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Cocaine is one of the most abused drugs worldwide. Therefore, it is crucial to develop and improve cocaine identification techniques. This article describes two new electrodes chemically modified with ([Co((±)-t-3MeOsalcn)] or ([Cu((±)-t-3MeOsalcn)] and their use in free-base cocaine (FB) and cocaine hydrochloride (HC) identification. The electrodes were not active toward FB, but cyclic voltammetry analysis revealed an increase of 0.1 V (vs Ag/AgCl) (Eoxi) for HC. The square-wave voltammetry results showed that FB@([Cu((±)-t-3MeOsalcn)] and HC@([Cu((±)-t-3MeOsalcn)] presented higher amperometric sensitivity than FB@([Cu((±)-t-3MeOsalcn)] and HC@([Cu((±)-t-3MeOsalcn)]. The limit of detection (LOD) and the limit of quantification (LOQ) for FB@([Cu((±)-t-3MeOsalcn)] were 0.61 μmol.L−1and 2.04 μmol.L−1, respectively. As for HC@([Cu((±)-t-3MeOsalcn)] the LOD and the LOQ were 0.58 μmol.L−1 and 1.92 μmol.L−1, respectively. The higher chemical stability of the cocaine@([Cu((±)-t-3MeOsalcn)] complexes and the lower binding energy of FB and HC with ([Cu((±)-t-3MeOsalcn)] predicted by theoretical calculations explain the results of the voltammetric analyses. Moreover, the topographic and compositional results confirmed that HC adsorbed onto the surface of the electrodes chemically modified with [Co((±)-t-3MeOsalcn)] or ([Cu((±)-t-3MeOsalcn)]. Overall, our results demonstrated that the electrodes chemically modified with [Co((±)-t-3MeOsalcn)] or ([Cu((±)-t-3MeOsalcn)] developed in this study have promising application in cocaine detection and quantification. At the end of the study, we propose a schematic mechanism for the HC oxidation process at the modified electrodes.

MDMA is the abbreviation for 3,4-methylenedioxymethamphetamine, which is commonly found in “ecstasy” pills. The psychoactive and euphoric effects that MDMA causes make this substance an illicit drug that is constantly seized by police forces. We describe a low-cost and fast voltammetric methodology that requires a carbon paste electrode (working electrode) in aqueous solution containing 0.1 mol L-1 LiClO4 as the supporting electrolyte. We conducted cyclic and square wave voltammetry and obtained limits of detection of 0.33 μg mL-1 and 0.36 μg mL-1, respectively, as others figures of merit for a complete validation. It includes the analysis main interfering substances, and results for seized samples were compared to those obtained by chromatography, which were close. An extended study of robustness were carried out by Youden’s test, that is inedited to electrochemical techniques when applied to forensic analysis. This test contributes to complete methodology validation and study of electrode cost and efficiency during electrochemical measurements involving a carbon paste electrode. In the end, this work presents a full validated methodology able to be applied in forensic laboratories.

The consequences of consuming and commercializing illicit drugs including cocaine, con­stitute a serious problem for authorities and the whole society. Cocaine is usually identified in the laboratory conditions by chromatographic or spectroscopic methods. Electro­che­mical techniques have also gained prominence because they are fast and easy to use, have many applications, and provide reproducible and reliable results. Therefore, in the present study, a voltammetric method was developed to detect freebase cocaine using carbon paste electrode and methanol as the main cocaine solvent. The developed method was applied to detect cocaine in the artificial saliva by the square wave voltammetry (SWV). The current values increased linearly with the concentration of cocaine, which afforded construction of the analytical curve. The limit of detection (LoD) and the limit of quantify­cation (LoQ) were determined as 0.90 µg/mL and 2.41 µg/mL, respectively. For compa­rison purposes, HPLC-DAD chromatographic method was also applied to detect cocaine. The corresponding analytical curve gave LoD = 0.043 µg/mL and LoQ = 0.130 µg/mL. Although showing better analytical results, HPLC-DAD method could not detect cocaine in saliva samples without previous treatment, what makes the electrochemical method much more attractive for this type of detection.

This article describes a method that uses a carbon paste chemically modified with N,N’-ethylene-bis-(salicylideneiminato) manganese(II) to detect cocaine hydrochloride by linear sweep voltammetry (LSV) in aqueous medium containing 0.1 mol L−1 KCl as supporting electrolyte. The potential scans were run from 0.4 to 0.9 V (vs Ag/AgCl), at 100 Mv s−1. The carbon paste chemically modified with the [Mn(salen)] complex had to be heated at 60 °C for paste agglutination. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were conducted to assess the thermal stability of the [Mn(salen)] complex, which remained stable up to 300 °C. Scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) analyses showed that the [Mn(salen)] complex was evenly and homogeneously distributed on the chemically modified electrode surface. The possible mechanism of electronic exchange between cocaine hydrochloride and the electrode surface was proposed: cocaine hydrochloride reduction at the working electrode surface produced the radical •C–OH due to reduction of the carbonyl group (C=O) stabilized by interaction of its free electron with orbital d electrons present in the manganese(II) Schiff base complex. Cathodic activity was verified at 0.8 V (vs Ag/AgCl). Cocaine hydrochloride detection presented linear dependence from 1 to 100 μmol L−1 with linear correlation coefficient of 0.9995 ± 0.0006, average amperometric sensitivity of 0.3367 μmol L−1, limit of detection (LOD) of 0.9349 μmol L−1, and limit of quantification (LOQ) of 3.11 μmol L−1. Notably, the [Mn(salen)] complex used in herein presented higher amperometric sensitivity than the complexes published so far, which is an important contribution to the development of techniques for cocaine detection.

