Journal of Analytical Chemistry最新文献

This work presents a novel on-line flow-batch dispersive liquid-liquid microextraction system for the determination of molybdenum in water, meat, and vegetable material with electrothermal atomic absorption spectroscopy (ET AAS) as detection technique. After optimizing the experimental conditions, the analytical performance of the new methodology was determined. A limit of detection of 0.03 µg/L for water and 0.02 µg/kg for the other matrices, as well as an enrichment factor of 130 were obtained employing this methodology. Standard reference materials were used for accuracy and precision evaluation. No significant differences were found at the 95% confidence level between the certified and obtained values, and precision expressed as repeatability (RSD) was better than 5% in all cases. The developed automated methodology offers great advantages when compared to manual dispersive liquid-liquid microextraction, such as low risk of contamination while working in closed systems, minimal handling, reduced exposure of the analyst to the chemical products, greater security, improvement in repeatability and the elimination of the laborious and time-consuming procedure of phase separation by centrifugation. The method was successfully applied for the determination of molybdenum in natural groundwater, bovine and sheep meat, and pasture samples.

A possibility of studying effects of the main background ions formed by the main elements of inductively coupled plasma (H, N, O, and Ar) at the working parameters of the normal (“hot”) plasma mode by thermodynamic modeling is assessed. Such ions, responsible for the strongest spectral interferences in the mass spectra are always observed upon the injection of aqueous (“wet”) sample solutions into inductively coupled plasma mass spectrometers (ICP MS). The quantitative composition of the main background ions in an ICP MS is calculated as a function of plasma temperature in the temperature range from 3000 to 8000 K using thermodynamic modeling. The results of modeling were compared with the experimental data on the measured mass spectra of the main background ions and a high degree of correlation between the theoretical and experimental results was shown. The agreement between the results of calculations the experimental data validates the thermodynamic model of thermochemical processes in an ICP MS used and its applicability to subsequent calculations in fulfilling analytical tasks. A possibility of the unambiguous assessment of gas-kinetic plasma temperature is confirmed by comparing the theoretical and experimental mass spectra of the main ICP background ions in a normal mode. It was found that the calculated and experimental data on the concentration of only NO⁺ ions do not agree with the regularities noticed for the other background ions in the normal ICP mode.

Inorganic zeolites, or microporous crystalline aluminosilicates, possess high porosity, well-developed specific surface area, uniform pores, and ion-exchange properties, which determine their molecular sieve and adsorption properties. The use of zeolites as catalysts, desiccants for solvents and gases, and selective adsorbents for the separation of low-molecular-weight compounds is widely known. Zeolites also serve extensively as packing materials for chromatographic columns in gas-adsorption chromatography. However, their application to high-performance liquid chromatography (HPLC) is less recognized. In HPLC, the retention of adsorbates depends not only on adsorption interactions but also on the molecular sieve effect in the micropores and kinetically selective effects. Additional interactions with the mobile phase components alter the thermodynamic parameters of the adsorbates interaction with the zeolite, decrease effective pore size, and hinder the diffusion of the separated compounds into the adsorbent’s pores. Despite these challenges, zeolites remain promising adsorbents due to their strictly determined pore size (d_pore) and geometry, as well as their customizable polarities, which ensure high selectivity for the separation of low-molecular-weight compounds. The most promising zeolites for HPLC are wide-pore zeolites (d_pore 0.6–0.8 nm) with 8, 10, 12, and 14-member ring channels. This review offers a concise overview of the classification, composition, and structure of zeolites and their impact on the adsorption properties of these adsorbents. Data on the use of zeolites in HPLC are also systematized.

