Batch injection analysis in tandem with electrochemical detection: the recent trends and an overview of the latest applications (2015–2020)

Determination of indium by adsorptive stripping voltammetry at the bismuth film electrode using combined electrode system facilitating medium exchange

A novel method of determining indium has been described in this article which uses adsorptive stripping voltammetry (AdSV) and 4-(2-pyridylazo)-resorcinol (PAR) as a chelating agent or as the preconcentration agent. The measurements were performed using square-wave voltammetry by using a combined electrode system, which allows for preconcentration and stripping without opening the circuit. Ex situ plated bismuth film electrode (BiFE) was used as the working electrode. A potential-time program was developed for the inversion cycle stages based on the various factors that affect the magnitude of the inversion signal. The calibration curve was linear in a concentration range of 2·10-7 to 4·10-6 М when the pH is 4.8, accumulation potential is -700 mV, and PAR concentration is 1·10-4 M. The detection limit for the 3σ criterion with an accumulation time of 120 s was 3.5·10-9 М. Several interferences caused by Tl(I), Zn(II), Cu(II), Pb(II), Co(II), Ni(II), Mn(II), Fe(III), Cr(III) ions have been studied, and it has been shown that medium exchange procedure can effectively eliminate some interferences. It was demonstrated that the method can be applied to the determination of indium in tap water and in ITO glass sample.

Improving the performance and versatility of microfluidic thread electroanalytical devices by automated injection with electronic pipettes: a new and powerful 3D-printed analytical platform

Microfluidic cotton thread-based electroanalytical devices (μTEDs) are analytical systems with attractive features such as spontaneous passive flow, low cost, minimal waste production, and good sensitivity. Currently, sample injection in µTEDs is performed by hand using manual micropipettes, which have drawbacks such as inconstant speed and position, dependence of skilled analysts, and need of physical effort of operator during prolonged times, leading to poor reproducibility and risk of strain injury. As an alternative to these inconveniences, we propose, for the first time, the use of electronic micropipettes to carry out automated injections in µTEDs. This new approach avoids all disadvantages of manual injections, while also improving the performance, experience, and versatility of µTEDs. The platform developed here is composed by three 3D-printed electrodes (detector) attached to a 3D-printed platform containing an adjustable holder that keeps the electronic pipette in the same x/y/z position. As a proof-of-concept, both injection modes (manual and electronic) were compared using three model analytes (nitrite, paracetamol, and 5-hydroxytryptophan) on µTED with amperometric detection. As result, improved analytical performance (limits of detection between 2.5- and 5-fold lower) was obtained when using electronic injections, as well as better repeatability/reproducibility and higher analytical frequencies. In addition, the determination of paracetamol in urine samples suggested better precision and accuracy for automated injection. Thus, electronic injection is a great advance and changes the state-of-art of µTEDs, mainly considering the use of more modern and versatile electronic pipettes (wider range of pre-programmed modes), which can lead to the development of even more automated systems.

Exploring the coating of 3D-printed insulating substrates with conductive composites: a simple, cheap and versatile strategy to prepare customized high-performance electrochemical sensors

The development of 3D-printed electrochemical sensors by fused deposition modeling (FDM) has been increasing exponentially in the last five years. In this context, commercial conductive filaments composed of a blend of carbon particles (e.g., graphene or carbon black (CB)) and insulating thermoplastic polymers (e.g., polylactic acid (PLA) or acrylonitrile butadiene styrene (ABS)) have been widely used for electrode fabrication. However, such materials may be expensive and the electrodes when used "as-printed" exhibit poor electrochemical performance as a function of the low content of conductive particles in the composition (∼10 to 20 wt%), which requires one or more post-treatment steps (e.g. polishing, chemical, electrochemical, and photochemical) to reach good electrochemical performance. In this technical note a less used approach to produce "ready-to-use" electrochemical platforms based on 3D printing is explored, which consists of the coating of 3D-printed insulating substrates with homemade conductive composites. To demonstrate the potentiality of this alternative protocol, 3D-printed ABS insulating substrates at two geometries were coated in a highly loaded graphite (55 wt%) homemade composite (G-ABS) and evaluated for the detection of the ferri/ferrocyanide redox probe and model analytes in stationary and hydrodynamic 3D-printed systems (nitrite in micro-flow injection analysis/μFIA and paracetamol in batch injection analysis/BIA, respectively). The analytical parameters acquired with the coated electrodes were comparable to those obtained using conventional electrodes (glassy carbon, boron-doped diamond and carbon screen-printed) and 3D-printed sensors fabricated with commercial filaments. Moreover, the inclusion of carbon black in the fluid conductive composite was demonstrated as a perspective to obtain modified coated 3D-printed surfaces easily for the first time. This alternative "do it yourself" strategy is promising for the large-scale production of very cheap (US$ 0.08) and high-performance electrodes based on FDM 3D printing. Moreover, this approach dispenses the acquisition of commercial conductive filaments and the laborious development of homemade filaments.