all-solid-state electronic tongue and its application for beverage analysis

Analytica Chimica Acta 468 (2002) 303–314

All-solid-state electronic tongue and its applicationfor beverage analysis

Larisa Lvovaa,b, Soon Shin Kima, Andrey Leginb, Yuri Vlasovb,Jong Soo Yangc, Geun Sig Chaa, Hakhyun Nama,∗

a Chemical Sensor Research Group, Department of Chemistry, Kwangwoon University, 447-1 Wolgye-dong,Nowon-ku, Seoul 139-701, South Korea

b Chemistry Department, St. Petersburg University, St. Petersburg 199034, Russiac Graduate School of East-West Medical Science, Kyung Hee University, Kyungki-Do 449-701, South Korea

Received 2 January 2002; received in revised form 22 July 2002; accepted 22 July 2002

Abstract

Disposable all-solid-state planar-type potentiometric electronic tongue has been developed with the carbon paste electrodearray screen-printed on a polymeric substrate. Highly cross-sensitive solvent polymeric membranes based on different matrices[e.g. poly(vinyl chloride) (PVC), aromatic polyurethane, and polypyrrole (Ppy)] and doped with common electroactivecomponents for potentiometric measurements (e.g. various plasticizers, and cation- and anion-selective ionophores) weredeposited on the screen-printed carbon paste electrodes (SCPEs). It was observed that an incorporation of 10 wt.% of PrussianBlue (PB; Fe4(III)[Fe(II)(CN)6]3) into a commercially available carbon paste and electrochemical preanodization of SCPEs inKCl solution at 1.6 V provide the all-solid-state planar-type electrodes with significantly improved potentiometric stability. Theproposed fabrication method gives possibility for simple and reproducible mass-production of low-cost disposable electronictongue microsystems. The practical utility of all-solid-state disposable electronic tongue chips has been demonstrated with aflow injection cell for the analysis of potable waters, soft drinks, and beers. It is shown that the potentiometric measurementswith the SCPE-based all-solid-state chips and the combined use of chemometric methods (e.g. principal components analysis,partial least regression (PLS), and principal component regression (PCR)) for the analysis of obtained data sets successfullydiscriminate various types of samples according to their tastes.© 2002 Elsevier Science B.V. All rights reserved.

Keywords: All-solid-state electronic tongue; Electrochemical sensors; Carbon paste electrodes

1. Introduction

Multicomponent analysis based on chemical sensorarrays combined with an appropriate chemometricmethods (e.g. pattern recognition) has attracted con-siderable interests of many researchers in various

∗ Corresponding author. Tel.:+82-29405246;fax: +82-29118584.E-mail address: [email protected] (H. Nam).

disciplines in the last decade. Following the devel-opment of electronic noses for gas analysis[1,2], thearrays of electrochemical sensors[3,4] and deviceslike taste sensor[5] and electronic tongues[6,7] havebeen devised for the analysis of complex liquid sam-ples. These devices provide global information aboutthe system instead of separating and/or measuringspecific components and parameters. Such global in-formation may be interpreted as the taste of a samplecorrelated with human perception, and utilized for

0003-2670/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved.PII: S0003-2670(02)00690-6

304 L. Lvova et al. / Analytica Chimica Acta 468 (2002) 303–314

on-line quality control, environmental monitoring andclinical analysis. The multisensor array is composedmostly of poorly-selective chemical sensors which re-spond to several components with different degrees ofcross-sensitivity[8], yielding signals that are collectiverepresentation of the sample characteristics. Advancedmathematical methods, e.g. multivariate regression,principal component analysis (PCA), artificial neuralnetworks, and fuzzy logic are often applied to extractthe representative pattern from the multivariate data.

