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A microfluidic thread electroanalytical device (μTED) containing an embedded electrochemical detector is presented for the first time in this work. This novel device was entirely produced in an automated way using the fused deposition modeling (FDM) 3D printing technique. The main platform was fabricated with acrylonitrile butadiene styrene (ABS) filament, while the integrated electrochemical detector was produced using a commercial conductive filament composed of carbon black and polylactic acid (CB/PLA). The microfluidic channels consisted of cotton threads, which act as passive pumps, and the μTED was used for microflow injection analysis (μFIA). As a proof of concept, this μFIA system was utilized for the amperometric sensing of nitrite in natural waters. This is the first report on the use of both μTEDs and 3D-printed CB/PLA electrodes to determine this species. This fully 3D-printed μTED was characterized and all experimental and instrumental parameters related to the method were studied and optimized. Using the best conditions, the proposed approach showed a linear response in the concentration range from 8 to 200 μmol L−1 and a limit of detection (LOD) of 2.39 μmol L−1. The LOD obtained here was ca. ten-fold lower than the maximum contaminant level for nitrite in drinking water established by the Brazilian and US legislation. Moreover, the platform presented good repeatability and reproducibility (relative standard deviations (RSDs) were 2.1% and 2.5%, respectively). Lastly, the 3D-printed μTED was applied for the quantification of nitrite in well water samples and the results obtained showed good precision (RSD < 3%) and excellent concordance (relative error was ca. ±3%) with those achieved by ion chromatography, used for validation.

Nowadays, the use of pesticides in world agriculture is fundamental. However, it leads to an increase in the illegal sale and smuggling of these products in various parts of the world, mainly in Brazil. Therefore, the development of new analytical methods for screening and analysis of these kind of substances is a relevant issue. We present in this work, for the first time, an electrochemical study and a novel electroanalytical method for determination of fungicide benzovindiflupyr (BENZO). According to our knowledge, the electrochemical behavior of BENZO, as well as its voltammetric determination, have never been reported before. The sensors used here consisted of disposable pencil graphite electrodes (PGEs). On this electrode surface and at optimal pH, BENZO behaved according to a quasi-reversible system and showed two voltammetric peaks, one anodic at E

A new contact stamping method for fabrication of paper-based analytical devices (PADs) is reported. It uses an all-purpose acrylic varnish and 3D-printed stamps to pattern hydrophobic structures on paper substrates. The use of 3D printing allows quickly prototyping the desired stamp shape without resorting to third-party services, which are often expensive and time consuming. To the best of our knowledge, this is the first report regarding the use of this material for creation of hydrophobic barriers in paper substrates, as well as this 3D printing-based stamping method. The acrylic varnish was characterized and the features of the stamping method were studied. The PADs developed here presented better compatibility with organic solvents and surfactants compared with similar protocols. Furthermore, the use of this contact stamping method for fabrication of paper electrochemical devices was also possible, as well as multiplexed microfluidic devices for lateral flow testing. The analytical applicability of the varnish-based PADs was demonstrated through the image-based colorimetric quantification of iron in pharmaceutical samples. A limit of detection of 0.61 mg L−1 was achieved. The results were compared with spectrophotometry for validation and presented great concordance (relative error was

Here we describe the investigation of the electrochemical behaviour and the electroanalytical quantification of hormonal contraceptive levonorgestrel using solid amalgam electrode fabricated with silver nanoparticles. Until now, to the best of our knowledge, this is the first report of the use of solid working electrodes for levonorgestrel determination. Over this electrodic surface, the substance showed one cathodic peak at Ep = −1.41 V. Moreover, the electrochemical reduction of levonorgestrel was defined as an irreversible and mainly adsorption-controlled process involving two protons and two electrons. Square-wave adsorptive stripping voltammetry (SWAdSV) was used for the quantification of levonorgestrel. The instrumental and experimental parameters were studied and optimized. The best conditions of analysis were observed when using 0.04 mol L−1 Britton–Robinson (BR) buffer at pH 6.0. The analytical signal of levonorgestrel showed a linear dependence on the concentration range from 5.03 × 10−7 mol L–1 to 1.01 × 10−5 mol L–1. The LOD and LOQ obtained were 9.09 × 10−8 mol L−1 and 3.03 × 10−7 mol L−1, respectively. The voltammetric method was employed for the quantification of levonorgestrel in real pharmaceutical formulations and urine samples. The results provided good concordance with the expected values. It makes the working electrode used here an interesting and less toxic option for the analysis of reducible substances in comparison with the HMDE.

In this work, the electrochemical activation of multi-walled carbon nanotube screen-printed electrode (SPE-MWCNT) was proposed for the electroanalytical determination of sulfentrazone (SFZ). Determination of SFZ was carried out by square wave voltammetry (SWV) in 0.04 mol L−1 Britton-Robinson (BR) buffer solution of pH 5.0 at electrochemically activated SPE-MWCNT. The effects of various parameters on the response of the electrode such as cleaning, pH of the buffer, and SWV parameters were investigated. The SFZ oxidation peak current obtained from SWV increased linearly with its concentration at the range of 1.0–25 μmol L−1, with the Pearson correlation coefficient r = 0.9995 and detection limits were lower than 0.8 μmol L−1 for pure water. The developed voltammetric method for SFZ determination using disposable sensor electrodes is low cost and revealed good accuracy, repeatability and reproducibility. The relative standard deviation (RSD) values obtained for repeatability and reproducibility studies were 0.94 and 0.59% respectively, which indicate no significant variation in the electrodes after electrochemical activation. Recovery rates for measurements in soy milk and groundwater samples were 98.67% and 99.00%, respectively, indicating that the proposed electroanalytical method can be employed to analyze SFZ in these samples.

