323,001 research outputs found
SALDI-MS of real world samples
No full textSurface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) is a method of mass spectrometry, ideal for the low mass range, as it reduces fragmentation and helps with clarity of sample analysis. Projected applications of this technology can be seen in medical and drug research.
• Quinine is a small, organic biomolecule (molecular weight 325 g/mol) that is derived from the bark of the cinchona plant. Native to the Americas, is historically used as an anti-malaria, but in recent years has emerged in drug analyses of heroin. Dealers dilute the sample in quinine, which has a similar bitter taste, as a way to conserve supply.
Due to its variety of functional groups and reactive units, quinine has many side effects. As of April 2019, the FDA limits quinine to 83ppm in beverage samples. Coupled with its increased use in illegal drugs and its regulated recreational use, a new, quick and easy method of detection is needed for its analysis.
• Quinine is commonly found dissolved in carbonated beverages to make tonic water.
• Transition metal oxide (TMOs) nanoparticles are used in SALDI-MS because they require minimal sample preparation, have large surface area to sample rations (which helps with desorption/ionization), and they are compatible with a wide range of different samples
Critical stationary Kirchhoff equations in RN involving nonlocal operators
No full textIn this paper we establish existence and multiplicity of nontrivial non-negative entire (weak) solutions of a stationary Kirchhoff eigenvalue problem, involving a general nonlocal integro-differential operator. The model under consideration depends on a real parameter and involves two superlinear nonlinearities, one of which could be critical or even supercritical
Dissolution rates of talc as a function of solution composition, pH and temperature
No full textSteady-state talc dissolution rates, at far-from-equilibrium conditions, were measured as a function of aqueous silica and magnesium activity, pH from 1 to 10.6, and temperature from 25 to 150 degrees C. All rates were measured in mixed flow reactors and exhibited stoichiometric or close to stoichiometric dissolution. All measured rates at pH > 2 obtained at a fixed ionic strength of 0.02 M can be described to within experimental uncertainty usingr(+) = S-BET (A(A) (a(H+)(2)/aMg(2+))(1/4) + A(B)) exp(-E-A/RT)where r+ signifies the BET surface area normalized forward talc steady-state dissolution rate, S-BET denotes the BET surface area of talc present in the reactor, A(A) and A(B) refer to pre-exponential factors equal to 5.0 x 10(-9) and 0.8 x 10(-9) mol/cm(2)/s, respectively, E-A designates an activation energy equal to 45 kJ mol(-1), R represents the gas constant, T denotes absolute temperature, and ai refers to the activity of the subscripted aqueous species. The first term of this rate expression is consistent with talc dissolution rates at acidic pH being controlled by the detachment of partially liberated silica tetrahedral formed at talc edge surfaces from the exchange of Mg2+ for two protons. Corresponding atomic force microscopic observations confirms that dissolution proceeds by the removal of T-O-T sheets from talc edges. At pH <=, 2, the Mg2+ for proton exchange is so extensive that talc T-O-T sheets break apart leading to increased surface area and accelerated rates, whereas rates appear to be pH independent at pH >= 7. (C) 2007 Published by Elsevier Ltd
Multiple Solutions for an Eigenvalue Problem Involving Non-local Elliptic p-Laplacian Operators
No full textIn this paper we establish the existence of two nontrivial weak solutions of a one parameter non-local eigenvalue problem under homogeneous Dirichlet boundary conditions in bounded regular domains, involving a general non-local elliptic p-Laplacian operator
Physician And Patient Barriers To Radiotherapy Service Access: Treatment Referral Implications
No full textRadiotherapy is one of the mainstays of cancer treatment, and about 60% of cancer patients receive this type of treatment during their course of treatment. An evident gap between optimal and actual radiotherapy utilization proportions has recently been reported, which has been ascribed to lack of referral to radiation oncology. There are many factors influencing the radiotherapy referral, including patient anxiety about toxicity, wrong perception of efficacy and side effects by physicians and patients, insufficient knowledge of referral process. These factors, defined as barriers can be categorized in health system barriers, physician and patient barriers. In the present brief narrative review, we discussed barriers to radiotherapy referral focusing on physician and patient barriers
Ion desorption efficiency and internal energy transfer in carbon-based surface-assisted laser desorption/ionization mass spectrometry: Desorption mechanism(s) and the design of SALDI substrates
No full textIon desorption efficiency and internal energy transfer were probed and correlated in carbon-based surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using benzylpyridinium (BP) salt as the thermometer chemical. In a SALDI-MS experiment with a N2 laser (at 337 nm) used as the excitation light source and with multiwalled carbon nanotubes (CNT), buckminsterfullerene (C60), nanoporous graphitic carbon (PGC), non-porous graphite particles (G), highly oriented pyrolytic graphite (HOPG), or nanodiamonds (ND) as the SALDI substrate, both the desorption efficiency in terms of ion intensity of BP and the extent of internal energy transfer to the ions are dependent on the type and size of the carbon substrates. The desorption efficiency (CNT ∼ C60 > PGC > G > HOPG > ND) in general exhibits an opposite trend to the extent of internal energy transfer (CNT < C60 ∼ PGC < G ∼ HOPG < ND), suggesting that increasing the extent of internal energy transfer in the SALDI process may not enhance the ion desorption efficiency. This phenomenon cannot be explained by a thermal desorption mechanism, and a non-thermal desorption mechanism is proposed to be involved in the SALDI process. The morphological change of the substrates after the laser irradiation and the high initial velocities of BP ions (1100-1400 ms-1) desorbed from the various carbon substrates suggest that phase transition/destruction of substrates is involved in the desorption process. Weaker bonding/interaction and/or a lower melting point of the carbon substrates favor the phase transition/ destruction of the SALDI substrates upon laser irradiation, consequently affecting the ion desorption efficiency. © 2009 American Chemical Society.link_to_subscribed_fulltex
Studio degli effetti di un impatto sui reef a vermeti mediante metodi di ecologia del paesaggio.
