Determination of Cd, Co, Cr, Cu, Fe, Mn, Ni and Pb in natural waters, alkali and alkaline earth salts by electrothermal atomic absorption spectrometry after preconcentration by column solid phase extraction

Methods are described for the determination of trace and ultra trace amounts of Cd, Co, Cr, Cu, Fe, Mn, Ni and Pb in natural waters, alkali and alkaline earth salts. Separation and preconcentration of trace metals is achieved by a column solid phase extraction procedure using silica gel modified with derivatives of dithiocarbamates — Na-DDTC (sodium diethyldithio-carbamate and HMDTC (ammonium hexamethylene-dithiocarbamate) as column packing material. The influence of the sorbent preparation procedure on the degree of sorption of the trace analytes is examined for different pH values of the sample solution. Isobutylmethyl ketone (IBMK) is proposed as an effective eluent for quantitative elution of retained metal ions. Optimal instrumental parameters for ETAAS determination of preconcentrated elements in organic eluate are presented. Practical application of sorbents in analysis of natural waters and alkali and alkaline earth salts is demonstrated. Proposed preconcentration procedure combined with ETAAS determination of trace analytes allows the determination of 0.04 g l^–1 Cd, 0.1 g l^–1 Cr, Cu, and Mn and 0.3 g l^–1 Co, Fe, Ni and Pb in natural waters and 1.10^–7% Cd, 3.10^–7% Cr and Mn, 7.10^–7% Co, Ni and Pb and 2.10^–6% Cu and Fe in alkali and alkaline earth salts.     

Chelate adsorption for trace voltammetric measurements of iron(III)

Summary A very sensitive electrochemical stripping procedure for trace measurements of iron(III) is described. The chelate of iron with Solochrome Violet RS is adsorbed on the hanging mercury drop electrode, and the reduction current of the accumulated chelate is measured by voltammetry. The adsorption and redox behaviours are explored by cyclic voltammetry. The height of the chelate peak, which is about 0.28 V more negative than the peak of the free dye, is shown to be proportional to the iron concentration. Optimal experimental conditions include a preconcentration potential of –0.40 V, solution pH of 5.1 and a linear scan mode. The sharp chelate peak, associated with the effective interfacial accumulation, coupled with the flat baseline, facilitates measurements at the nanomolar and submicromolar concentration levels using short preconcentration times. The limit of detection after 1 min preconcentration is 0.04 gl^–1 (7 × 10^–10 M), and the relative standard deviation at the 10^–7 M level is 4.7%. The effects of possible interferences, due to coexisting metal ions or organic surfactants, are evaluated. The ability of measuring iron(III) in the presence of iron(II) is illustrated. Actual analyses of sea and tap waters are reported.

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Chelat-Adsorption für voltammetrische Spurenanalyse von Eisen(III)

     

Flow procedure for ion-exchange preconcentration and on-line spectrophotometric determination of iron(III) as its thiocyanate complex

On-line ion-exchange preconcentration of iron(III) on a conventional cation exchange resin with spectrophotometric detection based on thiocyanate complexation is described. The calibration graph is linear over the range 0.01–0.2 g ml^–1 and the detection limit (3 ) is 6 ng ml^–1 for a 6-ml sample. No interference effects were detected. The recovery of iron from the resin is 95%. 12 samples h^–1 can be analysed.     

Time-based on-line preconcentration cold vapour generation procedure for ultra-trace mercury determination with inductively coupled plasma atomic emission spectrometry

A time-based sequential dispensing on-line column preconcentration procedure for mercury determination at trace levels by cold vapour generation inductively coupled plasma atomic emission spectrometry (CV-ICP-AES), by means of a unified module of a preconcentration column and a gas–liquid separator (PCGLS) is described. The complex of mercury formed on-line with ammonium pyrrolidine dithiocarbamate (APDC) is retained on the surface of the hydrophobic poly(tetrafluoroethylene) (PTFE) turnings, which are packed into the lower compartment of the PCGLS. Subsequently, mercury vapour is generated directly on the PTFE turnings by reductant SnCl₂ and separated from the liquid mixture via the PCGLS by argon purge gas. The outlet of the PCGLS is connected directly to the torch adapter of the plasma without the normal spray chamber and nebulizer. With 60-s preconcentration time and 12.0 mL min^–1 sample flow rate, the sampling frequency is 30 h^–1. The calibration curve is linear over the concentration range 0.02–5.0 g L^–1, the detection limit (c_L) is 0.01 g L^–1 and the relative standard deviation (s_r) is 3.1% at the 1.0 g L^–1 level. The proposed method was evaluated by analysis of BCR CRM 278 (Mytilus Edulis) reference material and applied to the determination of total mercury in digested urine, blood and hair samples.     