A micellar microextraction technique has been developed for the preconcentration and spectrophotometric determination of phosphate ions in aqueous media. This method is based on the formation of a reduced form of molybdophosphoric heteropolyacid and its extraction from the aqueous phase into a supramolecular solvent. The supramolecular solvent phase is formed in situ by introducing an amphiphile and a coacervation agent into the acidic aqueous phase. The feasibility of using biodegradable alkyl polyglucoside (C₈–C₁₀) as an amphiphile and carboxylic acids as coacervation agents has been investigated. In the acidic medium required for the formation of the reduced form of molybdophosphoric heteropolyacid, the phase of the supramolecular solvent is separated. The maximum absorbance of the extract is achieved using pivalic acid as the coacervation agent. The procedure is characterized by the limit of detection (3σ) for phosphate ions 5 µg/L. The technique is environmentally friendly and does not require the use of expensive equipment.

A technology is developed for manufacturing planar microfluidic chips (MFCs) based on Silgard 8040, encompassing template fabrication, mold production, sealing, and adsorbent filling. These MFCs, filled with a Porapak-Q adsorbent, facilitate sample preparation and calibration under uniform conditions, integrating both sample collection and preconcentration stages. Experimental investigations have identified optimal conditions for acetone preconcentration using Silgard 8040-based MFCs, achieving a maximum concentration factor of 43 at adsorption temperature (T_ads) of 0°C, desorption temperature (T_des) of 70°C, adsorption volume (V_ads) of 45 mL, and desorption time (t_des) of 1 s. The feasibility of using MFCs for sample collection and preparation, taking into account sample storage time, has been evaluated. The procedure maintains accuracy within 6–10% over 8 h without a necessity for additional drying of the collected samples from exhaled air.

An original bench-scale installation based on the principles of online magnetic solid-phase extraction is developed. The setup includes a borosilicate glass column packed with Fe₃O₄@MIP-BPA, which is fixed with two neodymium magnets. Compared to using one magnet, a design with two magnets ensures the uniform distribution of the sorbent over the entire cross-section of the column. The highest concentration factors (EF = 3216) and the degree of desorption of bisphenol A (BPA) are achieved, respectively, at a volumetric solution flow rate (W) of 2.0 mL/min and with eluting BPA with methanol (W = 0.4 mL/min). The determination of BPA in concentrates from model media by GC−MS provides high sensitivity of the developed method for determining BPA. In analyzing model solutions prepared in distilled water, the limit of detection (LOD) is 0.3 ng/L. In analyzing river water, the LOD increases by approximately 2 times. In analyzing soils, LOD = 2.2 ng/kg dry weight. Soils, compared to water bodies, contain a larger number of interfering components; the sensitivity of the method is reduced by 7–8 times. Bottom sediments are even more contaminated; the LOD more than doubles compared to the determination of BPA in soils.

Complex formation of vanadium(V) with 4-(2',3',4'-trihydroxyphenyl)-3-nitro-5-sulfoazobenzene (R) in the presence of cationic surfactants (CS), cetylpyridinium chloride (CPCl), cetylpyridinium bromide (CPBr), and cetyltrimethylammonium bromide (CTMABr), is studied. Vanadium(V) and R form a colored complex at a component ratio of 1 : 2 and pH of 5.0–5.5. The absorbance maximum of the complex is at 449 nm, while the reagent under these conditions absorbs light at 395 nm. In the presence of cationic surfactants, mixed-ligand complexes with a component ratio of V(V) : R : CS = 1 : 2 : 2 are formed, which results in a bathochromic shift of the absorbance maximum. Additionally, the pH value for the maximum complex formation shifts to a more acidic medium compared to the homoligand V(V)–R complex. The absorbance of the V(V) : R : CPCl, V(V): R : CPBr, and V(V) : R : CTMABr complexes is maximal at 457, 461, and 466 nm, respectively. The yield of these complexes is the highest at pH of 3.5–4.0 for VV(V) : R : CPCl and V(V): R : CPBr, and at a pH of 2.5–3.0 for V(V) : R : CTMABr. The formation of both homoligand and mixed-ligand vanadium(V) complexes depends on the reaction time, temperature, and concentrations of the reacting components. The determined stability constants indicate the high stability of the resulting mixed-ligand complexes. The specific conductivity of the complexes under the optimal conditions of complex formation was determined using conductometric titration. Calibration curves for the determination of vanadium(V) as homoligand and mixed-ligand complexes are linear. The effect of foreign ions and masking agents on the determination of V(V) as homoligand and mixed-ligand complexes was analyzed; it was shown that the presence of cationic surfactants significantly increases the selectivity of the reaction. An analysis of water samples from Lake Khanbulan, Lankaran District, Azerbaijan Republic using the developed procedure showed the presence of small amounts of vanadium(V).