A procedure based on liquid–liquid extraction (LLE) and phase separation using magnetically stirred salt-induced high-temperature liquid-liquid extraction (PS-MSSI-HT-LLE) was developed to extract and pre-concentrate ciprofloxacin (CIPRO) and enrofloxacin (ENRO) from animal food samples before electroanalysis. Firstly, simple LLE was used to extract the fluoroquinolones (FQs) from animal food samples, in which dilution was performed to reduce interference effects to below a tolerable threshold. Then, adapted PS-MSSI-HT-LLE protocols allowed re-extraction and further pre-concentration of target analytes in the diluted acid samples for simultaneous electrochemical quantification at low concentration levels. To improve the peak separation, in simultaneous detection, a baseline-corrected second-order derivative approach was processed. These approaches allowed quantification of target FQs from animal food samples spiked at levels of 0.80 to 2.00 µmol L−1 in chicken meat, with recovery values always higher than 80.5%, as well as in milk samples spiked at 4.00 µmol L−1, with recovery values close to 70.0%.

3D printing is a hot topic in electroanalytical chemistry, allowing the construction of custom cells and sensors at affordable prices. In this work, we describe a novel small and practical 3D-printed electrochemical cell. The cell's body, manufactured in ABS on a 3D printer, is composed by three parts easily screwed: solution vessel, stick and cover with two embedded 3D-pen-printed carbon black-polylactic acid (CB-PLA) electrodes (counter and pseudo-reference). The cell is compatible with any planar working electrode, in which boron-doped diamond, graphite sheet (GS) and 3D-printed CB-PLA were shown as examples. A new alternative protocol to quickly produce 3D-printed sensors using a 3D pen and other low-cost apparatus is also proposed. The voltammetric performance of each evaluated sensor was carried out in the presence of redox probe ferricyanide and paracetamol as model analyte, and the surfaces were characterized by electrochemical impedance spectroscopy and scanning electrochemical microscopy. To present an analytical application of the 3D-printed cell, low-cost flexible sensors (GS and CB-PLA) were used as integrated platforms for sampling and detection of solid drugs. As a proof-of-concept, traces of drugs with a historic of counterfeit or adulteration (sildenafil citrate, tadalafil, losartan and 17α-ethinylestradiol) were abrasively sampled over the sensor and assembled on 3D-printed cell to perform a fast voltammetric scan in the presence of only 500 μL of electrolyte. This protocol is attractive for pharmaceutical and forensic sciences as a simple preliminary screening method which could identify the presence or absence of the suspicious drug as well as impurities or adulterants. The 3D-printed cell was also used for the determination of 17α-ethinylestradiol in a contraceptive pill to demonstrate a quantitative analysis. The cell is quickly printed (90 min), cheap (US$ 0.30) and requires low electrolyte volumes (0.5–3.0 mL), being suitable to be used in several other electroanalyses, especially for on-site applications.

Here, a novel electrically conductive thermoplastic material composed of graphite/acrylonitrile butadiene styrene (G/ABS) is reported for the first time. This material was explored on the production of 3D printing-based electrochemical sensors with enhanced sensitivity using a novel fabrication approach. The developed G/ABS electrodes showed lower charge transfer resistance (157 vs. 3279 Ω), higher electroactive area (0.61 vs. 0.19 cm2) and peak currents ca. 69% higher when compared with electrodes fabricated using carbon black/polylactic acid (CB/PLA) commercial filament, which has been widely explored in recent literature. Moreover, the G/ABS sensor provided satisfactory repeatability, reproducibility and stability (relative standard deviations (RSDs) were 1.14%, 6.81% and 10.62%, respectively). This improved performance can be attributed to the fabrication protocol developed here, which allows the incorporation of greater amounts of conductive material in the polymeric matrix. The G/ABS electrode also required a simpler and quicker protocol for activation when compared to CB/PLA. As proof of concept, the G/ABS sensor was employed for electroanalytical quantification of paracetamol (PAR) in pharmaceutical products. The linear concentration range was observed from 0.20 to 30 μmol L−1 and the limit of detection achieved was 54 nmol L−1, much lower than several recent studies dealing with the same analyte. The sensitivity of the G/ABS electrode regarding PAR was also far better when compared to CB/PLA sensor (0.50 μA/μmol L−1 vs. 0.12 μA/μmol L−1). Analyses in commercial pill samples showed good accuracy (recoveries ca. 108%) and precision (RSDs

The primary antioxidant tert-butylhydroquinone (TBHQ) and an alternative additive, named 1,4-bis(ethylamino)-9,10-anthraquinone, were mixed to yield a potent blend able to be used in the field of biodiesel preservation. Physicochemical parameters such as peroxide value, total acid number, density and induction period were used to evaluate the effectiveness of the combination in stabilising soybean biodiesel during the accelerate storage period of degradation. The induction period values were also used to calculate the occurrence of synergistic effect, and it was observed a high percentage of synergism for the combined additives. The results showed that the presence of target alternative additive also enables lower the concentration of the primary antioxidant (TBHQ) in the blend. The cost-effective comparison was evaluated, and it was verified that the final cost of biodiesel can also be lowered, since the amount of additives (in the blend) required to meet the biodiesel specifications was reduced between 70 and 88%.

In this work we demonstrate, for the first time, the use of inexpensive commercial pencil graphite leads as simple amperometric sensors for microchip electrophoresis. A PDMS support containing one channel was fabricated through soft lithography and sanded pencil graphite leads were inserted into this channel to be used as working electrodes. The electrochemical and morphological characterization of the sensor was carried out. The graphite electrode was coupled to PDMS microchips in end-channel configuration and electrophoretic experiments were performed using nitrite and ascorbate as probe analytes. The analytes were successfully separated and detected in well-defined peaks with satisfactory resolution using the microfluidic platform proposed. The repeatability of the pencil graphite electrode was satisfactory (RSD values of 1.6% for nitrite and 12.3% for ascorbate, regarding the peak currents) and its lifetime was estimated to be ca. 700 electrophoretic runs over a cost of ca. $ 0.05 per electrode. The limits of detection achieved with this system were 2.8 μM for nitrite and 5.7 μM for ascorbate. For proof of principle, the pencil graphite electrode was employed for the real analysis of well water samples and nitrite was successfully quantified at levels below its maximum contaminant level established in Brazil and US.