The consumption of ecstasy has increased in recent years due to the psychostimulating effects of MDMA (3,4-methylenedioxymethamphetamine), its main active ingredient. With that, there is a great concern on the part of the authorities, mainly for the control of drivers who drive under the influence of drugs. The verification of the drug use is usually made by the presence of its metabolites in blood or urine, but alternative matrices such as oral fluid, sweat and hair have been investigated over past decades. For the oral fluid the collection is simple, noninvasive, and less susceptible to adulteration and can be used to show recent use of the drug. Portable equipment such as Drugwipe®, Cozart RapiScan, and Ora-Check are routinely used because they easy and simple to operate and give the result quickly. Another technique that features portability and easy handling is electrochemistry. This work demonstrates that it is possible to identify MDMA in oral fluid using the carbon paste electrode, as working and auxiliary electrodes, and the screen printed carbon electrode (SPCE) with cyclic and square wave voltammetry. The presence of the drug could also be identified in real saliva, mixed with 0.1 mol L−1 LiClO4 as supporting electrolyte, in a concentration of 2.53 µg mL−1, demonstrating that it can be applied to identify the recent use of the drug, as well as the rapid tests already commercialized. Also, SPCE was used for the detection and quantification of MDMA in seized samples, using aqueous solution of 0.1 mol L−1 LiClO4, with limits of detection and quantification of 1.75 and 5.82 µg mL−1, respectively, and a linear range of 1.75 – 19.98 µg mL−1. These results support the use of these procedures in forensic laboratories as simple, rapid, and alternative methods for detecting MDMA in saliva and for analyzing seized drugs.

The illegal use of formalin (commercial formaldehyde) in cosmetic products harms the health of individuals exposed to this substance. Over the last years, the commercial availability of these products, especially those containing irregular dosage of formaldehyde, has increased in Brazil. This work analyzes some products for hair treatment available in the Brazilian market and verifies their safety. The adopted analytical methodology involved sample derivatization with 2,4‐dinitrophenylhydrazine, followed by high‐performance liquid chromatography with ultraviolet detection (UV–VIS) at λ = 365 nm. The limit of quantification is 2.5 × 10−3% w/w, and the recovery tests were around 93%. Some of the samples contained high and illegal formaldehyde levels ranging from 9% to 19% (w/w) and others presented suitable concentrations of the analyte. On the basis of the results, this work discusses the efficiency and practicality of this analytical method for forensic purposes.

According to ONU reports, the use of abusive drugs has increased, requiring sensitive techniques for the detection of these substances [1]. This interconnection brings a scenario in which chemical detection of narcotics by conventional, low-cost methods is necessary for drug control. Thus, instrumental analytical techniques appear as indispensable tools for analysis of unknown substances in the forensic field because of their ability to bring low detection limits and selectivity. Thus, the carbon Screen-Printed electrode was elected to develop an electroanalytical method and to study the electrochemical behavior of MDMA for its drug detection potential, low cost, and easy applicability. So, our objective was to develop an electrochemical method with Carbon Screen-Printed electrodes for MDMA detection and study of its redox processes. Palmsens ® Screen-Printed electrodes were utilized in this work. The behavior de the redox processes of MDMA were carried out with a 1.3×10-3 mol L-1 solution in 0.1 mol L-1 phosphate buffer (PBS) at 2.0, 4.0, 6.0, 8.0, 9.0, and 10.0 pH, since MDMA structure can be protonated at the amino group and turns easier the π orbitals delocalization [2]. The MDMA quantification method development utilized PBS 0.1 M at pH 9.0. The absence of cathodic peaks narrowed the sweeps just as anodic. Thus, Cyclic Voltammetry (CV), Linear Sweep Stripping Voltammetry (LSSV), Differential Pulse Voltammetry (DPSV), and Square Wave Stripping Voltammetry (SWSV) were employed. Adulterants such as caffeine (0.31 mmol L-1), lidocaine (0.25 mmol L-1), acetaminophen (0.66 mmol L-1), AAS (0.28 mmol L-1) and phenacetin (0.56 mmol L-1) were utilized to observe possible interference in the MDMA detection. The scan rate study indicated that the anodic peak currents are directly proportional the square root of the scan speed in the range from 5 to 100 mV s-1, indicating that the electron transfer reaction of the MDMA on the electrode is diffusion controlled, as predicted by Randles-Sevcik equation. Using carbon SPE, the influence on the change of electrolyte pH through CV was evaluated. Its It was observed that the best currents are obtained at pH 9.0 with supporting electrolyte in 0.1 mol L-1 concentration. For the development of the analytical method, the investigation of the redox processes of MDMA were obtained with LSSV, SWSV and DPSV. The LSSV modality presented the best peak resolution (1.92 ×10-4 AV-1) when compared to SWSV (9.26 × 10-5 AV-1) and DPSV (1.7 × 10-5 AV-1) ). Using LSSV, the equilibrium time parameter was optimized (2.5 to 80 s), such as MDMA preconcentration potential (-1 to 1 V), electrodeposition time (20 to 600 s), and scan speed (5 to 100 mV.s-1) in the potential range from 0.2 to 1.2 V. The best oxidation currents of MDMA were observed at 10 s equilibrium time, -0.5 V preconcentration potential, and electrodeposition time of 20s, using ν = 20 mV.s-1. The merit figures for the developed method were evaluated through analytical curves. PBS solutions at pH 9.0 were prepared with MDMA concentrations ranging from 8.0×10-5 to 1.3×10-3 mol L-1. The analytical curve showed a linear range in this concentration range with detection limit of 7.3×10-5 mol L-1, amperometric sensitivity of 1.43×10-2 A.mol-1.L and linear correlation coefficient of 0.998. Just lidocaine and phenacetin showed electroactivity in this method, but did not demonstrate interference at MDMA response. The results indicated that the analytical method proposed using linear sweep stripping voltammetry showed good analytical performance indicating that the proposed electrode are able to the detection and determination of MDMA in ecstasy samples. Acknowledgements FAPESP (process n°2019/04439-3, and 2016/23825-3) and CAPES (Pro-Forenses 25/2014). References [1] United Nations Office on Drugs and Crime. (2018). World Drug Report 2018. Book 2 [2] Garrido, E. M. P. J. Electrochemical oxidation of amphetamine-like drugs and application to electroanalysis of ecstasy in human serum. Bioelectrochemistry 79 (2010) 77 - 83.