No full textSALDI-MS Method Development for Analysis of Pharmaceuticals and Polymer Degradation Products
No full textSurface assisted laser desorption ionization-mass spectrometry (SALDI-MS) was evaluated as a new tool for analysis of polymer degradation products. A SALDI method was developed enabling rapid analysis of low molecular mass polyesters and their degradation products. In addition, the possibility to utilize nanocomposite films as easy-to-handle surfaces for analysis of pharmaceutical compounds was investigated. Poly(ε-caprolactone) was used as a model compound for SALDI-MS method development. The signal-to-noise values obtained by SALDI-MS were 20 times higher compared to traditional matrix assisted laser desorption ionization-mass spectrometry (MALDI-MS) of the same samples with 2,5-dihydroxybenzoic acid as a matrix. Halloysite nanoclay and magnesium oxide showed best potential as surfaces and clean backgrounds in the low mass range were observed. The SALDI-MS method for the analysis of polyester degradation products was also verified by electrospray ionization-mass spectrometry (ESI-MS). An advantage over ESI-MS is the possibility to directly analyze degradation products in buffer solutions. Compared to gas chromatography-mass spectrometry (GC-MS) it is possible to analyze polar compounds and larger molecular mass ranges at the same time as complicated extraction steps are avoided. The possibility to use nanocomposite films as surfaces instead of free nanoparticles was evaluated by solution casting of poly(lactide) (PLA) films with eight inorganic nanoparticles. The S/N values of the pharmaceutical compounds, acebutolol, propranolol and carbamazepine, analyzed on the nanocomposite surfaces were higher than the values obtained on the surface of plain PLA showing that the nanoparticles participated in the ionization/desorption process even when they are immobilized. Beside the ease of handling, the risk for instrument contamination is reduced when nanocomposites are used instead of free nanoparticles. The signal intensities depended on the type of drug, type and concentration of nanoparticle. PLA with 10 % titanium oxide or 10 % silicon nitride functioned best as SALDI-MS surfaces.</p
Single-Walled Carbon Nanohorns as Boosting Surface for the Analysis of Low-Molecular-Weight Compounds by SALDI-MS
No full textLimits of Matrix-Assisted Laser Desorption Ionization (MALDI) mass spectrometry (MS) in the study of small molecules are due to matrix-related interfering species in the low m/z range. Single-walled carbon nanohorns (SWCNH) were here evaluated as a specific surface for the rapid analysis of amino acids and lipids by Surface-Assisted Laser Desorption Ionization (SALDI). The method was optimized for detecting twenty amino acids, mainly present as cationized species, with the [M+K]+ response generally 2-time larger than the [M+Na]+ one. The [M+Na]+/[M+K]+ signals ratio was tentatively correlated with the molecular weight, dipole moment and binding affinity, to describe the amino acids’ coordination ability. The SWCNH-based surface was also tested for analyzing triglycerides in olive oil samples, showing promising results in determining the percentage composition of fatty acids without any sample treatment. Results indicated that SWCNH is a promising substrate for the SALDI-MS analysis of low molecular weight compounds with different polarities, enlarging the analytical platforms for MALDI applications
Finite approximations in discrete-time stochastic control: quantized models and asymptotic optimality
No full textIn a unified form, this monograph presents fundamental results on the approximation of centralized and decentralized stochastic control problems, with uncountable state, measurement, and action spaces. It demonstrates how quantization provides a system-independent and constructive method for the reduction of a system with Borel spaces to one with finite state, measurement, and action spaces. In addition to this constructive view, the book considers both the information transmission approach for discretization of actions, and the computational approach for discretization of states and actions. Part I of the text discusses Markov decision processes and their finite-state or finite-action approximations, while Part II builds from there to finite approximations in decentralized stochastic control problems. This volume is perfect for researchers and graduate students interested in stochastic controls. With the tools presented, readers will be able to establish the convergence of approximation models to original models and the methods are general enough that researchers can build corresponding approximation results, typically with no additional assumptions
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