This paper demonstrates, for the first time, the use of paper-based electrochemical devices coupled to external solid working electrodes. The paper-based electrochemical cells were fabricated using inexpensive and largely available office paper, according to a simple protocol that consists on the creation of hydrophobic barriers using paraffinized paper and preheated metal stamp. The counter and reference electrodes were integrated to the paper platform through the deposition of carbon and silver inks, respectively. The electrochemical paper analytical device (ePAD) was coupled to external glassy carbon rod electrode modified with reduced graphene oxide doped with Cu nanoparticles through meniscus configuration. The analytical usefulness of this electrochemical approach was demonstrated through the simultaneous determination of paracetamol and caffeine in biological samples. The analytes were successfully quantified in real urine samples and limits of detection of 24.6 nM (paracetamol) and 36.1 nM (caffeine) were obtained. The paper platform showed good stability (RSD of 1.07 % for the peak currents and 1.43 % for the peak potentials) and satisfactory performance. The use of solid electrodes coupled to paper electrochemical devices, firstly demonstrated here, opens new possibilities for the utilization of ePADs in electrochemistry and electroanalytical chemistry and offers advantages such as the extremely reduced consumption of reagents and the minimal generation of wastes.

In this work we investigated the electrochemical behavior of insecticide thiodicarb and carried out its electroanalytical determination using novel solid amalgam electrode fabricated with silver nanoparticles for the first time. Cyclic voltammetry (CV) and square-wave adsorptive stripping voltammetry (SWAdSV) were used to carry out the electrochemical and analytical studies. The best voltammetric response was achieved through the optimization of the experimental and instrumental parameters. Thiodicarb presented its optimum analytical signal in a medium composed of 0.02 mol L −1 Britton-Robinson buffer at pH 6.0. Two voltammetric peaks were observed, one oxidation peak at E p = −0.51 V and one reduction peak at E p = −0.64 V ( vs. Ag/AgCl). The electrochemical process was characterized as an irreversible system. The cathodic signal was used for the quantitative studies performed with SWAdSV. Thiodicarb showed linear dependence over the surface of the amalgam electrode for the concentration range from 1.05 × 10 −7 to 1.52 × 10 −6 mol L −1 and the limit of detection achieved was 2.03 × 10 −8 mol L −1 . Good repeatability (RSD = 3.8%) and reproducibility (RSD = 6.1%) were found. The voltammetric method developed here allowed the determination of thiodicarb in soymilk samples at levels below those determined by European Union and Brazil with good accuracy. The results were validated using high-performance liquid chromatography and indicated satisfactory concordance. Based on the data described here, the novel silver solid amalgam electrode presented enhanced analytical performance and showed itself as promising to be used on the routine analysis of thiodicarb in food samples.

In this work we present the development of a simple handmade approach for the easy fabrication of three-electrode electrochemical devices based on newly in-house developed carbon ink composed of graphite powder and polystyrene. Different proportions of graphite/polystyrene were investigated for the optimization of the ink. The counter and reference electrodes were produced using commercial carbon ink and silver glue. Scanning electron microscopy, electrochemical impedance spectroscopy and cyclic voltammetry were used to investigate the morphology and the electrochemical properties of the sensor. The results showed that the electroactive area of the optimized working electrode was ca. 2.35 times larger than its geometric area. The RSD values obtained for repeatability and reproducibility were 0.20% and 2.78%, respectively, which suggest no significant variation on the electrodes fabricated. The analytical feasibility of the electrode was tested through its application for the determination of nitrite in drinking water. The quantifications were successfully performed at levels below the maximum contaminant level established for nitrite. A limit of detection of 1.42 × 10−6 mol L−1 and recoveries of ca. 103 % were achieved. The results were validated using ion-chromatography technique with good agreement. The performance of the unmodified sensor proposed here on nitrite determination was better than some recently reported modified electrodes obtained through complex procedures.

This paper describes a simple method for the fabrication of screen-printed based electrodes for amperometric detection on microchip electrophoresis (ME) devices. The procedure developed is quite simple and does not require expensive instrumentation or sophisticated protocols commonly employed on the production of amperometric sensors, such as photolithography or sputtering steps. The electrodes were fabricated through manual deposition of home-made conductive carbon ink over patterned acrylic substrate. Morphological structure and electrochemical behavior of the carbon electrodes were investigated by scanning electron microscopy and cyclic voltammetry. The produced amperometric sensors were coupled to polydimethylsiloxane (PDMS) microchips at end-channel configuration in order to evaluate their analytical performance. For this purpose, electrophoretic experiments were carried out using nitrite and ascorbic acid as model analytes. Separation of these substances was successfully performed within 50s with good resolution (R = 1.2) and sensitivities (713.5 pA/μM for nitrite and 255.4 pA/μM for ascorbate). The reproducibility of the fabrication method was evaluated and revealed good values concerning the peak currents obtained (8.7% for nitrite and 9.3% for ascorbate). The electrodes obtained through this method exhibited satisfactory lifetime (ca. 400 runs) over low fabrication cost (less than $1 per piece). The feasibility of the proposed device for real analysis was demonstrated through the determination of nitrite concentration levels in drinking water samples. Based on the results achieved, the approach proposed here shows itself as an interesting alternative for simple fabrication of carbon-based electrodes. Furthermore, the devices indicate great promise for other kind of analytical applications involving ME devices.

Red fruits are rich sources of antioxidant compounds with recognized health benefits. Since they are perishable, dried extracts emerge as more durable products and their quality control must include antioxidant capacity assays. In this study, the redox behavior of commercial dried products obtained from camu-camu, açai, acerola and cranberry red fruits was evaluated by electroanalytical approaches. The antioxidant potential was determined by 2,2-diphenyl-1-picrylhydrazyl free radical assay and the electrochemical index concept. The total phenol content was estimated by using a laccase based biosensor. A significant correlation was found between all methods and literature data. The voltammetric profile (cyclic, differential and square wave) obtained for each type of dried extract showed distinguishable features that were correlated with their main major markers, being also useful for identification purposes. The electrochemical methods were cheaper and more practical for evaluation of antioxidant properties and total phenol content in dried powders obtained from different red fruits.

