Plasticized open-cell polyurethane foam as a universal matrix for organic reagents in trace element preconcentration: Part I. Collection of silver traces on dithizone foam

The preparation of plasticized foam containing dithizone or zinc dithizonate is described. The foam was used successfully for the rapid and quantitative collection of trace amounts of silver in batch and column experiments. The preconcentration of small amounts of silver from dilute aqueous solutions was found to be possible. The effects of different plasticizers, pH of the aqueous phase, and dithizone concentration in the foam, on the collection rate of silver were critically investigated.     

Preconcentration of phenlymercury,methylmercury and inorganic mercury from natural waters with diethylammonium diethyldithiocarbamate-loaded polyurethane foam

The percentage extraction of organomercurials and inorganic mercury on polyurethane foam loaded with diethylammonium diethyldithiocarbamate is high over a wide pH range, particularly when a plasticizer is added to the foam. Flow rates up to 120 ml min^-1 give quantitative extraction of inorganic mercury. Mercury(II), methylmercury and phenylmercury ions at 1 μg l^-1 levels can be almost quantitatively preconcentrated from tap and saline water, and eluted from the foam with acetone.     

Polyurethane-pyridylazonaphthol foams in the preconcentration and separation of trace elements

The feasibility of using PAN—polyether and polyester polyurethane foams in batch and column operations has been examined. The effects of pH, plasticizer and various anions present in the aqueous solution on the extraction behaviour of cobalt, iron and manganese have been investigated. In dynamic systems, the effect of flow rate on the extraction efficiencies of these metal ions has been investigated. The uptake of cobalt(III) and manganese(II) on PAN—polyester foam columns is quantitative at flow rates up to 10 ml min^-1 and 2 ml min^-1, respectively. The retention of iron(III) by the foam column is not quantitative even at a flow rate of 1 ml min^-1. Preconcentration of cobalt and its separation from various concentrations of manganese are successful..     

Photochromism of silver(I) and mercury(II) dithizonates : Effect of excess of free ligand on the return to ground state and effect of silver(I) dithizonate on the return of mercury(II) dithizonate

The energy of photons producing highest yield in the photochromic excitation of both silver(I) and mercury(II) dithizonate is shown to be centered around 520 nm. The effect of silver(I) dithizonate on the return of the excited form of mercury(II) dithizonate to the ground state is described. The accelerating effect of the silver complex is interpreted by an empirical kinetic model that takes into consideration the concurrent excitation and relaxation of both complexes. As observed in the photochromism of mercury(II) dithizonate, the presence of excess of ligand proportionally hastens the relaxation of silver(I) dithizonate to the ground state.     

Dual-wavelength spectrophotometric determination of traces of mercury(II) with solubilized dithizone: An approach to simplified analytical procedures for environmental pollutants

A simple spectrophotometric procedure is described for the determination of traces of mercury, with solubilized copper(II) dithizonate. Sample water containing 0.05–0.25 μg of mercury(II) is mixed with an aqueous solution of copper dithizonate containing Triton X-100 at pH 1 (H₂SO₄ ). After 5 min, dual-wavelength photometry is used to measure the difference in absorbances at 507 and 493 nm, which is proportional to the mercury concentration. The advantages are that no reagent blank is necessary and the equipment is simple. Few cations interfere; silver(I) and iron(III) can be masked by chloride and fluoride, respectively.     

Preconcentration and separation of iron, zinc, cadmium and mercury, from waste water using Nile blue a grafted polyurethane foam

The present work describes a novel method for the incorporation of Nile blue A into polyurethane foam matrix. This foam material was found to be very suitable for the extraction of metal ions from aqueous solutions. The characterization of Nile blue A grafted foam and the effect of halide concentration, pH, shaking time, extraction isotherm and capacity have been investigated. This foam material was found to be suitable for the separation and preconcentration of iron (III), zinc (II), cadmium (II) and mercury (II) from waste water. The extraction was accomplished in (15-20) minutes. Iron was separated from acid medium (2-4 M HCl), zinc from (3-5 M HCl), cadmium from (4-6 M HCl) as thiocyanate complexes and mercury was separated from (1-2 M HCl) as chloride.     

