Journal of Analytical Chemistry最新文献

Effective solid-phase extractants (SPE) based on multi-walled carbon nanotubes (CNT) of various structures modified with an organic reagent, 2-mercaptobenzothiazole, were developed. Using scanning and transmission electron microscopy, the morphological and structural features of SPE samples and their elemental composition were determined. It was shown that the specific surface area of the modified CNT is approximately two times lower compared to the original CNT. It was revealed that the modified materials are CNT coils coated with a uniform organic shell 10−15 nm thick. The sorption capacity of the original nanotubes in 1.0 M HCl and of their modified forms (in 0.1−3.0 M HCl) at room temperature and at 80°C was determined. It was found out that in strongly acidic media, SPE based on G-183 CNT and 2-mercaptobenzothiazole, effectively sorbs Pt, Pd and Au at room temperature, and Ru and Rh at the temperature of 80°C. A possibility of the selective extraction of platinum group metals and gold with this sorbent in the presence of macroquantities of Al, Fe, Cu, Ca and Mg was assessed.

The aim of this work was to the obtaining novel mixed-mode stationary phases with increased hydrophilicity and applying them in ion and hydrophilic interaction liquid chromatography. The resins were obtained by the sequential covalent attachment of branched polyethylenimine and polyelectrolytes synthesized from diepoxide and a secondary amine on the surface of epoxidized polystyrene–divinylbenzene. To increase the shielding degree of the polymer substrate, an additional polymerization of glycidol was carried out in the functional layer of the sorbent at an increased pH of the reaction medium. The synthesized phases possessed increased hydrophilicity compared to most resins based on a styrene–divinylbenzene copolymer with covalently attached layers. This was evidenced in the ion chromatography mode by a decrease in the relative retention of polarizable anions, weakly hydrated oxyhalides (up to a change in the elution order of the bromate), and haloacetic acids. In the hydrophilic interaction liquid chromatography mode, an increased hydrophilicity of the phases was confirmed by an increase in the retention factors of polar analytes, as well as by the reversal of the elution order of ascorbic and nicotinic acids as compared to the phases based on polystyrene–divinylbenzene presented in the literature. The low efficiency of the obtained stationary phases in the ion chromatography mode was noted, which is associated with slow mass transfer in the bulk polymer functional layer. The negative impact of the polymer layer on efficiency in hydrophilic interaction liquid chromatography is less pronounced due to the presumably smaller thickness of the part of the functional layer involved in this mode. The proposed method for the synthesis of resins ensures an increase in the efficiency, selectivity, and separation ability of sorbents in the hydrophilic interaction liquid chromatography mode as compared to phases based on a styrene–divinylbenzene copolymer described previously in the literature. The resulting highly hydrophilic resins makes it possible to separate a mixture of 9 nitrogenous bases and nucleosides in 18 min, 6 vitamins in 24 min, and 8 sugars in 11 min. Thus, the method of substrate hydrophilization proposed in this work is promising for improving the chromatographic characteristics of phases in the hydrophilic interaction liquid chromatography mode and can be used to create sorbents with increased selectivity and efficiency.

In recent years, microRNAs have been used as cancer markers in clinical testing. In this study, an electrochemical biosensor was developed based on nanomaterials and the hybridization chain reaction (HCR) for highly sensitive and selective detection of the target miR-378 using K₃Fe(CN)₆/K₄Fe(CN)₆ as a redox indicator. MiR-378 is located on human chromosome 5q32 and serves as an important gene regulatory locus. Recent studies have found that aberrant expression of miR-378 is associated with cervical cancer, breast cancer, lung cancer, and other diseases. HCR is a simple and efficient isothermal amplification technique that does not require enzyme mediation and can be performed at room temperature. Evaluations of the specificity, stability, and sensitivity of the developed sensor revealed its ability to rapidly and specifically detect miR-378 in two hours with a detection limit as low as 100 cells in a volume of 400 µL, thereby indicating that this device could provide a novel approach for clinical diagnosis.

In this study, the composition and antibacterial activity of essential oil from the flower of Nyctanthes arbor-tristis were determined. The extraction was carried out utilizing the microwave-assisted extraction technique with a short extraction time of 60 min, yielding 0.342% (w/w). Separation and characterization were performed by gas chromatography-mass spectrometric analysis, identifying a total of 34 constituents, including major compounds: phenyl ethyl alcohol (26.1%), eucarvone (18.7%), furfural (10.7%), benzaldehyde (4.8%), phytol (4.7%), and methyl hexadecanoate (3.1%). In the next step, an agar disk diffusion assay was performed to assess the antimicrobial activity of the oil against four different bacterial strains, namely Staphylococcus aureus, Klebsiella pneumoniae, Escherichia coli, and Pseudomonas aeruginosa, resulting in zones of inhibition measuring 9, 12, 11, and 9 mm, respectively. However, the broth macrodilution method was carried out against Staphylococcus aureus and Klebsiella pneumoniae, revealing minimum inhibitory concentrations of 2.5 and 5 mg/mL, respectively.

