Evaluation of semiquantitative analysis mode in ICP-MS

Semiquantitative analysis mode in inductively coupled plasma mass spectrometry (ICP-MS) has been popularly used for fast screening purposes. Although the benefit of it has been studied by many researchers, its performance of application in real-world routine analyses has not been reported.

In this study, we evaluated the reliability of semiquantitative analysis mode through inter-laboratory comparison using two different ICP-MS systems with one multi-element calibration standard. The suitability of semiquantitative analysis mode in routine analysis laboratory was demonstrated by evaluating its application in different laboratories and in real production laboratory practices. Twenty one elements were measured, namely, Be, B, Al, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, As, Sr, Mo, Ag, Cd, Sn, Sb, Ba, Tl, and Pb in various fresh water reference samples. Good results concerning accuracy (relative percentage error within 10%) and reproducibility (relative standard deviation lower than 5%) were obtained in more than 90% analyzed samples at concentrations equal to or greater than 10 times the detection limit (DL). Semiquantitative analysis mode also enabled the determination of elements that are not present in the calibration standard. The results demonstrated the potential of semiquantitative analysis mode as a reliable approach in routine laboratory determination of simple matrices, where high throughput and cost-effectiveness are desired, as well as in emergency situations where speed of analysis is critical and quite often limited sample information is available.     

The cationic cascade route to longifolene

W. S. Johnson's total synthesis of the sesquiterpenoid longifolene is a classic example of the power of cationic polycyclizations for constructing complex molecular architectures. Herein we revisit the key polycyclization step of this synthesis using hybrid Hartree-Fock/density functional theory calculations and validate the feasibility of Johnson's proposed mechanism. We also explore perturbations to the 3-center 2-electron bonding array in a key intermediate that result from changing the polycyclic framework in which it is embedded.     

Boltzmann asymptotics with diffuse reflection boundary conditions

StrongL ¹-convergence towards a stationary solution when time tends to infinity is established for the solutions of the time-dependent nonlinear Boltzmann equation in a bounded domain ³ with constant temperature on the boundary. The collisionless case is first investigated in the varying temperature case.     

Structural Damage Identification Using an Adaptive Multi-stage Optimization Method Based on a Modified Particle Swarm Algorithm

An adaptive multi-stage optimization method utilizing a modified particle swarm optimization (MPSO) is proposed here to identify the multiple damage cases of structural systems. First the structural damage problem is defined as a standard optimization problem. An efficient objective function considering the first few natural frequencies of a structure, before and after damage, is utilized for optimization. A modified particle swarm optimization (MPSO) dealing with real values of damage variables is introduced to solve the optimization problem. In order to assess the performance of the proposed method, some illustrative examples with and without considering the measurement noise are tested. Numerical results demonstrate the high accuracy of the method proposed for determining the site and severity of multiple damage cases in the structural systems.     

Concerted and stepwise proton-coupled electron transfers in aquo/hydroxo complex couples in water: oxidative electrochemistry of [Os(II)(bpy)(2)(py)(OH(2))](2+)

Successive oxidation of transition metal(II) aqua complexes (M(II)OH(2) to M(III)OH) is a domain in which proton-coupled electron transfer reactions are extremely common. The mechanism of these PCET reactions-concerted or stepwise-is an important issue in the understanding and design of natural or artificial systems catalyzing the formation of dioxygen by four-electron oxidation of water. Concerted proton-coupled electron transfer from an aqua metal(II) to a hydroxo metal(III) complex requires the close proximity of a proton-accepting group with a pK value between those of the aqua complexes. Otherwise, stepwise electron-proton or proton-electron pathways involving high-energy intermediates are followed. Concerted proton-electron pathways involving water as proton-acceptor or proton-donor group are inefficient. Cyclic voltammetry of the title complex in buffered aqueous solution and re-examination of previous results for the same complex attached to an electrode surface are used to establish these conclusions, which provide a starting point on the route to higher degrees of oxidation, such as those involved in the catalysis of water oxidation.     

Method development and validation for trifluoroacetic acid determination by capillary electrophoresis in combination with capacitively coupled contactless conductivity detection (CE-C4D)

A method was developed to determine traces of trifluoroacetic acid as impurity in synthetic or semi-synthetic drugs as antibiotics, macropeptides, etc. Capillary electrophoresis in combination with capacitively coupled contactless conductivity detection (CE-C⁴D) was used due to lack of UV absorbance property of trifluoroacetic acid (TFA). The optimized method took less than 1 min with good linearity (R² = 0.9995) for trifluoroacetic acid concentration from 2 to 100 ppm. It also has a good repeatability expressed by the relative standard deviation (% RSD) which is 1.2 and 2.1% for intraday and interday precision, respectively, at 50 ppm TFA, and good sensitivity with 0.34 ppm, 1.2 ppm LOD and LOQ, respectively. In addition, the content of TFA in synthetic drug, was determined using the validated method which gave good linearity (R² = 0.9996) for trifluoroacetic acid spiked into drug in a concentration range of 2-80 ppm, with good intraday repeatability of 2.0%.The analysis is performed in a background electrolyte composed of 20 mM morpholinoethane-sulfonic acid (Mes) and 20 mM l-histidine (l-His) pH 6.1. Cetyltrimethylammonium bromide (CTAB) was added as flow modifier in a concentration (0.2 mM) lower than the critical micellar concentration. Ammonium formate 6 ppm was used as internal standard. The applied voltage was 30 kV in reverse polarity. A fused silica capillary with 75 μm internal diameter and total length 47 cm (31 cm to C⁴D detector and 37 cm to DAD detector) was used.     

Synthesis of the pyridinyl analogues of dibenzylideneacetone (pyr-dba) via an improved Claisen-Schmidt condensation, displaying diverse biological activities as curcumin analogues

An efficient and easy procedure to synthesize the pyridinyl analogues of dibenzylideneacetone (pyr-dba) was developed by the condensation of substituted nicotinaldehyde and acetone in the presence of K(2)CO(3) in toluene-EtOH-H(2)O solvent system. Structurally diverse pyr-dba, including quinolinyl dba, can be prepared conveniently in moderate to excellent yields under mild conditions with this method. The resulting pyr-dba functioned as the enone analogs of curcumin and efficiently inhibited the activation of NF-κB and the growth of colorectal carcinoma HCT116 p53+/+ cells as well as the HIV-1 IN-LEDGF/p75 interaction.