Simultaneous chiral determination of methamphetamine and its metabolites in urine by capillary electrophoresis-mass spectrometry

A capillary electrophoresis-mass spectrometry method for the simultaneous chiral determination of enantiomers of methamphetamine (MA), amphetamine (AP), dimethylamphetamine (DMA) and p-hydroxymethamphetamine (pOHMA), in urine has been developed. The internal standards used were 2-phenylethylamine and 1-amino4-phenylbutane. The electrolyte was 1 M formic acid (pH 2.2). The chiral selector, which was added to the electrolyte, was a mixture of 3 mM beta-cyclodextrin and 10 mM heptakis(2,6-di-O-methyl)-beta-cyclodextrin. The detection limits were 0.03 microg ml(-1) for the enantiomers of MA and AP and 0.05 microg ml(-1) for the enantiomers of pOHMA using selected ion monitoring. In the analysis of healthy adult urine samples spiked with MA, AP and pOHMA, the precision of within-run assays (n = 4) for the migration time after correction with two internal standards were under 0.04%, and the detection yields utilizing solid phase extraction were 95-105%. This method was applicable to the analysis of urine samples of MA addicts and DMA addicts.     

Preferential hydration of proteins: A Kirkwood-Buff approach

The presence of cosolvents affects the stability of proteins in aqueous solutions. Some (such as trehalose and polyethelene glycol) enhances the stability of proteins, whereas others (such as urea) denatures the proteins. We explain different actions of cosolvents based upon the recent theoretical developments in the application of Kirkwood-Buff theory.     

Exterior complex scaling and the AC-Stark effect in a Coulomb field

By means of the exterior complex scaling of B. Simon an existence proof of resonances is given for the time-dependent Schrödinger equation $$i\frac{{\partial \psi }}{{\partial t}} = - \left( { - \Delta + V + \mu x_1 \cos \omega t} \right)\psi ,$$ whereV belongs to a class of potentials which includes the Coulomb one. The resonance width is given by the Fermi Golden Rule to second order perturbation theory and is nonzero for μ small and almost every ε.     

Resonances for the AC-Stark effect

The resonance problem for the AC-Stark effect is discussed. We prove that all bound states of the system –(1/2) +V(x) will turn into resonances after an AC-electric field is switched on and the order of the imaginary part of a resonance is determined by the number of the photons it takes to ionize the bound state which is turning into the resonance; if two bound states have energy difference of the photon, there exists a state which oscillates between the two states for a long time.This work is supported by the U.S.N.S.F. under grant No. MCS-80-23339-A01     

Effects of solvation on partition and dimerization of benzoic acid in mixed solvent systems

The partition of benzoic acid between 0.1M perchloric acid solution and two kinds of mixed solvents has been carried out at 25 degrees C. The partition and dimerization constants of benzoic acid have been determined in the 1-octanol-benzene and 2-octanone-benzene systems. In both the mixed solvent systems, with increasing content of 1-octanol and 2-octanone in each mixed solvent, the partition constant of benzoic acid has been found to increase, and the dimerization constant of benzoic acid in each organic phase to decrease. These phenomena are attributable to solvation of monomeric benzoic acid by 1-octanol and 2-octanone molecules in each mixed solvent.     

Absolute Continuity of the Floquet Spectrum¶for a Nonlinearly Forced Harmonic Oscillator

We prove that the Floquet spectrum of the time periodic Schr?dinger equation corresponding to a mildly nonlinear resonant forcing, is purely absolutely continuous for μ suitably small. Received: 23 March 2000 / Accepted: 24 May 2000     

Measurements of cosmic-ray low-energy antiproton and proton spectra in a transient period of solar field reversal

The energy spectra of cosmic-ray low-energy antiprotons ( *p's) and protons ( p's) have been measured by BESS in 1999 and 2000, during a period covering reversal at the solar magnetic field. Based on these measurements, a sudden increase of the *p/p flux ratio following the solar magnetic field reversal was observed, and it generally agrees with a drift model of the solar modulation.     

A nonlinear correlation method using multiphoton ionization for the measurement of uv ultrashort pulses

A new nonlinear correlation method which makes it possible to measure the duration of uv ultrashort pulses has been proposed. In this method the multiphoton ionization of gases is used as a nonlinear process and the ion current caused by the process is detected. We have also experimentally demonstrated its usefulness in the uv region by observing the second- and the third-order auto-correlation profiles of picosecond pulses at 2661 Å (the fourth harmonic of a mode-locked YAG laser), using NO and Xe gases, respectively.