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A series of complexing adsorbents is prepared by coating silica particles with linear polyhexamethylene guanidinium (PHMG) chloride followed by saturation with a number of sulphonated nitrosonaphthols reagents electrostatically retained by positively charged polymer layer. PHMG coated silica is hydrolytically stable even during treatment with 6 M HCl heated up to 50 °C. The adsorption of 1-nitroso-2-naphthol-3,6-disulfonic acid (nitroso-R-salt), 2-nitroso-1-naphthol-4-sulfonic acid (nitroso-N-salt), and 2-nitroso-1-naphthol-3,6-disulfonic acid (nitroso-K-salt) on PHMG modified silica was studied. The effective immobilisation of sulphonated nitrosonaphthols was achieved in the range of pH of 3 - 8, while the adsorption of the monosulphonated reagent (nitroso-N-salt) is twice as high as the disulphonated analogues (nitroso-R-salt and nitroso-K-salt). The adsorption of Cu(II), Fe(III), Co(II), Ni(II), Al(III), Zn(II), Pb(II), Mn(II), and Cr(III) on prepared complexing adsorbents under static and dynamic conditions was studied as a function of time, pH, sample volume, and presence of interfering ions. Metal ions can be desorbed by using 1 M HCl or 1 M HNO3. The preconcentration factors of metals under optimized conditions are varied from 20 to 80. The developed method was used for the preconcentration of trace metals from natural waters followed by ICP-OES determination. The sub-ppb limits of detection of metals are achieved.

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...