CHEMICAL MODIFICATION OF ELECTRODE SURFACE IS A STRATEGY FOR IMPROVING THE ANALYTICAL PERFORMANCE OF CONVENTIONAL ELECTRODE MATERIALS FOR SPECIFIC APPLICATIONS IN VARIOUS FIELDS, ESPECIALLY ELECTROANALYSIS AND SENSORS. IN THE ELECTROANALYTICAL DETERMINATION OF TRACE ELEMENTS, CARBON PASTE ELECTRODES (CPES) HAVE BEEN EXTENSIVELY USED DUE TO THEIR WIDE ANODIC POTENTIAL RANGE, LOW RESIDUAL CURRENT, EASE OF FABRICATION, EASY SURFACE RENEWAL AND LOW COST. THE DETECTION LIMIT OF CPE CAN BE FURTHER IMPROVED BY CHEMICALLY MODIFYING THE ACTIVE ELECTRODE SURFACE WITH SUITABLE MODIFIERS. IN THIS WORK, THE PERFORMANCE OF A CPE MODIFIED WITH MULTI-WALLED CARBON NANOTUBES AND NEW LIGAND OF 4-[1-(4-METHOXYPHENYL) METHYLIDENE]-3-METHYL-5-ISOXAZOLONE (MMMI) WAS INVESTIGATED FOR DETECTING TRACE LEVELS OF BI (III) USING DIFFERENTIAL PULSE ANODIC STRIPPING VOLTAMMETRY (DPASV). THE EFFECT OF VARIABLES SUCH AS TYPE OF STRIPPING MEDIUM, DEPOSITION POTENTIAL AND TIME ON DIFFERENTIAL PULSE VOLTAMMOGRAMS PEAK CURRENT WAS OPTIMIZED. ANODIC PEAK POTENTIAL WAS OBTAINED ABOUT -50 MV (VERSUS AG/AGCL/KCL). THIS SENSOR PRESENTED GOOD SELECTIVITY AND SENSITIVITY TOWARDS THE BI (III) OVER A WIDE VARIETY OF CATIONS. UNDER THE OPTIMUM CONDITIONS, THE CALIBRATION CURVE WAS LINEAR IN THE RANGE OF 1.0-400.0 NG ML-1 WITH LIMIT OF DETECTION OF 0.22 NG ML-1. RELATIVE STANDARD DEVIATIONS (R.S.D.) FOR SEVEN REPLICATED DETERMINATIONS OF BISMUTH AT 30.0, 100.0 AND 300.0 NG ML-1 CONCENTRATION LEVELS WERE CALCULATED TO BE 3.6, 2.4 AND 1.6 %. THE PROPOSED ELECTRODE WAS SUCCESSFULLY USED AS A VOLTAMMETRIC SENSOR FOR DETERMINATION OF BISMUTH IN BISMUTH SUBCITRATE TABLET AND SEVERAL WATER SAMPLES.

CARBON NANOTUBES (CNTS) HAVE BEEN EXTENSIVELY USED IN A VARIETY OF APPLICATIONS BASED ON THEIR UNUSUAL PHYSICAL AND CHEMICAL PROPERTIES SUCH AS, HIGHLY ACCESSIBLE SURFACE AREA, EXCELLENT ELECTRICAL CONDUCTIVITY, HIGH MECHANICAL STRENGTH AND GOOD CHEMICAL STABILITY [1].IN THE ELECTROANALYTICAL DETERMINATION OF TRACE ELEMENTS, CARBON PASTE ELECTRODES (CPES) MODIFIED WITH CNTS HAVE BEEN EXTENSIVELY USED DUE TO THEIR WIDE ANODIC POTENTIAL RANGE, LOW RESIDUAL CURRENT, EASE OF FABRICATION, EASY SURFACE RENEWAL AND LOW COST [2]. IN THIS WORK, THE PERFORMANCE OF A CPE MODIFIED WITH MULTI-WALLED CARBON NANOTUBES FUNCTIONALIZED WITH 4- [1- (4-METHOXYPHENYL) METHYLIDENE] -3-METHYL-5-ISOXAZOLONE) WAS INVESTIGATED FOR DETECTING TRACE LEVELS OF BI (III). THE ANODIC PEAK CURRENT OF BISMUTH AT FUNCTIONALIZED CARBON NANOTUBE IS SEVERAL TIMES GREATER THAN THE UNMODIFIED ELECTRODE.THE BEST RESULTS USING THE MODIFIED ELECTRODE WAS OBTAINED IN 0.1 MOL L-1OF HCL SOLUTION IN -50 MV. THE MODIFIED ELECTRODE SHOWED GOOD SENSITIVITY AND SELECTIVITY. THE ELECTRODE HAS VERY GOOD REPRODUCIBILITY (R.S.D.≤4%), HIGH STABILITY IN ITS VOLTAMMETRIC RESPONSE AND LOW DETECTION LIMIT. THE PREPARED ELECTRODE IS SUCCESSFULLY APPLIED FOR THE VOLTAMMETRIC DETECTION OF BISMUTH IN PHARMACEUTICAL SAMPLES.

