Inspired by recent reports concerning the utilisation of hand drawn pencil macroelectrodes (PDEs), we report the fabrication, characterisation (physicochemical and electrochemical) and implementation (electrochemical sensing) of various PDEs drawn upon a flexible polyester substrate. Electrochemical characterisation reveals that there are no quantifiable electrochemical responses upon utilising these PDEs with an electroactive analyte that requires an electrochemical oxidation step first, therefore the PDEs have been examined towards the electroactive redox probes hexaammineruthenium(iii) chloride, potassium ferricyanide and ammonium iron(ii) sulfate. For the first time, characterisation of the number of drawn pencil layers and the grade of pencil are examined; these parameters are commonly overlooked when utilising PDEs. It is demonstrated that a PDE drawn ten times with a 6B pencil presented the most advantageous electrochemical platform, in terms of electrochemical reversibility and peak height/analytical signal. In consideration of the aforementioned limitation, analytes requiring an electrochemical reduction as the first process were solely analysed. We demonstrate the beneficial electroanalytical capabilities of these PDEs towards p-benzoquinone and the simultaneous detection of heavy metals, namely lead(ii) and cadmium(ii), all of which are explored for the first time utilising PDEs. Initially, the detection limits of this system were higher than desired for electroanalytical platforms, however upon implementation of the PDEs in a back-to-back configuration (in which two PDEs are placed back-to-back sharing a single connection to the potentiostat), the detection limits for lead(ii) and cadmium(ii) correspond to 10 μg L(-1) and 98 μg L(-1) respectively within model aqueous (0.1 M HCl) solutions.
Screen-printed back-to-back microband electroanalytical sensors are applied to the quantification of lead(II) ions for the first time. In this configuration the electrodes are positioned back-to-back with a common electrical connection to the two working electrodes with the counter and reference electrodes for each connected in the same manner as a normal "traditional" screen-printed sensor. Proof-of-concept is demonstrated for the electroanalytical sensing of lead(II) ions utilising square-wave anodic stripping voltammetry where an increase in the electroanalytical sensitivity is observed by a factor of 5 with the back-to-back microband configuration at a fixed lead(II) ion concentration of 5 μg L(-1) utilising a deposition potential and time of -1.2 V and 30 seconds respectively, compared to a conventional (single) microband electrode. The back-to-back microband configuration allows for the sensing of lead(II) ions with a linear range from 5 to 110 μg L(-1) with a limit of detection (based on 3σ) corresponding to 3.7 μg L(-1). The back-to-back microband configuration is demonstrated to quantify the levels of lead(II) ions within drinking water corresponding to a level of 2.8 (±0.3) μg L(-1). Independent validation was performed using ICP-OES with the levels of lead(II) ions found to correspond to 2.5 (±0.1) μg L(-1); the excellent agreement between the two methods validates the electroanalytical procedure for the quantification of lead(II) ions in drinking water. This back-to-back configuration exhibits an excellent validated analytical performance for the determination of lead(II) ions within drinking water at World Health Organisation levels (limited to 10 μg L(-1) within drinking water).
This study aims at analyzing the reaction mechanism of the electrooxidation of glycerol at copper surfaces in NaOH solutions using Scanning Electrochemical Microscopy (SECM) in the substrate generation/tip collection (SG/TC) mode. Experiments showed the dependence of the current at the tip on the distance between generator and tip, as well as on the concentration of the NaOH solution. The current at the tip decreased significantly after addition of glycerol, as a result of the competition between diffusion of the free‐soluble Cu(III) species and its consumption during the diffusion in the solution. The determination of the analyte in a castor biodiesel sample employing a single copper microelectrode was carried out.
[a] 1IntroductionOver recentd ecades the utilisationo fscreen-printed derived electrochemical sensorsh ave modernised the field of electroanalysis,w ith their ability to bridge the gap between laboratory experiments and in-field applications [1][2][3][4][5][6].T he incorporationo fs creen-printed electrodes has allowed scientists to take their knowledge and theoretical interpretations and place it into ad evice that possess great scales of economy allowing for simple,i nexpensive disposable electrochemical platforms [1,[7][8][9].T hrough carefuls elections of screen-printing inks and designs, unique sensors can be produced with different geometries such as screen-printed arrays [10][11][12][13],r ecessed electrodes [14] and microbands [15,16].I na ddition to this,t he ease of the mass production of screen-printed sensors enables their use as one-shot sensors, allowing possible contamination to be avoided, and alleviates the need for electrode pre-treatment as is the case for solid electrodes prior to theiru se [1,13,[17][18][19].Screen-printing technologies can be readily adapted to create sensors that can contain beneficial electrode materials such as carbon nanotubes whichh ave au seful geometric structure that provides the enhanced sensing of capsaicin [20] and the cobalt pthalocyanine mediator which has shown electrocatalytic signals towards hydrazine [21].A dditionally upon carefuls election of the screen-printing inks,s ensors can be readily produced containing metallic compoundss uch as palladium [19] Recently the concept of the back-to-back screen-printed graphite electrodec onfiguration has been introduced for the first timew hereathree-electrode system is printed upon both sides of ap olyester substrate,a sp resented in Figure 1[ 24].T his novel electrochemical sensor has been demonstrated to be usefulf or the electroanalytical sensing of NADH and nitritee xhibiting at wo-fold increase in the analytical sensitivity,a dditionally with improvements in the limit of detection [ 24].I nt his paper we build upon such report of the back-to-back electrode configuration [24] and extend this concept to the electroanalyticald etection of dopamine and capsaicin using as ingle walled carbon nanotube (CNT)b ack-to-back sensor and ac obalt phthalocyanine (CoPC)m ediated bulk modified back-to back sensor for the electrocatalytic detectiono fhydrazine for the first time.Abstract:I no ur previous paper (Analyst, 2014, 139, 5339) we introduced the concept of the back-to-back electrochemical design where the commonly overlooked back of screen-printed electrodesa re utilised to provide electroanalyticale nhancements in screen-printede lectroanalytical sensors.I nt his configuration the overall sensor comprises of af lexible polyester substrate which has at otal of two working,c ounter and reference electrodes presento nt he sensor,w ith as et of electrodes on each side of the substrate. Thes ensors are designed to allow for acommonly shared electrical connection to the potentiostat and do not require any specialised con...
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