The thermodegradation of soybean biodiesel stabilised with conventional antioxidants BHT (butylated hydroxytoluene) and PG (propyl gallate) in combination with an alternative additive based on the anthraquinone compound DHQ (1,4-dihydroxyanthraquinone) was investigated by simulating an accelerated storage process at temperatures from 85 to 110 °C. The effectiveness of different combinations of PG and BHT with DHQ were also evaluated by using the Rancimat® method. The results revealed that combinations of the conventional antioxidants and anthraquinone were more effective at imparting biodiesel stability than the individual compounds. By considering the optimum combination containing PG and BHT with DHQ, it was also determined that the final cost of biodiesel may be markedly reduced since the amount of additives used to stabilise the biodiesel can be decreased by 70–88%, requiring a lower content of conventional antioxidant in the mixture to meet the EN-14112 specification.

This report describes by the first time the use of a commercial screen-printed carbon electrode modified with multi-walled carbon nanotubes for voltammetric determination of the fungicide carbendazim in the presence of an anionic surfactant. The oxidation of the pesticide showed two anodic and two catodic peaks over a quasi-reversible system. The quantitative studies were performed using square-wave voltammetry technique at anodic direction, in that an oxidation peak was observed at +0.98 V vs. Ag/AgCl. Buffer, pH and voltammetric parameters were investigated and optimized. The use of the anionic surfactant sodium dodecyl sulphate provided a significative improvement on analytical sensitivity and its influence also was evaluated. The best conditions for analysis were achieved using a medium of 0.04 mol L−1 Britton-Robinson buffer at pH 4.00 containing 6.04×10−4 mol L−1 of surfactant. A calibration curve with good linearity (R=0.999) was obtained and the limit of detection achieved was 1.40×10−8 mol L−1 (2.7 ppb). Lastly, the developed method was successfully applied for determination of carbendazim in a spiked orange juice sample and a recovery of 101.7 % was obtained. The results were compared with HPLC technique with good agreement. Based on the data presented, the proposed method shows great promise to be applied in routine analysis of carbendazim in food samples and the approach based on the anionic surfactant effect can be an improvement for other applications.

This work describes a novel, simple and inexpensive pen-on-paper (PoP) method for patterning hydrophobic structures in paper substrates aiming the production of paper-based analytical devices (PADs). This fabrication protocol uses a commercially available plastic welding kit that can be easily acquired and is sold as a repair tool. It consists of an acrylate-based resin which is deposited on the paper and then cured using a UV led, or even the sunlight, for creation of the hydrophobic barriers. The protocol is instrument-free and can be easily implemented in any laboratory. To the best of our knowledge, this is the first report of the use of this material for production of analytical devices. The developed PADs were fully characterized and exhibited better chemical resistance than other recently reported PoP approaches regarding organic media and surfactants. Moreover, the fabrication method demonstrated good analytical versatility since it allowed the production of flexible devices, flow-based devices and pencil-drawn electrochemical devices. These findings are very interesting since overcome some limitations related by other PoP reports and expand the possibilities of using this technology in several aqueous and non-aqueous applications. Lastly, the analytical usefulness of the developed devices was successfully explored through colorimetric determination of nitrite. A detection limit of 0.14 mg L−1 was achieved and several samples of natural waters were analyzed. The results showed good agreement when compared with a reference technique. So, considering the simplicity and the results presented here, this fabrication method shows great potential for use in analytical chemistry.

In this work we propose the voltammetric analysis of contraceptive hormones ethinylestradiol (EE) and cyproterone acetate (CPA) using solid amalgam electrode fabricated with silver nanoparticles. To the best of our knowledge, this is the first report describing the simultaneous determination of these two compounds and also the first report of the use of amalgam electrode for analysis of EE and CPA. The voltammetric behavior of both substances was investigated by their reduction. An irreversible electrochemical process involving two protons and two electrons was found for each compound. The analytical assays were carried out using staircase voltammetry (SCV). Due to this, aiming to improve the analytical sensitivity, the cationic surfactant cetyltrimethylammonium bromide was also used. The instrumental and experimental parameters were studied and optimized to achieve the best conditions for the analysis. Under the optimum conditions, the voltammetric signals of EE and CPA showed dependence on the concentration range from 6.4 × 10−7 to 7.8 × 10−6 mol L−1 and from 1.0 × 10−6 to 1.0 × 10−5 mol L−1, respectively. The limits of detection obtained were 1.03 × 10−7 mol L−1 for EE and 2.99 × 10−7 mol L−1 for CPA. The analytical usefulness of the method was evaluated through its application on the simultaneous determination of EE and CPA in pharmaceutical formulations and urine samples. The two analytes were successfully quantified in these samples with good precision and the values found presented satisfactory concordance with the reference values, suggesting acceptable analytical efficiency for the approach described here.

The fabrication of PDMS microfluidic structures through soft lithography is widely reported. While this well-established method gives high precision microstructures and has been successfully used for many researchers, it often requires sophisticated instrumentation and expensive materials such as clean room facilities and photoresists. Thus, we present here a simple protocol that allows the rapid molding of simple linear microchannels in PDMS substrates aiming microfluidics-based applications. It might serve as an alternative to researchers that do not have access to sophisticated facilities such as clean rooms. The method developed here consists on the use of pencil graphite leads as template for the molding of PDMS channels. It yields structures that can be used for several applications, such as housing support for electrochemical sensors or channels for flow devices. Here, the microdevices produced through this protocol were employed for the accommodation of carbon black paste, which was utilized for the first time as amperometric sensor in microchip electrophoresis. This platform was successfully used for the separation and detection of model analytes. Ascorbic acid and iodide were separated within 45 s with peak resolution of 1.2 and sensitivities of 198 and 492 pA/μM, respectively. The background noise was ca. 84 pA. The analytical usefulness of the system developed was successfully tested through the quantification of iodide in commercial pharmaceutical formulations. It demonstrates good efficiency of the microfabrication protocol developed and enables its use for the easy and rapid prototyping of PDMS structures over a low fabrication cost.

