T. I. Tikhomirova

Sorption of noble-metal ions on silica with chemically bonded nitrogen-containing ligands

A study has been made of the sorption of Ir(IV), Rh(III), Pt(IV), Ru(IV), Os(VIII), Pd(II) and Au(III) from aqueous solutions by silica chemically modified with nitrogen-containing organic ligands, as a function of hydrochloric acid concentration, time of contact, concentration of the element and the ionic strength. Sorption of noble-metal ions at pH > 1 on a sorbent containing monoamine groups seems to be due to a complexation mechanism, and to an anion-exchange mechanism at pH < 1. With aminopropyl-silica 1000-fold concentration of Ir(IV) and Rh(III) from their 10(-8)-10(-7)M solutions was achieved and these metals were subsequently determined on the sorbent surface by X-ray fluorescence. Detection limits were 10-20 ng/ml. There was no interference from 1000-fold quantities of non-ferrous metal ions and Fe(III). With the sorbent containing bonded diethylenetriamine groups, 1000-fold concentration of Au(III) was achieved, and it was then determined on the sorbent surface by an atomic-emission method. Conditions for desorption of Au(III) with pyridine and potassium thiocyanate were developed.

Concentration, separation and determination of scandium, zirconium, hafnium and thorium with a silica-based sulphonic acid cation-exchanger

A study has been made of the dependence of the sorption of scandium, zirconium, hafnium and thorium from aqueous solutions with a silica-based sulphonic cation-exchanger (SCE-SiO(2)) on the concentration and nature of the acid medium, time of contact, concentration of the element, and the ionic strength. The selectivity decreases in the order Zr approximately Hf > Th > Sc > Fe(III). The sorption characteristics of silica gel and SCE-SiO(2) have been compared, and the sorption mechanism is discussed. The SCE-SiO(2) exchanger has been used for 100-fold concentration of scandium, zirconium, hafnium and thorium from their 10(-8)-10(-7) M solutions, and a spectrophotometric method has been developed for their determination with a detection limit of 0.5 ng/ml for Zr and Sc and 0.1 ng/ml for Hf and Th. Zirconium and hafnium have been determined in the solvent phase by X-ray fluorescence and atomic-emission methods.

Preparation, properties and analytical application of silica with chemically grafted hydroxamic acid groups

Abstract The synthesis of silica chemically modified with propanohydroxamic acid groups and salicylhydroxamic acid is described. Sorption of 13 metal ions is studied as a function of pH. The composition of the sorbed complexes is determined and the apparent stability constants of the complexes in the sorbent phase are calculated. A correlation between the stabilities of the complexes in the sorbent phase and in aqueous solution is observed in some cases. Some analytical applications of the sorbents are demonstrated: trace amounts of elements can be concentrated from large volumes; molybdenum(VI) and zirconium(IV) can be separated from 10 4 -fold amounts of accompanying elements, and vanadium(V) can be determined in the sorbent phase by using diffuse reflection and photoacoustic spectrometric techniques.

Dynamic Preconcentration of Organic Substances on Nonpolar Adsorbents

The possibilities of using dynamic adsorption preconcentration in the determination of organic substances were discussed. The effect of thermodynamic and kinetic factors on the extraction of organic compounds from aqueous solutions was considered. The main classes of adsorbents were presented, and the relationship between the adsorbent properties and the efficiency of preconcentration was discussed. Examples of using dynamic adsorption preconcentration for the determination of a wide spectrum of substances were given.

Sorption of palladium on hydrophobic polymers in the presence of alkylamines

Abstract Distribution ratios of palladium(II) between hydrochloric acid solutions and some non-polar sorbents in the presence of various reagents containing amino groups were determined. The sorption of palladium is caused by the formation of hydrophobic ionic associates of PdCl 4 2− anion with protonated amines. The recovery of palladium depends on the hydrophobic properties of ion associates and on the sorption behaviour of the amines themselves. The system involving hyper cross-linked polystyrene SSPS and 4- n -octyldiethylenetriamine was chosen for the on-line preconcentration of palladium. Conditions for the quantitative recovery and desorption of the metal were found. A FIA–FAAS method for the determination of palladium including on-line sorption preconcentration has been developed.

