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Rationale: Femtosecond (fs) laser ablation ion sources have allowed for improved measurement capabilities and figures of merit of laser ablation based spectroscopic and mass spectrometric measurement techniques. However, in comparison to longer pulse laser systems, the ablation plume from fs lasers is observed to be colder, which favors the formation of polyatomic species. Such species can limit the analytical capabilities of a system due to isobaric interferences. In this contribution, a double‐pulse femtosecond (DP‐fs) laser ablation ion source is coupled to our miniature Laser Ablation Ionization Mass Spectrometry (LIMS) system and its impact on the recorded stoichiometry of the generated plasma is analyzed in detail. Methods: A DP‐fs laser ablation ion source (temporal delays of +300 to – 300 ps between pulses) is connected to our miniature LIMS system. The first pulse is used for material removal from the sample surface and the second for post‐ionization of the ablation plume. To characterize the performance, parametric double‐ and single‐pulse studies (temporal delays, variation of the pulse energy, voltage applied on detector system) were conducted on three different NIST SRM alloy samples (SRM 661, 664 and 665). Results: At optimal instrument settings for both the double‐pulse laser ablation ion source and the detector voltage, relative sensitivity coefficients were observed to be closer (factor of ~2) to 1 compared with single‐pulse measurements. Furthermore, the optimized settings worked for all three samples, meaning no further optimization was necessary when changing to another alloy sample material during this study. Conclusions: The application of a double‐pulse femtosecond laser ablation ion source resulted in the recording of improved stoichiometry of the generated plasma using our LIMS measurement technique. This is of great importance for the quantitative chemical analysis of more complex solid materials, e.g., geological samples or metal alloys, especially when aiming for standard‐free quantification procedures for the determination of the chemical composition. [ABSTRACT FROM AUTHOR]

A series of new uranium compounds [MII(H2O)4][(UO2)3O3(OH)2]·H2O (MII – Mn, Co, Ni, Zn) were synthesized by the reaction of the metal salts with schoepite under hydrothermal conditions. X-Ray powder diffraction (XRD) studies have been carried out, and the indexing of diffraction peaks shows that all the phases [MII(H2O)4][(UO2)3O3(OH)2]·H2O crystallize in the triclinic crystal system and have lattice parameters similar to those of the known Ni uranyl oxide hydrate. IR spectroscopic studies were carried out; processes of dehydration and thermal decomposition were investigated and reported. A detailed investigation of the heterogeneous equilibria in the system "[MII(H2O)4][(UO2)3O3(OH)2]·H2O(cr) – aqueous solution" was performed. The pH ranges of the stability of the compounds and their solubility were experimentally established. Hydrolysis products isolated at the end of the solubility experiments were characterized by powder XRD and quantitative chemical analysis. For [MII(H2O)4][(UO2)3O3(OH)2]·H2O, the solubility products, Gibbs energies of formation (298 K), and solubility curves were calculated. Speciation diagrams of U(VI) and M(II) in saturated solutions and solids were constructed. The present work is the first complex research of the family of uranyl oxide hydrates with some bivalent cations (Mn2+, Co2+, Ni2+, Zn2+) including the study of the structure and chemical stability in aqueous solutions. The obtained results are important for the estimation of the long-term behavior of uranium in the environment and in spent fuels under repository disposal conditions. [ABSTRACT FROM AUTHOR]

The novelty in this investigation is the development of a new product, production of a pasteurized functional drink containing wheatgrass. The aim of this research was to develop a pasteurized functional drink containing wheatgrass and apple juice and to give some concrete data on the changes of nutritional values of the fruit juice as well as after adding wheatgrass in its recipes. It also aims to determine the most appropriate pasteurization scheme that ensures the food safety of the product and that minimally denaturizes the valuable health promoting phytochemicals. The raw materials and the produced juices have undergone quantitative chemical analyses for Chlorophyll, Vitamin C, total polyphenols, antioxidant activity, and minerals (P, Ca, Mg, Fe, Na, and Zn). Microbiological analyses for the presence of pathogens: E. coli, Salmonella and L. monocytogenes were conducted as well. Also, through this research, the identification of functional ingredients of wheatgrass is done; which is added to fruit juice thereby producing a stable functional beverage, which is safe in terms of food safety and that enriches the nutritional value of fruit juice. [ABSTRACT FROM AUTHOR]