We report in this work, for the first time, the voltammetric study and the development of an electroanalytical method for the determination of sodium diethyldithiocarbamate (Na-DDC) using solid amalgam electrode fabricated with silver nanoparticles. The experimental parameters were studied and the best voltammetric response was reached when using 0.02 mol L–1 Britton–Robinson buffer (pH = 5.5). Cyclic voltammograms of the substance presented two voltammetric signals: one cathodic peak at Ep = – 0.55 V and one anodic peak at Ep = – 0.49 V. The redox process of Na-DDC showed itself as an adsorption-controlled and quasi-reversible system. A mechanism for this electrochemical reaction was proposed. The analytical studies employed square-wave adsorptive stripping voltammetry (SWAdSV) and were based on the cathodic signal given by Na-DDC. Good linearity was observed in the concentration range from 2.83 × 10–7 mol L–1 to 6.89 × 10–6 mol L–1. The obtained limit of detection was 7.26 × 10–8 mol L–1. The electroanalytical approach described here was successfully employed for the determination of Na-DDC in river water at levels of concentration from 1.46 × 10–7 mol L–1 to 1.46 × 10–6 mol L–1 with good repeatability and reproducibility (RSD values of 4.2% and 5.9%, respectively). The values found during these determinations presented good concordance when compared with the expected values. According to the data presented here, the solid amalgam electrode fabricated with silver nanoparticles may be seen as an effective and green tool for the electrochemical analysis of Na-DDC and also other reducible compounds that usually require mercury-based electrode surfaces.

This report describes the development and application of a novel graphene-modified electrode to be used as amperometric sensor in microchip electrophoresis (ME) devices. The modified electrode was achieved based on electroreduction of graphene oxide on an integrated Pt working electrode of a commercial ME device. The surface modification was characterized by SEM and cyclic voltammetry techniques. The results indicated that graphene sheets were successfully deposited exhibiting higher surface conductivity and greater electrode sensitivity. The performance of the modified electrode for the amperometric detection on ME devices has been demonstrated by the separation and detection of an anionic mixture containing iodide and ascorbate. The graphene-modified electrode provided significantly higher sensitivity (896.7 vs. 210.9 pA/μM for iodide and 217.8 vs. 127.8 pA/μM for ascorbate), better separation efficiencies (3400 vs. 700 plates/m for iodide and 10 000 vs. 2400 plates/m for ascorbate), enhanced peak resolutions (1.6 vs. 1.0), and LODs (1.5 vs. 5.3 μM for iodide and 3.1 vs. 7.3 μM for ascorbate) in comparison with the unmodified Pt electrode. The proposed amperometric sensor was successfully applied for the analysis of ascorbic acid (through its anionic form) in a commercial medicine sample, and the results achieved were in agreement with the value provided by the supplier. Based on the data here presented, the modified graphene electrode shows great promise for ME applications.

A sensitive, straightforward electroanalytical method for determining pyrogallol (PY) in biodiesel in the presence of a surfactant was developed using a voltammetric technique and screen-printed electrodes. The influence of surfactant addition (sodium dodecyl sulfate (SDS), Triton X-100 (TX-100), cetyltrimethylammonium bromide (CTAB), tetrabutylammonium iodide (TBAI), tetrabutylammonium bromide (TBAB), or tetraethylammonium bromide (TEAB)) on the supporting electrolyte (0.04 mol L−1 BrittonRobinson buffer) was evaluated. Only CTAB significantly increased the oxidation peak current. Under optimal conditions, the method demonstrated linearity over the concentration range of 0.8–9.0×10−6 mol L−1, with limits of detection and quantification of 4.9×10−7 and 1.5×10−6 mol L−1, respectively. The results were satisfactory, relative to those obtained using high-performance liquid chromatography (HPLC).

The development of electroanalytical methods for determining three or more analytes simultaneously in a complex sample is highly desirable. Unfortunately, this is not an easy task in electrochemical studies of organic compounds, and alternative methods to achieve this goal have been increasingly sought in recent years. To this end, the present investigation employed a combination of screen-printed electrodes (SPEs), cetyltrimethylammonium bromide (CTAB), and a peak deconvolution procedure as an alternative approach to improve the sensitivity and selectivity in the simultaneous determination of three antioxidants in samples of biodiesel and cosmetic oils. The use of CTAB also prevents the occurrence of SPE fouling by matrix constituents, being essential in the simultaneous detection of the antioxidants tert-butylhydroquinone (TBHQ), propyl gallate (PG), and butylhydroxyanisole (BHA). Under optimized conditions, the limit of detection proved satisfactory, with relative standard deviations of 0.99% for TBHQ, 2.1% for PG, and 0.61% for BHA, indicating that the method has satisfactory repeatability. The approach was successfully applied to determine the target antioxidants in biodiesel samples at different concentrations after simple, rapid dilution, yielding recovery rates of 98–106% for TBHQ, 98–103% for PG, and 92–101% for BHA. In the analysis of cosmetic oils, a deconvolution procedure was applied to achieve separation of the oxidation peak potentials, with recovery rates of 94% for PG and 101% for BHA using the standard addition method. The results were satisfactory compared with those obtained using high-performance liquid chromatography.

The evaluation of the voltammetric behaviour and the determination of herbicide molinate were performed for the first time over the surface of solid amalgam electrode fabricated with silver nanoparticles using cyclic voltammetry and square-wave voltammetry techniques. The experimental and instrumental parameters were evaluated to reach the maximum analytical response for molinate. It was achieved when a medium composed of 0.04 mol L−1 Britton–Robinson buffer at the pH value of 4.0 was used. Under these conditions, molinate showed one pronounced reduction peak at Ep = −0.37 V (vs. Ag/AgCl 3 mol L−1) that was characterised as an irreversible system. An analytical curve was constructed at the concentration range from 9.36 to 243.49 µg L−1 and a limit of detection of 2.34 µg L−1 was obtained. The amalgam electrode presented good stability during the measurements with relative standard deviation (RSD) values of 2.9% for the repeatability and 5.4% for the reproducibility. The voltammetric method developed here could be conveniently applied for the determination of molinate in river water and rice spiked samples at levels below those established on the legislations of European Union and Brazil with good accuracy (RSD of less than 5% for all samples). Comparison with HPLC technique was carried out and the results indicated satisfactory concordance. According to the results depicted here, the silver nanoparticles solid amalgam electrode showed itself highly sensitive and an interesting alternative for the routine analysis of molinate in water and food samples. Furthermore, it introduces an environmentally acceptable alternative to the mercury electrodes, most commonly used for determination of reducible pesticides.