Various types of chemical sensors based on dif-ferent working principles (e.g. voltammetry[8–10],potentiometry[11,12], spectrophotometry[13], flu-orescence spectroscopy[14]) and prepared withdifferent sensing materials (e.g. chalcogenide glasselectrodes and polymeric films, wires of precious andrare metals like Au, Ir, Pd, Pt, Re, Rh, resin beadcovered with chemical indicators) have been reportedfor the analysis of liquid samples. Of those chem-ical sensors, electronic tongue has been fabricatedwith potentiometric electrodes because they requirerelatively simple measuring device and provide widerange of sensing elements (various polymeric films,glass and metallic electrodes). However, the elec-tronic tongue prepared with an array of conventionaltype potentiometric sensors requires a large volumeof sample for measurement, frequent recalibrations,and a long-term preconditioning before use. Suchfeatures are disadvantageous in most complex liquidmedia analysis, especially if only a small amount ofsample is available for measurements.

Electronic tongue may find a wider applicationwith the development of mass-producible miniatur-ized potentiometric sensors. There have been someattempts to miniaturize multisensor systems for liquidanalysis: a commercial version of taste sensor[15]and the flow injection systems with small sized sen-sors have been introduced[14,16,17]. However, therehave been few researches that utilized disposable-typeall-solid-state multisensor array to construct elec-tronic tongues[18,19]. A disposable electronic tonguemay be fabricated by screen-printing conductive elec-trodes on a solid substrate. Carbon paste has beenwidely used as the electrode material, and disposableelectrochemical sensors based on it has been appliedfor clinical analysis[20–24]. In this contribution, wereport the development of planar-type potentiometricelectronic tongue chips based on a carbon paste mod-

ified with Prussian Blue (Fe4(III)[Fe(II)(CN)6]3), andtheir application for beverage analysis.

2. Experimental

2.1. Reagents

The sources of used materials and reagents wereas follows: poly(vinyl chloride) (PVC), plasticizers[bis(2-ethylhexyl) adipate (DOA), bis(2-ethylhexyl)sebacate (DOS), ando-nitrophenyl octyl ether(o-NPOE)]. Other electroactive components (iono-phores and lipophilic additives) were purchased fromFluka Chemie AG (Buch, Switzerland); aromaticpolyurethane (ArPU) with 60 wt.% of soft segmentswas synthesized and purified as described in[25];polymer supported polypyrrole (Ppy), Fe4(III)[Fe(II)(CN)6]3 (Prussian Blue or PB) tetrahydrofurane(THF) and 1-methoxy-2-propanol were obtainedfrom Aldrich (Milwaukee, WI, USA); carbon paste(TU-15ST) was from Asahi Chemical Research Labo-ratory (Tokyo, Japan); insulator paste was from SeoulChemical Research Laboratory (Shiheung, SouthKorea); and flexible polyester (PE) substrate was fromKorea 3M (Seoul, South Korea). All other chemicalswere analytical grade. All aqueous solutions wereprepared with deionized water (18 M� cm).

2.2. Preparation of screen-printed carbon pasteelectrodes

The carbon paste used in this experiment was mod-ified by mixing 10 wt.% of Prussian Blue powder withthe commercial carbon paste using a ball mill. Thechips were fabricated by screen printing the carbonpaste on a PE substrate as patterned inFig. 1 usinga semi-automatic screen printer (Minong MPS 150S,Seoul, South Korea), thermally treating it for 10 minat 140◦C in a clean air oven, and overcoating theprinted electrodes with an insulating film which wasthermally fixed at 140◦C in the same oven. The sizeof each chip was 23 mm× 56 mm and contained 44working SCPE sites (d = 0.6 mm). Chips were cutin appropriate size and fitted to a specially designedelectrical connector. The SCPE surface has been pre-treated in various media (i.e. sat. Na2CO3, 1 M KCl,0.5 M K2SO4) by applying anodic potentials (range

L. Lvova et al. / Analytica Chimica Acta 468 (2002) 303–314 305

Fig. 1. The fabrication process for all-solid-state planar-type sensor array chip.

1.2–1.6 V) for 180–300 s in standard three-electrodecell with auxiliary Au plate electrode and Ag/AgClreference electrode under chromopotentiometric con-ditions. After activating the SCPEs, they were rinsedwith deionized water and dried in air prior to depositthe sensing membranes. Multiple numbers of the samesensing membranes (usually two or three) were de-posited on the SCPEs to obtain statistical results.

