Analytical science advances最新文献

Clay soils are rock-decomposed materials comprised of both clay- and non-clay-like minerals. Clays' physiochemical and mineralogical composition determines their applicability use in cosmetics. Because of their high bioburden, they must be effectively characterized before being incorporated into cosmetics. The scope of the current study was to characterize two different samples of red and white clays for their physical, chemical and biological properties; mined from Durban, South Africa. Characterization was performed using techniques like X-ray fluorescence, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope, hydrogen potential, soil colour, oil absorption, swelling capacity, texture, bulk density, plastic and apparent viscosity, sun protection factor and microbiological analysis.

Water stable isotopologue analysis is widely used to disentangle ecohydrological processes. Yet, there are increasing reports of measurement uncertainties for established and emerging methods, such as cryogenic vacuum extraction (CVE) or cavity ring-down spectroscopy (CRDS). With this study, we investigate two pitfalls, that potentially contribute to uncertainties in water-stable isotopologue research. To investigate fractionation sources in CVE, we extracted pure water of known isotopic composition with cotton, glass wool or without cover and compared the isotopologue results with non-extracted reference samples. To characterise the dependency of δ²H and δ¹⁸O on the water mixing ratio in CRDS, which is of high importance for in-situ applications with large natural variations in mixing ratios, we chose samples with a large range of isotopic compositions and determined δ²H and δ¹⁸O for different water mixing ratios with two CRDS analysers (Picarro, Inc.). Cotton wool had a strong fractionation effect on δ²H values, which increased with more ²H-enriched samples. δ²H and δ¹⁸O values showed a strong dependency on the water mixing ratio analysed with CRDS with differences of up to 34.5‰ (δ²H) and 3.9‰ (δ¹⁸O) for the same sample at different mixing ratios. CVE and CRDS, now routinely applied in water stable isotopologue research, come with pitfalls, namely fractionation effects of cover materials and water mixing ratio dependencies of δ²H and δ¹⁸O, which can lead to erroneous isotopologue results and thus, invalid conclusions about (ecohydrological) processes. These practical issues identified here should be reported and addressed adequately in water-stable isotopologue research.

In the development of bioanalytical methods, stabilizing drug molecules in biological matrices is crucial for ensuring reliable exposure data in pharmacokinetic and toxicokinetic sample analyses. This study focuses on the evaluation of stabilizing effects on the synthetic triterpenoid TX101, a cyanoenone triterpenoid Nrf2 activator with known instability in plasma samples. The molecule's unsaturated double bond is susceptible to oxidation, either nonenzymatically via oxygen or enzymatically through cytochrome P450 enzyme-catalyzed epoxidation. The research explores the impact of antioxidants (L-ascorbic acid, sodium metabisulfite, sodium sulfite) and P450 enzyme inhibitors (sodium diethyldithiocarbamate, memantine hydrochloride, 1-aminobenzotriazole) on TX101 stability in rat plasma samples. Results reveal that adding 2.5 mg/mL sodium sulfite or sodium metabisulfite effectively inhibits the nonenzymatic oxidation of TX101 to TX101-epoxide, while L-ascorbic acid shows minimal stabilizing effect. Among P450 enzyme inhibitors, sodium diethyldithiocarbamate and memantine hydrochloride exhibit modest stabilizing effects, likely attributed to their antioxidant activity. The developed High-formance liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS) method, incorporating Supported Liquid Extraction for sample cleanup, allows simultaneous monitoring of TX101 and TX101-epoxide. Application of this method in a rat dose-range finding study confirms successful inhibition of TX101-epoxide formation in samples treated with sodium sulfite or sodium metabisulfite. Overall, the study emphasizes the importance of stabilizers in preventing nonenzymatic oxidation reactions during sample storage, providing valuable insights for bioanalytical method development and validation.

Rationale: Soil microbial heterotrophic C-CO₂ respiration is important for C cycling. Soil CO₂ differentiation and quantification are vital for understanding soil C cycling and CO₂ emission mitigation. Presently, soil microbial respiration (SR) quantification models are based on native soil organic matter (SOM) and require consistent monitoring of δ¹³C and CO₂.