In this work, we present a simple homemade batch-injection analysis cell for screen-printed electrodes (BIA-SPE). The potential of the proposed system for on- site analysis was demonstrated by the determination of carbendazim, catechol, and hydroquinone in tap water. The system provided reduced injection volume (30 mL), high analytical frequency (! 200 h " 1 ) and low detection limits (nanomolar level). Moreover, the BIA-SPE cell presented better stability (RSD! 0.4%) than a conven- tional flow injection cell for SPE (RSD! 5.0%) in organ- ic media. The proposed homemade BIA-SPE cell is very simple, inexpensive and can be easily constructed in any laboratory.

This report describes the use of PDMS ME coupled with amperometric detection for rapid separation of ascorbic, gallic , ferulic, p-coumaric acids using reverse polarity. ME devices were fabricated in PDMS by soft lithography and detection was accomplished using an integrated carbon fiber working electrode aligned in the end-channel configuration. Separation and detection parameters were investigated and the best conditions were obtained using a run buffer consisting of 5 mM phosphate buffer (pH 6.9) and a detection voltage of 1.0 V versus Ag/AgCl reference electrode. All compounds were separated within 70 s using gated injection mode with baseline resolution and separation efficiencies between 1200 and 9000 plates. Calibration curves exhibited good linearity and the LODs achieved ranged from 1.7 to 9.7 μM. The precision for migration time and peak height provided maximum values of 4% for the intrachip studies. Lastly, the analytical method was successfully applied for the analysis of ascorbic and gallic acids in commercial beverage samples. The results achieved using ME coupled with amperometric detection were in good agreement with the values provided by the supplier. Based on the data reported here, the proposed method shows suitability to be applied for the routine analysis of beverage samples.

The use of anionic surfactants and the application of a deconvolution procedure were investigated as suitable methods to provide electrochemical peak separation in the simultaneous detection of the fluoroquinolones levofloxacin (LEVO) and norfloxacin (NOR). Concurrently, an electroanalytical methodology was developed based on the simultaneous determination of both fluoroquinolones using a mathematical treatment via baseline correction. We also developed a deconvolution procedure to separate overlapping peaks. These methods provided satisfactory peak separation and intensification of peak current, allowing efficient quantification of analytes in both tablets and biological samples with recovery values ranging from 88.1%–107.5%.

This paper reports the synthesis, characterization, and application of TiO2 and TiO2/Ag nanoparticles for use in photocatalysis, employing the herbicide methylviologen (MV) as a substrate for photocatalytic activity testing. At suitable metal to oxide ratios, increases in silver surface coating on TiO2 enhanced the efficiency of heterogeneous photocatalysis by increasing the electron transfer constant. The sol-gel method was used for TiO2 synthesis. P25 TiO2 was the control material. Both oxides were subjected to the same silver incorporation process. The materials were characterized by conventional spectroscopy, SEM micrography, X-ray diffraction, calculation of surface area per mass of catalyst, and thermogravimetry. Also, electron transfers between TiO2 or TiO2/Ag and MV in the absence and presence of sodium formate were investigated using laser flash photolysis. Oxides synthesized with 2.0 % silver exhibited superior photocatalytic activity for MV degradation.

An electroanalytical method for the simultaneous detection and quantification of tert -butylhydroquinone (TBHQ) and butyl hydroxyanisole (BHA) in biodiesel was developed using a voltammetric technique and screen-printed electrodes. The supporting electrolyte solution was composed of Britton–Robinson buffer (0.04 mol L −1 ) containing methanol (2.0%) and the cationic surfactant cetyltrimethylammonium bromide (CTAB). In the presence of CTAB, the peak current intensity and voltammetric resolution increased significantly for both studied antioxidants. Using the optimized conditions, the method presented a linear response in the concentration range of 5.0 × 10 −7 –1.0 × 10 −5 mol L −1 for TBHQ ( r = 0.999) and BHA ( r = 0.999) with detection limits of 3.40 × 10 −7 mol L −1 and 1.76 × 10 −7 mol L −1 , respectively. The proposed method was successfully applied for the quantification of TBHQ and BHA in biodiesel samples after a simple and rapid dilution with recoveries from 97.90% to 110.0% and 91.90% to 101.0%, respectively. The obtained results were satisfactory when compared with those obtained using high-performance liquid chromatography (HPLC). Additionally, the proposed method can be easily adapted for on-site analysis.

Ethanol with added water may be found during the process of assessing its physical and chemical properties. This addition can damage automotive vehicle engines and also may contribute to tax evasion. The present contribution describes a method based on a photothermal transparent transducer to determine the water content in ethanol. A chamber with a window of lithium tantalate coated with a thin layer of indium tin oxide was used, and a 1450-nm laser diode was employed as the excitation source. The results indicated a nearly linear response of the apparatus, as a function of the water content in water/ethanol solutions ranging from 0 to 100 (vol.%). The results for the dependency of the photothermal signal on the laser power and chopping frequency suggested that reliable results can be obtained using laser power and chopping rates above 100 mW and 10 Hz, respectively. The results reported here may be useful in the development of an alternative method that can provide real-time data on the water concentration in ethanol in a rapid, portable and unambiguous way, and that can be easily used in laboratory analyses or in gas stations.

In this work, an adsorptive cathodic stripping voltammetric method based on square wave voltammetry (SWV) was developed for determination of the sunscreen agent octocrylene (OCR) individually and simultaneously with 2-Hydroxy-4-methoxybenzophenone (BENZO-3) and octyl methoxycinnamate (OMC). All voltammetric experiments were conducted in a mixture 0.04 mol L− 1 BR buffer: ethanol (80:20, v:v) using a hanging mercury drop electrode (HMDE) as working electrode. The proposed method could be successfully used to analyze commercial sun-block preparations containing OCR alone and combined with BENZO-3 and OMC. For all analyzed samples, the voltammetric method has allowed fast, simple and reliable determination of these sunscreen agents with minimal sample pre-treatment requirements.

