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Amatatongchai M.,Ubon Ratchathani University | Amatatongchai M.,Flow Innovation Research for Science and Technology Laboratories FIRST Labs | Sroysee W.,Ubon Ratchathani University | Chairam S.,Ubon Ratchathani University | And 2 more authors.
Talanta | Year: 2015

We report a novel amperometric glucose biosensor based on glucose oxidase (GOx) immobilized on a carbon nanotube (CNTs)-poly(diallyldimethyl-ammonium chloride) (PDDA)-platinum nanoparticle (PtNPs) modified carbon-paste electrode (CNTs-PDDA-PtNPs/CPE). The CNTs-PDDA-PtNPs composite materials were characterized by TEM and electrochemical techniques. Cyclic voltammetric results reveal direct electron transfer of the immobilized GOx, indicated by two quasi-reversible redox peaks at a potential of 0.37V (vs. Ag/AgCl) in phosphate buffered solution (PBS) (0.10M, pH 7). The biosensor provides good glucose oxidation activity and retention of GOx electrocatalytic activity due to CNTs-PDDA-PtNPs enhancement of the redox response. The carbon paste electrode was installed as working electrode in a flow through electrochemical cell of a flow injection (FI) system. Glucose was quantified using amperometric measurements at 0.5V vs. Ag/AgCl and PBS carrier (0.10M, pH 7.0) at a flow rate of 1.0mLmin-1. The linear working ranges for glucose measurements were 0.1-3mM (r 2=0.995) and 5-100mM (r 2=0.997), with corresponding sensitivities of 0.127 and 0.060 (μAs) mM-1, respectively. The system provides good precision of 2.8% R.S.D with a calculated detection limit (3S/N) of 15μM. The proposed method was successfully applied to determination of glucose in food and pharmaceutical samples with throughput of 200 samplesh-1. © 2015 Elsevier B.V. Source


Phansi P.,Flow Innovation Research for Science and Technology Laboratories FIRST Labs | Phansi P.,Mahidol University | Henriquez C.,University of the Balearic Islands | Palacio E.,University of the Balearic Islands | And 3 more authors.
Talanta | Year: 2014

In this work, the automation of a catalytic spectrophotometric method for the determination of molybdenum is presented. For this purpose, a multisyringe flow injection system was coupled to an integrated microconduit that we have called "chip". Reagents and sample were simultaneously dispensed to the chip where complete mixing, heating, and measurement were carried out. The spectrophotometric method is based on the oxidation of 4-amino-3-hydroxy- naphthalenesulphonic acid (AHNA) by hydrogen peroxide catalyzed by Mo (VI). Absorbance of the reaction product was measured at 465 nm. Two optical fibers were used to conduct the light, one from the source to the chip, and the other from the output of the cell to the spectrophotometer. The detection cell was incorporated in the thermostated zone of the chip. The initial rate method, at controlled temperature, was employed to determine the Mo (VI) concentration. The estimated precision was 3.7%, with the working range of 4.0-40 μg L -1 of Mo (VI), and the limit of detection of 1.2 μg L-1 of Mo (VI). The system was successfully applied to water samples and pharmaceutical products with a sampling throughput of 20 injections h -1. © 2013 Elsevier B.V. Source


Amatatongchai M.,Ubon Ratchathani University | Amatatongchai M.,Flow Innovation Research for Science and Technology Laboratories FIRST Labs | Laosing S.,Ubon Ratchathani University | Chailapakul O.,Chulalongkorn University | And 2 more authors.
Talanta | Year: 2012

