Equilibrium constants were calculated from the second order rates of formation and pseudo-first order rates of dissociation reaction.     

Potentiometric Studies on Binary and Ternary Complexes of Di- and Trivalent Metal Ions Involving Some Hydroxamic Acids, Amino Acids, and Nucleic Acid Components

Summary. Formation of binary and ternary complexes of Cu^II, Co^II, Ni^II, Zn^II, Fe^III, Al^III, and Cr^III metal ions with some selected aliphatic and aromatic hydroxamic acids and some biologically important amino acids or nucleic acid components was investigated using the potentiometric technique at 25°C and I=0.10moldm^–3 NaNO₃. The acid-base properties of the ligands were investigated and discussed. The acidity constants of the ligands were determined and used for determining the stability constants of the complexes formed in aqueous medium under the experimental conditions. The ternary complex formation was found to occur in a stepwise manner. The stability constants of these binary and ternary systems were calculated. The order of stability of the ternary complexes in terms of the nature of hydroxamic acid, amino acid, nucleic acid component and metal ions was investigated and discussed as well as the values of log K and log X for the ternary systems. The concentration distribution of the various complex species in solution was evaluated. In addition, evaluation of the effect of temperature of the medium on the stability of the ternary system M^III – benzohydroxamic acid – L-histidine or adenine (M^III=Fe^III, Al^III, and Cr^III) has been studied. The thermodynamic parameters were calculated and discussed.     

The Dissociation Constants of 1,1'-Bis (pyridinium-4-aldoxime)trimethylene dibromide

The dissociation constants of the two oxime groups of 1,1-bis(pyridinium-4-aldoxime)trimethylene dibromide (TMB-4) were determined using spectrophotometric data. Two numerical methods were applied to treat the overlapping equilibria. The results obtained by both agreed with each other and their mean values at 25°C corrected for the ionic strength of 0.05moldm^–3 are pK_a1=7.49±0.11 and pK_a2=8.96±0.09. These values were discussed in terms of the pK_as of 1,1-bis(pyridinium-4-aldoxime)oxydimethylene dichloride (Toxogonin), a similar dioxime, which were derived by extrapolation of literature data.     

Determination of Total Selenium Content in Cereals and Bakery Products by Flow Injection Hydride Generation Graphite Furnace Atomic Absorption Spectrometry Applying in-situ Trapping on Iridium-Treated Graphite Platforms

A flow injection hydride generation graphite furnace atomic absorption spectrometric (FI-HG-GFAAS) method was applied to the determination of Se in Se-doped and undoped cereals and bakery products. For the purpose of doping, the soils used for the cultivation of the cereals were dosed with Se-doped foliar fertilizers. The samples were dissolved in a mixture of HNO₃ and H₂O₂ solutions using microwave-assisted digestion. The decomposition of H₂Se generated from the sample solutions and the trapping of elemental Se were performed at a temperature of 300°C on an Ir-pretreated integrated graphite platform of a transversally heated graphite atomizer (THGA). For release of the trapped Se within a fairly short atomization time (5s), an atomization temperature of 2200°C was observed to be optimal. The overall efficiency of hydride generation, transport and trapping was 86%.The upper limit of the linear dynamic range of calibration was 10µgL^–1, which corresponds to 0.5µgg^–1 for solid samples. Recovery of the samples spiked with Se^VI solutions was found to be 93±6% on average. The relative standard deviation of the determinations was less than 8%. The limit of detection was found to be 0.06µgL^–1, corresponding to 3ngg^–1 for solid samples. The accuracy of the method was verified with the use of IAEA-155 (whey powder) certified reference material. End-capped THGA tubes resulted in an extension of the linear calibration range compared to that of standard THGAs.The Se content in bakery products made of undoped cereals ranged from 7.7 to 68ngg^–1 (wet weight) in 18 samples, whereas the Se content of the corresponding cereals was found to be below 100ngg^–1 (wet weight). The Se level of cereals grown on soils treated with Se-doped fertilizers ranged from 128 to 1046ngg^–1 (wet weight), and it depended linearly on the Se concentration of the corresponding foliar fertilizer.     

