Determination of zineb in tap water and tomato samples by adsorptive catalytic stripping voltammetry

Turkish Journal of Chemistry http://journals.tubitak.gov.tr/chem/ Research Article Turk J Chem (2013) 37: 712 – 720 c TÜBİTAK ⃝ doi:10.3906/kim-1209-32 Determination of zineb in tap water and tomato samples by adsorptive catalytic stripping voltammetry 1 Özlem KARAKOÇ,1 Nuri NAKİBOĞLU2,∗ Science Education Division, Necatibey Education Faculty, Balıkesir University, Balıkesir, Turkey 2 Chemistry Department, Sciences and Arts Faculty, Balıkesir University, Balıkesir, Turkey Received: 17.09.2012 • Accepted: 26.01.2013 • Published Online: 16.09.2013 • Printed: 21.10.2013 Abstract: This paper describes a sensitive and accurate adsorptive catalytic stripping voltammetric method for the determination of zineb (zinc ethylene-bis- dithiocarbamate) in tap water and tomato samples. The method is based on the reduction of adsorbed zineb at a hanging mercury drop electrode following its catalytic oxidation using peroxydisulfate as an oxidizing reagent. Chemical and instrumental parameters of the process were optimized. The catalytic mechanism of the reduction of zineb is discussed as well. The limits of detection (3 s) and quantification (10 s) and linear range of the method for accumulation time of 60 s were calculated as 8.1 nM, 28 nM, and 0.028–7.00 µ M, respectively. The relative standard deviation of the method was 3.68% for 2.5 µ M zineb (N = 5). The proposed method was applied successfully for the determination of zineb in tap water and tomato samples. Key words: Catalytic, dithiocarbamate, peroxydisulfate, tomato, voltammetry, water, zineb 1. Introduction Ethylene-bis-dithiocarbamate (EBDCs) fungicides are widely used for preventing crop damage in the field and protecting harvested crops from deterioration during storage and transportation. However, residuals of this kind of compound can cause environmental and human health problems as they have toxic effects on the liver and are carcinogenic. The EBCD group, which can form complex compounds with ions such as Fe +2 , Mn +2 , Cu +2 , Na + , Ni +2 , and Zn +2 , has more toxic effects. 1−3 Zineb (zinc ethylene-bis-dithiocarbamate) (Figure 1) is a slightly yellow, odorless powder used as a fungicide to protect fruit and vegetable crops from a wide range of diseases. It is also used in water-cooling systems, and the sugar and rubber industries. The toxicity of zineb is low to humans and warm-blooded animals. On the other hand, it is toxic to birds and even more so to fish. Detailed information about the toxicity of zineb can be found elsewhere. 1 Therefore, determination of residual zineb is quite important in real samples and sensitive and accurate methods are still needed. Various methods have been reported for determination of zineb in samples by spectrophotometry, 3−7 high performance liquid chromatography, 8−11 liquid chromatography–mass spectrometry, 12 gas chromatography, 13 capillary electrophoresis, 7 and atomic absorption spectrometry. 14 Most of these methods are time-consuming, expensive, and based on indirect determination of zineb. For this reason, they exhibit poor selectivity and inadequate sensitivity. A recent method for determination of zineb and ziram by flow injection-photoinducedchemiluminescence has been also reported. 15 In addition to all of those methods, electrochemical techniques such ∗ Correspondence: 712 KARAKOÇ and NAKİBOĞLU/Turk J Chem Figure 1. Square wave voltammograms obtained for 3.0 µ M of standard zineb in the absence (1) and presence (2) of peroxydisulfate ion (2 mM) in acetate buffer at pH 3. The other conditions: accumulation potential: –100 mV, accumulation time: 60 s, waiting time: 5 s, and scan rate: 25 mV/s. as polarography and voltammetry can be also used for determination of pesticides. A polarographic method has been reported for determination of zineb and maneb (manganese ethylene-bis-dithiocarbamate) in 40% acetone–formamide mixture (4:1). 16 Another similar study was performed in potassium chloride and sulfuric acid in 40% acetonitrile–formamide (4:1). 17 Yet, both methods suffer from poor sensitivity. A differential pulse polarographic method based on the formation of carbondisulfide and carbonoxysulfide gases has been described by Schwack et al. 18 However, the method has poor selectivity because of the hydrolysis of other compounds, such as dithiocarbamate metabolites and amino acids also evolve carbondisulfide. A differential pulse anodic stripping voltammetric method has been reported for determination of ziram using a static mercury electrode. 19 The method was applied to rice samples with recoveries of 95%–99%. However, this method is based on indirect determination of ziram using oxidation of zinc in the ziram after the accumulation period. Lin et al. developed a sensitive method derived from the reduction of the adsorbed EBCD group on the electrode surface for determination of zineb by adsorptive stripping voltammetry. 2 The electrochemical properties and adsorption behavior of zineb were well-defined in that study. Possible interferences from copper(II), lead(II), cadmium(II), iron(II), hemoglobin, sodium dodecyl sulfate, gelatin, humic acid, and camphor have been also reported. However, there is no information about application of the method in real samples. Therefore, a validated voltammetric method for determination of zineb in real samples seemed necessary. As far as we know, no voltammetric study including the catalytic effect in the presence of an oxidant has been reported in terms of the determination of zineb. Catalytic waves are an important field in voltammetry due to sensitivity enhancement. It is well known that platinum group metal ions and organic compounds containing nitrogen, oxygen, and sulfur functional groups produce a polarographic catalytic hydrogen wave while transition metal ions give a parallel catalytic wave in 713 KARAKOÇ and NAKİBOĞLU/Turk J Chem the presence of oxidants such as chlorate, bromate, hydrogen peroxide, nitrate, and nitrite. 20 On the other hand, organic substances containing reducible functional groups also generate catalytic waves in the presence of inorganic oxidants such as iodate, 21,22 peroxydisulfate, 22−24 and dissolved oxygen. 25,26 High sensitivity can be achieved when the catalytic effect is combined with adsorption. The aim of the present study was to develop an accurate and sensitive voltammetric method for determination of zineb in real samples. The method is based on reduction of adsorbed zineb at a HMDE following catalytic reduction by using peroxydisulfate ion as an oxidizing reagent. Chemical and instrumental parameters (pH, type of buffer system and its concentration, ionic strength, concentration of peroxydisulfate, accumulation potential, accumulation time, and stripping mode) were optimized and the method was successfully applied for the determination of zineb in tap water and tomato samples. 2. Experimental 2.1. Apparatus and reagents Voltammetric measurements were reco (...truncated)