An amperometric flow injection (FI) method suitable for evaluation of 'total antioxidant capacity' (TAC) is presented. In this method, a carrier stream of a solution of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH •) continuously flows through an electrochemical cell, furnished with a carbon nanotube modified-glassy carbon electrode (CNT/GC) as the working electrode. At the applied voltage of 0.05 V (vs. Ag/AgCl), DPPH • is reduced resulting in a constant electric current. For measurement of the TAC, a sample zone containing antioxidant(s) is injected into the carrier stream therein reduction reaction of DPPH• occurring within the sample zone. The decreased amount of the radical in the sample zone leads to a drop of the amperometric signal at the CNT/GC electrode. We have also compared the performance of the CNT/GC electrode to the unmodified GC electrode using cyclic voltammetry. The sensitivity of the CNT/GC electrode was more than twenty five times greater than the bare GC electrode. The study of the sweep rate dependence showed that the cathodic and anodic current of 0.1 mM DPPH solution varied linearly (r2=0.998) with the square root of the scan rate, from 0.02 to 0.12 Vs-1. These results demonstrated that the CNT/GC electrode is appropriate for the quantitation of antioxidants via amperometric detection of the residual concentration of non-reacted DPPH •. We obtained linear calibrations for all the antioxidants tested including gallic acid, catechin, quercetin, caffeic acid and Trolox. The system offers rapid sample throughput (45 samples h-1) and good precision of 3.2% R.S.D., for 20 μL-injection of 2.5 μM Trolox (n=30). This method was applied to evaluate the TAC of extracts of some Thai indigenous vegetables. © 2012 Elsevier B.V. All rights reserved. Source


Phansi P.,Flow Innovation Research for Science and Technology Laboratories FIRST Labs | Phansi P.,Mahidol University | Henriquez C.,University of the Balearic Islands | Palacio E.,University of the Balearic Islands | And 3 more authors.
Analytical Methods | Year: 2014

In this work a fully automated catalytic-spectrophotometric method for determination of copper at trace levels using a multisyringe flow injection system (MSFIA) and a multipumping flow system (MPFS) coupled to a micro-chip (Chip-MSFIA-MPFS) is presented. The reaction is based on the catalytic effect of Cu(ii) on the oxidation of the in situ reduced form of 2,6-dichlorophenolindophenol (DCPI)r, by hydrogen peroxide. Due to the importance of the mixing order of the reagents, a new design of the chip is proposed. DCPI, ascorbic acid and buffer are first propelled to mix in the front section of the chip using MPFS. Then this reagent mixture, together with hydrogen peroxide and the sample, is simultaneously dispensed to the rear section of the chip by using a multisyringe for mixing, heating and absorbance measurement of the product at 600 nm. The optimum conditions are 0.9 mmol L-1 DCPI, 3.6 mmol L-1 ascorbic acid, 0.8 mol L-1 ammonium chloride buffer, pH 10.5, and 0.3 mol L-1 H2O2. The proposed system is simple, rapid, selective and sensitive. We can determine trace levels of Cu(ii) at room temperature (25 °C). The main analytical characteristics of the proposed method are a detection limit of 0.12 μg L-1 of Cu(ii), a working range of 0.4-35.0 μg L-1 of Cu(ii), and a relative standard deviation of 0.79% (10 μg L-1 Cu(ii), n = 15). The system was successfully applied to water samples, certified reference materials (CRMs) of river and waste water, acid digested multivitamins and animal tissues with a sample throughput of 31 injections h-1. This journal is © the Partner Organisations 2014. Source


Chan-Eam S.,Flow Innovation Research for Science and Technology Laboratories FIRST Labs | Chan-Eam S.,Mahidol University | Teerasong S.,Flow Innovation Research for Science and Technology Laboratories FIRST Labs | Teerasong S.,King Mongkuts University of Technology Thonburi | And 4 more authors.
Talanta | Year: 2011

This work presents a new flow-based coupled electrochemical technique for evaluation of "total antioxidant capacity (TAC)". A sequential injection (SI) with amperometric detection was applied to the TAC analysis of commercial instant ginger infusion beverages using 2,2′-azino-bis(3- ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay. Besides having chromogenic properties, the ABTS reagent behaves as an electroactive species at the glassy carbon electrode in phosphate buffer pH 7.0, the decrease of the cathodic current signal of the ABTS+ radical after reaction with antioxidants can be monitored. The SI system, furnished with an in-house electrochemical detection cell (ECD), was optimized with respect to the applied potential, sample and reagent volume, and flow rate to the detector. Gallic acid was used as the standard antioxidant and the capacity was reported as gallic acid equivalent (GAE) unit. TAC measurements of ginger infusions at the optimum condition were performed using the proposed technique and also with the classical batch spectrophotometric ABTS assay. TAC values obtained from our method and the standard method are in good agreement (r2 = 0.956). The SI-amperometric technique provided satisfactory precision (4.11% RSD) with rapid sample throughput (40 samples h-1). Also using this method, the consumption of the expensive ABTS reagent was greatly reduced. © 2011 Elsevier B.V. All rights reserved. Source

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