Simultaneous separation and electroanalysis in a single polydimethylsiloxane-based platform.

Channel-based microfluidic devices integrating the separation step and detection system are key factors to expand microanalysis application. However, these devices still depend on macroscale external equipment for pre-treatment of the sample, separation, or detection. The integration of all steps in only one stage is critical to improving feasibility. Herein, we use a low-cost protocol to solve part of the challenge by designing a dual-mode system onto single polydimethylsiloxane (PDMS)-based platform - overall dimensions of 65 mm length × 20 mm width × 14 mm height and the inner diameter of 297±10 µm height × 605±19 µm width - for column-free separation and simultaneous detection. As a proof-of-concept, we used this all-in-one PDMS platform to separate - without the packet-based phase - and determine salicylic acid (SA) and caffeine (CAF) with a detection limit of 0.20 and 0.18 µmol L-1 and quantification limit of 0.70 and 0.60 µmol L-1 for SA and CAF, respectively. We separated the mixture using forced convection into a chemically treated microchannel while detecting the analytes in amperometric mode. Here, we report new insights into how integrating analytes separation and further electroanalysis into a single miniaturized device.

Direct electrochemical detection of glyphosate at carbon paste electrode and its determination in samples of milk, orange juice, and agricultural formulation.

This paper describes a simple, inexpensive, highly sensitive, selective, and efficient electrochemical method to determine glyphosate (GLY) in samples of milk, orange juice, and agricultural formulation. The oxidation reaction on the electrode surface was electrochemically characterised by cyclic voltammetry (CV) and square wave voltammetry (SWV). The investigation of GLY at carbon paste electrode revealed a non-reversible oxidation peak at +0.95 V versus Ag/AgCl, which was used for electrochemical detection of GLY. The operating parameters (pH, frequency, step potential, and amplitude) were optimised in relation to the peak current intensity, and a calibration curve was set up in a concentration range of 4.40 × 10-8-2.80 × 10-6 mol L-1, with a detection limit of 2 × 10-9 mol L-1. After calibration curve was plotted, the developed procedure was applied to determine GLY in previously contaminated samples: milk and orange juice, and in a commercial formulation, obtaining recovery values between 98.31% and 103.75%. These results show that the proposed method can be used for GLY quantification in different samples with high sensitivity, specificity, stability, and reproducibility.