485 J. Indian Chem. Soc., Vol. 92, April 2015, pp. 485-488 MWCNT-chitosan composite chemically modified electrode as an electrochemical detector for highly selective flow injection analysis of H 2 O 2 Prakasam Gayathri and Annamalai Senthil Kumar* Environmental and Analytical Chemistry Division, School of Advanced Sciences, Vellore Institute of Technology University, Vellore-632 014, Tamilnadu, India E-mail : askumarchem@yahoo.com Abstract : Multi-walled carbon nanotube (MWCNT)-chitosan (CHIT) chemically modified glassy carbon electrode (GCE), designated as GCE/MWCNT-CHIT has been developed by modifying a suspension of MWCNT + CHIT-acetic acid mixture on a cleaned GCE and demonstrated as a selective electrochemical detector (ECD) for flow-injection analysis (FIA) of hydrogen peroxide. The GCE/MWCNT-CHIT showed stable surface confined redox feature at E 0 = –0.22 V vs Ag/ AgCl with surface excess value 13.63 nmol cm –2 in pH 7 PBS. Under an optimal condition, applied potential = –0.2 V vs Ag/AgCl, hydrodynamic flow rate = 0.75 mL min –1 and pH 7 phosphate buffer as a carrier solution, the FIA-ECD showed H 2 O 2 calibration plot in an range 50–2500 M with detection limit and current sensitivity values 9.7 M and 0.59 nA M –1 (0.8345 A M –1 cm –2 ) respectively. There was no interference from cysteine, ascorbic acid, uric acid, ni- trite, and nitrate. A cosmetic cream, clinical H 2 O 2 and milk were further tested as real samples with ~100% recovery values. Keywords : Carbon nanotube, chitosan, electrochemical detector, real sample. Introduction Selective determination of hydrogen peroxide (H 2 O 2 ) is important in several areas including food, pharmaceu- tical, industrial and environmental testing 1–4 . H 2 O 2 is a main product of enzyme catalysed reaction and involved with various biological processes such as immune cell activation, vascular remodelling, apoptosis, stomatal clo- sure and root growth etc. 5 . Exposure of high concentra- tion of H 2 O 2 (>1 M) irritates skin and harms the human health 6 . So far various analytical techniques were reported for the detection of H 2 O 2 . Those techniques are; spectro- photometric, fluorescence, coulometeric, polarographic and titrimetric techniques 4 . These methods are generally time consuming and suffer from serious interferences. On the other hand, flow injection analysis coupled elec- trochemical detection (FIA-ECD) offers simple, rapid and low working volume (10 L) based detection approach 7,8 . Here in, we introduce a new FIA-ECD technique, in which a impure multi-walled carbon nanotube (MWCNT)- chitosan (CHIT) chemically modified glassy carbon elec- trode (designated as GCE/MWCNT-CHIT) used as a de- tector, for selective hydrogen peroxide measurement in a physiological pH. Previously, numerous MWCNT-redox mediators based chemically modified electrodes (CMEs) have been reported for electrochemical detection of H 2 O 2 9–13 . However, very limited reports were available with FIA-ECD tech- niques 14–18 . Maintaining appreciable stability of CME under the hydrodynamic condition is a major problem with above CMEs. In further, most of the redox media- tor-CMEs are unstable in physiological pH (e.g. Prussian blue analogues) 15,16 . Chitosan (CHIT) is a linear polysaccharide and natu- rally occurring biopolymer with attractive chemical prop- erties 19 . Previously, functionalized MWCNT+CHIT modified thin film system for the electrochemical sensing of H 2 O 2 was reported 20 . Note that, the above modified electrode was prepared through covalent interaction be- tween the amino group of CHIT and -OH functional group of functionalized MWCNT 20 . Recently our group reported preparation, characterization and electrocatalytic H 2 O 2 reduction of impure-MWCNT+CHIT chemically modi- fied electrode 21 . In aim to extend to various H 2 O 2 real sample analyses we further extend our studies with FIA- ECD, in this work.