Solid silver mercury amalgam electrodes (AgSAEs) represent a suitable alternative to mercury electrodes due to their similar electrochemical properties and non-toxicity of the amalgam material. Based on this knowledge, we report the use of silver solid amalgam as working electrode to determine cefepime in human milk sample. Square-wave voltammogram registered for cefepime in Britton–Robinson buffer at pH 2.5, presented two well-defined reduction peaks, at −0.28 V (peak 1C) and −0.45 V (peak 2C). Under optimized condition, the calibration curves presented linear response from 3.0 × 10−7 to 2.1 × 10−6 mol L−1 with limits of detection and quantification of 8.51 × 10−9 and 2.84 × 10−8 mol L−1, respectively. The applicability of the method was verified using spiked human milk samples and testing recovery percentages, which were ranged from 98.00% to 100.5%. The obtained results were also compared with those provided with the HPLC technique.

An electroanalytical method was developed to detect and quantify the sunscreen agent octocrylene (OCR) in cosmetic products. The method was based on electrochemical reduction, using voltammetric techniques. OCR was reduced at -0.97 V vs. Ag/AgCl on a glassy carbon electrode using a mixture of Britton-Robinson buffer (0.04 mol L(-1)) and ethanol (7 : 3, v/v) as the supporting electrolyte solution. Under optimized conditions and square-wave voltammetry, OCR response was linear from 5.0 × 10(-6) to 8.0 × 10(-5) mol L(-1) (r = 0.9995), with a limit of detection of 2.8 × 10(-6) mol L(-1). The proposed electroanalytical method proved simple, fast and suitable for detection and quantification of OCR in samples of cosmetic products, with satisfactory results in the recovery test and analytical determination in real samples.

In this paper we present a new electroanalytical method for determination of ceftiofur based on the hydrolysis of this antibiotic in 0.04 mol L−1 Britton–Robinson buffer at pH 10 and 60 °C for 60 min (reduction peak at − 0.70 V). Conditions were optimized for complete hydrolysis and quantitative determination of ceftiofur in milk. The method can be successfully used for determination of the antibiotic directly from samples of fluid milk and powder milk spiked to concentrations of 6.0 × 10−8, 8.0 × 10−8, and 10 × 10−8 mol L−1, respectively. Recovery test ranged from 98.28% to 100.83%. The limits of detection and quantification were 3.73 × 10−10 and 1.24 × 10−9 mol L−1, respectively. The method has the advantage of eliminating interference from proteins present in the sample, thus obviating the need for exhaustive extraction, which often renders other procedures unfeasible in terms of time and reagent cost. In addition, waste generation was found to be lower than in other methods.

A sol–gel derived carbon ceramic biosensor was used for methomyl determination in vegetable extract samples based on the immobilization of laccase from Aspergillus oryzae. Esculetin was chosen as the substrate for laccase in order to measure inhibition by this pesticide. The analytical curve was linear for methomyl concentrations of 0.5 to 12.2 µM with a detection limit of 0.2 µM. The lifetime of the proposed biosensor was 60 days and the recovery from vegetable extract samples ranged from 98.0 to 104.2 %. The results using the proposed method are in agreement with those using HPLC at the 95 % confidence level.

This paper reports an electroanalytical method developed for tert-butylhydroquinone (TBHQ) determination in biodiesel in the presence of surfactant Triton X-100 (T-100). T-100 was shown to improve the electroanalytical signal and its use was decisive for direct analysis of TBHQ in biodiesel, only requiring previous dilution of biodiesel samples in methanol. Several parameters were studied and optimized for the development of this methodology. Under optimal conditions, oxidation peak current was proportional to TBHQ concentration in the range of 1.05–10.10 × 10−6 mol L−1, with limits of detection and quantification of 3.43 × 10−8 mol L−1 and 1.14 × 10−7 mol L−1, respectively, by square wave voltammetry (SWV). The results achieved with the proposed method were satisfactory, relative to those obtained using high-performance liquid chromatography (HPLC).

A carbon paste electrode was used for the electrochemical determination of linuron concentrations in water and vegetable extracts. Optimal conditions were established with respect to electrode activation (electrochemical pretreatment), time accumulation, potential accumulation, scan rate, and pH. The limit of detection achieved with a pre-concentration step was 23.0 μg L−1. Recovery measurements in vegetable extract and natural water samples were in the range of 98–103%, indicating that the proposed electrochemical method can be employed to analyze linuron in these matrices. The determination results were in good agreement with HPLC results.

A new electroanalytical procedure was developed for the determination of Benzophenone-3 (BENZO) in commercial sunscreen as the active ingredient. The procedure is based on the use of electrochemical methods as cyclic and square-wave voltammetry, with boron-doped diamond (BDD) electrodes. The reduction of BENZO in Britton-Robinson buffer (0.1 mol●L–1) using this type of electrode gives rise to one irreversible peak in –1.30 V (versus Ag/AgCl) in presence of cationic surfactant cetyltrimethylammonium bromide (CTABr). The proposed electrochemical method was successfully applied to the analysis of commercially available pharmaceutical preparations.

A simple electroanalytical method was developed to determine the antibiotic ceftiofur (CF) in milk. The method is based on the adsorptive accumulation of the drug on a hanging mercury-drop electrode (HMDE) and the accompanying initiation of a negative square wave, which yielded well-defined cathodic peaks at −0.60 V (1C) and −0.91 V (2C) vs. Ag/AgCl. Calibration graphs were constructed and statistical parameters were evaluated. At pH 2.5, the square-wave voltammetry method revealed linearity from 52.4 to 524 ng mL−1 (r = 0.997), which is in accordance with the tolerance level of 100 ng mL−1 for CF as a residue in bovine milk established by the Food and Drug Administration (FDA) and the European Union. The limits of detection and quantification were 1.86 and 6.20 ng mL−1, respectively. The method was tested to determine CF in spiked milk samples using HPLC as reference method.