Determination of traces of mercury using radioactive zinc dithizonate as a reagent

A radioreagent method for the analysis of traces of mercury using radioactive zinc dithizonate as the reagent has been developed. As small as 0,2 μg of mercury can be determined using this technique. Possible interferences from most of the metals which displace zinc from zinc dithizonate can be removed by a simple separation procedure. The method was tested by analyzing the NBS reference standard SRM 1064 and our value was found to be in agreement with the value certified by NBS. This paper was presented at the South-East and South-West ACS Regional Meeting, Memphis, Tenn., October 29–31, 1975.     

Kinetics and Mechanism of Electroreduction of Ammonia and Hydroxyammonia Complexes of Zinc(II) on a Dropping Mercury Electrode

It is found that the equilibrium potential of the Zn(Hg)/Zn(II) system depends on the concentration of ammonia molecules and solution pH. The dependence conforms to the literature data on the stability constants for ammonia and hydroxyammonia complexes of zinc. Their reduction on a dropping mercury electrode in solutions of pH 9.2–12 and [NH₃] = 0.05–2 M yields one irreversible cathodic wave with a diffusion limiting current. In dilute supporting electrolytes, the plateau of the latter is preceded by a maximum due to accumulation of insoluble reduction products on the surface of the mercury drop. The pH and [NH₃] dependences of the half-wave potential of waves that are undistorted by a maximum are analyzed with allowance made for a change in the composition of zinc(II) complexes in the bulk solution. According to the analysis, the slow two-electron electrochemical stage involves complexes Zn(NH₃)₂ ²⁺ that form from complexes present in solution in preceding reversible chemical reactions. The effect the supporting-electrolyte concentration has on the electroreduction rate of zinc(II) complexes and the mechanism of the electrochemical stage is discussed.     

Graphite rod atomization and atomic fluorescence for the simultaneous determination of silver and copper in jet engine oils

S-Methyldithizone(5-methylmercapto-1,5-diphenylformazan) reacts with the chlorides of copper(II), mercury(II) and phenylmercury(II) to give the 1:1 chelates [CuCl(MeDz), HgCl(MeDz) and C₆H₅Hg(MeDz)] and with nickel(II) and palladium(II) to give the 1:2 chelates, M(MeDz)₂. All these complexes are intensely coloured in chloroform solution. No complexes are formed from cobalt(II), manganese(II) or zinc(II) or from the nitrates or acetates of copper and mercury. Coordination increases the reactivity of the sulphur atom in dithizone. Whereas dithizone is unaffected by methyl iodide, nickel dithizonate, Ni(HDz)₂, gives Ni-(MeDz)₂ when heated with methyl iodide in ethanol in the presence of sodium acetate; palladium dithizonate behaves similarly. The 1:1 adduct of nickel dithizonate with 2,2'-bipyridyl gave only Ni(MeDz)₂ on treatment with methyl iodide, and this complex would not form an adduct with bipyridyl. On standing in the light, Ni(MeDz)₂ reacted photochemically to give the yellow isomer of S-methyl-dithizone.     

Kinetic studies of a catalyzed metalloporphyrin formation

Kinetics of the incorporation of mercury(II) ion in tetra (p-trimethylammoniumphenyl)porphine have been investigated in aqueous solution at 30.0°C and 0.2 M (NaNO₃) ionic strength. The reaction was found to be first order each in mercury(II) and the porphyrin. The forward (formation) and the reverse (dissociation) rate constants were found to be 1.9 ± 0.2 × 10³ M^?1 s^?1 and 7 ± 2 × 10⁶ M^?1 s^?1, respectively. Kinetics of zinc(II) incorporation in tetra(p-trimethylammoniumphenyl)porphine catalyzed by mercury(II) were also investigated. This catalysis is explained in terms of steady-state formation of mono mercury(II) porphyrin followed by zinc(II) displacement of mercury(II) ion from the porphyrin. Such a mechanism also illustrates the importance of porphyrin core deformation to metal incorporation.     

