Crosslinking metal-complexed chitosans (metal ions=Cu(II), Cd(II), Zn(II), Ni(II), and Fe(III)) with (chloromethyl)oxirane yields resins having higher abilities to adsorb Cu2+ than a resin obtained from chitosan in the absence of metal ion. Resins from Cd(II)–chitosan complex can act as effective adsorbents for Hg2+; their Langmuir’s adsorption parameters depend on the quantity of (chloromethyl)oxirane used.

A sensor based on the electrochemiluminescence (ECL) of the Ru(bpy) 3 2+ complex is attractive in analytical chemistry because of its high substrate selectivity and high sensitivity. 1 -4 It is desired that the ECL sensor has a higher selectivity compared to ECL-based flow-through detectors for HPLC which have been reported by many reseachers. 5 We have prepared an ECL-optic oxalic acid sensor having a Pt electrode coated with chitosan to which Ru(bpy) 3 2+ complex moieties are covalently bonded. 6 The oxalic acid sensor takes advantage of some characteristic properties of chitosan: the high content of a basic amino group, the high hydrophilicity and the ability to form a transparent thin film. The selectivity toward oxalic acid, however, is not very satisfactory for applications to practical samples. The sol-gel method, on the other hand, gives a simple process which can be used to prepare gel materials that can immobilize different functional reagents in working electrodes. For example, Glezer and Lev 7 have prepared a glucose sensor having a Pt electrode coated with a vanadium pentaoxide matrix entrapping glucose oxidase. Dvorak and Armond 8 have reported a determination of Ru(bpy) 3 2+ by preconcentration into Pt and ITO electrodes coated with silica gel. Dominguez et al. 9 have studied the electrochemical behaviors of graphite electrodes coated with an ionexchange polymers/silica gel. We have recently prepared a Pt electrode coated doubly with Ru(bpy) 3 2+ -modified chitosan and silica-gel layers, which has been successfully applied to an ECL optic sensor with improved selectivity toward oxalic acid. 10 In the present paper we report on the fundamental behaviors, such as the potential dependence and the decay of the responses. Experimental Materials and apparatusRu(bpy) 3 2+ complex-modified chitosan was prepared from chitosan and bis(2,2¢-bipyridine)[4-methyl-4¢-(6-bromohexyl)-2,2¢-(bipyridine)]ruthenium(II) perchlorate.6 Tetramethoxysilane (TMOS) was purchased from Shin-etsu Chem. Co. All other chemicals were of reagent grade or better and used without further purification.Voltammetric experiments were performed using a system constructed by a Hokuto Denko HB 104 function generator, a Hokuto Denko HA 301 potentiostat and a Yokogawa 3086 X-Y recorder. The standard three-electrode arrangement consisted of a coated Pt disk (1.6 mmf), a Pt counter electrode and a Ag/AgCl reference electrode. A solution containing 0.1 M KNO 3 and 0.05 M phosphate buffer of pH 6.8 was used as the supporting electrolyte. Highly pure nitrogen was passed through an electrolytic cell thermostated at 25.0±0.2˚C prior to a measurement. ECL experiments were carried out using the same apparatus as reported previously 6,10 at room temperature; the potential applied to the photomultiplier was 900 V. The thickness of the membranes on the working electrode was determined by a Surfcom 575A surface texture measuring instrument (Tokyo Seimitsu Co., Japan). Preparation of sensor probeTMOS, water and methanol were mixed with a 2% ethanol solut...

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A tris(2,2'-bipyridine)ruthenium(II)/Nafion-modified Pt gauze electrode, where CO2 was generated by oxidation of substrates, was combined with a CO2 sensor. The combined sensor responded most effectively to oxalate among the organic acids examined. The response to oxalate was enhanced by use of a doubly-piled, modified Pt gauze electrode. The most suitable applied potential was +0.95 V vs. Ag/AgCI; the stationary response was attained in 10 min after the potential application. The response to 0.5 mM oxalate was reproducible within 3% on 10 repeated runs and remained virtually unchanged over 10 days. The calibration curve for oxalate was linear in the concentration range of 0.1 to 5 mM, and the detection limit was 0.05 mM (S/N=3).

The substrate selectivity of the known Ru(bpy)32+ eleetrochemiluminescence (ECL) is changed by coating a Pt working electrode with a Ru(bpy)32+-modified chitosan membrane and successively with a silica gel membrane that was prepared by the sol-gel method using tetramethoxysilane as a precursor. The double coating resulted in a high selectivity toward oxalic acid at pH 6.8, lowering relative ECL responses to trimethylamine, proline and 4-hydrox.yproline about 2.8, 3.4 and 3.8 times, respectively, compared to those obtained with a Pt electrode coated singly with the modified chitosan.

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A bifurcated fiber-optic sensor for Zn2+, Cd2+ and Ga3+ ions was fabricated. Chitosan modified with 5-formyl-3-hydroxy-4-hydroxymethyl-2-methylpyridine was immobilized on an agarose gel and used as a fluorogenic probe. The reproducibility of the response to Zn2+ was within 5% in eight successive measurements at 5.0X10-5 M (1 M=1 mol dm-3). A linear relationship with a correlation coefficient of 0.994 was obtained in the Zn2+ concentration range of 0 -2.0X105 M, and the detection limit was 1.0X106 M (S/ N=3). Cd2+ and Ga3+ ions were also detected, though with sensitivities somewhat lower than that for Zn2+. KeywordsFiber-optic sensor, modified chitosan, zinc ion, fluorometric determination, Schiff base formationChitosan, an aminopolysaccharide, has a high metalchelating ability.l This ability is enhanced by a chemical modification of the amino group. For example, the Cu2+ adsorption capacity of a Schiff-base derivative with salicylaldehyde is 5-times higher than that of chitosan itself.2 On the other hand, metal complexes of many aromatic Schiff bases are known to emit fluorescence. Determinations of Zn2+,3 A13+,4,5 Mgt+,6 Ga3+,' and Be2+ s using this phenomenon have been investigated, and some of these metal ions have been determined in practical samples such as blood plasma6, alloys7'8 and human urine' with high sensitivities and selectivities. These prompted us to employ an aromatic Schiff-base derivative of chitosan in fluorometric analyses of these metal ions.Recently, many types of fiber-optic sensors for metal ions have been developed: for example, A13+ has been determined by the use of morin immobilized on a biomembrane from mutton muscle9 or on a cellulose powder10 as a fluorogenic reagent. The advantages of fiber-optic sensors include a feasible avoidance of electrical interference and ready miniaturization.In the present paper, we report on a fiber-optic fluorosensor having a Schiff-base polymer derived from chitosan and a pyridoxal (4-formyl-3-hydroxy-5-hydroxymethyl-2-methylpyridine) isomer, 5-formyl-3-hydroxy-4-hydroxymethyl-

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