Chromatographia最新文献

The study used the prototype device enabling the development of isocratic and gradient thin-layer chromatograms with controlled eluent velocity to obtain fingerprints of extracts from buds of various poplar species. This equipment can deliver an eluent to virtually any place on the adsorbent layer of the chromatographic plate. Moreover, the composition of a mobile phase can be easily modified even when the chromatogram is developing. This paper shows the effect of various operating variables of the prototype in a normal phase system, e.g., eluent velocity and composition, on the chromatographic behavior of the mixture. The prototype’s results were compared to conventional TLC development in horizontal DS chambers. The UV light (366 nm) was used to detect the solute zones and document both systems. The results prove that the prototype device has great potential in plant material standardization. The mobile phase gradient improves the separation of the bands of strongly retained solutes. Additionally, this fact does not enhance the blurring of low-retained bands.

Membrane emulsification can obtain microspheres with relatively uniform particle size and pore size, which has unique advantages in the synthesis of polymer microsphere adsorbents and the enrichment and separation of organic compounds. In this study, the Hydrophilic Lipophilic Balance (HLB) solid phase extraction microspheres were prepared by membrane emulsification technique and was used in the pretreatment of samples to detect 25-hydroxy vitamin D₂ (25OH-VD₂) and 25-hydroxy vitamin D₃ (25OH-VD₃) in serum by UPLC-MS/MS for the first time. To confirm the efficacy of membrane-emulsified (ME) HLB microspheres, three types of microspheres, including ME HLB microspheres, non-membrane-emulsified (non-ME) HLB microspheres and commercial HLB microspheres, were compared for the pretreatment of 25OH-VD₂ and 25OH-VD₃. The performance of HLB microspheres was characterized based on the sample recovery values acquired by UPLC-MS/MS analysis. Results showed that among the three types of microspheres, ME HLB microspheres showed the best performance and demonstrated good adsorption properties for 25OH-VD₂ and 25OH-VD₃. The recoveries range of 25OH-VD₂ and 25OH-VD₃ were 96.7–101.4 and 98.7–104.9%, respectively, and the coefficients of variation were 0.67–1.24 and 1.39–2.28%, respectively, which were superior to those of commercial HLB microspheres and non-ME HLB microspheres. Additionally, due to their excellent homogeneity, the ME HLB microspheres exhibited good precision in the determination of low values of 25OH-VD₂ and 25OH-VD₃, indicating accurate and simple detection of 25OH-VD₂ and 25OH-VD₃ with a broad potential for further development.

This study focused on the chromatographic measurements of the distribution constants of hydrocarbons at the air–solid interface for indirect quantification of the hydrocarbon compositions in solid substrates via headspace-solid phase microextraction (HS-SPME). Packed column gas chromatography and other experimental data were used to measure the distribution constants of six hydrocarbons (n-heptane, n-octane, n-nonane, toluene, p-xylene, and 1,2,4-trimethylbenzene) between the headspace (HS) and two solid substrates (cardboard and cotton fabric) at 60 and 90 °C. To validate the accuracies of the measured distribution constants in this work, model HS samples were prepared in vials containing known amounts of solid substrates and a mixture of vaporized hydrocarbons at 60 and 90 °C. These HS samples were analyzed with gas chromatography using both direct vapor analysis and HS-SPME. The experimental hydrocarbon compositions of HS samples were compared with the calculated HS compositions from the measured distribution constants and other experimental parameters. The Wilcoxon signed-rank test results indicated that the calculated hydrocarbon compositions of the model samples were comparable with the experimental hydrocarbon compositions. This work suggests that gas chromatographic measurements using packed columns can provide a reliable and convenient method for measuring the distribution constants of hydrocarbons between air and various solid substrates.