In this work a new model of carbon paste electrode was employed to determine sulfamethoxazole (SMX), an antibiotic used to treat infections in human and veterinary medicine, by the square wave voltammetric modality (SWV). More specifically, the elec­trochemical behavior of SMX was investigated by cyclic voltammetry (CV), and the quantitative analysis of SMX was provided by SWV. The analytical curve was obtained with a linear correlation coefficient (r) of 0.985 and standard deviation (SD) of 0.005 μA. Limits of detection and quantification were found as 2.3×10-6 and 7.7×10-6 mol L-1, respectively. According to the obtained results, the new carbon paste prototype electrode can successfully be employed in this kind of electroanalytical applications.

A voltammetric method for the determination of ethyl acetate in ethanol fuel using a Fe3+/Nafion®-coated glassy carbon electrode (GCE) is proposed. The ethyl acetate present in the ethanol fuel was previously converted to acetohydroxamic acid via pretreatment with hydroxylamine chloride. The acetohydroxamic acid promptly reacted with the iron (III) present in the film, producing iron (III) acetohydroxamate, which presents a well-defined voltammetric peak current at −0.02 V. Optimization of the voltammetric parameters for the cyclic, linear sweep, square wave, and differential pulse modalities was carried out for this chemically-modified electrode. Square wave voltammetry afforded the best response for acetohydroxamic acid detection. The analytical curve for this species was linear from 9 to 100 μmol L−1 according to the following equation: ip (μA) = 0.27 + 2.55Cacetohydroxamic acid (μmol L−1), with linear correlation coefficient equal to 0.993. The technique presented limit of detection equal to 5.3 μmol L−1 and quantification limit of 17.6 μmol L−1. The proposed method was compared to the official method of ethyl acetate analysis (Gas Chromatography), and a satisfactory correlation was found between these techniques.

Procymidone, a potentially carcinogenic and mutagenic pesticide, can contribute to environmental and human contamination when applied to apple crops. In this work, we propose a reliable and sensitive method to determine procymidone in Brazilian apples. The method involves differential pulse (DPV) and square-wave voltammetry (SWV) techniques on a glassy carbon electrode. In a supporting electrolyte solution of 0.5 mol L−1 NaOH, procymidone undergoes an irreversible one-electron oxidation at +1.42 V by cyclic voltammetric vs. Ag|AgCl, KCl 3 M reference electrode. The proposed DPV and SWV methods have a good linear response in the 8.00–20.0 mg L−1 range, with limits of detection (LOD) of 0.678 and 0.228 mg L−1, respectively, in the absence of the matrix. We obtained improved LOD (0.097 mg L−1) in the presence of apple matrix and the supporting electrolyte solution. We used three commercial apple samples to evaluate recovery, and we achieved recovery percentages ranging from 94.6 to 110 % for procymidone determinations. We also tested the proposed voltammetric method for reproducibility, repeatability, and potential interferents, and the results were satisfactory for electroanalytical purposes.

Chemically modified screen printed electrodes (CM-SPE) using [UO2(4-MeOSalen)(H2O)] ⋅ H2O films were employed in the voltammetric determination of cocaine. The chemical modification was performed by dip coating electrode surfaces (carbon, gold, and platinum) with methanolic solution containing the Schiff base complex with subsequent drying step at room temperature. The optimized amount of the chemical modifier over the working electrode was found to be 2.39 µg mm−2 (geometric area). The voltammetric measurements were carried out in 50 : 50 v/v methanol:water solution containing 0.05 mol L−1 KCl and 0.1 mol L−1 LiCl as a supporting electrolyte without oxygen elimination by inert gas flow. The best results were obtained with carbon electrodes. Cocaine exhibits a well defined irreversible anodic peak current (ipa) at a potential (Epa) of 0.85 V vs Ag/AgCl. The current is directly proportional to the drug concentration. An optimal accumulation potential (Eprec), and time (tprec) of −0.80 V (vs Ag/AgCl), and 120 s, respectively, were determined. The linear dependence of ipa with square root of scan rate (υ) indicates that the mass transport at the electrode surface is controlled by diffusion. An optimized scan rate of 100 mV s−1 was obtained for analytical purposes. A limit of detection (LOD) and limit of quantification (LOQ) in 110 and 390 µmol L−1, respectively, with intra and inter-day repeatability of 2.61 % and 3.77 %, respectively, were obtained. In interference studies the proposed method demonstrated high specificity for cocaine in the presence of morphine and 3,4-methylenedioxymethanphetamine. The above results demonstrate that this method provides a fast and low cost procedure for determination of cocaine in trace levels.

An eletroanalytical method for determination of arsenic in sugar cane brandy using an electrode consisting of carbon paste modified with carbon nanotubes (CNTPE) and mineral oil has been developed. The cyclic (CV) and linear sweep voltammetry modes (LSV) with cathodic stripping were employed for CNTPE containing mineral oil. The analytical curves were linear from 30.0 to 80.0 µg L-1 for LSV. The limit of detection (L.O.D.) was 10.45 μg L-1 and limit of quantification (L.O.Q.) was 34.33 μg L-1. The developed method was applied to the determination of arsenic in tree commercial sugar cane brandy samples. The results were in good agreement with those obtained by HGAAS, showing that CNTPE containing mineral oil can be successfully employed to the simultaneous determination of arsenic in sugar cane brandy samples.

methanol, and 30% NaOH 0.3 mol L −1 at −1.43, −1.57, −1.73, −1.88, and −2.05 V. The proposed DPV method has a good linear response in the 3.00 ‐ 10.0 μmol L −1 range, with a limit of detection (L.O.D) of 0.756 μmol L −1 and 0.831 μmol L −1 in the absence and in the presence of the matrix, respectively. Moreover, improved L.O.D results (0.607 μmol L −1 ) have been achieved in the absence of DMF from the supporting electrolyte solution. Recovery has been evaluated in five commercial green bell pepper samples, and recovery percentages ranging from 91.0 to 109 have been obtained for tetradifon determinations. The proposed voltammetric method has also been tested for reproducibility, repeatability, and potential interferents, and the results obtained for these three analytical parameters are satisfactory for electroanalytical purposes.