The catalytic adsorptive stripping voltammetric determination of chromium with TTHA and nitrate

A sensitive voltammetric method is presented for the determination of trace amounts of total chromium (Cr(III) and Cr(VI)) in natural waters, employing the square wave mode. The method is based on the preconcentration of the Cr(III)-TTHA complex by adsorption at the HMDE at the potential of –1.0 V vs. Ag/AgCl. The adsorbed complex is then reduced producing a response with a peak potential of –1.29 V and the peak height of the Cr(III) reduction is measured. The catalytic action of the nitrate ions on the Cr(III)-TTHA reduction has been elucidated using cyclic voltammetry. The adsorption of chromium complexes at the HMDE was investigated using out-of-phase a.c. voltammetry and the potential range of adsorption was determined.Based on these investigations optimal conditions for the determination of the total chromium concentration in the range 155–2000 ng 1^–1 have been established. The determination limit is 15 ng 1^–1 and the RSD is 3.5% for chromium concentrations 200 ng 1^–1.The usefulness and wide scope of this method for reliable and highly sensitive chromium analysis down to the ultra trace levels existing in various types of natural waters is demonstrated by determinations of the total chromium content in lake, sea and rain water.     

A new selective and high affinity polymeric complexing agent for transition metal ions

Summary The synthesis and characteristics of a new chelating glycinohydroxamate-containing polymer resin is described. The functionality of the polymer is 1.76 mmolg^–1. The hydrogen capacity, water regain and adsorption capacities for iron(III), cadmium(II), cobalt(II), copper(II), nickel(II) and zinc(II) were measured at various pH values; uptake of the metal ions increased with pH and was quantitative above pH 3 for most of the metal ions. All cations studied showed high exchange rates towards the resin. The half saturation times for iron(III), cadmium(II), copper(II) and zinc(II) were all less than 1 min. The coordination behaviour of the resin was studied with the help of e.p.r., i.r., u.v. and potentiometry. The pK _a of the resin is 10.70 and the log value of the stability constants for iron(III), copper(II), lead(II), zinc(II), cobalt(II), manganese(II), cadmium(II) and nickel(II) were measured as 21.81, 19.50, 19.20, 18.59, 18.51, 18.46, 18.37 and 18.36, respectively, at 25 ° C and I = 0.2M KCl.     

Synthesis and Efficiency of a Spherical Macroporous Epoxy-Polyamide Chelating Resin for Preconcentrating and Separating Trace Noble Metal Ions

A new spherical macroporous epoxy-polyamide chelating resin was synthesized from epoxy resin by simple and rapid means and used for the preconcentration and separation of trace noble metal ions from solution samples. The acidity, flow rate, reusability, capacity and interference with the adsorption of ions on the resin as well as the conditions of desorption of these ions from the resin are discussed. The results show that the relative standard deviations for the determination of 50ng mL^–1 Au(III), Pt(IV) and Pd(IV) by inductively coupled plasma atomic emission spectrometry are in the range of 0.5–3.6%. The procedure was applied to determine metal smelter samples with satisfactory results.     

Application of a poly(dithiocarbamate) resin with macroreticular support to the determination of trace amounts of cadmium and lead in non-saline waters.

The chelating poly(dithiocarbamate) resin with macroreticular support is shown to be effective for the preconcentration of cadmium and lead from non-saline waters. The retained ions can be eluted efficiently in 5 ml of 8 mol dm-3 nitric acid from 1-20 cm columns of resin. Poly(dithiocarbamate) resin is used for preconcentration in the determination of cadmium and lead by flame atomic absorption spectrometry. The common ions present in non-saline waters do not interfere. The sensitivity was 0.10 micrograms l-1 of Cd and 0.73 micrograms l-1 of Pb. The detection limits were 0.03 and 0.34 micrograms l-1 for Cd and Pb, respectively. The cadmium and lead concentration rages, determined in mineral and tap waters, were between 0.1 and 0.8 micrograms l-1 and between 0.7 and 16.9 micrograms l-1, respectively.     

Simultaneous determination of zinc,iron and chlorides in radiopharmaceutical gallium /67Ga/ citrate injections by FSDP or DP polarography

A method for simultaneous determination of traces of zinc, iron, and chloride ions by fast scan or ordinary differential pulse polarography has been proposed. The method is especially suited to check the purity of radiopharmaceutical gallium /⁶⁷Ga/ citrate injections. The interference of citrate ions was eliminated by using a complex-forming base electrolyte containing triethanolamine and ammonia. The relative standard deviation of the determination of iron, zinc, and Cl^– ions in the range of 0.05–1.00 g of Fe or Zn and 3–25 g of Cl^– per ml solution was found to be 5–10%.     