A novel green microextraction supramolecular (SUPRA)-based method for simultaneous preconcentration of seven pesticides, acetamiprid, azoxystrobin, bifenthrin, carbendazim, chlorpyrifos, imidacloprid, and tebuconazole, in water samples and cereal flours with further determination by HPLC-DAD was developed. The method uses 113 µL of 1-decanol as amphiphilic extractor and 500 µL of tetrahydrofuran as disperser solvent. To perform the method optimization, a 2⁵ factorial design and Doehlert design combined with Derringer–Suich desirability function and response surface methodology were used. The microextraction of the pesticides was carried out at pH 6.3 in the presence of 5% NaCl (w/v), low vortex-assisted extraction time (30 s) and it was provided high preconcentration factors (3.6–266.1), and low LOQs (8.98–29.92 µg L⁻¹). The intra-day (n = 10) and inter-day (n  = 10) precision assessed as the percentage of relative standard deviation (%RSD) for concentrations of 50.0 and 200.0 µg L⁻¹ varied from 1.7 to 4.1%. The method was successfully applied to determine pesticides in river and lake water samples using external calibration curves. Considering the property of restricted access materials of SUPRAs, the microextraction method was also applied to the direct treatment of solid samples of wheat, oat, and rice flours. High recovery values in the range of 80–112% were obtained, thereby proving the absence of possible interference from matrix components.

Graphical Abstract

Dibenzoazecines are a new class of potential neuroleptics with a high potential for the treatment of schizophrenia. Initial stress tests indicated that the lead compound, LE404, decomposes when exposed to oxygen and sunlight. In this follow-up study, the influence of oxidative stress and photosensitivity was investigated in accordance with the ICH guidelines. These studies are of great importance for new APIs, as phototoxic and photoallergic reactions pose a significant risk to patients, especially with long-term medication, as it is not possible to completely avoid exposure to sunlight. Furthermore, the identification and prediction of the chemical lability of LE404 can be used to determine suitable storage conditions to prevent compound degradation. The effects of exposure of LE404 to a light source similar in spectrum and intensity to natural sunlight were investigated according to ICH-Q1B. Furthermore, the influence of oxidizing agents was investigated under exclusion of light. Two degradation products were identified. The extent and rate of degradation were continuously monitored using RP-HPLC–UV. Chromatographic separations were performed with a phenomenex™ Gemini 5 µm C18 (250 × 4.60 mm) column and acetonitrile/KH₂PO₄ buffer (4 mmol L⁻¹, pH 2.5) as mobile phase at 220 nm. The photodegradation product was isolated using semi-preparative RP-HPLC. The oxidation product was obtained by quantitative conversion of LE404 in hydrogen peroxide and subsequent purification by preparative TLC. The structures of both degradation products were elucidated using HR-MS/MS, 1D- and 2D-NMR as well as FT-IR spectroscopy. The characterization of the degradation products serves as the basis for subsequent investigations into their toxicity.

This paper introduces a new derivatization agent for the simultaneous quantification of formaldehyde and methanol during curing reactions of complex organic coatings. Formaldehyde emitted from a polyester-melamine coating is derivatized in a gas phase reaction with unsymmetrical dimethylhydrazine (UDMH) to form formaldehyde dimethylhydrazone (FDMH). UDMH and FDMH tend to degrade at temperatures above 200 °C rather fast. The applicability of derivatization agent and analyte as well as their degradation products are therefore discussed thoroughly. In this method curing temperatures of 150 °C with incubation times between 0.1 and 60 min are used to trigger crosslinking reactions. The emissions of formaldehyde and methanol are continuously quantified with headspace gas chromatography to obtain an emission trend. While one of the main sources of formaldehyde is the demethylolation during crosslinking, methanol is produced via hexamethoxymethylmelamine (HMMM) deetherification and as a condensation byproduct. The emission monitoring shows a high potential for comparative and mechanistic investigations. Results show good repeatability with low standard deviations (< 7%) with a quantification limit of 2.09 µg for formaldehyde and 2.08 µg for methanol.