A mercury-free electrode chemically modified with carbon paste containing dimethylglyoxime was used for determination of nickel in fuel ethanol. The instrumental parameters and composition of the modified paste were optimized. The analytical curve for nickel determination from 5.0 × 10−9 to 5.0 × 10−7 mol L−1 was obtained using 25 min of accumulation time. The detection limit and amperometric sensitivity obtained for this method were 2.7 × 10−9 mol L−1 and 5.2 × 108 µA mol−1 L, respectively. The values for nickel concentration in four commercial samples of fuel ethanol were obtained in the range of 1.1 × 10−8 to 6.9 × 10−8 mol L−1. A comparison to graphite furnace atomic absorption spectrometry (GFAAS) was performed for nickel determination in commercial samples of ethanol.

The development of methodologies using inexpensive, fast, and reliable instrumention is desirable in illicit drug analysis. The purpose of this study was based on cyclic voltammetry technique to differentiate the electrochemical behavior of ∆(9) -THC, the psychoactive substance in marijuana, and five different extract plants to yield false positive results after analysis protocol for cannabinoids using thin-layer chromatography and Fast Blue B salt. After applying a deposition potential of -0.5 V in a glassy carbon working electrode, the results indicated an anodic peak current at 0.0 V versus Ag/AgCl after addition of ∆(9) -THC solution in the electrochemical cell, and limits of detection and quantification were 1.0 ng mL(-1) and 3.5 ng mL(-1) , respectively. Other interfering plants showed distinct amperometric responses. This methodology was useful to detect ∆(9) -THC even in the presence of the Fast Blue B salt, which avoided false positive results for all the studied extract plants.

A high-performance liquid chromatography (HPLC) method for the determination of acetaldehyde in fuel ethanol was developed. Acetaldehyde was derivatized with 0.900 mL 2,4-dinitrophenylhydrazine (DNPHi) reagent and 50 microL phosphoric acid 1 mol L(-1) at a controlled room temperature of 15 degrees C for 20 min. The separation of acetaldehyde-DNPH (ADNPH) was carried out on a Shimadzu Shim-pack C18 column, using methanol/LiCl((aq)) 1.0 mM (80/20, v/v) as a mobile phase under isocratic elution and UV-Vis detection at 365 nm. The standard curve of ADNPH was linear in the range 3-300 mg L(-1) per injection (20 microL) and the limit of detection (LOD) for acetaldehyde was 2.03 microg L(-1), with a correlation coefficient greater than 0.999 and a precision (relative standard deviation, RSD) of 5.6% (n = 5). Recovery studies were performed by fortifying fuel samples with acetaldehyde at various concentrations and the results were in the range 98.7-102%, with a coefficient of variation (CV) from 0.2% to 7.2%. Several fuel samples collected from various gas stations were analyzed and the method was successfully applied to the analysis of acetaldehyde in fuel ethanol samples.

Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-27T11:20:58Z No. of bitstreams: 0Bitstream added on 2014-05-27T14:39:45Z : No. of bitstreams: 1 2-s2.0-18444381760.pdf: 184940 bytes, checksum: 84637731bea55ff47d7a1b3ee7f85de3 (MD5) Made available in DSpace on 2014-05-27T11:20:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2003-12-01 A flow-injection system with a glassy carbon disk electrode modified with Prussian Blue film is proposed for the determination of persulfate in commercial samples of hair bleaching boosters by amperometry. The detection was obtained by chronoamperometric technique and the sample is injected into the electrochemical cell in a wall jet configuration. Potassium chloride at concentration of 0.1 mol L-1 acted as sample carrier at a flow rate of 4.0 mL min-1 and supporting-electrolyte. For 0.025 V (vs. Ag/AgCl) applied voltage, the proposed system handles ca. 160 samples per hour (1.0 10-4 - 1.0 10-3 mol L-1 of persulfate), consuming about 200 μL sample and 11 mg KCl per determination. Typical linear correlations between electrocatalytic current and persulfate concentration was ca. 0.9998. The detection limit is 9.0 10-5 mol L-1 and the calculated amperometric sensibility 3.6 103 μA L mol -1. Relative standard deviation (n =12) of a 1.0 10-4 mol L-1 sample is about 2.2%. The method was applied to persulfate determination in commercial hair-bleaching samples and results are in agreement with those obtained by titrimetry at 95% confidence level and good recoveries (95 - 112%) of spiked samples were found. © 2003 by MDPI. Departameno de Quimica Analitica Universidade Estadual Paulista, PO Box 355, 14800-900, Araraquara-SP Departameno de Quimica Analitica Universidade Estadual Paulista, PO Box 355, 14800-900, Araraquara-SP

Marijuana is a widely consumed illicit drug. Therefore, drug dealers have sought new ways to mask its forensic (spot test) analysis. In this article we describe a methodology for delta-9-tetrahydrocannabinol (Δ9-THC) detection by square-wave voltammetric (SWV) analysis in organic medium (N,N-dimethylformamide) using tetrabutylammonium tetrafluoroborate (TBATFB) as supporting electrolyte, and glassy carbon and platinum disc as working electrode. Applying a potential of -0.5 ± 0.01 V vs. Ag/AgCl, KCl(sat), we detected a well-defined anodic peak current after the pre-concentration step; Δ9-THC detection presented linear dependence at concentrations ranging from 1.0 × 10-9 mol L-1 to 2.2 × 10-8 mol L-1, with a linear correlation coefficient 0.999 and a detection limit of 6.2 × 10-10 mol L-1, using the glassy carbon disc working electrode. These results confirm that optimized SWV technique using glassy carbon disc working electrode enables qualitative analysis of Δ9-THC at concentrations higher than 1.0 nmol L-1.

