Nitrosonaphthols have long been known as organic reagents in inorganic analysis. They have found the widest application to the photometric determination of cobalt [1]. In the complex formation of cobalt(II) with 1 nitroso 2 naphthol and its isomer, 2 nitroso 1 naphthol, cobalt(II) is oxidized to cobalt(III) [2]. The neutral CoL 3 compounds formed are extracted with nonpolar solvents [1,3] or with hydrophobic adsorbents, for example, with С 16 silica [4]; the last named adsorbents are used for the preconcentration and separation of cobalt from other metals followed by its photometric determination. The introduction of sulfo groups into 1 nitroso 2 naphthol with the for mation of 1 nitroso 2 naphthol 3,6 disulfonic acid, nitroso R salt (NRS), offers a number of advantages, i.e., reduces the рК а of the hydroxyl group in compar ison to that of the not sulfonated analogue and enhances the solubility of the reagent and its com plexes in water.Procedures for the photometric determination of cobalt as its complex with nitroso R salt are suffi ciently specific but not very sensitive, like the proce dures using 1 nitroso 2 naphthol. To increase sensi tivity, analysts use preconcentration, namely, copre cipitation [5] or extraction in the presence of quaternary ammonium bases [6,7]. Two phase aque ous extraction systems based on polyethylene glycols were proposed in [8] for the thermal lens determina tion of cobalt.Adsorption preconcentration allows analysts to extract an analyte with a rather small portion of an adsorbent, to exclude the use of organic solvents, and is easy to perform. Adsorbents of different nature are widely used for the adsorption preconcentration and subsequent photometric determination of cobalt [9][10][11][12][13][14][15]. In determining cobalt in natural and process waters, it was extracted with a KB 4P 2 cation exchanger, treated with an NRS solution, and cobalt was determined by the color of its complex [9]. A QAE Sephadex A 25 anion exchanger [10] and silica chemically modified with triphenylphosphonium groups [11] were used for the adsorption preconcen tration of a cobalt(III) complex with NRS and its sub sequent photometric determination. Adsorbents selective to cobalt were obtained by the immobiliza tion of NRS on an Amberlite CG 400 [12] anion exchanger and gels based on chitosan [13] and gelatin [14,15]. To attach NRS to a silica surface, we pro posed the preliminary modification of silica with poly(hexamethylene guanidine) (PHMG) [16]. The adsorbent synthesis is simple and requires available reagents, which opens up a possibility of its wide appli cation.In this work we consider the use of silicas consecu tively modified with poly(hexamethylene guanidine) Abstract-An adsorbent based on silica consecutively modified with poly(hexamethylene guanidine) and nitroso R salt is proposed for the adsorption preconcentration and photometric determination of cobalt. The approach gives adsorbents with the controlled surface concentration of the reagent. The adsorbent extracts cobalt(II) from solutions...

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Silica gel, sequentially modified with polyhexamethylene guanidine and pyrocatechin-3,5-disulfonic acid (Tiron), was suggested for sorption separation and determination of Fe(III) and Fe(II). It was found that quantitative extraction of Fe(III) and its separation from Fe(II) were attained at pH 2.5–4.0, while quantitative extraction of Fe(II) was observed at pH 6.0–7.5. An intensive signal with g = 4.27, which is characteristic for Fe(III), appeared in EPR spectra of the sorbents after Fe(II) and Fe(III) sorption. During interaction between Fe(II) and Tiron, fixed on the sorbent surface, its oxidation up to Fe(III) occurred. Red-lilac complexes of the composition FeL3 were formed on the sorbent surface during sorption regardless of initial oxidation level of iron. Diffuse reflectance spectrum of surface complexes exhibited wide band with slightly expressed maxima at 480 and 510 nm. Procedures for separation and photometric determination of Fe(III) and Fe(II) at the joint presence and total Fe content determination as Fe(II) in waste and natural waters was developed. The limit of detection for iron was 0.05 μg per 0.100 g of the sorbent. The calibration graph was linear up to 20.0 μg of Fe per 0.100 g of the sorbent. The RSD in the determination of more than 0.2 μg of Fe was less than 0.06.

⎯Adsorbents based on silica chemically modified by sulfur-containing groups (dithiocarbamate, thiodiazolethiol, mercaptophenyl, and aminobenzothiazole) quantitatively extract (recovery ≥99%) platinum(IV) from solutions ranging from 4 M HCl to pH 6. Under the conditions of the adsorption separation of platinum(IV), rhenium(VII) is not extracted and remains in the solution. The subsequent quantitative (98-99%) adsorption of rhenium(VII) is achieved in the presence of a 1000-fold excess of tin(II) chloride. Adsorption on the surface of adsorbents leads to the formation of platinum(II) complexes with sulfur-containing groups, luminescent at 77 K on irradiation with UV light. The luminescence spectra of surface platinum(II) complexes are located in the region of 550-700 nm. In the adsorption of rhenium(III) in the presence of tin(II) chloride, intensely colored brown complexes of rhenium formed on the surface of adsorbents. Electron paramagnetic resonance showed that, in the surface complexes, rhenium is in the oxidation state 2+. Silicas chemically modified by sulfur-containing groups were used in the development of procedures for the sequential isolation and determination of platinum and rhenium in solutions after the decomposition of aluminum-platinum-rhenium catalysts.