Tutorial review on validation of liquid chromatography–mass spectrometry methods: Part II

This is the part II of a tutorial review intending to give an overview of the state of the art of method validation in liquid chromatography mass spectrometry (LC–MS) and discuss specific issues that arise with MS (and MS–MS) detection in LC (as opposed to the “conventional” detectors). The Part II starts with briefly introducing the main quantitation methods and then addresses the performance related to quantification: linearity of signal, sensitivity, precision, trueness, accuracy, stability and measurement uncertainty. The last section is devoted to practical considerations in validation. With every performance characteristic its essence and terminology are addressed, the current status of treating it is reviewed and recommendations are given, how to handle it, specifically in the case of LC–MS methods.     

Tutorial review on validation of liquid chromatography–mass spectrometry methods: Part I

This is the part I of a tutorial review intending to give an overview of the state of the art of method validation in liquid chromatography mass spectrometry (LC–MS) and discuss specific issues that arise with MS (and MS/MS) detection in LC (as opposed to the “conventional” detectors). The Part I briefly introduces the principles of operation of LC–MS (emphasizing the aspects important from the validation point of view, in particular the ionization process and ionization suppression/enhancement); reviews the main validation guideline documents and discusses in detail the following performance parameters: selectivity/specificity/identity, ruggedness/robustness, limit of detection, limit of quantification, decision limit and detection capability. With every method performance characteristic its essence and terminology are addressed, the current status of treating it is reviewed and recommendations are given, how to determine it, specifically in the case of LC–MS methods.     

Two‐Photon Voltmeter for Measuring a Molecular Electric Field

We present a new approach for determining the strength of the dipolar solute‐induced reaction field, along with the ground‐ and excited‐state electrostatic dipole moments and polarizability of a solvated chromophore, using exclusively one‐photon and two‐photon absorption measurements. We verify the approach on two benchmark chromophores N,N‐dimethyl‐6‐propionyl‐2‐naphthylamine (prodan) and coumarin 153 (C153) in a series of toluene/dimethyl sulfoxide (DMSO) mixtures and find that the experimental values show good quantitative agreement with literature and our quantum‐chemical calculations. Our results indicate that the reaction field varies in a surprisingly broad range, 0–10⁷ V cm^?1, and that at close proximity, on the order of the chromophore radius, the effective dielectric constant of the solute–solvent system displays a unique functional dependence on the bulk dielectric constant, offering new insight into the close‐range molecular interaction.     

Slow decoherence and the radiative decay limit in rare-earth-doped crystals for coherent optical storage

We analyze the material requirements for recording, storage, and processing of optically encoded information using coherent optical transients in resonant solids. We introduce new figures of merit (FOM’s) that explicitly account for the ratio between the rate of the decoherence and the rate of the spontaneous radiative decay. Highest FOM values are achieved when the decoherence rate approaches the fundamental limit set by spontaneous emission under the condition that the total transition oscillator strength is concentrated between a single pair of energy levels. We analyze FOM’s of some of the most promising rare-earth-doped crystals at cryogenic temperatures.     

Instability of an elastically compressed silicon surface under etching

An unusual relief in the form of linear defects resembling quasicracks or grooves was observed on a compressionally stressed surface of a bent silicon surface subjected to chemical etching. The average distance between the forming defects was determined by the magnitude of the surface mechanical strain. The reason for this is assumed to be an Asaro-Tiller-Srolovitz instability in the compressed-surface-etching-agent system. A simple technique is proposed for producing considerable mechanical strains, up to 0.5%, in a silicon surface at room temperature. Fiz. Tverd. Tela (St. Petersburg) 41, 1416–1418 (August 1999)     

Symmetry and boundness of four-particle coulomb systems

The problem of boundness of a ⁺ b ⁺ c ⁻ d ⁻ four-particle Coulomb systems (quadrions) is studied versus the masses of the particles involved. Inequalities that make it possible to deduce that, if some reference quadrions form a bound state, the same is true for a large number of quadrions formed by particles having various masses were derived. A compendium of calculations for energies of reference systems that possess various symmetries [positronium molecules (e ⁺ e ⁺ e ⁻ e ⁻) and quadrions of the a ⁺ b ⁺ b ⁻ b ⁻, a ⁺ b ⁺ a ⁻ b ⁻, and a ⁺ a ⁺ b ⁻ c ⁻ types] is given, and groups of bound asymmetric quadrions corresponding to them are determined. An inequality for kinetic energies of particles that makes it possible to find out, by using asymmetric reference systems, whether specific quadrions are bound is obtained. It is shown that the boundness of many quadrions is ensured by the boundness of respective three-particle systems. The entire body of the present results permits proving that, of the total number of 406 quadrions containing electrons, muons, pions, kaons, protons, deuterons, and tritons and their antiparticles, 227 quadrions are bound.     

Semiempirical functions of the precession magnetic shielding of the proton in the molecules of hydrogen and hydrogen halides

Journal of Structural Chemistry -     

Dephasing processes as studied by two pulse photon echoes and photochemically accumulated echoes: The question of spectral diffusion in a doped organic polymer matrix

Two pulse photon echoes (2PPE) and photochemically accumulated stimulated photon echoes (PASPE) were measured under identical conditions for the system octaethylporphin in a polystyrene matrix. Experiments at 1.9 K show that both echoes have a different decay behavior. Whereas the 2PPE-signal decays with a time constant of 1300 ps, the PASPE-signal decays faster with a time constant of 600 ps. The different temporal behavior of both signals is tentatively attributed to spectral diffusion.     

Kinetic mechanism of surface instability evolution during etching, corrosion, and growth of elastically stressed solids

Corrosion precursors in the form of microgrooves appearing on the elastically compressed surface of a silicon plate under etching are investigated. No corrosion precursors are observed on the elastically stretched surface. This distinguishes the observed effect from corrosion cracking of metals, during which corrosion usually takes place on stretched surfaces. The general dynamic model proposed for the evolution of surface microgrooves during etching, corrosion, and growth of elastically stressed solids is based on the concept of two local etching (growth) rates which are linear functions of the local stress tensor. The model describes the kinetics of the process, and the asymmetry of corrosion evolution to the deformation sign. The role of stacking faults, dislocations, and artificially created surface steps in the evolution of corrosion in stressed silicon crystals is studied.