This study aimed to develop an electrode chemically modified with cucurbit[6]uril to detect 3,4-methylenedioxymethamphetamine (MDMA), the main active principle of ecstasy samples, by voltammetry. We modified the electrode surface with a film containing cucurbit[6]uril, Nafion, and methanol, using the dip coating or the spin coating technique. During analysis, we employed an electrochemical cell with a conventional three-electrode system and KCl solution (0.1 mol L−1) as the supporting electrolyte. We conducted cyclic voltammetry at concentrations ranging from 4.2 × 10−6 to 4.8 × 10−5mol L−1. We also accomplished scanning electron microscopy, to investigate the structural behavior of the film that originated on the electrode surface. We obtained the following results when we used dip coating to prepare the modified electrode: standard deviation (SD) = 0.024 μA, limit of detection (LOD) = 3.5 μmol L−1, limit of quantification (LOQ) = 11.7 μmol L−1, and amperometric sensitivity (m) = 20.9 × 103 μA L mol−1. As for spin coating, we obtained SD = 0.024 μA, LOD = 2.7 μmol L−1, LOQ = 9.1 μmol L−1 and m = 25.9 × 103 μA mol L−1. These are very promising data: the modified electrode is more sensitive than the conventional glassy carbon electrode under the studied experimental conditions.

A simple, rapid inexpensive voltammetric method have been developed for the quantitative determination of albendazole (ABZ) as the pure assay, by direct dissolution of commercial tablets in HCl solutions. Studies with linear sweep (LSV), square-wave (SWV) and differential pulse voltammetry (DPV) were carried out ABZ in aqueous medium at a glassy carbon electrode. A well defined irreversible oxidation peak current was obtained at 1,00V vs. SCE. The method permits a precise quantitative determination of ABZ using the standard addition method. The detection limits for the three voltammetric techniques were found to be 3.0×10−5M (LSV), 6.2× 10−5M (SWV) and 4.0×10−5M (DPV).

We have developed an eletroanalytical method that employs Cu 2+ solutions to determine arsenic in sugarcane brandy using an electrode consisting of carbon paste modified with carbon nanotubes (CNTPE) and polymeric resins. We used linear sweep (LSV) and differential-pulse (DPV) voltammetry with cathodic stripping for CNTPE containing mineral oil or silicone as binder. The analytical curves were linear from 30 to 110 μg L −1 and from 10 to 110 μg L −1 for LSV and DPV, respectively. The limits of detection (L.O.D.) and quantification (L.O.Q.) of CNTPE were 10.3 and 34.5 μg L −1 for mineral oil and 3.4 and 11.2 μg L −1 for silicone. We applied this method to determine arsenic in five commercial sugarcane brandy samples. The results agreed well with those obtained by hydride generation combined with atomic absorption spectrometry (HG AAS).

A new voltammetric method for the determination of Δ9-tetrahydrocannabinol (Δ9-THC) is described. The voltammetric experiments were accomplished in N-N dimethylformamide/water (9:1, v/v), using tetrabutylammonium tetrafluoroborate (TBATFB) 0.1 mol/L as supporting electrolyte and a glassy carbon disk electrode as the working electrode. The anodic peak current was observed at 0.0 V (vs. Ag/AgCl) after a 30 s pre-concentration step under an applied potential of −1.2 V (vs. Ag/AgCl). A linear dependence of Δ9-THC detection was obtained in the concentration range 2.4–11.3 ng/mL, with a linear correlation coefficient of 0.999 and a detection limit of 0.34 ng/mL. The voltammetric method was used to measure the content of Δ9-THC in samples (hemp and hashish) confiscated by the police. The elimination of chemical interferences from the samples was promptly achieved through prior purification using the TLC technique, by employing methanol/water (4:1, v/v) as the mobile phase. The results showed excellent correlation with results attained by HPLC.

A low-cost electrochemical method was developed for the determination of trace-level of methyl parathion (MP) based on the properties of graphite-modified basal plane pyrolytic graphite electrode (graphite-bppg). A combination of graphite-bppg with square-wave voltammetric (SWV) analysis resulted in an original, sensitive and selective electrochemical method for determination of MP pesticide in drinking water. The electrode was constructed and the electrochemical behavior of MP was studied. Immobilization is achieved via film modification from dispersing graphite powder in deionized water and through pipeting a small volume onto the electrode surface allowing the solvent to volatilize. The strong affinity of the graphite modifier for the phosphorous group of the MP allowed the deposition of a significant amount of MP in less than 60 seconds. The cyclic voltammetric results indicate that the graphite-bppg electrode can enhance sensitivity in current intensity towards the quasi-reversible redox peaks of the products of the cathodic reduction of the nitro group at negative potential (peak I = 0.077 V and peak II = -0.062 V) and that the cathodic irreversible peak (peak III = -0.586 V) in comparison with bare bppg electrode and is also adsorption controlled process. Under optimized conditions, the concentration range and detection limit for MP pesticide are respectively 79.0 to 263.3 μmol L-1 and 3.00 μmol L-1. The proposed method was successfully applied to MP determination in drinking water and the performance of this electrochemical sensor has been evaluated in terms of analytical figures of merit. Um método eletroquímico de baixo custo foi desenvolvido para a determinação de traços de metil paration (MP) baseado nas propriedades do eletrodo de grafite pirolítico de plano basal modificado com grafite (grafite-bppg). A combinação do grafite-bppg com voltametria de onda quadrada (VOQ) resultou em um método eletroquímico seletivo, sensível e original para a determinação do pesticida MP em água potável. O eletrodo foi construído e o comportamento eletroquímico do MP foi estudado. A imobilização foi feita através de modificação por formação de filme a partir da dispersão de pó de grafite em água destilada e através de pipetagem de um volume pequeno sobre a superfície do eletrodo, permitindo que o solvente volatilizasse. A forte afinidade do modificador grafite com o grupo fósforo do MP permitiu o depósito de uma quantidade significativa de MP em menos de 60 segundos. Os resultados de voltametria cíclica mostraram que o eletrodo de grafite-bppg pode aumentar a sensibilidade na intensidade de corrente para os picos redox quasi-reversíveis dos produtos da redução catódica do grupo nitro em potencial negativo (pico I = 0,077 V e o pico II = -0,062 V) e para o pico catódico irreversível (pico III = -0,586 V) em comparação com o eletrodo não modificado bppg e que o processo é também controlado por adsorção. Sob condições otimizadas, o intervalo de concentração e limite de detecção para o pesticida MP são 79,0 a 263,3 μmol L-1 e 3,00 μmol L-1, respectivamente. O método proposto foi aplicado com sucesso → determinação do MP em água potável e o desempenho deste sensor eletroquímico foi avaliado em termos de figuras de mérito analíticas.