The fabrication procedure for all-solid-state planar-type electronic tongue chip is illustrated inFig. 1.The electronic tongue chips were stored in a cleandesiccator before use.

2.3. Sensor array

A multisensor array has been fabricated by deposi-ting 12 different highly cross-sensitive solvent poly-meric membranes on the screen-printed carbon pasteelectrodes (SCPEs) on PE substrate, and appliedfor the measurements of mineral water, soft drinksand beers. Cation-sensitive PVC-based membraneswere prepared with various ionophores [e.g. sodiumionophore III (ETH 2120), magnesium ionophoreI (ETH 1117), calcium ionophore II (ETH 129),hydrogen ionophore I (tridodecylamine; TDDA), hy-drogen ionophore III (N,N-dioctadecylmethylamine;DODMA), lithium ionophore V (12-crown-4-ester)]and varying amounts of lipophilic additives [e.g. potas-sium tetrakis(p-chlorophenyl)borate (KTpClPB) andtridodecylmethyl-ammonium chloride (TDMACl)]as described in our previous reports[26]. Mem-branes containing lithium ionophore III (ETH 1810),chloride ionophore I [5,10,15,20-tetraphenyl-21H,23H-porphin manganese (III) chloride; MnTPPCl],

magnesium ionophore IV (ETH 7075) were also pre-pared as suggested with known compositions and in-cluded in the electrode array. Solutions of PVC-basedmembranes were prepared in accordance with com-mon methods given elsewhere by dissolving the mix-ture of PVC (30–35 wt.%), plasticizer (66–70 wt.%)and membrane active components (0.1–3 wt.%) withappropriate amount of THF.

Electrodes coated with ArPU-based membranescontaining hydrogen ionophores I and III, and Ppy-based membranes with lipophilic additives, andmultiionophore-based PVC membranes reported in[27] have been also tested as the sensor componentof electronic tongue. ArPU-based membrane cock-tails contained 70 wt.% of polymer with less amountof plasticizer (29 wt.%) and 1 wt.% of ionophore.Ppy-based membranes were prepared with the samemethod as described in[28]; appropriate amountsof polymer supported Ppy and lipophilic additiveswere dissolved in 1-methoxy-2-propanol. Finally, theDOA-plasticized PVC membrane without other elec-trode active components was also included in thesensor array, which is similar to the lipid membranesintroduced by Toko[29]. The compositions of sensingmembranes used in this study are given inTable 1,and the cross-sensitivity of each membrane has beenevaluated as suggested in[30].

2.4. Potentiometric evaluation of electrodes

All potentiometric measurements have been per-formed by measuring the potential differences be-tween sensing electrodes in chip and the conventionalreference electrode (Orion Model 90-02) using a PC


Table 1Compositions of sensing membranes used in the electronic tongue array

Matrix Plasticizer Ionophore Additive Discriminative for analysis of

Mineral water Soft drinks Beer

PVC DOA TDDA KTpClPB O O OArPU DOS DODMA NaTPB X O OPVC o-NPOE MnTPPCl – X O OPVC o-NPOE ETH 1810 KTpClPB O O OPVC DOA ETH 2120/ ETH 129/

valinomicin/ nonactinKTpClPB X O X

PVC DOS Nonactin – X O OPVC o-NPOE ETH 7075 ETH-500 X O XPVC DOA – – O O OPpy 1-Methoxy-2-propanol – – X X OPVC DOS 12-Crown-4-ether – X X OPVC DOS ETH 2120 – X X OPVC o-NPOE ETH 1117 KTpClPB X X O

O: discriminative; X: indiscriminative.

equipped with a high-impedance input 48-channelA/D converter (KOSENTECH, Busan, South Korea).The potentiometric performance of each membranewas examined in 0.005 M Tris–H2SO4 (pH 7.2) byvarying the concentration of different ions stepwisefrom 10−5 to 10−1 M at every 100 s. The same back-ground electrolyte was used as a conditioning solutionfor the electronic tongue chips before and betweenthe measurements of various beverage samples.

