Elsevier

Talanta

Volume 63, Issue 2, 28 May 2004, Pages 397-403
Talanta

Sulphoxine immobilized onto chitosan microspheres by spray drying: application for metal ions preconcentration by flow injection analysis

https://doi.org/10.1016/j.talanta.2003.11.011Get rights and content

Abstract

A new chelating resin based on chitosan biopolymer modified with 5-sulphonic acid 8-hydroxyquinoline using the spray drying technique for immobilization is proposed. The chelating resin was characterized by thermogravimetric analysis (TGA) and X-ray diffraction (XRD) and surface area by nitrogen sorption. The efficiency of the chelating resin was evaluated by the preconcentration of metal ions Cu(II) and Cd(II) present in aqueous samples in trace amounts. The metal ions were previously enriched in a minicolumn and the concentrations of the analytes were determined on-line by flame atomic absorption spectrometry (FAAS). The maximum retention for Cu(II) occurred in the pH range 8–10, and for Cd(II) at pH 7. The optimum flow rate for sorption was found to be 7.2 ml min−1 for the preconcentration of the metal ions. The analytes gave relative standard deviations (R.S.D.) of 0.7 and 0.6% for solutions containing 20 μg l−1 of Cu(II) and 15 μg l−1 of Cd (II), respectively (n=7). The enrichment factors for Cu(II) and Cd (II) were 19.1 and 13.9, respectively, and the limits of detection (LOD) were 0.2 μg l−1 for Cd(II) and 0.3 μg l−1 for Cu(II), using a preconcentration time of 90 s (n=11). The accuracy of the proposed method was evaluated by the metal ion recovery technique, in the analysis of potable water and water from a lake, with recoveries being between 97.2 and 107.3%.

Introduction

The development of new analytical methodologies for the separation and preconcentration of analytes, present in environmental samples at trace and ultratrace levels has awoken the interest of many researchers [1], [2]. A current trend in the study of the synthesis of new materials is the modification of the polymeric matrices for the production of more versatile materials at low cost. These chelating resins have functional groups that are chemically bonded to a polymeric matrix, which can form chelates with metal ions [3], [4], [5]. The formation of chelates in the solid phase can be affected by different factors, such as the chemical activity of the complexing group, the physical nature of the polymeric matrix, the hydrated ion charge and the pH of the solution [6].

The 8-hydroxyquinoline has been immobilized chemically on a variety of supports such as cellulose [7], [8], [9], [10], Amberlite XAD-series resins [11], [12] and silica gel to effect separations of trace metals from high-purity water and lake water and seawater [13], [14], [15], [16].

The 5-sulphonic acid 8-hydroxyquinoline, also know as sulphoxine, is a ligand which has characteristics similar to the 8-hydroxyquinoline ligand, both have basic nitrogen and phenolic groups which are the sites responsible for the complexation of the metal ions through the formation of a chelate ring. 5-Sulphonic acid 8-hydroxyquinoline cellulose was prepared by the Mannich reaction [17], and was used for the preconcentration of trace metals in mineralized water, and the recovery was quantitative at pH 5 for the metal ions studied.

Resins with chelating properties, can also be prepared by simple immobilization of complexing organic reagents and react with a large variety of metal ions [1].

The chitosan, obtained through partial chitin deacetylation, contains a high percentage of reactive amino groups that favors its modification, and makes it highly selective when modified with chelating agents [18], [19], [20], [21], [22], [23]. The adsorption characteristics of chitosan are due to the flexible structure of the polymer chain that enables it to adopt the appropriate configuration and its high hydrophilicity is due to the presence of hydroxyl groups.

In general, the procedures for immobilization of chelating agents on polymeric matrices employ the static method using conventional resins. In this process the ion exchanger is added to a given volume of reagent solution and the mixture is shaken. In the present work, complexing agent sulphoxine was immobilized on biopolymer chitosan using the spray drying technique obtaining particles in the order of microns with a uniform distribution in relation to their size. The technique basically consists of the removal of the solvent, resulting the formation of microspheres of chitosan containing the reagent sulphoxine. The sorbent material obtained by the spray drying technique, was applied to enhance the sensitivity of flame atomic absorption spectrometry (FAAS) and to avoid interference caused by the matrix.

Section snippets

Instrumentation

A Varian Spectra AA 50 atomic absorption spectrometer (Varian, Australia), equipped with a flame atomizer and a Hitachi hollow cathode lamp (HLA-4S), was used for the determination of the analytes. The absorption readings were taken according to the operational conditions as peak area. The Ismatec-IPC peristaltic pump with eight channels and provided with Tygon® tubes was utilized to pump all solutions through the minicolumn in the flow system. A Mettler Toledo 320 pH meter was utilized to

Degree of deacetylation and surface area (N2)

The knowledge of the quantity of amino groups is an essential factor in the study of the relation between the structure and properties of biopolymer chitosan. The average degree of deacetylation was 91% and the biopolymer had 5.6 mmol of NH2 groups per gram of chitosan. The biopolymer modified had a low surface area with a value of 2 m2 g−1 and a pore volume of 2.65.10−3 cc g−1.

X-ray diffraction

The spectra of diffraction of X-ray for chitosan and modified chitosan in Fig. 3 show different degrees of crystallinity.

Conclusions

In this work the spray drying technique for preparation of chelating resin sulphoxine chitosan offers the possibility for the development of other chelating resins in the form of microspheres, immobilizing different complexing organic reagents on biopolymer chitosan or other different polymers.

The modified chitosan was shown to be chemically stable in all the analyses carried out in this study. The sorbent packed minicolumn did not show any over pressure or swelling. This chelating resin

Acknowledgements

The authors wish to thank the CNPq for its financial support.

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