Zhurnal Analiticheskoi Khimii

The review systematizes information on nanostructured materials used in solid-phase extraction (SPE) and its modern versions. The main attention is paid to the consideration of nanostructured analogues of MCM-41 and SBA-15 both in classical SPE and in modern versions of solid-phase microextraction, microextraction by matrix solid-phase dispersion, dispersive solid-phase extraction, and magnetic SPE. The use of silica with a hexagonal and cubic mesophase structure makes it possible to significantly increase the completeness of analyte extraction, improve the metrological characteristics of determining both metal ions and biologically active substances in complex multicomponent matrices of real objects of analysis. An abnormally high surface area (up to 1000 m²/g and more), adjustable mesopore size, ease of modification by grafting functional groups allow to significantly increase the selectivity of solid-phase materials compared to traditionally used silica gels and polymer ion exchangers. The advantages of ordered silica when used at the stage of extraction and concentration of analytes in solid-phase extraction options, as well as chromatographic separation of substances similar in nature, make it possible to expand the range of linearity of the analytical signal response of the analysis methods used, and the detection limits of ions and molecules can be reduced to the level of ng/mL, ng/g.

Ionic liquids based on quaternary ammonium cations – tetrahexylammonium dioctyl sulfosuccinates (THADOSS) and tetrabutylammonium are obtained in situ by mixing salts in an aqueous solution – suppliers of the cation and anion, constituting the ionic liquid, and studied for the extraction of heavy metal ions from aqueous solutions. Cd(II), Co(II), Cu(II), Ni(II), Pb(II), and Zn(II) ions are quantitatively extracted in the presence of 4-(2-pyridylazo)resorcinol (1 × 10^–3 M) into the in situ formed THADOSS at pH 4.9 in 1 min. The possibility of determining metals by microwave plasma atomic emission spectrometry after extraction into ionic liquids is demonstrated; the detection limits are from 2 to 25 μg/L.

It is shown that the interaction of dopamine with fluorescamine can be used as a basis for the luminescent determination of dopamine using a camera, since the product formed as a result of this interaction is characterized by a luminescence maximum in the visible region (485 nm), and a light-emitting diode emitting light in the near ultraviolet region (395 nm) is sufficient to excite the luminescence. The reaction should be carried out at pH 8–8.5 in a phosphate buffer solution for 5 min; fluorescamine should be added to the reaction mixture last. Some analytical characteristics of the determination using a camera are assessed and compared with the characteristics of a similar determination of dopamine using a professional spectrofluorometer and spectrophotometer. The detection limits of dopamine using a camera, spectrophotometer and spectrofluorometer were 1.8, 1.6 and 0.5 μM, the range of determined contents was 5.4–50 μM, 4.8–100 μM, 1.5–100 μM, respectively. The presence of common inorganic ions, the content of which is 10 times higher than the content of dopamine, does not interfere with the determination. The proposed method for determining dopamine can be used for quality control of drugs.

A procedure for separating the microcomponent of gallium from the macrocomponents of Cr, Mo, W, Ni and Co is proposed for determining gallium by inductively coupled plasma atomic emission spectrometry in nickel- and iron-based alloys (precision nickel alloys, alloyed and high-alloy steel). Sodium fluoride was used as a precipitant. Optimum conditions for gallium coprecipitation on the sediment during separation from the considered macrocomponents were determined. The detection limit of gallium during separation from macroquantities of Cr, Mo, W, Ni, Co was 5 × 10^–4 wt. %.

The chromatographic retention of neutral polar compounds (alcohols, ketones, carboxylic acids, carbohydrates, and sweeteners) and compounds in ionized form (mono- and dibasic organic acids) on cation exchange columns filled with sulfonated poly(styrene-divinylbenzene) with a crosslinking degree of 8 % (Nautilus-IE) and 10 % (Sevko AA) is studied in a variant of ion exclusion chromatography. Using 5 mM sulfuric acid, the retention parameters of the compounds are determined and new patterns are obtained that clarify the mechanism of retention of organic acids in the ion-exclusion chromatography variant. It is found that the retention of all the studied compounds (logk’) is directly proportional to the hydrophobicity values logP_exp). In this case, the electrostatic repulsion of organic acids from the sulfo groups of the cation exchanger shifts the logk’–logP_exp dependences by a fixed value proportional to the number of carboxyl groups. The possibility of using the Sevko AA column not only for amino acid analysis, but also for ion exclusion chromatographic determination of organic acids and alcohols in complex samples with simultaneous spectrophotometric and refractometric detection is shown.