Chromatographic analysis by the HPLC technique with Diode Array Detector was employed for MDMA determination. A mobile phase of methanol/water (90:10v/v) allowed a peak signal for MDMA in 16 minutes. Optimized spectrophotometric signal was obtained at a wavelength of 240 nm. The analytical curve from 5.0 to 100.0ppm of MDMA was obtained, showing a linear correlation coefficient of 0.9997 and a detection limit of 2.94ppm. This methodology was employed at the dosage of confiscated samples of ecstasy in the Scientific Police Laboratory of Ribeirao Preto-SP city.

In this work, a fast, non destructive voltammetric method for cocaine detection in acetonitrile medium using a platinum disk electrode chemically modified with cobalt-hexacyanoferrate (CoHCFe) film is described. The deposition of CoHCFe film at platinum disk (working electrode) was carried out in aqueous solution containing NaClO 4 at 0.1 mol L −1 as supporting electrolite. Stability studies of the film and subsequent voltammetric analysis of cocaine were made in acetonitrile medium with NaClO 4 at 0.1 mol L −1 as supporting electrolite. A reversible interaction between cocaine and CoHCFe at the film produces a proportional decrease of original peak current, due to the formation of a complex between cocaine and cobalt ions, with subsequent partial passivation of the film surface, being the intensity of current decrease used as analytical signal for cocaine. A linear dependence of cocaine detection was carried out in the range from 2.4 × 10 −4 to 1.5 × 10 −3 mol L −1 , with a linear correlation coefficient of 0.994 and a detection limit of 1.4 × 10 −4 mol L −1 . The analysis of confiscated samples by the proposed method indicated cocaine levels from 37% to 95% (m/m) and these results were validated by comparison to HPLC technique, being obtained good correlation between both methods.

Made available in DSpace on 2013-08-28T14:11:53Z (GMT). No. of bitstreams: 1 WOS000254340700035.pdf: 115446 bytes, checksum: b5ba1c8598579dbf9fa50a3e3e6a9e0f (MD5) Made available in DSpace on 2013-09-30T19:22:41Z (GMT). No. of bitstreams: 2 WOS000254340700035.pdf: 115446 bytes, checksum: b5ba1c8598579dbf9fa50a3e3e6a9e0f (MD5) WOS000254340700035.pdf.txt: 25597 bytes, checksum: 45111b8732e4e645a8f0eebaeb30204f (MD5) Previous issue date: 2008-03-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T15:33:54Z No. of bitstreams: 2 WOS000254340700035.pdf: 115446 bytes, checksum: b5ba1c8598579dbf9fa50a3e3e6a9e0f (MD5) WOS000254340700035.pdf.txt: 25597 bytes, checksum: 45111b8732e4e645a8f0eebaeb30204f (MD5) Made available in DSpace on 2014-05-20T15:33:54Z (GMT). No. of bitstreams: 2 WOS000254340700035.pdf: 115446 bytes, checksum: b5ba1c8598579dbf9fa50a3e3e6a9e0f (MD5) WOS000254340700035.pdf.txt: 25597 bytes, checksum: 45111b8732e4e645a8f0eebaeb30204f (MD5) Previous issue date: 2008-03-01 The electrocatalysis of dopamine has been studied using a cobalt hexacyanoferrate film (CoHCFe)-modified glassy carbon electrode. Using a rotating disk CoHCFe-modified electrode, the reaction rate constant for dopamine was found to be 3.5 x 105 cm(3) mol(-1) s(-1) at a concentration of 5.0 x 10(-5) mol L-1. When a Nafion (R) film is applied to the CoHCFe-modified electrode surface a high selectivity for the determination of dopamine over ascorbic acid was obtained. The analytical curve for dopamine presented linear dependence over the concentration range from 1.2 x 10(-5) to 5.0 x 10(-4) mol L-1 with a slope of 23.5 mA mol(-1) L and a linear correlation coefficient of 0.999. The detection limit of this method was 8.9 x 10(-6) mol L-1 and the relative standard deviation for five measurements of 2.5 x 10(-4) mol L-1 dopamine was 0.58%. UNESP, Inst Quim, Dept Quim Analit, BR-14800900 Araraquara, SP, Brazil UERN, FANAT, Dept Quim, BR-59600010 Mossoro, RN, Brazil Univ Loughborough, Dept Chem, Loughborough LE11 3TU, Leics, England USP, Fac Filosofia Ciencias & Letras Ribeirao Pret, Dept Quim, BR-14040901 Ribeirao Preto, SP, Brazil UNESP, Inst Quim, Dept Quim Analit, BR-14800900 Araraquara, SP, Brazil