Synthesis and magnetic properties of μ-oxalato-bridged Cu2 IIFeIII-type heterotrinuclear complexes

Three new -oxalato-bridged heterotrinuclear copper(II)–iron(III)–copper(II) complexes have been synthesized and identified: [Cu₂Fe(ox)₃L₂]ClO₄ [L = 5-nitro-1,10-phenanthroline (NO₂phen); 2,9-dimethyl-1,10-phenanthroline (Me₂phen) or 2,2-bipyridine (bpy), respectively]; ox = the oxalato dianions. Based on elemental analyses, molar conductivity and magnetic moment (at room-temperature) measurements, i.r. and electronic spectral studies, extended ox-bridged structures consisting of two copper(II) and an iron(III) ions, in which the central iron(III) ion has an octahedral environment and the end-capped two copper(II) ions a square-planar environment, are proposed for these complexes. The [Cu₂Fe(ox)₃(Me₂phen)₂]ClO₄ (1) and [Cu₂Fe(ox)₃(bpy)₂]ClO₄ (2) complexes were characterized further by variable-temperature magnetic susceptibility (4.2–300 K) measurements and the observed data were simulated by the equation based on the spin Hamiltonian operator, = –2J₁ · ₂, giving the exchange integrals J = –12.85 cm^–1 for (1) and J = –11.28 cm^–1 for (2). The results indicate the presence of an antiferromagnetic spin-exchange interaction between the copper(II) and iron(III) ions through the oxalato-bridge in both complexes (1) and (2).     

Application of a Chelate Forming Calix[4]arene-o-vanillinthiosemicarbazone Resin to the Separation,Preconcentration and Trace Determination of Cu(II), Cd(II) and Pb(II) in Natural Water Samples

A very stable calixarene-based polymeric chelating resin has been synthesized by covalently linking calix[4]arene-o-vanillinthiosemicarbazone through its lower rim to Merrifield resin. It was characterized by FT IR, ¹H NMR and elemental analysis. The resin was efficiently employed to separate and preconcentrate toxic metal ions such as Cu(II), Cd(II) and Pb(II) in a column prior to their determination by UV-Vis spectrophotometry and atomic absorption spectrophotometry (GFAAS) with a relative standard deviation ranging between 1.0–1.4%. Various physico-chemical parameters such as pH, concentration of eluting agents, flow rate, total sorption capacity, metal-ligand stoichiometry, exchange kinetics, preconcentration factor, distribution coefficient, breakthrough capacity, resin stability, effect of electrolytes and associated metal ions have been studied. Uptake and stripping of these metal ions on the resin were fast, indicating better access of the metal ions to the chelating sites. Detection limits (3_B) of 4.22µgL^–1, 11.89µgL^–1 and 19.61µgL^–1, along with preconcentration factors of 100, 125 and 111 for Cu(II), Cd(II) and Pb(II), respectively, were achieved. The proposed method was successfully applied to the separation and trace determination of Cu(II), Cd(II) and Pb(II) from natural water samples of Ahmedabad city.     

Spectroscopic studies of novel porphyrin-copper(II) and zinc(II) complexes that share the pinch-porphyrin family structure of iron(III) complex models of peroxidases

Six novel pinch-porphyrin complexes [(picdien)(protoporphyrinate dimethyl ester)]copper(II) (7), [(picdien)(mesoporphyrinate dimethyl ester)]copper(II) (8) and [(picdien)(deuteroporphyrinate dimethyl ester)]copper(II) (9), [(picdien)(protoporphyrinate dimethyl ester)]zinc(II) (13), [(picdien)(mesoporphyrinate dimethyl ester)]zinc(II) (14) and [(picdien)(deuteroporphyrinate dimethyl ester)]zinc(II) (15), were prepared from the corresponding free copper(II)-porphyrins (4–6), and zinc(II)-porphyrins (10–12) and picdien (N-(3H-imidazol-4-ylmethyl)-N-{2-[(3H-imidazol-4-ylmethyl)-amino]-ethyl}-ethane-2,3-diamine). Spectroscopic studies show that complexes (7–9) and (13–15) have the pinch-porphyrin type structure previously found in iron(III) complex models of peroxidases. Complexes (7–9), were characterized by u.v.–vis., m.c.d., and e.s.r. spectroscopy. E.s.r. spectra of the copper parent compounds (4–6) at ca. 10^–2–10^–4 M concentrations were typical of copper(II)-dimers. The addition of the picdien ligand broke up the dimers as detected by e.s.r. Compounds (7–9) are predominantly monomeric at ca. 10^–3 M concentration. The presence of picdien in (7–9) distorts the porphyrin internal portion of the plane so as to make these four internal nitrogen atoms, coordinated to copper(II), e.s.r.-distinguishable. MO and ligand field theories were used to characterize and to evaluate the directional covalence parameters of compounds (7–9). A non-fully axial, out-of-the-porphyrin-plane bonding was found for (7–9), similar to the bonding of the pinch-porphyrins-iron(III). However the in-plane distortion produced by the presence of the picdien ligand on copper(II) is significantly larger than in pinch-porphyrin-iron(III). The n.m.r. data show that the porphyrin-zinc(II) is the less strained and has the weakest bonded structure. The coordination number of the pinch-porphyrin with iron(III), copper(II) and zinc(II), is in all cases six.     

