Agustín G. Crevillén

Microchips for CE: Breakthroughs in real-world food analysis

The well‐known complexity of food matrices is approached using CE microchips with different strategies to improve the selectivity and sensitivity of the analysis by avoiding and/or making the sample preparation as simple as possible: (i) enhancing the peak capacity in order to perform direct injection, (ii) using the microchip platform to measure one target analyte/group of analytes with or without separating other related interferences, (iii) integrating sample preparation steps on the microchip platform, and (iv) integrating new analytical tools from nanotechnology in the detection stage. New analyte separations of food significance involving DNA probes, biogenic amines, vanilla flavors, and dyes have been reported as successfully breaking new barriers in areas of high impact in the market, such as transgenic food analysis, as well as the detection of frauds and toxins. Simple microchip layouts are still the most common designs used, though sophisticated new ones are emerging. In contrast to other application areas, electrochemical detection continues to be the most common detection route, followed by LIF, though non‐conventional detection routes are also emerging, such as chemiluminescence or UV. In terms of analytical performance, the integration of calibration and quality control on a microchip platform, and remarkable accuracy and precision are being obtained using creative analytical methodologies that enhance the analytical potency of microfluidic chips for their future commercialization. This review critically states the most important advances derived from work done in the field over the past 2–3 years.

Carbon nanotube disposable detectors in microchip capillary electrophoresis for water-soluble vitamin determination : Analytical possibilities in pharmaceutical quality control

In this work, the synergy of one mature example from “lab‐on‐chip” domain, such as CE microchips with emerging miniaturized carbon nanotube detectors in analytical science, is presented. Two different carbon electrodes (glassy carbon electrode (GCE) 3 mm diameter, and screen‐printed electrode (SPE) 0.3 mm×2.5 mm) were modified with multiwalled carbon nanotubes (MWCNTs) and their electrochemical behavior was evaluated as detectors in CE microchip using water‐soluble vitamins (pyridoxine, ascorbic acid, and folic acid) in pharmaceutical preparations as representative examples. The SPE modified with MWCNT was the best electrode for the vitamin analysis in terms of analytical performance. In addition, accurate determination of the three vitamins in four different pharmaceuticals was obtained (systematic error less than 9%) in only 400 s using a protocol that combined the sample analysis and the methodological calibration.

Electrochemical valveless flow microsystems for ultra fast and accurate analysis of total isoflavones with integrated calibration

A novel strategy integrating methodological calibration and analysis on board on a planar first-generation microfluidics system for the determination of total isoflavones in soy samples is proposed. The analytical strategy is conceptually proposed and successfully demonstrated on the basis of (i) the microchip design (with the possibility to use both reservoirs), (ii) the analytical characteristics of the developed method (statically zero intercept and excellent robustness between calibration slopes, RSDs < 5%), (iii) the irreversible electrochemical behaviour of isoflavone oxidation (no significant electrode fouling effect was observed between calibration and analysis runs) and (iv) the inherent versatility of the electrochemical end-channel configurations (possibility of use different pumping and detection media). Repeatability obtained in both standard (calibration) and real soy samples (analysis) with values of RSD less than 1% for the migration times indicated the stability of electroosmotic flow (EOF) during both integrated operations. The accuracy (an error of less than 6%) is demonstrated for the first time in these microsystems using a documented secondary standard from the Drug Master File (SW/1211/03) as reference material. Ultra fast calibration and analysis of total isoflavones in soy samples was integrated successfully employing 60 s each; enhancing notably the analytical performance of these microdevices with an important decrease in overall analysis times (less than 120 s) and with an increase in accuracy by a factor of 3.