The cyclic voltammetric behavior of acetaldehyde and the derivatized product with 2,4-dinitrophenylhydrazine (DNPHi) has been studied at a glassy carbon electrode. This study was used to optimize the best experimental conditions for its determination by high-performance liquid chromatographic (HPLC) separation coupled with electrochemical detection. The acetaldehyde-2,4-dinitrophenylhydrazone (ADNPH) was eluted and separated by a reversed-phase column, C18, under isocratic conditions with the mobile phase containing a binary mixture of methanol/LiCl(aq) at a concentration of 1.0 x 10(-3) M (80:20 v/v) and a flow rate of 1.0 mL min(-1). The optimum condition for the electrochemical detection of ADNPH was +1.0 V vs. Ag/AgCl as a reference electrode. The proposed method was simple, rapid (analysis time 7 min) and sensitive (detection limit 3.80 microg L(-1)) at a signal-to-noise ratio of 3:1. It was also highly selective and reproducible [standard deviation 8.2% +/- 0.36 (n = 5)]. The analytical curve of ADNPH was linear over the range of 3-300 mg L(-1) per injection (20 microL), and the analytical recovery was > 99%.

In this work, electrochemical oxidation of albendazole (ABZ) was carried out using a glassy carbon-rotating disk electrode. Development of electroanalytical methodology for ABZ quantification in pharmaceutical formulations was also proposed by using linear sweep voltammetric technique. Electrochemical oxidation is observed for ABZ at E(1/2)=0.99 V vs. Ag/AgCl(sat), when an anodic wave is observed. Kinetic parameters obtained for ABZ oxidation exhibited a standard heterogeneous rate constant for the electrodic process equal to (1.51+/-0.07) x 10(-5) cm s(-1), with a alphan(a) value equal to 0.76. Limiting current dependence against ABZ concentration exhibited linearity on 5.0 x 10(-5) to 1.0 x 10(-2) mol l(-1) range, being obtained a detection limit of 2.4 x 10(-5) mol l(-1). Proposed methodology was applied to ABZ quantification in pharmaceutical formulations.

A versatile voltammetric method for quantitative determination of fenbendazole (FBZ) in commercial tablets has been proposed, where direct dissolution of tablets is carried out in 0.1 mol l −1 tetrabutylamoniun tetrafluorborate containing dimethylformamide solutions. Linear sweep (LSV), square wave (SWV) and differential pulse (DPV) voltammetry techniques were applied to study FBZ at a glassy carbon electrode, exhibiting a well defined irreversible oxidation peak at 1.15 V vs. SCE. This methodology allows a precise quantitative determination of FBZ presenting detection limits of 5.2×10 −5 (LSV), 5.0×10 −6 (DPV) and 5.0×10 −5 mol l −1 (SWV).

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T18:49:11Z No. of bitstreams: 0 Made available in DSpace on 2013-08-22T18:49:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-01-01 Made available in DSpace on 2013-09-30T19:09:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-01-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T14:19:40Z No. of bitstreams: 0 Made available in DSpace on 2014-05-20T14:19:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-01-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Este estudo descreve o comportamento voltamétrico da redução de 2-furfuraldeído em etanol utilizando-se eletrodo de carbono vítreo, visando estabelecer condições experimentais adequadas para a determinação de 2-furfuraldeído em álcool combustível. Os voltamogramas obtidos para o 2-furfuraldeído em uma velocidade de varredura (v) de 100mV.s-1 apresentaram uma corrente de pico catódica (i pc) definida em um potencial de -1,45V (vs. ECS) para o meio aquoso e -1,71V (vs. ECS) para o meio alcoólico, não sendo observadas correntes de pico anódicas nestes meios reacionais. A relação entre i pc e v½ apresentou-se linear em ambos os meios, exibindo um transporte de massa controlado por difusão. A análise dos parâmetros eletroquímicos obtidos neste estudo revelou que o processo eletródico apresenta um comportamento irreversível. A dependência de i pc com a concentração da espécie reacional apresentou-se linear no intervalo de concentração estudado, de 9,5x10-4 a 5,8x10-3 mol L-1 para ambos os meios. A sensibilidade do método em meio aquoso e alcoólico foi de 13,4 e 13,0 (x 10-3) mA mol-1 L respectivamente. Os limites de detecção (L.D.) referentes à determinação de 2-furfuraldeído, em meio aquoso e alcoólico situam-se entre 0,70 e 0,80 (x 10-3) mol L-1 respectivamente. This study reports the electrochemical behavior of 2-furfuraldehide reduction in ethanol using glassy carbon electrode, aiming to correlate adequate experimental conditions for determination of this 2-furfuraldehide in fuel ethanol. Obtained voltammograms for 2-furfuraldehide in a scan rate of 100mV.s-1 present a cathodic peak current in a potential of -1,45V vs. SCE for aqueous medium and -1,71V vs. SCE for alcoholic medium, being observed no anodic currents in these reactional media. The relation of i pc with v½ showed linear behavior in both media, exhibiting a mass transport controlled by diffusion. The analysis of electrochemical parameters obtained in this work has exhibited an irreversible behavior for the electrodic process. The dependence of cathodic peak current against concentration showed linearity in the interval of 9,5x10-4 to 5,8x10-3 mol L-1 for both media. The sensitivity of method on the aqueous and alcoholic medium was 13,4 and 13,0 (x 10-3) mA mol-1 L respectively. The limits of detection (L.D.) for 2-furfuraldehide, on the aqueous and alcoholic medium was 0,70 e 0,80 (x 10-3) mol L-1 respectively. UNESP Instituto de Química Departamento de Química Analítica UNESP Instituto de Química Departamento de Química Analítica