Syntheses and properties of mixed dinuclear copper(II) complexes with heterocyclic dithiocarbamates and a cyclic octadentate tertiary amine

Five new Cu^II complexes of general formula [Cu₂(Rdtc)tpmc](ClO₄)₃, (1)–(5), where tpmc and Rdtc ^– refer to N,N,N,N-tetrakis(2-pyridylmethyl)-1,4,8,11-teraazacyclotetradecane and piperidine- (Pipdtc), 4-morpholine- (Morphdtc), 4-thiomorpholine- (Timdtc), piperazine- (Pzdtc) or N-methylpiperazine- (N-Mepzdtc) dithiocarbamates, respectively, have been prepared. Elemental analyses, conductometric and magnetic measurements, u.v./vis, i.r., e.p.r. and mass spectroscopy have been employed to characterize them. The complexes adopt an exo coordination of Cu^II ions and tpmc. The dithiocarbamate ion joins both the sulphur and the copper atoms acting as a bridging ligand The presence of different heteroatoms in the piperidine ring influences the (C=N) and (C=S) vibrations which decrease in the order of the complexes: Pipdtc>N-Mepipdtc>Pzdtc>Morphdtc>Timdtc ligands. Attention has been paid to the detailed mechanism of the mass spectral fragmentation of the complexes. The g _eff factors of the complexes have been also estimated by e.p.r. spectra. Finally, the complexes obtained demonstrate microbiologycal activity against some bacteria.     

On the Applicability of Duolite GT-73 to Column Preconcentration of Gold and Palladium Prior to Determination by Inductively Coupled Plasma Atomic Emission Spectrometry

The preconcentration of Au and Pd on Duolite GT-73 chelating resin with the thiol functional group was investigated prior to determination of these noble metals by means of inductively coupled plasma atomic emission spectrometry. It was found that Au^III and Pd^II were retained on the resin along with other concomitant metals (Al, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb and Zn) from different HCl-containing media. A two-step elution procedure was developed for the release of the noble metals. First 4.0molL^–1 HNO₃ solution was used to elute the base metals. The recovery of Au and Pd was performed afterwards using 0.50molL^–1 solution of (NH₂)₂CS. Retrieval of Au and Pd retained on Duolite GT-73 was also carried out by decomposition of the resin in the open vessel system using H₂SO₄ with H₂O₂. The detection limits of Au and Pd evaluated for the devised protocol, with a preconcentration factor of 50, were 0.085µgL^–1 and 0.28µgL^–1, respectively. The proposed method was applied to the determination of Au and Pd in spiked electrolytic bath samples.     

Au-Induced Faceting of Si(5 5 12)

The growth of Au on the stable, high-index Si(5512) surface has been studied using scanning tunneling microscopy (STM). At very low coverages and moderate annealing temperatures (0.1ML, 400–500°C), Au appears to decorate the underlying Si rows and form an array of rows that maintains the underlying (5512) periodicity of 5.4nm. For higher annealing temperatures and coverages, however, Au causes faceting to a number of nearby planes. The two primary facets formed at lower (0.15ML) and higher (0.5–2ML) coverages are the (337) and (225) planes, which are tilted 0.7° down [towards (111)] and 1.1° up from (5512), respectively. Both orientations are in fact subunits of the (5512) unit cell, so their presence is not surprising. In addition to these facets, two types of sawtooth morphologies composed of planes oriented further from (5512) are found at very high annealing temperatures (800–900°C). These include (113)+(7715) planes at very low coverage (0.05ml) and (113)+(5511) planes at higher coverage (1ML), where (113) is tilted up by 5.3° and (7715) and (5511) are tilted down by 2.9° and 2.2°, respectively. Au adsorption on Si(5512) therefore results in the formation of five possible facet planes: (113), (225), (337), (5511), and (7715).