The first part of the review provides general information about the solvent extraction of organic compounds from solid samples and discusses various methods for its implementation: extraction in a Soxhlet apparatus, ultrasonic extraction, microwave-assisted extraction. Based on an analysis of review papers, information on the features of sample preparation using these methods is systematized, experimental parameters affecting extraction efficiency are considered, and examples of using these methods for isolating organic compounds in the analysis of solid environmental samples, food products, and plants are given.

The work is devoted to the study of the distribution of γ-hexachlorocyclohexane in turnips and beets between their bulbs, tops, and skin. The sample preparation procedure recommended by GOST is supplemented by the use of liquid nitrogen for the deeper crushing and destruction of plant cells. It was found that the use of liquid nitrogen, with other experimental parameters being constant, leads to a 2–3-fold increase in the amount of the pesticide being determined. It was found that the distribution of γ-HCCH in plants is uneven: the highest concentration of the pesticide is found in the skin, while the amount of γ-HCCH in the tops was the lowest. It was shown that the pesticide is better accumulated in beet skin than in turnip skin; for the tops the pattern is reversed, and the accumulation of γ-HCCH in the bulbs of these root crops is similar in magnitude. The obtained data can be useful for analytical quality control services of agricultural products.

A procedure for the simultaneous determination of nine uremic toxins and choline in blood serum is presented. Target substances are selected based on the published data as promising biomarkers for establishing the severity and nature of the progression of immunoglobulin A nephropathy, a kidney disease leading to disability, and in the absence of timely treatment, to the death of young and middle-aged people. Using ultrafiltration, separate determination of free and protein-bound indole uremic toxins was achieved. The use of high-performance liquid chromatography in combination with high-resolution tandem mass spectrometry provides satisfactory analytical accuracy in the absence of the complete chromatographic separation of analytes under standard reversed-phase HPLC conditions. In calibration a solution of albumin in a phosphate buffer solution was used as a surrogate blood serum. Protein concentration of 45 mg/mL and pH 7.4 correspond to these characteristics of native blood serum. The pilot experiment showed the promise of determining the most important indicators of the state of the intestinal microbiome—choline and trimethylamine oxide in dried blood spots.

Murraya koenigii is an important medicinal plant for its diverse pharmacological activities. It has been utilized in various indigenous systems of medicine for preparing different herbal formulations. M. koenigii is a rich source of bioactive carbazole alkaloids, among which mahanimbine, koenimbine, mahanine, and girinimbine are the major carbazole alkaloids isolated from the leaves of this plant. Mahanimbine has been utilized to treat cancer and diabetes, playing an important role in the pharmacological effects of this plant. Standardization is an essential process in the pharmaceutical industry to maintain the purity, quality, efficacy, and, safety of herbal raw materials. Different analytical techniques, including HPTLC, HPLC, GC-MS, and LC-MS have been used for this purpose. In the present study, a simple, specific, and rapid semi-automated TLC method was developed to determine the mahanimbine content in leaf samples collected from three geographical regions of India. This study revealed that the ethyl acetate extract prepared from leaf samples collected from Andhra Pradesh contains the highest amount of mahanimbine (507.2 µg), which indicates that this sample can be utilized for further research or in the preparation of herbal formulations.

A novel reagent derived from salicylaldehyde has been synthesized and characterized by determining its crystalline structure through X-ray diffraction analysis. The complex formation of this reagent with iron(III) has been investigated by spectrophotometric methods. The dissociation constant of the reagent was determined by potentiometry in an aqueous–ethanolic medium, yielding pK = 9.66 ± 0.02. The interaction of iron(III) with 2-(((1-(3-bromophenyl)ethylidene)hydrazono)methyl)phenol in the presence and absence of diantipyrylmethane (DAM), diantipyrylphenylmethane (DAPhM), and diantipyrylpropylmethane (DAPrM) has been thoroughly studied. Optimal conditions for complex formation (λ_opt, pH_opt) were found. Iron(III) forms colored mixed-ligand complexes with the reagent in the presence of the third component—DAM, DAPhM, or DAPrM,—resulting in a hypsochromic shift in the absorption spectrum. The maximum yield of complexes was achieved in a more acidic medium compared to the binary complex. Molar absorption coefficients of the complexes and the ranges of compliance with Beer’s law were determined. Component ratios in the homogeneous and mixed-ligand complexes were established using isomolar series methods, as well as the relative yield of the Starik–Barbanel and equilibrium shift methods. These analyses revealed that the component ratio of Fe(III)–R in the binary complex is 1 : 2, while in the mixed-ligand complexes Fe(III)–R–DAM, Fe(III)–R–DAPhM, and Fe(III)–R–DAPrM, the ratios are 1 : 2 : 1, 1 : 1 : 1, and 1 : 1 : 2, respectively. The mixed-ligand complexes of iron(III) with 2-(((1-(3-bromophenyl)ethylidene)hydrazono)methyl)phenol exhibit favorable chemical-analytical characteristics. The developed procedure was successfully applied to the determination of trace amounts of iron(III) in oil sludge.