A novel pequi fruit ( Caryocar brasiliense Camb.) homogenate source of polyphenol oxidase was obtained and immobilized in chitosan crosslinked with cyanuric chloride (CHcych-PPO). A biosensor was developed and used for the square-wave voltammetric determination of thiodicarb. Several parameters were investigated to evaluate the performance of this biosensor in the presence of hydroquinone and thiodicarb. The best response was obtained using 70:20:10% (w/w/w) of graphite powder:Nujol:CHcych-PPO, 250 U mL −1 of PPO and phosphate buffer solution (0.1 M; pH 7.0) with frequency, pulse amplitude and scan increment of 10 Hz, 150 mV, and 15 mV, respectively. Under optimized operational conditions the thiodicarb concentration was linear in the range of 3.75 × 10 −7 to 2.23 × 10 −6 M with a detection limit of 1.58 × 10 −7 M. The biosensor was applied in the determination of thiodicarb in fresh fruit and vegetable samples and the results compared with those obtained using high-performance liquid chromatography.

The direct amperometric determination of tert-butylhydroquinone (TBHQ) in biodiesel at an unmodified glassy carbon electrode is reported. A biodiesel aliquot was added into an electrochemical cell containing a 75% (v/v) ethanol-water solution under stirring (with final concentration of 50 mmol L(-1) HClO(4)). The amperometric method involved the continuous application of three sequential potential pulses to the working electrode (700 mV for 300 ms, 0 mV for 100 ms and -50 mV for 1s). TBHQ was continuously monitored at the first (direct oxidation) and optionally at the second (reduction) potential pulse while the third potential pulse was applied for cleaning of the electrode surface. For comparison, the samples were also analyzed by high-performance liquid-chromatography and a good agreement between the results was verified. Recovery values for spiked samples were between 90% and 95% and the reproducibility of the proposed method was around 5% (n=5). The proposed method can be easily adapted for on-site analysis.

This paper proposes a methodology based on electrochemical reduction for a fast, specific and sensitive determination of genistein by square-wave voltammetry (SWV). The highest peak currents and optimal definition of reduction peak of genistein was obtained by using a supporting electrolyte consisted of 0.04 mol L(-1) phosphate buffer-methanol (8:2, v/v) solution at pH 7.5 and cationic surfactant 2.21 x 10(-4) mol L(-1) cetyltrimethylammonium bromide (CTAB). The peak current was proportional to the concentration of genistein in the range 1.14 x 10(-7) to 1.09 x 10(-6) mol L(-1), with a detection limit and quantification of 3.43 x 10(-8) mol L(-1) and 1.14 x 10(-7) mol L(-1), respectively. The extraction procedure was evaluated for a better determination of genistein contained in soy flour and soy based supplements. The efficiency of the proposed methodology was demonstrated by comparing the results obtained by SWV with those obtained by the high-performance liquid chromatography (HPLC) method.

Forty four samples of type C gasoline, obtained from service stations of five different distributors, and samples of type A gasoline were analyzed by gas chromatography–flame ionization detection (GC–FID) using a low-polarity capillary column. Linear retention indices (LRI) were calculated, and individual components of the gasoline samples were characterized using a detailed hydrocarbon analysis software (StarDHA™). The quantitative data obtained by the chromatographic method were compared with data obtained by official standard methods. Hierarchical cluster analysis was used to determine the degree of similarity between the samples. Detailed hydrocarbon analysis revealed that some of the samples from service stations were probably adulterated with organic solvents.

This paper proposes a methodology based on electrochemical reduction for the simultaneous determination of three sunscreen agents, namely 4-methylbenzylidene camphor (MBC), benzophenone-3 (BENZO) and 2-ethylhexyl-4-methoxycinnamate (EHMC) by differential-pulse polarography (DPP). The highest peak currents and optimal separation of reduction peaks were obtained by using a supporting electrolyte consisted of Britton-Robinson buffer-methanol (8:2) solution at pH 4.0 and cationic surfactant 3.0 x 10(-4)mol L(-1) cetyltrimethylammonium bromide (CTAB). The methodology was validated using four commercial sunscreen preparation as a sample and the results showed high recovery rates. The efficiency of the proposed methodology was demonstrated by comparing the results obtained by DPP with those obtained by the high-performance liquid chromatography (HPLC) method.

A new electroanalytical procedure was developed for the determination of lidocaine in commercial local anesthetics products containing lidocaine as the active ingredient. The procedure is based on the use of electrochemical methods as cyclic and square-wave voltammetry, with boron-doped diamond electrodes. The oxidation of lidocaine in Britton–Robinson buffer (0.1 mol L−1) using this type of electrode gives rise to one irreversible peak in 1.68 V (versus Ag/AgCl). The detection and quantification limits obtained from pure water were 10.0 and 34.4 μg/L, respectively. The proposed electrochemical method was also successfully applied to the analysis of commercially available pharmaceutical preparations. The electrochemical responses of pharmaceutical preparations (gels) were identical to those of standard lidocaine. No influence of propyleneglycol present in the gels on the voltammetric responses was observed. Lidocaine recoveries ranged from 97.6% to 99.2%.

The voltammetric behavior of 4-methylbenzelidene camphor (MBC) was studied by square wave voltammetry (SWV) using mercury electrode. The experimental condition that provided the highest peak current with the best reduction signal definition of MBC was found in Britton-Robinson buffer and cationic surfactants, cetyltrimethylammoniun bromide (CTABr). A single peak of MBC reduction was observed at − 1.21 V versus Ag/AgCl. The developed methodology was applied for determination of MBC in commercial sunscreen SPF 15, 20 and 30 and for the simultaneous determination when other protection agents were associated, such as benzophenone-3 (BENZO) and octyl methoxycinammate (OMC). Both methodologies had shown good determination values for the analyzed samples. The calculated detection limit was 2.99 × 10− 9 mol L− 1 and the quantification limit was 9.98 × 10− 9 mol L− 1.