Analytica Chimica Acta 703 (2011) 31–40 Contents lists available at ScienceDirect Analytica Chimica Acta j ourna l ho me page: www.elsevier.com/locate/aca Potentiometric stripping analysis of antimony based on carbon paste electrode modified with hexathia crown ether and rice husk Nayan S. Gadhari, Bankim J. Sanghavi, Ashwini K. Srivastava ∗ Department of Chemistry, University of Mumbai, Vidyanagari, Santacruz (East), Mumbai 400098, India a r t i c l e i n f o Article history: Received 7 May 2011 Received in revised form 8 July 2011 Accepted 11 July 2011 Available online 20 July 2011 Keywords: Antimony Hexathia 18 crown 6 Rice husk Potentiometric stripping analysis a b s t r a c t An electrochemical method based on potentiometric stripping analysis (PSA) employing a hexathia 18C6 (HT18C6) and rice husk (RH) modified carbon paste electrode (HT18C6–RH-CPE) has been proposed for the subnanomolar determination of antimony. The characterization of the electrode surface has been carried out by means of scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy and chronocoulometry. By employing HT18C6–RH-CPE, a 12-fold enhancement in the PSA signal (dt/dE) was observed as compared to plain carbon paste electrode (PCPE). Under the optimized conditions, dt/dE (s V -1 ) was proportional to the Sb(III) concentration in the range of 1.42 × 10 -8 to 6.89 × 10 -11 M (r = 0.9944) with the detection limit (S/N = 3) of 2.11 × 10 -11 M. The practical analytical utilities of the modified electrode were demonstrated by the determination of antimony in pharmaceuti- cal formulations, human hair, sea water, urine and blood serum samples. The prepared modified electrode showed several advantages, such as simple preparation method, high sensitivity, very low detection limit and excellent reproducibility. Moreover, the results obtained for antimony analysis in commercial and real samples using HT18C6–RH-CPE and those obtained by inductively coupled plasma-atomic emission spectrometry (ICP-AES) are in agreement at the 95% confidence level. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Antimony is a toxic element and known to cause adverse health effects on humans and animals due to environmental and occupational exposure [1]. Antimony has been classified as a pri- ority pollutant by the United States Environmental Protection Agency and the German Research Council [2]. Antimony drugs are also employed for the treatment of multiple lesions caused by human leishmaniasis disease [3]. The toxicological and physiolog- ical behavior of Sb is dependent on its oxidation state. Elemental antimony is more toxic than its salts, and trivalent antimony salts are 10 times more toxic than pentavalent salts [4]. At present, almost all forms of leishmaniasis are initially treated with tri- and penta-valent antimonials in the form of sodium stibogluconate (pentostam), N-methyl glucamine antimoniate or meglumine anti- moniate (glucantime). However, an overdose of Sb is highly toxic. Hence, its determination is very important because of its implica- tions in health as well as in pharmaceutical formulations. Literature reports a wide variety of methods for the trace level determination of Sb. A few of the methods available for the determi- nation of antimony are, viz., high-performance liquid chromatog- ∗ Corresponding author. Tel.: +91 22 26527956; fax: +91 22 26528547. E-mail addresses: aksrivastava@chem.mu.ac.in, akschbu@yahoo.com (A.K. Srivastava). raphy with hydride generation-atomic fluorescence spectrometry (HPLC–HG-AFS) [5], non chromatographic HG-AFS [6], electrother- mal atomic absorption spectrometry [7] and high-resolution continuum source graphite furnace atomic absorption spectrom- etry [8], high performance liquid chromatography–inductively coupled plasma-mass spectrometry [9,10]. However, these meth- ods are time consuming, costly and laborious. Electroanalytical methods [11–15], on the other hand, offer the advantages of low-cost, ease in sample handling, and above all, extremely high sensitivity and are thus the methods of choice for the detection and trace-level determination of Sb. Chemically mod- ified electrodes (CMEs) have been employed widely in the trace level determination of both metal ions [16,17] as well as organic molecules [18,19]. CMEs in the form of carbon paste electrodes (CPEs) have been extensively used due to their wide anodic poten- tial range, low residual current, ease of fabrication, easy surface renewal, and low cost. Plain carbon paste electrode (PCPE) has been modified employing various modifiers, viz., nanomaterials [20,21], surfactants [22], copper complexes [23,24], macrocycles [25,26], etc. Many procedures are available for the preconcentration and removal of antimony from various matrices. Out of these, rice husk (RH) is preferred due to its low cost, easy availability and above all a very good adsorbing property for antimony [27]. Rice husk is the hard protecting coverings of grains of rice. In addition to pro- tecting rice during the growing season, rice husk can be put to use 0003-2670/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2011.07.017