All-solid-state electronic tongue chip was placed ina flow cell, which clamps the chip between the flowchannel (0.5 mm × 2 mm × 5 mm) block and sup-porting block, for real sample measurements. Conven-tional reference electrode has been placed in separatechamber connected with the flow cell outlet. The re-quired sample volume was normally less than 5�lwith the flow cell. Potential readings were switchedon 100 s after the injection and collected every secondfor 200–300 s. All measurements were carried out atroom temperature (25± 1◦C).

Three different kinds of beverage samples avail-able in local groceries have been analyzed with theelectronic tongue chips: they include eight commer-cial mineral waters and tap water; four popular softdrinks in South Korea (Pine Bud Drink, Good Rice,Dr. Pepper, and Coca-Cola); local and imported beers(OB Lager, Hite, Cass, Cafri, Red Rock, Budweiser,Beck’s Dark, Beck’s Light). All samples were mea-sured immediately after opening the bottle or can.

New chips were washed with deionized water andplaced in conditioning solution (0.005 M Tris–H2SO4,pH 7.2) until the array electrodes exhibited constantpotentials before analysis, which normally took about300–500 s. Samples were analyzed in continuousflow injection mode. The chip was stabilized everytime by flowing conditioning solution for each mea-surement. Depending on membrane composition, thechip-to-chip reproducibility of sensor potential valuesvaried in the 1–10 mV ranges.

2.5. Data processing

Multicomponent data processing has been per-formed using PCA for qualitative sample discrimina-tion. Principal component regression (PCR), partialleast regression (PLS) and a back-propagation neu-ral network method were employed for quantitativeanalysis of mineral waters. Since the experimentaldata from electronic tongue chip were distributed in awide range of potentials, they were preprocessed (i.e.by mean normalization) prior to analysis to treat thevariances and the average values in a similar scalerange. The normalization process was performed onvectors corresponding to every sample by dividingeach variable value for the sample with the sampleaverage. Thus, the original variables were replacedby a profile centered about 1; only the relative valuesof the variables were used to describe the sample.


The following computer softwares were used formultivariate analysis: Unscrambler (version 6.0, 1997,CAMO ASA, Trondheim, Norway) and Matlab (ver-sion 6.0, 2000, The MathWorks Inc.).

3. Results and discussion

While SCPEs are commonly used for fabricatingmass-producible all-solid-state electrochemical sen-sors, the overall analytical performance of the sensorsbased on SCPEs is less satisfactory possibly due tothe ill-defined ion-to-electron transfer communicationbetween the sensing membrane and the solid electricalconductor. To improve the electrochemical reversibil-ity at the membrane/SCPE interface, two differentapproaches were examined in this study: mixed va-lence redox couple Fe4(III)[Fe(II)(CN)6]3 (PB) wasused as an ion-to-electron transfer promoter and/orthe surface of SCPEs were electrochemically pre-treated in various electrolytes (e.g. Na2CO3, K2SO4,and KCl) prior to sensing membrane deposition.

Fig. 2shows the potentiometric dynamic responsesof two highly cross-sensitive ion-selective membranesbased on ETH 1810 and MnTPPCl to the step addi-tion of NaNO3 from 10−5 to 10−1 M. Ion-selectivemembranes were deposited on three different types ofSCPEs, i.e. those prepared with the original carbonpaste (Type A), those modified by depositing a layerof PB on the Type A electrode (Type B), and thoseprepared with the 10 wt.% PB-mixed carbon paste(Type C). The potentiometric response curves shownin Fig. 2A show that the ETH 1810-based membranescoated on Types B and C electrodes provide signif-icantly improved potentiometric response (curves 2and 3) compared to that deposited on Type A electrode(curve 1). In case of MnTPPCl-based anion-sensitivemembranes, those coated on Types A and B elec-trodes exhibited very poor responses (curves 4 and 5in Fig. 2B) while the responses of the membrane onType C electrode was sufficiently sensitive and stable(curve 6 inFig. 2B). Since the membranes used in thiswork are cross-sensitive to several different ions otherthan the primary ions, they exhibited high responseslopes to sodium ((40.4 mV/pNa+) with the ETH1810-based membrane on Type C electrode) and tonitrate ((−32.6 mV/pNO3

−) with the MnTPPCl-basedmembrane on Type C electrode), respectively.

