Multicomponent analysis of Korean green tea by means of disposable all-solid-state potentiometric electronic tongue microsystem

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Abstract

All-solid-state ‘electronic tongue’ microsystem comprised of polymeric sensors of different types such as highly cross-sensitive sensors based both on PVC and aromatic polyurethane (ArPU) matrices doped with various membrane active components, electrochemically deposited conductive films of polypyrrole (PPy) and polyaniline (PAn) and potentiometric glucose biosensors has been developed and applied for the analysis of beverages: natural coffee, black tea and different sorts of green teas. The system can discriminate different kinds of teas (black and green) and natural coffees. Components that are responsible for giving unique taste such as caffeine, catechines, sugar, amino acid l-arginine have been determined for green tea samples with unknown manufacturer specifications.

Introduction

An application of multisensor systems, an electronic tongue in particular, opened a new promising direction for the analysis of liquid phase foodstuffs, and has been increasing quickly in the last decade [1]. Different tasks such as discrimination and classification, quality evaluation and control, process monitoring, quantitative analysis have been successfully performed with electronic tongues. The low cost, easy-to-handle measurement set-up and rapidness are the advantages of multisensor systems over the well-established analytical methods like liquid chromatography and spectroscopy.

The main principle used in ‘electronic tongue’ devices is the application of the array of non-specific chemical sensors with wide sensitivity toward several media components. The ‘electronic tongue’ output contains, thus, the overlapped information about the sample due to cross-sensitivity of sensors. Considerable results may be extracted from this overlapped information with the help of multivariate data analysis.

Several sensing systems have been developed for the analysis of foodstuffs. For example, the “taste sensors” introduced by Toko [2] are composed of eight lipid/polymer membranes, and claimed to be applicable for qualitative discrimination of mineral waters, beverages (beers and sake), and foodstuffs (tomatoes, sake mash, soybean paste, etc). The “taste sensors” have been demonstrated to be useful for quantitative taste representation. Potentiometric ‘electronic tongue’ comprised both of chalcogenide glass and PVC-based film electrodes was applied for the discrimination of beverages [3] and quantitative analysis of mineral waters and wine [4], [5]. Voltammetric electronic tongue was used for classifying different beverages [6], and for environmental monitoring of drinking water [7]. An application of hybrid electronic tongue based on combination of both voltammetric metallic electrodes and potentiometric ion-selective electrodes (ISEs) complied by conductivity measurements for classification of six types of fermented milk has been shown [8]. The influence of different applied waveforms on discrimination ability between green and black teas by means of pulse voltammetric electronic tongue has been also investigated [9].

The present investigation is concerned with further development and an application of disposable all-solid-state potentiometric ‘electronic tongue’ microsystem based on screen-printing technology [10] for the discrimination of Korean green teas (Sulloc teas) and quantitative determination of main components responsible for the taste of different teas, such as catechines, caffeine, sugars and amino acid l-arginine.

Section snippets

Reagents

Poly(vinyl chloride) (PVC), plasticizers and other electroactive components (ionophores and lipophilic additives) were purchased from Fluka Chemie AG (Buch, Switzerland); aromatic polyurethane (ArPU) was synthesized and purified in our laboratories [11]; aniline, polymer supported polypyrrole (PPy), poly(sodium 4-styrenesulfonate), iron hexacyanoferrate Prussian Blue, Fe4III[FeII(CN)6]3, tetrahydrofurane (THF) and 1-methoxy-2-propanol were obtained from Aldrich (Milwaukee, WI); carbon paste

Results and discussion

First, we examined the discriminative ability of disposable electronic tongue system in distinguishing the tastes of most common beverages such as teas (both green and black) and natural black coffee. The PCA score plot in Fig. 1(A) shows that the all-solid-state electronic tongue chip effectively discriminates Sulloc green teas, fermented black tea (Lipton) and natural black coffee (Lavazza). The first three principal components PC1 (59%), PC2 (37%), PC3 (3%) explain 99% of total system

Conclusions

A disposable all-solid-state electronic tongue microsystem has been applied for the qualitative discrimination of teas and coffee, and for the quantitative analysis of main components responsible for the taste of Korean green teas. It has been found that the electronic tongue microsystem is capable of discriminating different kinds of teas (black and green) and natural coffee. The output of electronic tongue in green teas correlated well with the manufacture’s specifications for (−)-EGC

Acknowledgements

NH, CGS and LL acknowledge Mr. Yoon Chul Oh and Mr. Kim Jong Hak of McScience Inc. (Suwon, Korea) for providing various tea samples and useful discussion. H. Nam gratefully acknowledges the financial support from the Korea Research Foundation made in the program year of 2000 (Project No. 2000-015-DS0024). Dr. L. Lvova was supported by the BK 21 Program during her leave from St. Petersburg University from 2000 to 2001.

