Vol 74, No 2 (2019)

This study presents a simple, safe, cheap, and efficient cloud point extraction method for the simultaneous pre-concentration and determination of Allura Red (AR) and Carmoisine (CA) in food samples. Wavelet orthogonal signal correction was applied to denoise the spectrophotometric data and in combination with partial least squares regression was used to determine each compound simultaneously after cloud point extraction. The effects of different variables on the extraction of both dyes were investigated and optimized. Calibration graphs were linear in the range of 0.06 to 2.0 µg/mL for AR and 0.05 to 1.5 µg/mL for CA. Limits of detection for AR and CA were 0.016 and 0.015 µg/mL, respectively. The root mean square error of prediction for AR and CA was 0.014 and 0.024 µg/mL, respectively.

The conditions of the simultaneous preconcentration of Ti(IV), V(V), Mo(VI), and Ni(II) on a double-layer support and their sequential determination using organic reagents are studied by diffuse reflectance spectroscopy. Disks of polyacrylonitrile fiber filled with an anion exchanger (PANV–AV-17) or a cation exchanger (PANV–KU-2) are used as supports. The determination of titanium and nickel on PANV–KU-2 disks is based on the successive interaction of nickel with dimethylglyoxime (DMG) and titanium with 2,7-dichlorochromotropic acid (DCCA). The determination of vanadium and molybdenum on PANV–AV-17 disks is based on the interaction of vanadium with 8-hydroxyquinoline-5-sulfonic acid (HOS) and 0.1 M HCl and molybdenum with phenylfluorone (PF). The dependences of the analytical signals of Ti‒DCCA and Ni‒DMG complexes on PANV‒KU-2 and V‒HOS and Mo‒PF complexes on PANV‒AV-17 on the pH of solutions in sorption in the dynamic mode are studied. The optimal pH value of the solutions for the simultaneous sorption of four elements is 3.5 ± 0.1. The influence of accompanying elements in the mixture on the determination of Ti, V, Mo, and Ni is studied. Characteristics of the sorption-spectroscopic determination of elements are given, i.e., the sequence of the treatment of support disks with reagent solutions, the conditions for eliminating the signal of the previous element, the coefficients of calibration equations and the linearity ranges of the calibration curves, and the limits of detection of elements. Selectivity factors are determined and a procedure for the sorption-spectroscopic determination of Ti, V, Mo, and Ni on their simultaneous presence is developed. The results of analysis of model solutions with different ratios of elements are presented; RSD < 15%.

Using reversed-phase HPLC, we developed a procedure for the qualitative and quantitative analytical control of the production of N-octadecyl-1,3-diaminopropane from stearic acid by the nitrile method. The optimum composition of the eluent is determined, which ensures the control of each stage of the process. The calibration dependences for the mixtures initial reagent–reaction product are obtained, suggesting a quantitative estimation of the conversion. The possibility of determining the presence of synthesis by products is shown. The analysis time for each stage does not exceed 20 min.

A new ion-selective polyvinyl chloride membrane electrode based on Schiff base [N,N′-bis(1-hydroxynaphthalene-2-carbaldehyde)-o-phenylenediamine] as an ionophore is successfully worked out as sensor for Zn(II) ions. The electrode shows excellent potentiometric response characteristics and displays a linear emf versus log[Zn²⁺] response over a wide concentration range of 1.0 × 10^–7‒0.1 M with nernstian slope of 29.0 ± 0.1 mV/decade with the detection limit of 1.8 × 10^–8 M. The sensor exhibits the advantages of fast response time (<10 s). The lifetime of the sensor is about 3 months. It was used as an indicator electrode in the potentiometric titration of Zn(II) with EDTA and for the determination of Zn(II) in pharma samples. The results were validated by using quantum mechanical density functional theoretical calculations. Theoretical studies proved prominent affinity of ligand towards Zn(II) ion.

Organic sensor arrays based on photonic crystals of submicrometer polystyrene particles, coated by a layer of polydimethylsiloxane, were studied using diffuse reflectance spectroscopy. The spectral characteristics obtained on instruments with different measurement geometries are compared. The conditions for obtaining the most informative analytical signal of sensor arrays based on photonic crystals are selected. Under the proposed conditions, the kinetic differences in the operation of these arrays upon exposure to nonpolar organic solvents (toluene and o-xylene) are compared. The work was performed at the Division of Analytical Chemistry, Department of Chemistry, Moscow State University.

The review is dedicated to polymers of 2- and 3-aminophenylboronic acid. In contrast to the majority of other conducto- and impedimetric sensors, the ones developed by the authors can discriminate between specific and unspecific processes: conductivity as an analytical signal of the sensor is increasing upon specific binding being opposite to the result of an unspecific process. The increase of conductivity as a result of a specific process is demonstrated for the first time by our group, and the effect was confirmed by physicochemical investigations. The developed sensors are applicable to aerosol analysis as well as to aqueous media. Human whole sweat analysis performed by the sensors succeeded to determine the concentration of lactate (which is recognized as a hypoxia marker and the second important metabolite after in clinical diagnostics) in the range of 10−40 mM. The developed sensors are also applicable to reagentless mold detection in bioaerosols in the concentrations in the range 200−800 CFU/m³ that includes Russian hygienic standard for locality (500 CFU/m³).

The problem of determining the most toxic halogen- and sulfur-containing organic compounds at the trace level in different media by rapid screening based on the high-temperature oxidative conversion of a sample in combination with ion chromatography being solved at the Department of Analytical Chemistry of Moscow State University is considered. This approach ensures the rapid control of the total content of organic compounds containing F, Cl, Br, and S atoms in a molecule, regardless of the availability of data on their presence in the sample.

The atmospheric pressure photoionization and photochemical ionization mass spectrometry (APPI/APPCI−MS) makes it possible to compare the number of peaks in a mass spectrum with the number of components in the test mixture because of the measurements of the mass spectra of individual compounds, which mainly consist of the peaks of a molecular ion (M⁺) or a protonated molecule (MH⁺). The capabilities of gas chromatography–electron ionization (EI) and atmospheric pressure ionization mass spectrometry for the identification of trace components of complex mixtures are considered. The advantages of APPI/APPCI−MS, which makes it possible to increase the reliability of the detection of components in the complex mixtures of organic compounds, over EI mass spectrometry are shown. The work was performed at the Department of Analytical Chemistry, Faculty of Chemistry, Moscow State University.