Smartphone-based simultaneous pH and nitrite colorimetric determination for paper microfluidic devices

In this work, an Android application for measurement of nitrite concentration and pH determination in combination with a low-cost paper-based microfluidic device is presented. The application uses seven sensing areas, containing the corresponding immobilized reagents, to produce selective color changes when a sample solution is placed in the sampling area. Under controlled conditions of light, using the flash of the smartphone as a light source, the image captured with the built-in camera is processed using a customized algorithm for multidetection of the colored sensing areas. The developed imageprocessing allows reducing the influence of the light source and the positioning of the microfluidic device in the picture. Then, the H (hue) and S (saturation) coordinates of the HSV color space are extracted and related to pH and nitrite concentration, respectively. A complete characterization of the sensing elements has been carried out as well as a full description of the image analysis for detection. The results show good use of a mobile phone as an analytical instrument. For the pH, the resolution obtained is 0.04 units of pH, 0.09 of accuracy, and a mean squared error of 0.167. With regard to nitrite, 0.51% at 4.0 mg L−1 of resolution and 0.52 mg L−1 as the limit of detection was achieved

Chitosan-modified cotton thread for the preconcentration and colorimetric trace determination of Co(II)

In this work we propose a thread-based microfluidic device (μTAD) for the preconcentration and colorimetric determination of Co(II) in water using a digital image. The reaction is based on complexation of Co(II) by 4-(2- pyridylazo) resorcinol (PAR), which changes the detection zone from yellow to red. PAR is immobilized in a chitosan membrane to retain the complex in the detection zone. The designed μTAD makes it possible to pre- concentrate and determine cobalt between 25 and 600 µg·L−1 with a relative standard deviation of 4% (n = 5), and a detection limit of 6.5 µg·L−1. The device permits an enhancement factor of 11 by combining the use of a chitosan retention membrane and a sample volume of 50 µL. Recovery experiments were performed in tap water to evaluate the accuracy of the method, and the results obtained compared to a reference method presents an error no higher than 5.7%This work was founded by Spanish “Ministerio de Economía y Competitividad” under Project CTQ2016-78754-C2-1-R and Junta de Andalucía under Projects B-FQM-243-UGR18 and P18-RT-2961. The project was partially supported by European Regional Development Funds (ERDF). Supporting Research in the State of Minas Gerais (Fapemig) (CEX-APQ-02436-15)

Colorimetric detection, quantification and extraction of Fe(III) in water by acrylic polymers with pendant Kojic acid motifs

We synthesized a solid sensory material for the extraction, detection and quantification of iron(III) in aqueous media. The material is a film-shaped colorless polymer membrane that exhibits gel behavior. The Fe(III) extraction and sensing characteristics are imparted by a new monomer derived from a natural product (i.e., Kojic acid), which exhibits chelating properties toward Fe(III). The sorption of Fe(III) on the membrane in water has been thoroughly characterized, including the sorption kinetics, sorption isotherms and profiles as a function of the pH. Fe(III) sorption followed pseudo first-order kinetics and required approximately 30 min to reach equilibrium. The maximum sorption capacity was approximately 0.04 mmol/g, and the sorption isotherms are well modeled by the Langmuir equation. The complexes that were found in the solid phase are in good agreement with those previously identified in the aqueous phase. Moreover, the sorption is highly specific (i.e., a recognition process) and results from the formation of a colored complex (iron(III)-Kojic acid derivative moieties). Therefore, the colorless sensory membrane turns red upon immersion in aqueous solutions containing Fe(III). The color output allows for both the qualitative visual determination of the Fe(III) concentration as well as also titration of Fe(III) using a) a UV/vis technique (limit of detection of 3.6 × 10−5 M; dynamic range of five decades, lower concentration = 1.65 × 10−6 M) and b) a computer vision-based analytical chemistry approach via color definition of the sensory membrane (RGB parameters) obtained from an image recorded with a handy device (e.g., a smartphone) (limit of detection of 2.0 × 10−5 M).Spanish Ministerio de Economía y Competitividad-Feder(MAT2014-54137-R) and by the Consejería de Educación—Junta deCastilla y León (BU232U13)

Coupling Sensing and Imaging Devices: Towards a Complete Handheld Analytical System

The development of new outside-the-lab analytical methodologies and technologies to gather in situ and real time chemical information using low cost and compact devices is one of the most challenging issues facing the analytical sciences. [...