Bubble extraction as a preconcentration step in trace elemental analysis: a preliminary study

Summary Surface active properties of dithizone and mercury(II) dithizonate have been analyzed by means of a laboratory apparatus for bubble extraction in view of utilizing it as a preconcentration device. Dependence of extraction efficiency on various parameters has been analyzed. Particularly, the dependence on concentration has been discussed in terms of adsorption isotherm and compared with that of a typical surface-active dye (crystal violet). It has been found that quantitative recovery ( 90%) of mercury, as mercury(II) dithizonate, is obtained from solutions of sufficiently low concentration ( 0.3 g/l).

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Fraktionierextraktion als Anreicherungsstufe in der Spurenelementanalyse. Eine vorläufige Untersuchung

     

Determination of Hg from Cu concentrates by X-ray fluorescence through preconcentration on polyurethane foam

A methodology was developed for the separation and determination of microamounts of mercury from copper concentrate samples by wavelength dispersive X-ray fluorescence (WDXRF) after solid-phase extraction of mercury from iodide medium using polyurethane foam (PUF). The best sorption conditions for the Hg-KI-PUF system were settled using X-ray fluorescence technique after collection of ground PUF on a filter paper by vacuum filtration and direct measurement of the intensity signal of the sorbed mercury on PUF. The main parameters of sorption such as iodide concentration, pH, shaking time and sample dilution effect were studied. The system shows rapid kinetic sorption and maximum X-ray intensity signal was achieved after shaking for 2 min a 0.01 mol l⁻¹ iodide solution containing microamounts of mercury in the pH range from 1.0 to 9.0. Effective sorption up to a volume of 0.9 l allows preconcentration of mercury. A linear fit up to 50 μg mercury was obtained by the plot of the initial mercury mass in the bulk solution (0.5 l) vs. its respective XRF intensity signal measurement on ground PUF after the sorption process. The calibration sensitivity, quantification and detection limits found were 9.09 CPS μg⁻¹, 9.0 and 2.7 μg, respectively. The sorption of many elements was also evaluated under the best conditions. High concentrations of Cu(II) and Fe(III) interfere seriously. Mercury-selective separation could be achieved using citrate or EDTA as masking agent; no interference due to copper matrix samples was observed in citrate medium. This methodology was evaluated by recovery for mercury determination in copper concentrate ore samples supplied by a mining industry and copper sulfate salts; the results were between 98% and 106%.     

Crystal and molecular structure of zinc dithizonate

The structure of zinc(II) dithizonate has been determined by X-ray analysis. The co-ordination round the zinc is slightly distorted tetrahedral and the proximal phenyl rings have been shown to be almost coplanar with the chelate rings.     

A sensitive optical element for mercury(II)

A transparent polymethacrylate matrix modified with copper dithizonate was used to determine mercury(II). Optimum conditions for modifying the polymethacrylate matrix with copper dithizonate were found, and its reaction with mercury(II) in model solutions was studied.     

Simple semiquantitative determination of trace metal ions by use of reagent gel columns-I: determination of mercury with dithizone gel

Mercury(II) at the sub-ppm level was determined by using a column packed with gel beads containing dithizone stabilized as the zinc complex. The beads turned from pink to green when the acidified sample solution was passed through the column. If the solution contained mercury (II), the colour of the gel beads turned to orange owing to the formation of mercury dithizonate. The length of the coloured zone was proportional to the amount of mercury in the sample. With 0.01% dithizone gel, as little as 0.1 ppm of mercury(II) could be determined in a 20-ml sample at a flow-rate of 1 ml/min.     

Extraction of zinc and cadmium thiocyanate complexes in the presence of pyridine and some metal ion separations

Extraction of zinc(II) and cadmium(II) from ammonium thiocyanate solutions has been studied in benzene in the presence of pyridine. The effect of such variables as the pH of aqueous phase and concentration of metal, thiocyanate and pyridine on extraction has been investigated and the extracting species identified. Extraction behaviour of silver(I), manganese(II), cobalt(II), mercury(II) and thallium(III) has also been studied under identical conditions and some binary metal ion separations of analytical and radiochemical importance are reported.     