Larisa Lvova received her MSc degree (1996) and her PhD (1999) in physical chemistry from St. Petersburg State University. Her PhD work was concerned with the development and investigation of film sensing materials and application of them for multicomponent qualitative and quantitative analysis of complex liquid media, elaboration of the sensors arrays and multisensor systems, an electronic tongue in particular. She continued her research in area of chemical sensors development as postdoc

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    Larisa Lvova received her MSc degree (1996) and her PhD (1999) in physical chemistry from St. Petersburg State University. Her PhD work was concerned with the development and investigation of film sensing materials and application of them for multicomponent qualitative and quantitative analysis of complex liquid media, elaboration of the sensors arrays and multisensor systems, an electronic tongue in particular. She continued her research in area of chemical sensors development as postdoc fellow in the Chemical Sensors Research Group in the Chemistry Department of Kwangwoon University, Seoul, South Korea. At present, Larisa Lvova is a junior scientist in the laboratory of Soil Biochemistry in Biology Research Institute of St. Petersburg University. Her current research interest involves the development of new ion-selective membrane electrodes and their application for analysis of natural objects, soils in particular, investigation the carbon–nitrogen cycle and the greenhouse effect. She has published about 10 scientific papers.

    Andrey Legin graduated from Leningrad University (Chemistry Department) in 1981. After a 4-year work as a post-graduate student he received his PhD in Chemistry from Leningrad University in 1985 for the thesis devoted to chemical sensors on the basis of chalcogenide glasses. Since 1985, he has been working as a research scientist at the Research Institute of Chemistry of St. Petersburg University and at present time he is senior research scientist/associate professor. His current research interest involves the investigation of new sensing material synthesis, their transport properties, surface and interfaces investigation, electrochemical and sensing mechanism studies. Special attention is paid for analytical application of chemical sensors such as development of principals of sensor application, the development of analytical procedures, implementation of the sensors into industrial process control systems, application of the sensors for environmental monitoring, development and application of multisensor systems (‘lectronic tongue’). Dr. Legin has authored about 180 scientific papers and took part as a speaker in a number of international conferences devoted to sensor science and analytical problems.

    Yuri Vlasov received his MSc degree in chemistry from Leningrad (now St. Petersburg) University in 1957. He received his PhD degree in 1964 and the Doctor of Science degree in chemistry in 1986. From 1959 to 1974, he worked in Leningrad University as a teacher, research scientist and dean assistant. From 1974 to 1990, he was the Director of the Research Institute of Chemistry at Leningrad University and concurrently the Head of the Laboratory of Ion-selective Electrodes and Solid Electrolytes. Since 1988, Professor Vlasov has been the Head of the Laboratory of Chemical Sensors and the Head of the Radiochemistry Department. Professor Vlasov is the Professor of Chemistry, a full member of the Russian Academy of Natural Sciences, an active member of the New York Academy of Sciences, the Head of the Radiochemistry Department, and the Head of the Laboratory of Chemical Sensors. Professor Vlasov is a well-known scientist in the field of the development, fundamental study and analytical applications of chemical sensors including ion-selective field-effect transistors (ISFETs) and non-selective sensors (‘electronic tongue’). His research involves the study of the properties of membrane materials, the electrochemical behavior and analytical characteristics of chemical sensors, and the determination of the sensing mechanism of ion-selective electrodes of different types. Professor Vlasov is the author of more than 400 scientific papers.

    Geun Sig Cha received his BS degree from Korea University in 1977 and his PhD in Analytical Chemistry from the University of Michigan in 1989. He continued his research at the University of Michigan as a joint research fellow in the Department of Chemistry and Electrical Engineering and Computer Science until January 1991. He is now a Full Professor of Analytical Chemistry in the Department of Chemistry at Kwangwoon University. His current research interests involve the development of polymer membrane-based ion sensors, bio sensors and gas sensors and the design of enzyme-linked competitive and non-competitive binding assay methods.

    Hakhyun Nam received his BS degree from Seoul National University in 1982 and PhD in Physical Chemistry from Michigan State University in 1989. He continued his postdoctoral work in laser spectroscopy at the University of California at Berkeley until 1992. He is now a Full Professor of Physical Chemistry at Kwangwoon University. His current research interests involve the development of various types of chemical sensors based on molecular recognition principles, electrochemical detection methods for microfluidic systems, and industrialization of chemical sensor systems.

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