No abstract

Chemical analysis performed at the place of the sampling ("in loco" analysis) rather than in a conventional laboratory is often attractive. A portable assay method for field work enables sample collection and data analysis in realtime, the reduction in time consumption and total analyses costs [1]. Furthermore, portable assays is one of the main trends in analytical chemistry due to the rapid growth of the potentials of such analysis [2] and the increasing demands in field analysis for fuel [3], forensic [4], and environmental [5] samples. In electrochemical detection, many companies commercialize a series of portable instruments suitable to in field analysis, as handheld potentiostats and screen-printed electrodes (SPEs) containing a series of modifiers (e.g., multi-and singlewalled carbon nanotubes, graphene, bismuth and Prussian blue) [6]. These simple devices allows the simple adjustment of SPEs in many electrochemical cells, as batch [7] and flow [8,9] systems, as well measurements in drops of solution ( % 50 mL) [10]. Other suitable approach to development of portable analytical methods is Batch Injection Analysis (BIA) [11]. This system is based on the injection of a sample plug through a micropipette tip directly onto the working electrode surface (wall-jet configuration) which is immersed in a large-volume of blank solution. BIA and flow injection analysis (FIA) [12] have high analytical frequency, low consumption of reagents and samples. Nevertheless, BIA is more simple and portable, because the absence of pump, valves and tubes [13]. This work proposes the use of a very simple and portable homemade batch-injection analysis cell to accommodate screen-printed electrodes (BIA-SPE) to determination of herbicide carbendazim (CZIM), hydroquinone (HQ), and catechol (CAT) in tap water. The BIA-SPE system has capability to increase the applicability of electrochemical methods for in field analysis.The BIA-SPE homemade electrochemical cell was constructed from an acrylic rod (1i = 4.0 cm, height = 4.0 cm). As presented in Figure 1, a hole (diameter = 3.1 cm; height = 4.0 cm) was drilled from one side of the rod (top side) and the other side was maintained closed (bottom side). The top side was closed with an acrylic cover with two holes. The first was used for insertion/exchange of the supporting electrolyte and the second was used for the reproducible positioning of the 1 mL combitip of electronic pipette (Figure 1). The combitip with a regular external diameter (6 mm) was firmly introduced into the hole (diameter = 6.1 mm) in such a manner that the distance between the pipette tip and the electrode surface was always the same (highly reproducible injection procedure). Optionally an insulin syringe also can be ) and low detection limits (nanomolar level). Moreover, the BIA-SPE cell presented better stability (RSD % 0.4 %) than a conventional flow injection cell for SPE (RSD % 5.0 %) in organic media. The proposed homemade BIA-SPE cell is very simple, inexpensive and can be easily constructed in any laboratory.

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 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...

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.