Using silica modified by poly(hexamethylene guanidine) and nitroso-R-salt for the preconcentration and determination of cobalt

Abstract

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...

Determination of Cobalt in Soils and Natural Waters Using Silica Gel Modified with Polyhexamethylene Guanidine and Nitroso-N-Salt

“…A comparison of the proposed procedure with other preconcentration systems which use various adsorbents for the determination of cobalt can be seen in (Table 6). Analytical features such as detection range, detection limits and precision are comparable to the methods presented in the literature [37,38,40,42,44,[46][47][48][49].…”

“…At equal concentrations of HNO 3 and HCl the desorption of the reagent was comparable. Presence only one sulfonate group in the NNS molecule causes weaker fixation of NNS on the surface of SiO 2 -PHMG than NRS, having two sulfonate groups [42].…”

“…The limit of detection of developed sorptionphotometric method is comparable with the limit of detection of ICP-OES determination; the obtained results have good accuracy and reproducibility. Application of the sorbent with functional groups of NNS allows two times reduce the detection limit of cobalt determination compared with limit of detection of cobalt determination using silica modified with PHMG and NRS [42]. Application of mini-column filled with SiO2-PHMG-NNS sorbent allows rapid and reliable visual estimation of cobalt content in natural waters and soil extracts in the field.…”

“…To eliminate the interference with these ions masking agents were used in the earlier work EDTA, citrate and acetate ions. However, as we have shown previously, these masking agents are ineffective to eliminate the interfering effect of the Cu (II), Ni (II) and Fe (II) in the sorption-photometric determination of cobalt using silica, sequentially modified with PHMG and NRS [40,42,43].…”

“…Therefore, formation of intermediate layer of polymeric polyamine that is able to interact with both surface silanol groups and sulfonic groups of the reagent was suggested. This approach has been used previously for synthesis of silica based sorbent sequentially modified with PHMG and NRS [42].…”