Conventional high performance capillary electrophoresis (HPCE) detection modes mainly rely on chromogenic, fluorogenic, ionizable, or redox properties of analytes, greatly limiting the scope of analysis. Therefore, the development of a universal HPCE detection system has raised great attention. Herein, by tandem connection of different diameter capillaries (TCDDC), a novel and universal HPCE detection system called interface-induced current detector (IICRD) was constructed. The current signal peaks of analytes in the current-electrophoretograms (CR-EGs) can be observed for the first time. The results of detector performance tests showed good repeatability and high sensitivity. The theoretical deduction and experimental verification were further carried out. To prove the detection ability, several substances with or without special responsive groups were qualitatively and quantitatively analyzed. Firstly, cations and anions in inorganic electrolytes (inorganic salts, acids and alkalis) can be simultaneously separated and analyzed. Furthermore, several small molecular weight organic compounds, monosaccharides and disaccharides were also analyzed. The current signal peaks in CR-EGs were identified and discussed. For quantitative analysis, system suitability tests were evaluated, the results of quantitative analysis methodology validation showed that the new method was qualified for quantitative analysis. The linear relationship between the values of current intensity and the concentrations of analytes can be obtained over the investigated concentration ranges. In summary, the HPCE-DAD-IICRD system showed lower baseline noise, higher sensitivity and higher S/N especially for samples without special responsive groups, showing complementary advantages when combined with other detectors. It is expected to be a novel HPCE detection system for extensive applications.

Graphical Abstract

Fipronil belongs to the phenylpyrazole family of insecticides and functions by interrupting the γ-aminobutyric acid system and chloride ion channels of pests. Studies have shown Fipronil can undergo several degradation pathways in the environment to form degradants that may be toxic to non-target aquatic life. In this study, a comprehensive forced degradation study of Fipronil was carried out following ICH guidelines to generate, characterize, and identify the major degradation products of Fipronil. Stress conditions included acidic, alkaline, oxidative, thermal (solid and solution states), and photolytic (solid and solution states). Separation of six major degradation products (DPs) was achieved using reversed phase high-performance liquid chromatography (HPLC) with gradient elution. The DPs were characterized and identified using HPLC-high-resolution mass spectrometry (HPLC-HRMS) and comparison of tandem MS/MS fragmentation profiles. The Fipronil dimer required isolation through semi-preparative HPLC and analysis by nuclear magnetic resonance (NMR) to elucidate and confirm its structure. The proposed structures of DPs were based upon the given degradation pathways of Fipronil. The key results and findings of this study will provide better understanding of Fipronil stability and its major degradation products including degradation/formation pathways, which would assist designing of more stable Fipronil formulations and finished products with extended shelf-life including enhanced efficacy with decreased adverse effects.

Progress in theory of separation mechanisms controlling the Micro-Thermal Field-Flow Fractionation of the macromolecular and particulate species inspired the development of the experimental methodology and instrumental techniques. Three really functioning separation mechanisms are polarization, steric and focusing. However, steric mechanism is rather exceptionally operative for the separation of large particles at low flow rates of the carrier liquid. On the other hand, two modus operandi taking advantage of focusing mechanism emerging at high flow rates and, consequently, resulting in very rapid separations are elaborated. One exploits the action of the lift force and the other one makes use of the kinetic energy generated by the collisions among the particles in bi-disperse suspension of the particulate species. Surface properties and their topographical heterogeneity influence the migration of particulate species exposed to the force of thermal diffusion. The shape of the spherical versus non-spherical particles distinguishes their behavior when exposed to thermal diffusion and to hydrodynamic stress. It was theoretically calculated that the separations of the particles, based on the mentioned differences, are possible by Focusing Micro-Thermal Field-Flow Fractionation. Since our earlier theoretical models were not developed in sufficient details, some of the previous results are corrected by the present paper. The theoretical conclusions are supported by preceding real separations.