Characterization and classification of matrix effects in biological samples analyses

An exhaustive classification of matrix effects occurring when a sample preparation is performed prior to liquid-chromatography coupled to mass spectrometry (LC–MS) analyses was proposed. A total of eight different situations were identified allowing the recognition of the matrix effect typology via the calculation of four recovery values. A set of 198 compounds was used to evaluate matrix effects after solid phase extraction (SPE) from plasma or urine samples prior to LC–ESI-MS analysis. Matrix effect identification was achieved for all compounds and classified through an organization chart. Only 17% of the tested compounds did not present significant matrix effects.     

Flow injection analysis of ethyl xanthate by gas diffusion and UV detection as CS2 for process monitoring of sulfide ore flotation

A sensitive and robust analytical method for spectrophotometric determination of ethyl xanthate, CH₃CH₂OCS₂⁻ at trace concentrations in pulp solutions from froth flotation process is proposed. The analytical method is based on the decomposition of ethyl xanthate, EtX⁻, with 2.0 mol L⁻¹ HCl generating ethanol and carbon disulfide, CS₂. A gas diffusion cell assures that only the volatile compounds diffuse through a PTFE membrane towards an acceptor stream of deionized water, thus avoiding the interferences of non-volatile compounds and suspended particles. The CS₂ is selectively detected by UV absorbance at 206 nm (? = 65,000 L mol⁻¹ cm⁻¹). The measured absorbance is directly proportional to EtX⁻ concentration present in the sample solutions. The Beer's law is obeyed in a 1 × 10⁻⁶ to 2 × 10⁻⁴ mol L⁻¹ concentration range of ethyl xanthate in the pulp with an excellent correlation coefficient (r = 0.999) and a detection limit of 3.1 × 10⁻⁷ mol L⁻¹, corresponding to 38 μg L⁻¹. At flow rates of 200 μL min⁻¹ of the donor stream and 100 μL min⁻¹ of the acceptor channel a sampling rate of 15 injections per hour could be achieved with RSD < 2.3% (n = 10, 300 μL injections of 1 × 10⁻⁵ mol L⁻¹ EtX⁻). Two practical applications demonstrate the versatility of the FIA method: (i) evaluation the free EtX⁻ concentration during a laboratory study of the EtX⁻ adsorption capacity on pulverized sulfide ore (pyrite) and (ii) monitoring of EtX⁻ at different stages (from starting load to washing effluents) of a flotation pilot plant processing a Cu-Zn sulfide ore.     

On the Discrimination Between Classical and Quantum States

With the purpose of introducing a useful tool for researches concerning foundations of quantum mechanics and applications to quantum technologies, here we address three quantumness quantifiers for bipartite optical systems: one is based on sub-shot-noise correlations, one is related to antibunching and one springs from entanglement determination. The specific cases of parametric downconversion seeded by thermal, coherent and squeezed states are discussed in detail.     

Spectrophotometric and potentiometric study of the cobalt(II)-thiocyanate system in aqueous medium

The cobalt(II)—thiocyanate system was spectrophotometrically studied at 2.0 M ionic strength (NaClO₄) and 25°C. The following formation constants were obtained: β₁ = 6.9 M^?, β₂ = 28.9 M^?2, β₃ = 12.1 M^?3 and β₄ = 1.30 M^?4. Three wavelengths were considered, 515, 590 and 615 nm, and the molar absorptivities of each species were calculated. Linear relationships were obtained for $\text{ε}$ vs $\text{n}$ and α_i. There is strong evidence that the tetrahedral [Co(SCN)₄]^2? is virtually the only species absorbing at 590 and 615 nm. An indirect potentiometric method led to comparable equilibrium constants. The cadmium(II)—thiocyanate formation constants used in the indirect method, under the same conditions, were found to be β₁ = 21.51 ± 0.09 M^?1, β₂ = 123 ± 1 M^?2, β₃ = 130 ± 3 M^?3 and β₄ = 173 ± 1.2 M^?4, in good agreement with earlier literature data.     

Cellular copper management—a draft user's guide

Copper is essential to many organisms as a cofactor for many proteins and enzymes involved in key biological processes such as respiration and protection from oxidative stress. However, as copper is potentially toxic to living systems, regulatory mechanisms have evolved for its acquisition, trafficking, and release. These mechanisms, whose malfunction is typically associated with severe cellular damage, rely on the concerted action of protein systems that implement mechanisms for copper homeostasis and usage. The ensemble of copper proteins in given organisms can now be predicted with bioinformatics methods from an analysis of amino acid sequences. This work has endeavored to study the copper binding sites in these proteins, and to classify them based on their structural features. When associated with information on occurrence throughout the domains of life and intracellular localization, some generalized perspectives on copper management emerge that may provide a basis for the creation of models of cellular copper metabolism within a systems framework.     

13C direct detected NMR increases the detectability of residual dipolar couplings

13C direct detection is becoming an increasingly efficient approach to identify signals of residues that escape detection in 1H detected experiments. Pulse sequences have been developed to obtain 1H partially recoupled experiments for the measurement of the 1JHalphaCalpha and 1JHN couplings with the same resolution available in conventional 1H detected experiments. A consistent set of backbone rdc obtained without any 1H-based experiment has been obtained and shown to be effective for protein solution structure determination.     

Serum protein pattern during cow pregnancy: Acute-phase proteins increase in the peripartum period

Serum collected in a time-course mode during the pregnancy of a group of heifers was analyzed by 2-DE under various experimental conditions to optimize resolution of all protein spots. Changes in the levels of some components were detected during the last phase of pregnancy and early postpartum. These included a decrease of alpha2-HS-glycoprotein, an increase of alpha1-antichymotrypsin and, with a much larger and more abrupt variation, of orosomucoid and haptoglobin. These findings associate the weeks preceding calving with an acute-phase reaction. Analysis of individual animal's sera by 1-DE demonstrated a higher level of orosomucoid in the sera of cows developing postpartum endometritis during the 2 wk after calving (i.e., in the course of the infection) but a lower level during the 2 wk before calving. This observation could represent an important tool for the prepartum detection of animals prone to develop postpartum endometritis and lead to a more accurate peripartum management of those animals.