Fig. 2A and Balso show that the Type C electrodesprovides better potentiometric performance than theType B electrodes. It appears that the electronic con-duction at the membrane/SCPE interface is more ef-fective when the particles of mixed valence compoundis brought near to the carbon particles by homogenizedmixing than they are placed on the SCPE as an inter-mediate layer. Although the electrochemical deposi-tion of mixed valence compounds on the SCPE resultsin improved potentiometric performance compared tothe simple drop-and-dry deposition method, we did notattempt to optimize such process in this work becausethe use of PB-mixed carbon paste provided sufficientlystable SCPEs for preparing all-solid-state multisensorarray chip.

It was shown earlier[31] that a mild anodizationof SCPE surface improves the response of amper-ometric sensors. Hence, we examined if the sameelectrochemical pretreatment of SCPE would result inenhanced performance for the potentiometric multi-sensor array.Fig. 3shows the potentiometric dynamicresponses of the ETH 1810 and MnTPPCl-basedmembranes coated on the SCPEs of Types A and C.The SCPEs were pretreated in different media (e.g.Na2CO3, K2SO4, and KCl) prior to sensing mem-brane deposition. Comparison of curve 1 inFigs. 2and 3 reveals that the pretreatment of the SCPE inNa2CO3 clearly improves the cationic responses ofthe electrodes. However, the effect of same pretreat-ment was less obvious for the anion-selective mem-branes (curve 5 inFig. 3). Again, the SCPEs printedwith the PB-mixed carbon paste provided greatly en-hanced potentiometric performance (curves 2–4 and6–8 in Fig. 3A and B). Fig. 3 also indicates that thepreanodization of the electrodes greatly change theirpotentiometric performance.

The preanodization of the Type C electrode maydrive the oxidation of PB mixed in the paste to BerlinGreen by the following process:

Fe4(III )[Fe(II )(CN)6]3 + 3A−Prussian Blue

→ Fe4(III )[Fe(II )(CN)6A]3 + 3e−Berlin Green

(1)

The reaction (1) indicates that the oxidation of PBinvolves the anions (A−) to maintain electroneutralityof the compounds. Hence, the resulting process maybe influenced by the nature of supporting electrolyte


Fig. 2. Effect of Prussian Blue (PB; Fe4(III)[Fe(II)(CN)6]3) on the potentiometric properties of the cation-selective membranes (A) andanion-selective membranes (B) deposited on the screen-printed carbon paste electrodes (SCPEs): 1 and 4—unmodified SCPEs (Type A);2 and 5—SCPEs modified with a layer of PB (Type B); 3 and 6—SCPEs prepared with the 10 wt.% PB-mixed carbon paste (Type C).Background solution: 0.005 M Tris–H2SO4, pH 7.2; analyte: NaNO3 was added stepwise from 10−5 to 10−1 M.


Fig. 3. Potentiometric responses of the cation-selective membranes (A) and anion-selective membranes (B) deposited on electrochemicallypretreated SCPEs: curves 1 and 5—Type A electrodes pretreated in a saturated Na2CO3 at 1.2 V; curves 2 and 6—Type C electrodespretreated in saturated Na2CO3 at 1.2 V; curves 3 and 7—Type C electrodes pretreated in 0.5 M K2SO4 at 1.6 V; curves 4 and 8—Type Celectrodes pretreated in 1 M KCl at 1.6 V. Background solution: 0.005 M Tris–H2SO4, pH 7.2; analyte: NaNO3 added stepwise from 10−5

to 10−1 M.


Fig. 4. Principal component analysis (PCA) plots for potable water analysis obtained from the all-solid-state electronic tongue chips: tastemap for eight kinds of commercial mineral water and a tap water (A); correlation between the results from electronic tongue chip outputand the values by the manufactures (B).