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T18:49:11Z No. of bitstreams: 0 Made available in DSpace on 2013-08-22T18:49:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-01-01 Made available in DSpace on 2013-09-30T19:09:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-01-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T14:19:40Z No. of bitstreams: 0 Made available in DSpace on 2014-05-20T14:19:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-01-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Os íons fosfito constituem um importante componente inorgânico como fonte de fósforo na fertilização de solos, apresentando incontáveis vantagens em relação ao fosfato. A determinação desse ânion em produtos fertilizantes é usualmente realizada empregando-se método clássico de análise como gravimetria, sob a forma de pirofosfato de magnésio ou pela formação de cloreto mercuroso. Entretanto, existem algumas desvantagens nesta metodologia, como a necessidade de um elevado tempo de digestão e a possível produção de resíduos tóxicos. Sendo assim, este trabalho teve como objetivo propor uma metodologia eletroquímica alternativa para a determinação de fosfito. A modificação eletroquímica na superfície de eletrodos de platina realizada por eletrodeposição de paládio apresentou efeito catalítico para a oxidação de íons fosfito a fosfato em meio de ácido sulfúrico 1,0 mol.L-1. Uma dependência linear em relação à concentração de fosfito foi obtida no intervalo de 5,0x10-6 a 5,0x10-4 mol.L-1 tendo uma sensibilidade amperométrica de 8,5x10(4) miA.mol-1.L e um limite de detecção de 3.67x10-6 mol.L-1. Phosphite ions constitute an important inorganic component as phosphorus source in soil fertilization, showing a large number of advantages in relation to phosphate. The determination of this compound in fertilizing products is realized by classical methods of analysis as gravimetry, in the form of magnesium pyrophosphate or by mercurous chloride formation. However, there are some disadvantages in these methods as the necessity of high times of digestion and possible toxic residue production. So, this work has the objective to propose an alternative electrochemical method for phosphite determination. Electrochemical modification on electrode surface by electrodeposition of palladium has exhibited catalytic effect for oxidation of phosphite to phosphate ions in 1,0mol.L-1 sulfuric acid aqueous medium, being obtained a linear dependence in relation to phosphite concentration from 5,0x10-6 to 5,0x10-4 mol.L-1 with an amperometric sensibility of 8,5x10(4) muA.mol-1.L and a detection limit of 3.67x10-6 mol.L-1. In the absence of palladium film on platinum electrode no anodic peak current is observed for phosphite oxidation. UNESP Instituto de Química Departamento de Química Analítica UNESP Instituto de Química Departamento de Química Analítica

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T18:49:11Z No. of bitstreams: 0 Made available in DSpace on 2013-08-22T18:49:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-01-01 Made available in DSpace on 2013-09-30T19:09:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-01-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T14:19:48Z No. of bitstreams: 0 Made available in DSpace on 2014-05-20T14:19:48Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-01-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) A presença de metais pesados em álcool combustível origina-se na produção e armazenamento do álcool etílico, constituindo uma contaminação inorgânica. A análise quantitativa deste contaminante tem sido usualmente monitorada empregando-se técnicas convencionais de análise tal como espectrofotometria de absorção atômica. Tendo em vista a alta sensibilidade das técnicas voltamétricas de redissolução anódica para a quantificação de metais e que poucos estudos foram realizados para este tipo de matriz, este trabalho tem por objetivo desenvolver uma metodologia eletroanalítica para a determinação de zinco em álcool combustível. A determinação eletroquímica para o zinco em meio aquoso utilizando-se a modalidade de varredura linear exibe uma corrente de pico anódica em um potencial de -1,12 V vs. ECS, apresentando uma dependência linear em relação à concentração de zinco no intervalo de 5,0x10-7 a 5,0x10-6 mol.L-1 com uma sensibilidade amperométrica de 1,2x10(6) miA.mol-1.L e um limite de detecção de 2,6x10-7 mol.L-1. A análise de íons zinco em amostra comercial de álcool combustível foi determinada pela adição de 200 miL de amostra em um volume final de 20 mL de eletrólito-suporte, sendo obtida a concentração de zinco na amostra pelo método de adição de padrão com um valor correspondente a 5,7± 0,19x10-5 mol.L-1 em zinco. The presence of heavy metals in fuel ethanol is obtained in different steps as production and storage of ethanol, constituting an inorganic contamination. Quantitative analysis of these contaminants has been usually carried out by conventional techniques as atomic absorption spectrofotometry. According to high sensibility of stripping voltammetric techniques for quantification of heavy metals and a few number of realized works for this kind of matrix, the aim of this work was to develop an electroanalytical procedure for zinc determination in fuel ethanol. Electrochemical determination for zinc in aqueous media by linear sweep voltammetry exhibited an anodic peak current in a potential of -1,12V vs. SCE, presenting linear dependence against zinc concentration in an interval of 5,0x10-7 to 5,0x10-6 mol.L-1 with an amperommetric sensibility of 1,2x10(6) muA.mol-1.L and a detection limit of 2,6x10-7 mol.L-1. Zinc determination in fuel ethanol commercial sample was obtained by addiction of 200 mL of sample in a final volume of 20 mL of supporting electrolite. The concentration of zinc in the sample was obtained by standard addiction method, presenting a value of 5,7± 0,19x10-5 mol.L-1 in zinc. UNESP Instituto de Química Departamento de Química Analítica UNESP Instituto de Química Departamento de Química Analítica

In this work, an electrode chemically modified with polypyrrole (PCME) was employed for determination of sulfate in ethanol fuel using a FIA system. The PCME was prepared by polymerization of pyrrole at a glassy carbon electrode by means of cyclic voltammetry technique. An analytical curve from 1.0 x 10−5 to 8.0 x 10−5 mol L−1 was obtained in flow injection system based on the PCME. An amperometric sensibility of 2.3 x 10−3 A mol−1 L and a detection limit of 2.5 x 10−6 mol L−1 were achieved. The proposed method was employed for determination of sulfate ions in commercial samples of ethanol fuel. The results were in good agreement with those obtained by the ionic chromatographic method.