Amberlite XAD-2 functionalized with 2-aminothiophenol as a new sorbent for on-line preconcentration of cadmium and copper

A new functionalized resin has been applied in an on-line preconcentration system for copper and cadmium determination. Amberlite XAD-2 was functionalized by coupling it to 2-aminothiophenol (AT-XAD) by means of an NN spacer. This resin was packed in a minicolumn and used as sorbent in the on-line system. Metal ions were sorbed in the minicolumn, from which it could be eluted directly to the nebulizer-burner system of the flame atomic absorption spectrometer (FAAS). Elution of Cd(II) and Cu(II) from minicolumn can be made with 0.50 mol l⁻¹ HCl or HNO₃. The enrichment factors obtained were 28 (Cd) and 14 (Cu), for 60 s preconcentration time, and 74 (Cd) and 35 (Cu), if used 180 s preconcentration time. The proposed procedure allowed the determination of cadmium and copper with detection limits of 0.14 and 0.54 μg l⁻¹, respectively, when used preconcentration periods of 180 s. The effects of foreign ions on the adsorption of these metal ions are reported. The validation of the procedure was carried out by analysis of certified reference material. This procedure was applied to cadmium and copper determination in natural, drink and tap water samples.     

Kinetic Spectrophotometric Determination of Total Iron in Natural Water by Flow Injection Analysis Using On-Line Preconcentration

A new flow injection catalytic spectrophotometric method for on-line preconcentration and determination of total iron in natural water is described. The method is based on a combination of iron-catalyzed oxidation of diaminoditolyl by potassium bromate and the use of on-line preconcentration of iron onto 8-hydroxy-quinoline immobilized on silica gel. The corresponding calibration graph is linear over the range of 2.0–110ngmL^–1 for Fe(III) using a time-based technique for 5min preconcentration. The relative standard deviation of 11 measurements of 60ngmL^–1 Fe(III) was 0.67%. The method was applied to the determination of iron in natural water. The results obtained by the proposed method were compared with those obtained by ICP-AES. The t-test showed no significant differences between the two methods at a confidence level of 95%.     

Use of solid-phase extraction to eliminate interferences in the determination of mercury by flow-injection CV AAS

Solid-phase extraction with two-step elution has been developed for effective elimination of copper and iron interference with mercury determination by flow-injection cold vapour atomic absorption spectrometry (CV AAS). Sodium tetrahydroborate(III) was used as reducing agent. Cation-exchanger Dowex 50Wx4 was applied for the sorption of mercury and both interfering ions. In the first step elution of Cu(II) and Fe(III) was performed using 0.5 mol L^–1 KF solution. Then mercury was eluted with 0.1% thiourea in 8% HCl. The detection limit (3) for Hg(II) was 27 ng L^–1. The expanded uncertainty estimated for the whole procedure was about 6%. The accuracy of the proposed method was evaluated by determination of the recovery of known amount of mercury added to mineral, spring, and tap waters, and by analysis of a certified reference material BCR-144R (sewage sludge).     

