A Three-Reagent "Green" Paper-Based Analytical Device for Solid-Phase Spectrometric and Colorimetric Determination of Dihydroquercetin.

Microfluidic paper-based analytical devices (µPADs) represent one of the promising green analytical strategies for low-cost and simple determination of various analytes. The actual task is the development of such devices for quantitation of antioxidants, e.g., flavonoids. In this paper, possibilities of a novel three-reagent µPAD including silver nitrate, 4-nitrophenyldiazonium tetrafluoroborate, and iron(III) chloride as reagents are assessed with respect to the determination of dihydroquercetin. It is shown that all the three reagents produce different colorimetric responses that can be detected by a mini-spectrophotometer-monitor calibrator or by a smartphone. The method is applicable to direct measuring high contents of dihydroquercetin (the linearity range is 0.026-1 mg mL-1, and the limit of detection is 7.7 µg mL-1), which is favorable for many dietary supplements. The analysis of a food supplement was possible with the relative standard deviations of 9-26%, which is satisfactory for quantitative and semiquantitative determinations. It was found that plotting a calibration graph in 3D space of the three reagents' responses allows us to distinguish dihydroquercetin from its close structural analogue, quercetin.

Label-free silver triangular nanoplates for spectrophotometric determination of catecholamines and their metabolites.

A novel method towards spectrophotometric determination of catecholamines and their metabolites differing in their functional groups has been developed. This method is based on a change in morphology of silver triangular nanoplates upon the action of cateсholamines and their metabolites, which is manifested by the decrease of the nanoparticle local surface plasmon resonance (LSPR) band intensity or its shift to the short-wavelength region of the spectrum. The shift value of the LSPR band or the change of its intensity increases with increasing concentration of catecholamines or their metabolites, which is proposed for their spectrophotometric determination. The limits of detection of catecholamines and their metabolites under selected conditions increase in the series homovanillic acid < vanillylmandelic acid < L-epinephrine < L-norepinephrine < dopamine and are 0.25, 1.2, 3.0, 64, and 130 µmol L-1, respectively. The selectivity of the proposed method was assessed using vanillylmandelic acid as example. It was found that the determination of vanillylmandelic acid does is not interfered in the presence of 4000-fold excess of Na+, K+, CH3COO-, and 1000-fold excess of Mg2+, Ca2+, Al3+, NO3-. The method also allows for the selective determination of vanillylmandelic acid in the presence of a 1000-fold excess of structurally related substances that do not contain either a catechol fragment or an electron donor substituent. The proposed approach was successfully applied to the determination of catecholamines in pharmaceuticals and artificial urine. Graphical abstract.

An improved step-by-step airflow/paper-based colorimetric method for highly selective determination of halides in complex matrices.

An improved step-by-step colorimetric method for determination of halides has been developed. The method is based on successive selective oxidation of iodide, bromide and chloride into corresponding free halogens, their extraction by airflow and colorimetric detection with different paper test-strips. This procedure can be performed in a single analyzed solution and possesses high selectivity and good sensitivity due to the extraction step. Three types of paper test-strips were examined: paper modified with tetramethylammonium iodide and starch, paper modified with methyl orange and paper modified with silver triangular nanoplates. Limits of detection for iodide, bromide and chloride are 0.01, 0.02, and 0.04 mg L-1 respectively in case of the last mentioned paper. The method was applied to the analysis of samples having complex matrices, such as various seafood, preserves, bread, and natural waters, showing good accuracy of the analysis with recoveries of 95-105% and relative standard deviations not higher than 6%.

Dynamic gas extraction of iodine in combination with a silver triangular nanoplate-modified paper strip for colorimetric determination of iodine and of iodine-interacting compounds.

A method is described for sensitive and selective detection of iodine by using a paper strip modified with silver triangular nanoplates (AgTNPs). It is based on the extraction of iodine from a solution into a flow of air via dynamic gas extraction and transferring it through a reactive paper modified with AgTNPs. The interaction of AgTNPs with iodine results in a color change from blue to white. This can be visually detected and monitored by digital colorimetry. The dynamic gas extraction is highly selective for volatile compounds so that a sample pretreatment is minimal. Due to the sensitivity of AgTNPs for iodine, the limit of its detection is as low as 7 µg L-1, and the analytical range is of 20-200 µg L-1. The method also was applied in a new approach for determination of organic compounds that can interact with iodine. The organic compound is exposed to an excess of iodine, and this is followed by detection of residual iodine as described above. The method was applied to the determination of ascorbic acid, caffeine and the drug metamizole. Graphical abstract Schematic representation of a procedure of organic iodine-interacting compounds (Org.) determination. It is based on their iodination followed by gas extraction of the residual iodine, its interaction with silver triangular nanoplates and colorimetric detection with a scanner.

Towards highly selective detection using metal nanoparticles: A case of silver triangular nanoplates and chlorine.

The article describes a novel approach towards improving selectivity of volatile compounds detection using metal nanoparticles. It is based on combination of sensitive optical detection using convenient nanoparticle-modified paper test strips and dynamic gas extraction improving selectivity to volatile compounds. A simple and inexpensive setup allowing for realization of this combination is described. Analytical prospects of the approach are shown by the example of chlorine determination in highly salted aqueous solutions using silver triangular nanoplates and digital colorimetry. The limit of detection is equal to 0.03mgL-1 and the determination range is 0.1-2mgL-1. This determination can be successfully carried out in solutions containing at least 2·105 greater molar amounts of Na+, K+, Zn2+, Cl-, SO42-, and H2PO4- with no sample pretreatment. The approach seems to be compatible with different types of nanoparticles with respect to detection of various analytes, thus having good opportunities for further development.

Facile synthesis of magnetic hypercrosslinked polystyrene and its application in the magnetic solid-phase extraction of sulfonamides from water and milk samples before their HPLC determination.

In this study, a novel magnetic solid-phase extraction (MSPE) sorbent, magnetic hypercrosslinked polystyrene (HCP/Fe3O4), was prepared and used for preconcentration of four sulfonamides (sulfamethoxypyridazine, sulfamethazine, sulfamethoxazole and sulfachloropyridazine) from natural water and milk samples. This material was prepared by sorption of pre-synthesized Fe3O4 nanoparticles (NPs) onto HCP. A number of sorbents with varying Fe3O4NPs content were prepared, and their structural, magnetic and sorption properties were studied. Various experimental parameters affecting the extraction efficiencies such as the amount of the magnetic nanocomposite, extraction time, pH of the sample solution and desorption conditions were studied and optimized. Under the optimal conditions, a convenient and efficient method for the determination of sulfonamides in water and milk samples was developed by combining MSPE and high-performance liquid chromatography with amperometric detection. The results showed that the recoveries of these compounds were in the range of 84-105% with the relative standard deviations ranging between 3% and 10%; the limit of detection were in the range of 0.21-0.33 ng mL(-1) for water and 2.0-2.5 ng mL(-1) for milk.