Vol 74, No 9 (2019)

The state-of-the-art of metrological support of chemical analysis is considered. The specificity of this field of metrology is discussed, that is, the absence of a primary material standard of the fundamental physical quantity, mole, and the dependence of the results of measurements on the chemical composition of a sample. Advances in the development of the metrology of chemical analysis are noted. The focus of the review is on the problems that remain unresolved or incompletely resolved. These are the metrology of sampling, the control of the accuracy of analysis, the assurance of metrological traceability, the nomenclature of the existing standard samples of composition, and the estimation of the budget of uncertainty. Particular emphasis is placed on metrology regarding new types of chemical analysis, for example, surface analysis, local analysis, and analysis of nanodimensional samples. The priority of improving the metrology of electron-probe analysis, Auger electron spectroscopy, electron spectroscopy for chemical analysis, and secondary-ion mass spectrometry is noted. A conclusion is made about the need in intensifying research for decreasing the number of unsolved problems cardinally.

A procedure for the determination of AICAR (5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside, Acadesine), an AMP-activated protein kinase agonist prohibited by the World Anti-Doping Agency since 2009, in urine has been proposed including sample clean-up from matrix components by means of solid-phase extraction and detection of the analyte by ultra-high performance liquid chromatography–tandem mass-spectrometry with heated electrospray ionization ion source. Due to the endogenous nature of AICAR, standard additions approach was applied to quantify AICAR and evaluate matrix effects. The limit of detection was 5 ng/mL, calibration curves were linear in the concentration range of 50–5000 ng/mL. The proposed procedure was applied to the analysis of real samples.

The efficiencies of various carbon sorbents in the preconcentration of volatile organic substances from a stream of humid air for their subsequent gas-chromatographic determination are compared. A hybrid procedure for rapid analysis including the sorption preconcentration of analytes on a selected carbon–fluoroplastic composite sorbent and their one-stage thermal desorption in the injector of a chromatograph with a capillary column and a flame-ionization detector is proposed. This procedure makes it possible to determine lower alcohols and ketones in air saturated with water vapor for 5–10 min with determination limits at a level of several μg/m³.

We analyzed the products of alkylphenol (ortho-, meta-, and para-cresols and 4-isopropylphenol) oxidation by iron(III) chloride in aqueous solutions by HPLC with electrospray ionization and mass-spectrometric detection in the negative ion mode. It was found that the main products formed by the nucleophilic addition of the initial alkylphenols to reactive intermediates, quinone methides. The resulting adducts can be further oxidized, which, after several oxidation–addition cycles, leads to the appearance of a series of compounds with molecular weights belonging to sequences of values of 108, 214, 320, 426, 536, 638, … for cresols and 136, 270, 404, 538, 672, … for 4-isopropylphenol. Such processes are similar to the oxidation of alkylphenols by air oxygen in aqueous solutions and to their electrochemical oxidation yielding dimeric and oligomeric products.

A sensitive method for semicarbazide determination was developed by differential pulse voltammetry. Comparing to traditional methods, such as HPLC‒mass spectrometry and HPLC–fluorescence detection, it provides several advantages including using low consumption of organic solvents and low cost of analysis. Accordingly, 2-nitrobenzaldehyde was used as an active reagent to react with semicarbazide. The reaction product, 2-nitrobenzaldehyde semicarbazone (2-NSEM), was quantified by differential pulse voltammetry. A linear relationship was obtained between the peak current and 2-NSEM concentration in the range from 0 to 100 μg/L (R² = 0.999). The limit of detection (LOD) was calculated to be 3 μg/kg (signal to noise ratio of 3), which is lower than LOD obtained by direct differential pulse voltammetry determination of semicarbazide. The developed method was successfully applied to determine semicarbazide in flour samples with satisfactory recoveries from 92 to 99% (relative standard deviation < 4.3%, n = 6) indicating this method to be potential and valuable for semicarbazide detection.

A colorimetric biosensor for glucose detection has been studied based on chitosan cryogel supporting material for enzyme immobilization. The detection was based on the glucose conversion to hydrogen peroxide by glucose oxidase, then a titanium(IV) oxysulfate was used to measure hydrogen peroxide, indicated by the formation of yellow color. The color change with the concentration was then recorded by a commercial scanner and analyzed using an ImageJ software. The fabricated biosensor allows to easily prepare by in-tips enzyme immobilization with user-friendly operating using micropipette by the suck-hold-release method for the determination of glucose. Enzyme immobilization has been optimized including the amount of enzyme and the reaction time. The biosensor showed a high operational stability for up to 56 measurements using a single immobilized enzyme, with a wide linear range (0.3 to 3.0 mM glucose), high specificity, and also agreed with the standard method used in hospitals to detect blood glucose (the Wilcoxon signed-rank test, P > 0.05).

The composition and properties of heparin preparations are studied by NMR spectrometry. Approaches to the determination of the most important heparin quality indicators (biological origin and manufacturing company) based on multivariate modeling of the NMR profile of a sample are considered. Chemometric modeling of two-dimensional (2D) NMR spectra (DOSY, HSQC, HMBC) by the principal component and discriminant analysis is performed to increase the efficiency of analysis. Multivariate regression models (partial least squares) are built for the first time to determine the average molecular weight of heparin. Quantitative NMR spectrometry is applied to the determination of water, calcium and sodium cations, and also chloride and acetate anions in heparin preparations. The determination of all characteristics requires five consecutive measurements by NMR (¹H, ²D, ³⁵Cl, ²³Na, and 2D DOSY) spectrometry and one sample preparation. The duration of analysis of one sample, including measurements and signal processing, takes no more than 20 min. The proposed approach is universal and can be used in the analysis of other medicinal preparations.