6,7- AND 7,8-DIHYDROXYBENZOPYRYLIUM DERIVATIVES: SYNTHESIS, PROPERTIES AND ANALYTICAL APPLICATION (REVIEW)

The present review is devoted to a class of organic analytical reagents 6,7- and 7,8-dihydroxybenzopyrylium derivatives: their synthetic pathways, physicochemical properties, state in solutions, and analytical applications are described. Anion nature influence on spectral characteristics and some physico-chemical properties of 6,7-dihydroxybenzopyrylium derivatives was noted. Pathways of acid-base transformations in aqueous solutions of 6,7-dihydroxybenzopyrylium derivatives were described. It has been shown that derivatives of 6,7- and 7,8-dihydroxybenzopyrylium are capable for complexation with a number of p-, d-, and f-elements (Cu (II), Ga (III), In (III), Tl (III), Ge (IV), La (III), titanium subgroup, Bi (III), Mo (VI), W(VI) and others). Information on their composition, structure and analytical characteristics is summarized. It is noted that with the 6,7-dihydroxybenzopyrylium derivatives the simple and highly sensitive methods for the direct spectrophotometric and extraction-photometric determination of Ga(III), In(III), Tl(III), Ti(IV), Zr(IV), Hf(IV), Mo(VI), Ge(IV), Bi(III), Cu(II) have been developed. It is noted that 6,7-dihydroxybenzopyrilium derivatives complexes with Mo(VI) and Cu(II) are effectively extracted by Triton X‑100 micellar phase, which forms the basis for highly sensitive combined spectrophotometric and atomic absorption methods for their determination. The simplicity of targeted synthesis of 7,8- and 6,7-dihydroxybenzopyrylium derivatives opens the way to their use in the development of combined cloud point extraction and liquid-liquid microextraction with spectrophotometric or atomic absorption detection methods for the determination of a number of p- and d-elements.

Optical pH Sensing in Milk: A Small Puzzle of Indicator Concentrations and the Best Detection Method

Optical chemical sensors can yield distinctively different responses that are dependent on the method applied for readout and evaluation. We therefore present a comprehensive study on the pH determined non-continuously with optical sensors in real milk samples by either photometry or colorimetry (via the RGB-readout of digital images) compared to the pH values obtained electrochemically by potentiometry. Additionally, the photometric determination of pH was conducted with single-wavelength and a dual wavelength ratiometric evaluation of the absorbance. It was found that both the precision and accuracy of the pH determined by photometry benefit from lower concentrations of bromocresol purple, which served as the pH indicator inside the sensor membrane. A further improvement is obtained by the ratiometric evaluation of the photometric sensor response. The pH values obtained from the colorimetric evaluation, however, gain in precision and accuracy if a higher concentration of the indicator is immobilized inside the sensor membrane. This has a major impact on the future fabrication of optical pH sensor membranes because they can be better tuned to match to the most precise and accurate range of the planned detection method.

Anion exchange extraction of tallium (III) and mercury (II) complex salts and application of the procedure to extraction-photometric determination of the microquantities of mercury (II)

The goal is to study the anion-exchange extraction of complex thallium (III) and mercury (II) halides (chlorides, bromides, iodides) by a method of a competing intermediate ion using the anions of various dyes — methyl orange, sodium picrate, 2,4-dinitrophenol, methyl red. Mercury (II) and thallium (III) are poisons of high toxicity. The developed method was used to study the anion-exchange extraction of acidocomplexes A solution of methyl orange trinonyloctadecylammonium (TNODA) in toluene was used as an extractant. The method provides determination of mercury (II) with an accuracy of ±2% when the concentration in the initial solution ranges within 2 – 8 × 10–8 mol/liter. It is shown that the values of the exchange constants for the same metal are larger for iodide complexes than for bromide and chloride ones. The extractability of metal halide complexes is mainly determined by their mass. Anions with a large mass have a large surface area, a low charge density, and are weakly hydrated, and thus are better extracted. The results of anion-exchange extraction were used to develop a procedure for the extraction-photometric determination of mercury (II) in granosan (ethylmercury chloride a prohibited insectofungicide of the 1st hazard class) the illegal use and storage of which could be a source of mercury pollution of groundwater in a number of regions of the Republic of Belarus. The relative error of determination does not exceed ±2%.

An Environmentally Friendly Flow Injection-Gas Diffusion System Using Roselle (Hibiscus sabdariffa L.) Extract as Natural Reagent for the Photometric Determination of Sulfite in Wines

In this work, a green and simpler method for photometric determination of sulfite based on a flow injection-gas diffusion (FI-GD) system using a natural reagent extracted from roselle (Hibiscus sabdariffa L.) was proposed. Despite the fact that the employed reaction is not selective to sulfite, its sensitivity is high, and the selectivity can be improved by coupling a GD unit to the FI system. The method involves monitoring a decrease in absorbance of the reagent solution that is used as an acceptor solution. When a standard solution or sample solution was injected into an acidic donor stream, the liberated sulfur dioxide diffuses through a gas-permeable membrane of the GD unit into the acceptor solution, causing color fading of the reagent. A linear analytical curve in the range of 5–100 mg L−1 was obtained with a detection limit of 2 mg·L−1. Relative standard deviations of 0.9%, 0.6%, and 0.6% were obtained for the determination of 30, 70, and 100 mg·L−1 SO32- (n = 11). The developed method was applied to wine samples, giving results that agreed with those obtained with the Ripper titrimetric method. The proposed method offers advantages of simplicity, cost-effectiveness, and being environmentally friendly such as reduced chemical consumption and less waste generation.

DISTRIBUTION OF THORIUM (IV) IONS IN AQUEOUS EXFOLIATING SYSTEM CONTAINING ANTIPYRINE AND SULFOSALICYLIC ACID

The possibilities of an aqueous delaminating system containing antipyrine (AP) and sulfosalicylic acid (SSA) for extracting macro - and microamounts of thorium (IV) were studied. The proposed extraction system eliminates the use of toxic organic solvents. The dependences of the distribution of metal from nitrate solutions between phases on the concentration of reagents, acidity of the medium, the amount of inorganic salting-out agent (NaNO3, NH4NO3, Na2SO4) and the volume of the aqueous phase are determined, and optimal conditions for extraction are found. It is shown that in the organic phase with a volume of 1.6 ml at room temperature, macro-and microamounts of thorium (IV) are extracted by 88 and 90%, respectively. The maximum extraction of the cation is achieved at the ratio of AP: SSA = 2.0 : 1.0 and their concentration, mol/l: 0.6: 0.3, while the acidity of the medium created by nitric acid should be equal to 0.015 mol/l (pHequ. = 1.8-1.9). The extraction of thorium (IV) becomes quantitative if inorganic salts (sodium sulfate, sodium nitrate) are introduced into the AP – SSA – 0,015 mol/l HNO3 – H2O system, which, by reducing the activity of water, increase the concentration of reagents in the aqueous phase. The concentration of salting-out agents should correspond to 1.0 and 2.5 mol/l. A mechanism for the distribution of a mixed thorium (IV) complex containing AP, SSA, nitrate ions, solvated with a salt of antipyrinium sulfosalicylate is proposed. The extract is mixed in any relationship with distilled water, providing the use of various instrumental methods of analysis. A method for extraction-photometric determination of thorium (IV) with a toron indicator has been developed. The limit for the fulfillment of the Bouguer-Lambert-Beer law is established. The apparent coefficient of light absorption is calculated (ε = 1.7∙104).