Methods: We present a new apparatus for achieving in situ soil static chamber incubation and simultaneous CO₂ and δ¹³C monitoring by cavity ring-down spectroscopy (CRDS) coupled with a soil culture and gas introduction module (SCGIM) with multi-channel. After a meticulous five-point inter-calibration, the repeatability of CO₂ and δ¹³C values by using CRDS-SCGIM were determined, and compared with those obtained using gas chromatography (GC) and isotope ratio mass spectrometry (IRMS), respectively. We examined the method regarding quantifying SR with various concentrations and enrichment of glucose and then applied it to investigate the responses of SR to the addition of different exogenous organic materials (glucose and rice residues) into paddy soils during a 21-day incubation.

Results: The CRDS-SCGIM CO₂ and δ¹³C measurements were conducted with high precision (< 1.0 µmol/mol and 1‰, respectively). The optimal sampling interval and the amount added were not exceeded 4 h and 200 mg C/100 g dry soil in a 1 L incubation bottle, respectively; the ¹³C-enrichment of 3%–7% was appropriate. The total SR rates observed were 0.6–4.2 µL/h/g and the exogenous organic materials induced -49%–28% of priming effects in native SOM mineralisation.

Conclusions: Our results show that CRDS-SCGIM is a method suitable for the quantification of soil microbial CO₂ respiration, requiring less extensive lab resources than GC/IRMS.

Raman spectroscopy provides label-free, specific analysis of biomolecular structure and interactions. It could have a greater impact with improved characterization of complex fingerprint vibrations. Many Raman peaks have been assigned to cholesterol, for example, but the molecular vibrations associated with those peaks are not known. In this report, time-dependent density functional theory calculations of the Raman spectrum of cholesterol are compared to measurements on microcrystalline powder to identify 23 peaks in the Raman spectrum. Among them, a band of six peaks is found to be sensitive to the conformational structure of cholesterol's iso-octyl chain. Calculations on 10 conformers in this spectral band are fit to experimental spectra to probe the cholesterol chain structure in purified powder and in phospholipid vesicles. In vesicles, the chain is found to bend perpendicular to the steroid rings, supporting the case that the chain is a dynamic structure that contributes to lipid condensation and other effects of cholesterol in biomembranes.

Statement of Significance: Here we use density functional theory to identify a band of six peaks in cholesterol's Raman spectrum that is sensitive to the conformational structure of cholesterol's chain. Raman spectra were analyzed to show that in fluid-phase lipid membranes, about half of the cholesterol chains point perpendicular to the steroid rings. This new method of label-free structural analysis could make significant contributions to our understanding of cholesterol's critical role in biomembrane structure and function. More broadly, the results show that computational quantum chemistry Raman spectroscopy can make significant new contributions to molecular structure when spectra are interpreted with computational quantum chemistry.

Ammonium fluoride has been shown to improve sensitivity when using electrospray ionization (ESI) coupled with mass spectrometry (MS). Recent internal investigation furthered that claim, through the observation of improved sensitivity when analyzing steroid molecules. This work focuses on extending those observations to other small molecules to understand the impact ammonium fluoride has on detection sensitivity with optimized instrument conditions. Using conventional liquid chromatography ESI-MS we investigated sensitivity differences between ammonium fluoride, formic acid, or ammonium hydroxide as mobile phase additives. Full source optimization was performed for nine compounds at three different organic concentrations (30%, 60%, or 90%) with formic acid, ammonium fluoride, and ammonium hydroxide adjustment. Optimization results were compiled to generate individual methods by compound, polarity, mobile phase, and organic concentration. Flow injection analysis was performed with fully optimized methods to compare compounds across different solvent systems under optimal conditions. Negative ESI data showed 2–22-fold sensitivity improvements for all compounds with ammonium fluoride. Positive ESI data showed > 1–11-fold improvement in sensitivity for four of seven compounds and no change for three of seven compounds with ammonium fluoride. Ammonium fluoride improved ESI⁻ sensitivity for all compounds studied when using optimized source conditions. Investigation with ESI⁺ analyses showed mixed results, with four of seven compounds showing improvement and others showing equivalency or slight loss in sensitivity, suggesting potential sensitivity gains for some analogs with ESI⁺.

Through a collection of editorials titled “Emerging Scientists in Analytical Sciences,” we aim to spotlight promising individuals who are actively engaged in the realm of analytical sciences. For this editorial, we invited Niklas Geue who recently submitted his PhD thesis at The University of Manchester (UK). We are keen for anyone working in this field to nominate somebody for a Q&A by sending an email to one of the editors and explaining to us why this person should be highlighted.