Table 2Results of quantitative analysis on mineral water using all-solid-state electronic tongue

Water samples CO2 content Total inorganic components contention (Ca2+, Mg2+, K+, Na+, F−)

Label (g/l) Measured (g/l) Mean error (%)

Commercial mineral waterPuriss – 0.0123 0.0133 8Sam Da Soo – 0.0124 0.0110 11Yakult – 0.0154 0.0188 22Dongwon Saemmul – 0.0357 0.0303 15Soon Soo – 0.0357 0.0323 10Cho Jung Su – 0.0581 0.0450 22Chojung Carbonated Water High – – –Souce Perrier, Vergeze, France High – – –

Tap water – – – –

anion [32], and the electrochemical properties ofSCPE as well.Fig. 3B suggests that the anodic pre-treatment in 1 M KCl at 1.6 V resulted in the moststable and reproducible responses (curves 4 and 8 inFig. 3A and B) for both anion- and cation-selectiveSCPEs containing PB, while the anion-selective elec-trode pretreated in other media (Na2CO3 and K2SO4)exhibited unstable responses. Hence, the all-solid-statemultisensor array chips were prepared by screen

Fig. 5. PCA plots for soft drink analysis obtained from the all-solid-state electronic tongue chips; all uncircled points represent Coca-Cola.

printing the electrodes with the carbon paste contain-ing 10 wt.% PB, and electrochemically pretreating theSCPEs in 1 M KCl. The electronic tongue chips werethen fabricated by depositing various cross-sensitiveion-selective membranes on the multisensor arraychip. Newly developed all-solid-state planar-type elec-tronic tongue chips have been applied for the analysisof some commercial mineral waters, soft drinks, andbeers available in local stores in Seoul, South Korea.


Fig. 4 shows a PCA discrimination plot of thepotentiometric readings of all-solid-state planar-typemultisensor array for eight different commercial min-eral waters (seeTable 1 for information about dis-criminative sensors andTable 2for information about

Fig. 6. PCA plots for beer analysis obtained from the all-solid-state electronic tongue chips: classification of several beers available inSouth Korea (A); taste map for the beers shown in A (B).

samples) and tap water. It was found that the first twoprincipal components, PC1 (55%) and PC2 (25%),account for the 80% of all system variance. The PC1axis closely reflects the variations in pH of water sam-ples, which is related to the degree of carbonation. The


PC2 axis varies with the total mineral contents in wa-ter samples. Thus, in terms of human tasting, the PC1may indicate sharp taste, while the PC2 bitter-saltytastes. The results suggest that the all-solid-stateelectronic tongue chips developed in this study arevery useful to discriminate the types of potable watersamples. The third principal component, PC3, axis ac-counts for 8% of system variance and closely relatedto the variations in sensor performance with time, in-dicating the effective use life of the electronic tonguechips.

Quantitative analysis was also performed for sixmineral waters (e.g. Puriss, Sam Da Soo, Yakult,Dongwon Saemmul, Soon Soo, Cho Jung Su) with theelectronic tongue chip, and the results were comparedwith the values supplied by the bottlers (Table 2).Full cross-validation method[33] was applied to testvarious calibration models, and the same sampleswere used for both model estimation and testing. Ofthe calibration models examined with the PCR, PLSand back-propagation neural network methods, thePLS scheme provided the best results.Fig. 4B com-pares the total inorganic contents measured with theelectronic tongue and those specified on the labels.Although we have not separately verified the accu-racy of the values given in the labels, the results wellmatch with the specified values.