Effect of photostability of mercury(II) dithizonate on photoacoustic spectroscopic determination of trace mercury

The solvent effect on the photostability of Hg(II) dithizonate in daylight and under laser irradiation has been confirmed and benzene found to be the best solvent to use in photometric work with Hg(II) dithizonate. A 1:1 v/v mixture of benzene and carbon tetrachloride is recommended for use in the laser-induced photoacoustic spectrometric determination of Hg(II) dithizonate. A detection limit of 0.8 ng/ml has been attained, together with a linear dynamic range of 3 orders of magnitude. Coupled with a concentration factor of 50 obtained by extraction, the method shows promise for the detection of Hg(II) at the 5-pg/ml level in water.     

Quantitative separation of zinc traces from cadmium matrices by solid-phase extraction with polyurethane foam

A system for separation of zinc traces from large amounts of cadmium is proposed in this paper. It is based on the solid-phase extraction of the zinc in the form of thiocyanate complexes by the polyurethane foam. The following parameters were studied: effect of pH and of the thiocyanate concentration on the zinc extraction, shaking time required for quantitative extraction, amount of PU foam necessary for complete extraction, conditions for the separation of zinc from cadmium, influence of other cations and anions on the zinc sorption by PU foam, and required conditions for back extraction of zinc from the PU foam. The results show that zinc traces can be separated from large amounts of cadmium at pH 3.0±0.50, with the range of thiocyanate concentration from 0.15 to 0.20 mol l⁻¹, and the shaking time of 5 min. The back extraction of zinc can be done by shaking it with water for 10 min. Calcium, barium, strontium, magnesium, aluminum, nickel and iron(II) are efficiently separated. Iron(III), copper(II) and cobalt(II) are extracted simultaneously with zinc, but the iron reduction with ascorbic acid and the use of citrate to mask copper(II) and cobalt(II) increase the selectivity of the zinc extraction. The anions nitrate, chloride, sulfate, acetate, thiosulphate, tartarate, oxalate, fluoride, citrate, and carbonate do not affect the zinc extraction. Phosphate and EDTA must be absent. The method proposed was applied to determine zinc in cadmium salts using 4-(2-pyridylazo)-resorcinol (PAR) as a spectrophotometric reagent. The result achieved did not show significant difference in the accuracy and precision (95% confidence level) with those obtained by ICP–AES analysis.     

Enhanced capacity of chitosan for transition-metal ions in sulphate-sulphuric acid solutions

Batch measurements have shown that the collection yields of chitosan for chromium(III), iron(III), nickel, copper(II), zinc and mercury(II) from sulphuric acid solutions are higher when the solutions contain ammonium sulphate, or when chitosan conditioned in ammonium sulphate is used, particularly at pH 3.0 and 5.0. The contrary is verified for the oxy-anions vanadate, chromate and molybdate. Manganese is never collected. At pH 1.0 no collection occurs. A procedure for recycling chromatographic columns includes fixation of Cu or Ni from a sulphate solution at pH 3-5 on sulphate-conditioned chitosan, and elution with 0.1M sulphuric acid/0.1M ammonium sulphate at pH 1.0; the presence of sulphate in the eluent obviates the detrimental effect of sulphuric acid on the next cycle. Sulphate is the favoured counter-ion of the chelated cations and its action produces shorter chromatographic bands. The interaction of sulphate with chitosan is discussed in terms of crystallinity and steric distribution of the protonated amino-groups in the polymer. Data on the new diethylaminohydroxypropylcellulose are included.     

Extractive separation and spectrophotometric determination of palladium and platinum with dithizone in the presence of stannous chloride

The conditions [acid used, presence of chloride and tin(II)] for the extractive separation and spectrophotometric determination of palladium and platinum as the dithizonates Pd(HDz)(2) and Pt(HDz)(2) have been examined. In the absence of stannous chloride platinum does not undergo extraction. Conditions for the separation and determination of these metals in the presence of mercury, gold and copper, which are also extracted with dithizone into carbon tetrachloride or chloroform under the conditions suitable for palladium (1M sulphuric acid/0.1M hydrochloric acid), have been defined. The mercury and gold dithizonates are formed quickly and can be removed before the palladium and platinum compounds have had time to form. They can be decomposed with iodide. Copper dithizonate is decomposed by reduction with tin(II). The proposed procedure has been applied to the determination of palladium in technical platinum metal.