I grew up in Magdeburg, a middle-sized city in East Germany, and went to a high school with a focus on maths, science, and technology. Thereby, I was exposed to a lot of science, and early on I participated in competitions, seminars, and other science events. My main interest was always chemistry, evidenced by a considerable lab in my grandparent's garage — much to everyone's annoyance. In my late high school years, I also participated in the International Chemistry Olympiad and made it to the final German selection round twice (among the best 16). The question of what I wanted to study was never really in doubt.

For my Bachelor's I went to Leipzig, a great student city, and graduated as the best student of my year. During and following my undergraduate years, I undertook three research internships. These experiences took me to diverse locations around the world: one internship was based in Santiago de Chile focusing on kinetics/spectroscopy (related to my Bachelor's thesis), another in Sydney centred around mass spectrometry (MS), and a third in Los Angeles, where I further worked on my spectroscopic skills. During these research stays, I realized two things: my strong inclination to remain within the realm of analytical and physical chemistry and my eagerness to actively engage in research at the earliest opportunity. The UK was ideally suited for the latter as I could start my PhD here directly after my Bachelor's. I was also always fascinated by how things work on a molecular level, and similarly enthusiastic about the interdisciplinarity with instrumentation and engineering. I became very interested in MS while I was in Australia, and decided that I wanted to stay in this field for my PhD work (Figure 1).

My PhD project is about the characterisation of metallosupramolecular complexes using advanced MS techniques. These and similar molecular architectures are important in a range of fields (e.g., catalysis, medicine, and materials), and quite prominent, not just since the Nobel prize for molecular machines in 2016. Unfortunately, it is not straightforward to structurally characterise them properly.¹ MS, particularly in combination with tandem MS and ion mobility (IM), is a great tool to enhance our understanding of such assemblies, by probing their stability as well as their size and shape.

During my PhD, I have successfully shown that it is possible to evaluate the stability of (metallo)supramolecular compou

Surface-enhanced Raman scattering (SERS) is a sensitive and fast technique for sensing applications such as chemical trace analysis. However, a successful, high-throughput practical implementation necessitates the availability of simple-to-use and economical SERS substrates. In this work, we present a robust, reproducible, flexible and yet cost-effective SERS substrate suited for the sensitive detection of analytes at near-infrared (NIR) excitation wavelengths. The fabrication is based on a simple dropcast deposition of silver or gold nanomaterials on an aluminium foil support, making the design suitable for mass production. The fabricated SERS substrates can withstand very high average Raman laser power of up to 400 mW in the NIR wavelength range while maintaining a linear signal response of the analyte. This enables a combined high signal enhancement potential provided by (i) the field enhancement via the localized surface plasmon resonance introduced by the noble metal nanomaterials and (ii) additional enhancement proportional to an increase of the applicable Raman laser power without causing the thermal decomposition of the analyte. The application of the SERS substrates for the trace detection of melamine and rhodamine 6G is demonstrated, which shows limits of detection smaller than 0.1 ppm and analytical enhancement factors on the order of 10⁴ as compared to bare aluminium foil.

Measurement of hormones is important for the diagnosis and management of endocrine diseases. The thyroid hormones thyroxine (T4) and triiodothyronine (T3) are among the most commonly measured hormones in clinical laboratories, and it is the concentration of free (not bound to proteins) thyroid hormones that is clinically most relevant. Free thyroid hormones are commonly measured using automated immunoassays, however, these are known to produce erroneous results due to interferences for some patients. Measurement of free thyroid hormones using equilibrium dialysis or ultrafiltration combined with liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) is considered a more accurate and robust method for free thyroid hormone analysis and overcomes many of the limitations of immunoassays. However, LC-MS/MS-based methods are often considered too technically difficult and not amendable to high throughput by clinical chemists and are not offered by many clinical laboratories. This mini-review aims to make it easier for clinical laboratories to implement LC-MS/MS-based measurement of free thyroid hormones. It describes the medical rationale for measuring free thyroid hormones, the benefits of LC-MS/MS-based methods with respect to interferences affecting immunoassay-based methods and physical separation methods. This mini-review highlights important parameters for ultrafiltration and equilibrium dialysis to obtain physiologically relevant free thyroid hormone concentrations and focuses on methods and devices used in clinical chemistry.