The all-solid-state electronic tongue chip was alsoapplied to analyze soft drinks. A PCA plot for fourdifferent soft drinks (Pine Bud Drink, Good rice, Dr.Pepper, and Coca-Cola) obtained from local grocerystores in South Korea is given inFig. 5. Eight elec-trodes in electronic tongue chip exhibited discrim-inative potentiometric responses to each soft drinksample. To examine the chip-to-chip reproducibility,four different electronic tongue chips were used forrepeated analysis. As shown inFig. 5, reproducibleidentification of all soft drinks and the conditioningsolution (Tris–H2SO4 buffer, pH 7.2) could be made.However, it was observed that the variances for thehighly carbonated drinks such as Dr. Pepper andCoca-Cola are widely scattered in the PCA plot duein part to the varying carbon dioxide concentration ofuncapped samples during measurements. The resultin Fig. 5 clearly demonstrates that the all-solid-stateplanar-type electronic tongue chips effectively dis-tinguish different type of soft drinks with sufficientchip-to-chip reproducibility.

We also explored the possibility if all-solid-stateelectronic tongue can be employed to distinguishdifferent types of beers. While the multisensor ar-ray was prepared with two same sets of 12 differentcross-sensitive membranes on one chip, the smallersubarray consisting of 10 membranes appeared to beenough for classification. The PCA plot for six local(OB Lager can and bottle, Hite, Cafri, Red Rock, andCass) and three imported beers (Budweiser, Beck’sLight and Beck’s Dark) are shown inFig. 6. Datapoints were collected from six different sensor chipsto test the sensor-to-sensor reproducibility in clas-sifying the types of beers. As observed from PCAclassification (Fig. 6), and also from the data classi-fication using the soft independent modeling of classanalogy (SIMCA) method[32], the beer samplescould be divided into five main classes: Budweiser,Cafri, Beck’s dark, Beck’s light and one commonclass of Korean beers. A two dimensional taste mapwith PC1 and PC2 components was plotted using thedata obtained from one chip (instead of using the datafrom six chips for the sake of clear presentation); asshown inFig. 6B, the PC1 and PC2 explain 62% ofsystem variance. The map was correlated with humansensory perception of beer taste; the PC1 may rep-resent the direction of the density of beers, and PC2with light taste direction. In general, the taste mapwell represent the type of beers as the manufacturersclaim, showing the usefulness of all-solid-state elec-tronic tongue chips for classifying the taste of popularliquors.

4. Conclusion

In this contribution, we have shown that the all-solid-state planar-type potentiometric electronic ton-gue microsystem is a useful tool for discriminatingthe types of drinking water, soft drinks and lightliquors. The all-solid-state chips were fabricated byscreen-printing carbon paste modified with PB; itwas shown that the redox couple mixed in the pastegreatly helps stabilizing unstable potential drifts inall-solid-state electrodes. Electrochemical pretreat-ment of the carbon paste-based electrodes in KClsolution further enhances the potentiometric perfor-mance of all-solid-state electrode. Electronic tonguebased on all-solid-state electrode chips were prepared


by depositing of 12 different ion-selective membranes,and successfully applied for classifying the types ofvarious drinks by combining both stable electronictongue chips and chemometric methods (e.g. principalcomponents analysis).

Acknowledgements

H. Nam gratefully acknowledge the financial sup-port from the Korea Research Foundation made inthe program year of 2000 (Project No. 2000-015-DS0024). Dr. L. Lvova was supported by the BK 21Program during her leave from St. Petersburg Univer-sity from 2000 to 2001.

References

[1] J.W. Gardner, P.N. Bartlett, Sens. Actuators B 18/19 (1994)211.

[2] W. Göpel, Sens. Actuators B 65 (2000) 70.[3] M. Otto, J.D.R. Thomas, Anal. Chem. 57 (1985) 2647.[4] M. Bos, A. Bos, W.E. van der Linden, Anal. Chim. Acta 233

(1990) 31.[5] K. Toko, Sens. Actuators B 64 (2000) 205–215.[6] Y.G. Vlasov, A.V. Legin, A.M. Rudnitskaya, A. D’Amico, C.

DiNatale, Sens. Actuators B 65 (2000) 235.[7] F. Winquist, S. Holmin, C. Krantz-Rülcker, P. Wide, I.

