Colorimetric detection of Ni2+ based on an anionic triphenylmethane dye and a cationic polyelectrolyte in aqueous solution

A Novel Polymer Inclusion Membrane-Based Green Optical Sensor for Selective Determination of Iron: Design, Characterization, and Analytical Applications

The design, characterization, and analytical application of a green optical sensor for the selective determination of Fe(II) ions is proposed. The sensor is based on the immobilization of the chromogenic reagent picolinaldehyde salicyloylhydrazone (SHPA) within a polymer inclusion membrane. To reduce solvent usage, the reagent was synthesized using a green mechanochemical procedure. The components for sensor preparation were optimized with a sequential simplex method and the optimal composition was found to be 0.59 g cellulose triacetate (base polymer), 0.04 g SHPA (chemosensor reagent), 4.9 mL dibutyl phthalate (plasticizer), and 38 mL dichloromethane (solvent). The conditions of iron analysis were also optimized resulting in pH 6 for aqueous solution, 90 min exposure time and 10 min short-term stability. The optical sensor showed a linear range from the limit of detection (0.48 µmol L-1) to 54 µmol L-1 Fe(II). The precision of the method was found to be 1.44% and 1.19% for 17.9 and 45 µmol L-1 Fe(II), respectively. The characteristics of the sensor allowed the design of a Fe(II)/Fe(III) speciation scheme. The methodology was successfully applied to the determination of iron in food preservatives, food additives, and dietary supplement. Additionally, the Fe speciation scheme was successfully applied to an agricultural fertilizer.

Colorimetric Probe for Mn2+ Using a Mixture of an Anionic Dye and a Cationic Polyelectrolyte in an Aqueous Solution

A novel colorimetric probe for Mn²⁺ was easily prepared by mixing negatively charged alizarin complexone (ALC) with positively charged poly[bis(2-chloroethyl)ether-alt-1,3-bis[3-(dimethylamino)propyl]urea] (PQ-2) in aqueous solutions at pH 6.0. Upon adding Mn²⁺ to ALC alone, the solution underwent no distinct color change, while the mixture displayed selective detection of Mn²⁺ over different physiological and environmentally significant metal ions by an efficient naked-eye color change from red to purple. The detection of Mn²⁺ by the mixture was achieved from the electrostatic interactions between ALC and PQ-2. The quantitative determination of Mn²⁺ was obtained by spectrophotometric measurement and naked-eye observation. This sensing strategy can be an attractive approach for the development of new colorimetric probes due to the advantages such as no organic synthesis, facile fabrication, and simple visual detection.

Application of electrocolorimetric extraction for the determination of Ni(II) ions in chocolate samples: A green methodology for food analysis

This study developed an electrocolorimetric extraction technique as a simple, rapid, and green method for the simultaneous preconcentration and determination of Ni(II) in chocolate samples. The system was designed using an agarose gel (3% w/v) solution containing 10% v/v 80 mM dimethylglyoxime (DMG) and 10% v/v 0.03 M ammonia as colorimetric reagents to determine Ni(II) ions. When voltage was applied to the system, Ni(II) ions were extracted from the donor solution into the gel and formed Ni-DMG complexes with a pink color. Under the optimal conditions, a good linear range was obtained from 30 to 750 µg L^-1 (R² > 0.998) with a detection limit of 1 µg L^-1. Inter- and intra-assay results showing relative standard deviations were less than 2.6% and 1.9%, respectively. Our developed method was applied to determine Ni(II) in chocolate samples. The results were in agreement with those obtained using ICP-OES.

Chalcone-Based Colorimetric Chemosensor for Detecting Ni2+

The first chalcone-based colorimetric chemosensor DPP (sodium (E)-2,4-dichloro-6-(3-oxo-3-(pyridine-2-yl)prop-1-en-1-yl)phenolate) was synthesized for detecting Ni2+ in near-perfect water. The synthesis of DPP was validated by using 1H, 13C NMR and ESI-MS. DPP selectively sensed Ni2+ through the color variation from yellow to purple. Detection limit of DPP for Ni2+ was calculated to be 0.36 μM (3σ/slope), which is below the standard (1.2 μM) set by the United States Environmental Protection Agency (EPA).The binding ratio of DPP to Ni2+ was determined as a 1:1 by using a Job plot and ESI-mass. The association constant of DPP and Ni2+ was calculated as 1.06 × 104 M−1 by the non-linear fitting analysis. In real samples, the sensing application of DPP for Ni2+ was successfully performed. DPP-coated paper-supported strips could also be used for detecting Ni2+. The binding mechanism of DPP to Ni2+ was proposed by ESI-MS, Job plot, UV-vis, FT-IR spectroscopy, and DFT calculations.

A novel rhodamine-based Hg2+ sensor with a simple structure and fine performance

An excellent spectral sensor for Hg2+ named 2-(2-((2-aminoethyl)thio)ethyl)-3',6'-bis(diethylamino)spiro[isoindoline-1,9'-xanthen]-3-one (RMTE) was achieved by a one-step reaction between rhodamine B and thiobisethylamine. RMTE could detect Hg2+ in nearly pure water reversibly and highly selectively, indicated by a new increasing absorption peak at 561 nm and 170-fold enhanced fluorescence at 578 nm coupled with remarkable visual and fluorescence color changes. When the Hg2+ concentration ([Hg2+]) varied from 0 to 120 μM, the absorbance and fluorescence intensity of the RMTE solution responded linearly to [Hg2+] with the detection limits of 2.08 and 0.14 μM, respectively. RMTE could work in ecologically and biologically favorable pH values of 6.41-8.33. The binding mode of RMTE toward Hg2+ was 1 : 1. RMTE could monitor Hg2+ in environmental water and living cells effectively with low cytotoxicity.