Studies on the kinetics and mechanism of dissociation of copper(II) and nickel(II) complexes of the macrocyclic ligand 1, 5, 9, 13-tetraaza-2, 4, 4, 10, 12, 12-hexamethyl-cyclohexadecane-1, 9-diene in perchloric acid media

Summary Acid catalysed dissociation of the copper(II) and nickel(II) complexes (ML²⁺ of the quadridentate macrocyclic ligand 1, 5, 9, 13-tetraaza-2, 4, 4, 10, 12, 12-hexamethyl-cyclohexadecane-1, 9-diene (L) has been studied spectrophotometrically. Both complexes dissociate quite slowly with the observed pseudo-first order rate constants (k_obs) showing acid dependence; for the nickel(II) complex (k_obs)=k_O+k_H[H⁺], the k_o path is however absent with the copper(II) complex. At 60°C (I=0.1M) the k_H values areca 10^–4 M^–1 s^–1 for both complexes; k _H ^Cu /k _H ^Ni =ca. 3.9, comparable to some other square-planar complexes of these metal ions. The rate difference is primarily due to H values [copper(II) complex, 29.4±0.5 kJ mol^–1; nickel(II) complex, 35.6±1.5 kJ mol^–1] with highly negative S values [for copper(II), –215.5 ±6.1 JK^–1 mol^–1 and for nickel(II), –208.1 ±5.6 JK^–1 mol^–1] which are much higher than the entropy of solvation of Ni²⁺ (ca. –160 JK^–1 mol^–1) and Cu²⁺ (ca. –99 JK^–1 mol^–1) ions; significant solvation of the released metal ions and the ligand is indicated.     

Kinetic Determination of Iodide by the Oxidation Reaction of o-Phenylenediamine with Chloramine B

A kinetic method was developed for the determination of iodide ions. The method is based on the catalytic effect of iodide ions on the oxidation reaction of o-phenylenediamine with Chloramine B in an acidic solution and has a detection limit of 1 × 10^–4 g/mL. It was demonstrated that the method could be used for the determination of iodides in natural waters.     

Preconcentration of trace amounts of manganese from natural waters by means of a macroreticular poly(dithiocarbamate) resin

A chelating poly(dithiocarbamate) resin (PDTC) with macroreticular support is characterized as effective collector for traces of manganese from natural waters. Using small PDTC columns preconcentration of manganese can be achieved even at high flow-rates (5-6 ml/min) and sample volumes (1500 ml). Accordingly, PDTC resin is used for the preconcentration of manganese from water samples prior to its determination by flame atomic-absorption spectrometry. A series of ions abundant in natural waters do not interfere. The sensitivity and detection limit were 2.5 and 0.5 mug/l., respectively. The relative standard deviations of the results for a manganese concentration of 40-400 mug/l. are in the range 1.1-6.2%. In mineral and tap waters analysed, the manganese concentration range was between 2.9 and 30.8 mug/l.     

Continuous sonoassisted digestion coupled to flow injection minicolumn separation for the determination of total and labile Cu and Fe in fresh waters by flame atomic absorption spectrometry

An automatic on-line system is developed for the trace determination of copper and iron species in fresh waters by flame atomic absorption spectrometry using only 5 and 2?mL of sample, for copper and iron determination, respectively. This system, which includes a home-made minicolumn of commercially available resin containing aminomethylphosphonic acid functional groups (Chelite P), comprises two operational modes. The first, used for the determination of the dissolved labile fraction (free copper and iron ions and their weak complexes) is based on the elution of this fraction from a minicolumn containing the chelating resin loaded in-situ with the sample. The second mode is used for the determination of total trace copper and iron concentrations. This last mode is based on the retention/preconcentration of total metals on the Chelite P resin after on-line sonoassisted digestion of water samples acidified with nitric acid (0.5?mol?L^?1 final concentration) to break down metal organic complexes present in fresh waters as river waters. The figures of merit for copper and iron determination in both fractions are given and the obtained values are discussed. The analytical method was characterized and the limit of detection and limit of quantification for the two metals were 0.5 and 1.6?µg?L^?1 for Cu and 2.3 and 6.1?µg?L^?1 for Fe, respectively. The repeatability, expressed as relative standard deviation, was in the range 1.0–2.1%. The speciation scheme was applied to the analysis of river surface water samples collected in Galicia (Northwest, Spain).     

Determination of copper(I)-ethylene complexes, [Cu(C2H4)]+ and [Cu(C2H4)2]+, with aid of EDTA titration of copper(I) and copper(II) ions

Summary Volumetric measurements of ethylene and simple EDTA titration of copper(I) and copper(II) ions confirm that [CuL]⁺ and [CuL₂]⁺ are formed when an aqueous solution of copper(II) is reduced by copper metal in the presence of ethylene, (L). The formation constants,K ₁=[CuL⁺]²[Cu²⁺]^–1[L]^–2 andK ₂=[CuL ₂ ⁺ ]^–1[L]^–1, have been estimated. The formation of [CuL]⁺ is accompanied by an enthalpy change, H, of –25 kJ mol^–1, and a positive entropy change, S, of 13 J mol^–1 K^–1.