With the development of the tobacco industry, rapid, accurate, and high sensitive analysis of tobacco samples has become an inevitable trend and a practical need for the development of the tobacco industry. In this paper, extractive atmospheric pressure photoionization mass spectrometry ( EAPPI-MS) was used to directly and rapidly analyze the chemical components in 5 kinds of tobacco products including 1R5F, 3R4F, Derby, Seven Stars, and Wang Guan. This method did not require sample pretreatment and chromatography separation. The whole detection took only one minute for one sample. 46 kinds of chemical components in tobacco including alcohols, ketones, acids, esters, aldehydes, phenols, alkaloids, amino acids, and terpenoids were identified. Compared with the traditional electrospray ionization (ESI), EAPPI has the advantages of nopolar discrimination and higher tolerance to the complex matrix. More than this, more chemical components can be detected by EAPPI-MS than liquid chromatographyelectrospray ionization mass spectrometry (LC-ESI-MS). After comparing the extraction capacity of extraction solvents with different polarities, dichloromethane- methanol (2 : 3, V /V) showed a higher extraction effect, which was selected as the optimized extraction solvent. Under optimized parameters, the relative contents of the main alkaloids, organic acids, and phenols in the 5 kinds of tobacco products were analyzed using EAPPI-MS, respectively. Meanwhile, the correlation between the relative contents of tobacco chemicals and tobacco quality was discussed. Overall, different types of tobacco products were unique because of their unique chemical contents. Among these three commercial tobaccos, Derby and Seven Stars were more flavored than Wang Guan. According to the obtained mass spectra of m/ z 50-350 using EAPPI-MS, the 5 kinds of tobacco products could be rapidly distinguished using principal component analysis (PCA). EAPPI-MS provides a simple, rapid, and accurate qualitative and quantitative analysis for tobacco chemicals. This method can be used for rapid batch test of chemical components in tobacco leaves and various tobacco products. [ABSTRACT FROM AUTHOR]

This contribution is part of a series featuring teaching analytical science during the pandemic in order to support instructors in preparing their courses. Additionally, for this course the instructor live-streamed five laboratory experiences engaging students in the execution of experimental procedures to gather accurate data in real time. The lecture component has an enrollment of 25-50 students per semester, while enrollment for the laboratory is limited to 24 students per session. Course demographics The Quantitative and Instrumental Chemical Analysis are semester courses typically taken consecutively by undergraduate students in their second or third year. [Extracted from the article]

We have proposed a combination of techniques for quantitative chemical analysis of high-purity germanium and germanium oxide by inductively coupled plasma atomic emission spectrometry. The techniques are intended for determination of the rare-earth (RE) elements (except Pm), platinum group metals (PGMs) (except Os), I, S, Th, Tl, and U after acid dissolution of a sample (instrumental technique) and after separation of the matrix in the form of a highly volatile compound (combined technique). The instrumental technique allows all of the above elements to be determined. To take into account the effect of germanium on analytical signals of analytes, use is made of Be, Dy, or Gd internal standards. The best results in spike experiments have been obtained for the RE elements, PGMs, and I with the Be 234.861 nm; for Th, Tl, and U with the Dy 353.170 nm; and for S with no internal standards. The analyte detection limits (DLs) lie in the range n × 10–6 to n × 10–5 wt %. The combined technique is intended for lowering the DLs for Ir, Pd, Pt, Rh, Ru, S, Th, Tl, and U. Germanium was removed from weighed samples of germanium metal and germanium dioxide in the form of GeCl4 to above 99.99%. The analyte DLs were then from n × 10–7 to n × 10–6 wt %. [ABSTRACT FROM AUTHOR]

As managers and decision makers evaluate pollutant risk, it is critical that we are able to measure an assessment of the injury. Often, these estimates are difficult to determine for benthic organisms, so in 2017 a chronic polychlorinated biphenyl (PCB) sediment dose–response model to predict benthic invertebrate injury was proposed. Given both natural resource trustee and consultant questions following publication concerning that the aqueous chronic toxicity testing data used in the 2017 model development were primarily from the 1970s and 1980s, this follow‐up short communication is meant to provide the user some additional data that are more recent. With the advances in analytical and quantitative environmental chemistry (i.e., better detection limits and congener separation), we chose to complete acute aquatic toxicity testing using 3 estuarine invertebrates and lethal endpoints (20 and 50% lethal concentrations). This acute testing was selected because chronic aquatic testing for PCBs outside of the data used in the 2017 study was not available to us. The aquatic results used in the present study were changed to sediment using equilibrium partitioning, as done in the 2017 chronic model, after using the same organic–carbon partition coefficient and total organic carbon for our equilibrium partitioning (EqP)–measured calculations. Based on these acute aquatic toxicity results and a general acute‐to‐chronic injury concentration ratio of approximately 10, we found that the 2017 model was valid and, hence, that a 1.0 µg/g chronic PCB sediment criterion is a reasonable estimation of potential benthic invertebrate injury. This was followed by spiked sediment tests where percent acute sediment injury was compared to the EqP‐derived chronic value and the results from 2017; modest agreement is shown. Environ Toxicol Chem 2021;40:1188–1193. Published 2020. This article is a U.S. Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

The aim of this work was to characterize the changes in microstructure and chemical composition of the austenitic overlays on a pressure vessel steel that occur in the vicinity of the interface between the overlay and the base material. The investigations were carried out on a 16Mo3 boiler pipes weld overlaid by 309 and 310 steels. The microstructural examinations were performed on longitudinal cross-sectioned samples. The qualitative and quantitative chemical composition analyses on metallographic samples were determined on Scanning Electron Microscopy (SEM) by means of Energy Dispersive Spectrometry (EDS). The article analyzes the influence of the solidification sequence in both types of steel on final microstructure. [ABSTRACT FROM AUTHOR]