Lundström, Anal. Chim. Acta 406 (2000) 147.[8] A.V. Legin, A.M. Rudnitskaya, Yu.G. Vlasov, C. Di Natale,

A. D’Amico, Sens. Actuators B 58 (1999) 464.[9] Q. Chen, J. Wang, G. Rayson, B. Tian, Y. Lin, Anal. Chem.

65 (1993) 251.[10] C. Krantz-Rülcker, M. Stenberg, F. Winquist, I. Lundström,

Anal. Chim. Acta 426 (2000) 217.[11] K. Toko, Biosens. Bioelectron. 13 (1998) 701.[12] A. Legin, A. Rudnitskaya, Yu. Vlasov, C. Di Natale,

E. Mazzone, A. D’Amico, Sens. Actuators B 65 (2000)232.

[13] J. Lavigne, S. Savoy, M.B. Clevenger, J.E. Ritchie, B.McDoniel, S.J. Yoo, E.V. Anslyn, J.T. McDevitt, J.B. Shear,D. Neikirk, J. Am. Chem. Soc. 120 (1998) 6429.

[14] A.E. Bruno, S. Barnard, M. Rouilly, A. Waldner, J. Berger,M. Ehrat, Anal. Chem. 69 (1997) 507.

[15] Taste Sensing System SA401, Anritsu Corp., Japan.[16] J. Wang, G.D. Rayson, Z. Lu, H. Wu, Anal. Chem. 62 (1990)

1924.[17] J. Mortensen, A. Legin, A. Ipatov, A. Rudnitskaya, Yu.

Vlasov, K. Hjuler, Anal. Chim. Acta 402 (2000) 273.[18] Yu.G. Mourzina, J. Schubert, W. Zander, A. Legin, Yu.G.

Vlasov, H. Luth, M.J. Schoning, Electrochim. Acta 47 (2001)251.

[19] H. Sangodkar, S. Sukeerthi, R.S. Srinivasa, R. Lal, A.Q.Contractor, Anal. Chem. 68 (1996) 779.

[20] C. Fernandez-Sanchez, M.B. Gonzalez-Garcýa, A. Costa-Garcýa, Biosens. Bioelectron. 14 (2000) 917.

[21] G. Cui, J.H. Yoo, B.W. Yoo, S.S. Kim, G.S. Cha, H. Nam,Talanta 54 (2001) 1105.

[22] H.J. Yoon, J.H. Shin, S.D. Lee, H. Nam, G.S. Cha, T.D.Strong, R.B. Brown, Sens. Actuators B 64 (2000) 8.

[23] T.A. Johnson, L.A. Dunlap, W.E. Cascio, Anal. Chem. 70(1998) 5054.

[24] R. Koncki, S. Glab, J. Dziwulska, I. Palchetti, M. Mascini,Anal. Chim. Acta 385 (1999) 451.

[25] S.Y. Yun, Y.K. Hong, B.K. Oh, G.S. Cha, H. Nam, S.B. Lee,J.I. Jin, Anal. Chem. 67 (1997) 868.

[26] A. Legin, A. Rudnitskaya, A. Smirnova, L. Lvova, Y. Vlasov,J. Appl. Chem. 72 (1999) 114 (Russian).

[27] K.S. Lee, J.H. Shin, M.J. Cha, G.S. Cha, M. Trojanowicz,D. Liu, H.D. Goldberg, R.W. Hower, R.B. Brown, Sens.Actuators B 29 (1994) 239.

[28] J. Bobacka, A. Ivaska, A. Lewenstam, Anal. Chim. Acta 385(1999) 195.

[29] K. Toko, Electroanalysis 10 (1998) 657.[30] Yu.G. Vlasov, A.V. Legin, A.M. Rudnitskaya, Sens. Actuators

B 44 (1997) 532.[31] G. Cui, J.H. Yoo, J. Yoo, S.W. Lee, H. Nam, G.S. Cha, Elec-

troanalysis 13 (2001) 224.[32] K. Itaya, H. Akahoshi, S. Toshima, J. Am. Chem. Soc. 104

(1982) 4767.[33] K. Esbensen, T. Midtgaard, S. Schonkopf, Multivariate Analy-

sis in Practice, Camo ASA, Trondheim, Norway, 1994.

all-solid-state electronic tongue and its application for beverage analysis

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