On-line sorption-chromatographic determination of phenols with amperometric detection

Conditions of the preconcentration of phenol on a microcolumn filled with MN-200 hypercrosslinked polystyrene were determined using the linear sorption dynamics model. Conditions of the on-line determination of phenol and its chloro derivatives by reversed-phase high-performance liquid chromatography with amperometric detection were optimized. The detection limit of phenol and chlorophenols for preconcentration from 30 mL of a sample was 3 and 15 ng/L, respectively. The proposed procedure was used for the determination of phenols in tap and river water.

A hybrid sorption - Spectrometric method for determination of synthetic anionic dyes in foodstuffs.

A sorption-spectrometric method for determination of the anionic synthetic dyes based on their sorption on silica sorbent modified with hexadecyl groups (C16) followed by measuring the diffuse reflectance spectra on the surface of the sorbent has been proposed. Adsorption of sulfonated azo dyes Tartrazine (E102), Sunset Yellow FCF (E110), Ponceau 4R (E124) reaches maximum in acidic medium (1M HCl - pH 1). For the quinophthalone type dye Quinoline Yellow (E104), the adsorption is also maximal in an acidic medium (1M HCl - pH 2). The triphenylmethane dye Fast Green FCF (E143) is absorbed in the wider area of pH (1M HCl - pH 6). Increasing concentration of the dyes in a solution led to the increase in absorption band intensity in diffuse reflectance spectra of the adsorbent, which was used for their direct determination. The proposed method was applied to the determination of dyes in beverages and pharmaceuticals.

Preconcentration of metal ions on aluminum oxide modified with tiron

It is found that iron(III), titanium(IV), vanadium(V), copper(II), lead(II), and zinc(II) ions are adsorbed on aluminum oxide modified with Tiron. The adsorption of iron(III) is accompanied by the violet coloration of the adsorbent (560 nm), which indicates the formation of a 1: 2 complex on the adsorbent surface; copper forms a 1: 1 yellowish green complex (430 nm). The group preconcentration of metal ions on this adsorbent in a dynamic mode is possible; the preconcentration rate is 2.5 × 103. The method for the determination of metal ions is proposed based on the adsorption recovery of the elements followed by the direct determination by X-ray fluorescence spectroscopy on the adsorbent surface.

Sorbent Based on Aluminum Oxide Modified with Tiron

The adsorption of Tiron (disodium 4,5-dihydroxy-m-benzenedisulfonate) on aluminum oxide surface was studied, and optimum conditions for the modification of aluminum oxide surface were determined. The sorption of copper(II) on aluminum oxide modified with Tiron was studied. It was shown that the sorption of copper occurs by the mechanism of complex formation with the modifier (Tiron). The composition of the surface complex and its stability constant were determined: Cu: Tiron = 1: 1, logβ = 14.0 ± 0.4.

Complex formation of ruthenium(IV) and osmium(VIII) with 1,10-phenanthroline on the surface of silica sorbents

Abstract A study was made of the sorption of ruthenium(IV) and osmium(VIII) by silica and silica with chemically grafted sulpho groups from solutions containing 1,10-phenanthroline. Using diffuse reflection, luminescence and x-ray photoelectron spectroscopic methods, it was found that during sorption at pH 6–7 and room temperature on the surface of silica sorbents phenanthrolinate complexes of various composition are formed, bis- and tris(1,10-phenanthroline)metal (II, III), the Os(II) to Os(III) mole ratio being 2:1. A quantitative yield of tris(1,10-phenanthroline)metal(II) complex is obtained at 98 /+- 2 °C. The rate of complex formation on the surface of the sorbents considerably exceeds the rate of formation of the corresponding complexes in solution. It is suggested that silica sorbents have a catalytic action on the process of formation of complexes of ruthenium and osmium with 1,10-phenanthroline on the sorbent surface. A rapid sorption-luminescence method for determining ruthenium and osmium is proposed. The detection limit is 7 × 10 −4 μg ml −1 for ruthenium and 1 × 10 −3 μg ml −1 for osmium.