Understanding the stabilities of proteins in nanopores requires a quantitative description of confinement induced interactions between amino acid side chains. We use molecular dynamics simulations to study the nature of interactions between the side chain pairs ALA-PHE, SER-ASN, and LYS-GLU in bulk water and in water-filled nanopores. The temperature dependence of the bulk solvent potentials of mean force and the interaction free energies in cylindrical and spherical nanopores is used to identify the corresponding entropic and enthalpic components. The entropically stabilized hydrophobic interaction between ALA and PHE in bulk water is enthalpically dominated upon confinement depending on the relative orientations between the side chains. In the case of SER-ASN, hydrogen bonded configurations that are similar in bulk water are thermodynamically distinct in a cylindrical pore, thus making rotamer distributions different from those in the bulk. Remarkably, salt bridge formation between LYS-GLU is stabilized by entropy in contrast to the bulk. Implications of our findings for confinement-induced alterations in protein stability are briefly outlined. [ABSTRACT FROM AUTHOR]

Obtaining quantitative agreement between theory and experiment for dissociative adsorption of hydrogen on and associative desorption of hydrogen from Cu(111) remains challenging. Particularly troubling is the fact that theory gives values for the high energy limit to the dissociative adsorption probability that is as much as two times larger than experiment. In the present work we approach this discrepancy in three ways. First, we carry out a new analysis of the raw experimental data for D2 associatively desorbing from Cu(111). We also perform new ab initio molecular dynamics (AIMD) calculations that include effects of surface atom motion. Finally, we simulate time-of-flight (TOF) spectra from the theoretical reaction probability curves and we directly compare them to the raw experimental data. The results show that the use of more flexible functional forms for fitting the raw TOF spectra gives fits that are in slightly better agreement with the raw data and in considerably better agreement with theory, even though the theoretical reaction probabilities still achieve higher values at high energies. The mean absolute error (MAE) for the energy E0 at which the reaction probability equals half the experimental saturation value is now lower than 1 kcal/mol, the limit that defines chemical accuracy, while a MAE of 1.5 kcal/mol was previously obtained. The new AIMD results are only slightly different from the previous static surface results and in slightly better agreement with experiment. [ABSTRACT FROM AUTHOR]

Quantitative predictions of biomembrane/water partition coefficients are important, as they are a key property in pharmaceutical applications and toxicological studies. Molecular dynamics (MD) simulations are used to calculate free energy profiles for different solutes in lipid bilayers. How to calculate partition coefficients from these profiles is discussed in detail and different definitions of partition coefficients are compared. Importantly, it is shown that the calculated coefficients are in quantitative agreement with experimental results. Furthermore, we compare free energy profiles from MD simulations to profiles obtained by the recent method COSMOmic, which is an extension of the conductor-like screening model for realistic solvation to micelles and biomembranes. The free energy profiles from these molecular methods are in good agreement. Additionally, solute orientations calculated with MD and COSMOmic are compared and again a good agreement is found. Four different solutes are investigated in detail: 4-ethylphenol, propanol, 5-phenylvaleric acid, and dibenz[a,h]anthracene, whereby the latter belongs to the class of polycyclic aromatic hydrocarbons. The convergence of the free energy profiles from biased MD simulations is discussed and the results are shown to be comparable to equilibrium MD simulations. For 5-phenylvaleric acid the influence of the carboxyl group dihedral angle on free energy profiles is analyzed with MD simulations. [ABSTRACT FROM AUTHOR]

The refinement of the Robert-Bonamy formalism by considering the line coupling for linear molecules developed in our previous studies [Q. Ma, C. Boulet, and R. H. Tipping, J. Chem. Phys. 139, 034305 (2013); 140, 104304 (2014)] have been extended to asymmetric-top molecules. For H2O immersed in N2 bath, the line coupling selection rules applicable for the pure rotational band to determine whether two specified lines are coupled or not are established. Meanwhile, because the coupling strengths are determined by relative importance of off-diagonal matrix elements versus diagonal elements of the operator -iS1 - S2, quantitative tools are developed with which one is able to remove weakly coupled lines from consideration. By applying these tools, we have found that within reasonable tolerances, most of the H2O lines in the pure rotational band are not coupled. This reflects the fact that differences of energy levels of the H2O states are pretty large. But, there are several dozen strongly coupled lines and they can be categorized into different groups such that the line couplings occur only within the same groups. In practice, to identify those strongly coupled lines and to confine them into sub-linespaces are crucial steps in considering the line coupling. We have calculated half-widths and shifts for some groups, including the line coupling. Based on these calculations, one can conclude that for most of the H2O lines, it is unnecessary to consider the line coupling. However, for several dozens of lines, effects on the calculated half-widths from the line coupling are small, but remain noticeable and reductions of calculated half-widths due to including the line coupling could reach to 5%. Meanwhile, effects on the calculated shifts are very significant and variations of calculated shifts could be as large as 25%. [ABSTRACT FROM AUTHOR]