The presented work focused on the preparation of a voltammetric sensor for hydroquinone (HQ) determination using a polycrystalline platinum electrode modified with Alizarin Red S (ARS). The electrode was prepared by electropolymerization of ARS on a platinum electrode through the application of 100 cyclic voltammetric segments between –0.4 and 1.2 V against Ag/AgCl (quasi-reference electrode). The modified poly (ARS)-Pt electrode was characterized in terms of stability and cyclic voltammetric behavior as a sensor for HQ in aqueous media. The modified electrode showed excellent stability and higher current than the unmodified electrode for the electrooxidation of HQ. Thus, the oxidation of HQ at poly (ARS)-Pt electrode exhibits notable electrocatalytic performance. The limit of detection is 0.16 µM, and the standard curve exhibits a linear relationship over the range from 0.25 to 15 µM (R² = 0.999). Investigation of the response to some potential interferences indicated that the electrode is unresponsive to Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺, Mn²⁺, Mo²⁺, Co²⁺, Bi²⁺, Cd²⁺, Ni²⁺, Al³⁺, ({text{NO}}_{3}^{ - }), ({text{SO}}_{4}^{{2 - }}), Cl^–, phenol and resorcinol, but shows marginal change towards Hg²⁺ and Cu²⁺. Recovery tests indicated recovery values between 97.0% and 100.81% when analyzing real samples at the modified electrode.

A magnetic solid-phase extraction method with the dispersion of magnetic hypercrosslinked polystyrene (MHCPS) by carbon dioxide is proposed for the extraction and preconcentration of amphenicols (chloramphenicol, florfenicol, and thiamphenicol) from honey and milk before their determination by HPLC–MS/MS. Effervescent tablets, consisting of sodium bicarbonate, citric acid, and MHCPS in the case of honey and sodium bicarbonate and MHCPS in the case of milk, were used. The conditions for obtaining tablets were selected (the amount and ratio of the acid, base, and MHCPS in the composition of a tablet and its mass), ensuring the quantitative release of amphenicols. Procedures for the determination of amphenicols in honey and milk with the dispersion of the sorbent by carbon dioxide and the subsequent determination of the compounds by HPLC–MS/MS are developed. The limits of detection are 0.3–1 and 0.02–0.05 μg/kg for honey and milk, respectively.

The results of an experiment assessing the applicability of solutions of 6-oxo-2-phenylimidazo[1,2-b]pyrido[4,3-e][1,2,4]triazine-7(6H)-yl)acetic acid on plates and cellulose substrates for detecting excessive levels of volatile organic compounds associated with endometritis inflammation relative to biologically normal levels are considered. The fluorescent properties of the dye are studied using gynecological mucus from cows collected in various periods (pre- and post-partum) and nasal mucus from newborn calves. The test system responses were compared with clinically established diagnoses and the results of a microbiological study. An evaluation of the test systems revealed a false positive rate of no more than 11% and a false negative rate of 2%. Other characteristics, such as specificity, accuracy, and precision of the test systems based on 6-oxo-2-phenylimidazo[1,2-b]pyrido[4,3-e][1,2,4]triazine-7(6H)-yl)acetic acid were also assessed. The potential application of this fluorophore to the rapid on-site diagnosis of endometritis inflammation in cows is considered promising based on these findings.