Talanta 77 (2008) 394–399 Contents lists available at ScienceDirect Talanta journal homepage: www.elsevier.com/locate/talanta Determination of chlorogenic acid in coffee using a biomimetic sensor based on a new tetranuclear copper(II) complex Mirella Lucas de Carvalho, Murilo Santhiago, Rosely A. Peralta, Ademir Neves, Gustavo Amadeu Micke, Iolanda Cruz Vieira ∗ Departamento de Química, Universidade Federal de Santa Catarina, CEP 88040-900 Florianópolis, SC, Brazil article info Article history: Received 15 May 2008 Received in revised form 30 June 2008 Accepted 1 July 2008 Available online 10 July 2008 Keywords: Biomimetic sensor Chlorogenic acid Catechol oxidase Coffee abstract A new tetranuclear copper(II) complex which mimics the active site of catechol oxidase was synthesized and characterized by IR, CHN, electronic spectroscopic and 1 H NMR methods. The title complex [Cu 2 (- OH)(bpbpmp-NO 2 )] 2 [ClO 4 ] 2 was employed in the construction of a novel biomimetic sensor and used in the determination of chlorogenic acid by square wave voltammetry. The performance and optimization of the resulting biomimetic sensor were studied in detail. The best response of this sensor was obtained for 75:15:10% (w/w/w) ratio of the graphite powder:nujol:Cu(II) complex, 0.1molL -1 phosphate buffer solution (pH 7.0), with frequency, pulse amplitude, and scan increment at 30 Hz, 100 mV, and 3.0 mV, respectively. The chlorogenic acid concentration was linear in the range of 5.0 × 10 -6 to 1.45 × 10 -4 mol L -1 (r = 0.9985) with a detection limit of 8.0 × 10 -7 mol L -1 . This biomimetic sensor demonstrated long-term stability (250 days; 640 determinations) and reproducibility, with a relative standard deviation of 10.0%. The recovery study of chlorogenic acid in coffee samples gave values from 93.2% to 106.1% and the con- centrations determined showed good agreement when compared with those obtained using capillary electrophoresis at the 95% confidence level. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Coffee is among the most widely consumed pharmacologically active beverages in the world. It represents a giant global indus- try and ranks second only to petroleum in terms of dollars traded worldwide. Currently, 6.3 million tons of coffee is produced glob- ally, with Brazil and Colombia contributing to nearly 44% of this figure. The major polyphenol in coffee is chlorogenic acid, an ester formed between trans cinnamic acids and quinic acid. The cin- namic acids most commonly encountered are caffeic, p coumaric and ferulic acid [1–6]. The acid content in coffee is an important indication of its qual- ity, and is greatly dependent upon the degree of roasting, the type of roaster and method of infusion. The determination of chlorogenic acid in coffee is an important aspect of the quality control of the final product, since its aroma characteristics determine the com- mercial value [7]. The development of reliable, rapid, sensitive and simple methods for the quantification of this substance is of great importance. Methods for the determination of this acid include chromatography [8–11], capillary electrophoresis [12], flow injec- tion chemiluminescence [13] and electrochemistry [14]. Kriˇ zman ∗ Corresponding author. Tel.: +55 48 3721 6844; fax: +55 48 3721 6850. E-mail address: iolanda@qmc.ufsc.br (I.C. Vieira). et al. [8] employed a reversed-phase HPLC method for analyzing phenolic compounds in fennel (Foeniculum vulgare). The limits of detection ranged from 0.05 to 1.0 g mL -1 . The simultaneous determination of chlorogenic acid, caffeic and ferulic acid in coffee samples by micellar electrokinetic chromatography was used by Risso et al. [9]. The proposed method showed good linearity for chlorogenic acid and was able to resolve the two positional isomers of caffeoylquinic acid. A gas chromatographic–mass spectrometric method was used by Füzfai and Molnár-Perl [10] for the determina- tion of flavonoids, sugars, carboxylic acids and amino acids in citrus fruits. The authors found 33 compounds in the fruit samples after hydrolysis with trifluoroacetic acid. Nishitani and Sagesaka [11] used high-performance liquid chromatographic (HPLC) for simul- taneous determination of catechins, caffeine and other phenolic compounds in tea. The separation of polyphenolic compounds extracted from plant matrices using capillary electrophoresis has been proposed by Vaher and Koel [12]. Wang et al. [13] showed a new flow injection chemiluminescence method for the determina- tion of chlorogenic acid in fruits based on the reaction of potassium permanganate with this acid in the presence of formaldehyde as an enhancer. The linearity of the method ranged from 5.0 × 10 -8 to 5.0 × 10 -5 g mL -1 . Mello et al. [14] developed a biosensor based on horseradish peroxidase for the determination of chlorogenic acid in tea and coffee samples. The analytical curve was linear from 1 to 50 mol L -1 using chronoamperometry as the electrochemical 0039-9140/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2008.07.003