BISMUTH IS A RARE METAL FOUND IN THE EARTH’S CRUST. BISMUTH APPEARS TO BE ENVIRONMENTALLY SIGNIFICANT BECAUSE ITS PHYSICAL AND CHEMICAL PROPERTIES HAVE LED IT TO BE USED IN DIFFERENT AREAS OF LIFE [1]. BISMUTH AND ITS COMPOUND ARE USED IN SEMICONDUCTORS, COSMETIC PREPARATIONS, ALLOYS, MEDICINES, METALLURGICAL ADDITIVES AND IN THE PREPARATION AND RECYCLING OF URANIUM NUCLEAR FUELS [2]...

DISPERSIVE LIQUID-LIQUID MICRO EXTRACTION (DLLME) [1] IS EASY, HIGH SPEED, HIGH EFFICIENCY, THE METHOD USED FOR THE SEPARATION AND DETERMINATION OF TRACE AMOUNT OF METAL. IN TECHNIQUE, OPTIMIZATION FACTORS EFFICIENTLY WITH TWO METHODS ONE AT A TIME AND DOE [2]. MULTIVARIATE EXPERIMENTAL DESIGN TECHNIQUES, WHICH PERMIT THE SIMULTANEOUS OPTIMIZATION OF SEVERAL CONTROL VARIABLES, ARE FASTER TO IMPLEMENT AND MORE COST EFFECTIVE THAN TRADITIONAL UNIVARIATE (ONE AT A TIME) APPROACHES (FIG. 1.).IN THE ORDER TO FIND OPTIMUM CONDITIONS DIFFERENT PARAMETERS WERE ALSO EVALUATED INCLUDING: PH, LIGAND CONCENTRATION, VOLUME OF DISPERSER SOLVENT AND EXTRACTION SOLVENT. THE STUDY WAS CARRIED OUT IN THE PH 9.5 AND CONCENTRATION 5´10-5 OF DITHIZONE, VOLUME OF DISPERSER SOLVENT (ETHANOL) 900 ML, VOLUME OF EXTRACTION SOLVENT (CARBON TETRACHLORIDE) 150 ML. UNDER OPTIMUM CONDITIONS, THE METHOD WAS LINEARITY RANG FOR COMPELEXATION BI WITH DITHIZONE EQUAL 20-270 (NG ML-1), R.S.D. EQUAL TO 1.7% WITH (N=8), AMOUNT ENHANCEMENT FACTOR EQUAL 375 AND DETECTION LIMIT EQUAL 7 (NG ML-1).

AN OPTICAL SENSOR (OPTODE) [1] FOR BISMUTH (III) IONS [2] ANALYSIS HAS BEEN DESIGNED BY IMMOBILIZATION OF PYROCATECHOL VIOLET (PCV) [3]. WHEN MEMBRANE PLACED IN ACIDIC SOLUTION (PH=3.8), COLOR CHANGES FROM YELLOW TO BLUE. THIS OPTODE HAS A REVERSIBLE AND REPRODUCIBLE RESPONSE. UNDER OPTIMUM CONDITION, THE PROPOSED METHOD IS CAPABLE OF DETERMINING OF BI (III) IONS OVER A DYNAMIC RANGE BETWEEN 6.6 TO 0.47 MM WITH A LIMIT OF DETECTION 0.58 MM. THE RELATIVE STANDARD DEVIATION FOR REPEATABILITY AND REPRODUCIBILITY FOR SIX REPLICATE MEASUREMENTS WAS OBTAINED 4.87% AND 4.32%, RESPECTIVELY. THE SENSOR CAN EASILY BE REGENERATED BY 1.00×10-5 MM HYDROCHLORIC ACID SOLUTION IN LESS THAN 30 S. THE RESPONSE TIME OF SENSOR WAS WITHIN10 MIN DEPENDING ON BI (III) IONS CONCENTRATION. THE SENSOR WAS SUCCESSFULLY APPLIED TO THE DETERMINATION OF BISMUTH IONS IN WATER AND TABLET SAMPLES [4].