Fully automated determination of eserine N-oxide in human plasma using on-line solid-phase extraction with liquid chromatography coupled with electrospray ionization tandem mass spectrometry

A sensitive and entirely automated solid-phase extraction/liquid chromatography/electrospray ionization tandem mass spectrometric (SPE/LC/ESI-MS/MS) method was developed and validated for the determination of eserine N-oxide (ENO), a cholinesterase inhibitor-like physostigmine in human plasma, for use in pharmacokinetic studies. ENO is light-sensitive and the use of a fully on-line process increased the reliability of the assay. Plasma samples previously mixed with neostigmine bromide to prevent in vitro degradation, and tacrine as internal standard (IS), were directly injected into the SPE/LC/ESI-MS/MS system. MS software piloted the overall system. MS/MS detection of ENO and the IS was performed in the positive ion ESI mode using multiple reaction monitoring. The linear calibration curve for ENO ranged from 25 pg ml(-1) to 12.5 ng ml(-1). The limit of quantitation was 25 pg ml(-1) with 250 microl of plasma injected. Precision, accuracy and stability tests were within the acceptable range and just one analyst is required to analyze 50 unknown samples a day five days per week, from the preparation of the samples (i.e. thawing and centrifugation) to data processing. A pilot pharmacokinetic study in three healthy volunteers treated with 4.5 mg of ENO (Génésérine3((R))) showed that the method was suitable for pharmacokinetic studies in humans.     

Determination of teicoplanin in human plasma and urine by affinity and reversed-phase high-performance liquid chromatography

A sensitive, highly selective and simple high-performance liquid chromatographic method for the determination of teicoplanin, a novel glycopeptide antibiotic, composed of six components, in human plasma and urine is described. After an isolation step by affinity chromatography, the antibiotic substances were chromatographed on a Nucleosil C18 column with phosphate buffer-acetonitrile according to a gradient profile. All the components were detected by their UV absorption at 240 nm. The concentration of teicoplanin was determined by using the external standard procedure. This method was applied to the sum of the six major components as well as to each of them separately. The linearity of the method was checked between 0.5 and 50 micrograms/ml for plasma and between 2 and 50 micrograms/ml for urine. The limit of detection was 0.1 microgram/ml for both biological fluids. The coefficients of variation of the between-day assays did not exceed 8.6 and 8.9% in plasma and urine, respectively. The application of the method to a pharmacokinetic study of teicoplanin after a single intravenous therapeutic dose in a patient is reported. This rapid technique also appears to be suitable for drug monitoring.     

An improved system for data acquisition and analysis for viscoelastic measurements of dilute macromolecular solutions with the modified birnboim-schrag multiple lumped resonator

A new system of data acquisition and analysis has been developed for the modified Birnboim-Schrag multiple lumped resonator apparatus which is used to measure the viscoelastic properties of long-chain macromolecules in dilute solution. The modifications to the original apparatus include improved temperature control and vibration isolation. The original theory has been reworked so that each resonance mode can be characterized by a greater number of data points. The entire data acquistion/processing system is automated and placed under computer control; a correlation for mode coupling is derived. The modifications result in improved precision in the measured viscoelastic moduli and increased instrumental reliability.     

Some mildly wild circles in Sn arising from algebraic K-Theory

We study wild embeddings of S ¹ in S ⁿ which are tame in a sense introduced by Quinn. We show that if is a finitely presented group with H ₁()=H ₂()=0, then any finiteness obstruction K ₀() can be realized on the complement of such an embedded S ¹. We also realize trivially symmetric K _–1() obstructions on the complements of such embeddings. For trivially symmetric , the embeddings constructed are shown to be isotopy homogeneous.     

Stress relaxation in styrene-butadiene-styrene block copolymers containing unattached linear polybutadiene and styrene-butadiene diblocks

Stress relaxation has been studied in networks of styrene-butadiene-styrene triblock copolymers with spherical styrene domain structure containing 0.10 weight fraction of unattached linear polybutadiene (M_w = 389,000) or styrene-butadiene diblocks with very long butadiene segments (M = 225,000 or 510,000). The stretch ratio (uniaxial extension) was usually 1.15 and the temperature ranged from ?20 to +20°C. The contribution of the linear polybutadiene species to relaxation was essentially the same in two triblock networks with very different butadiene block lengths, as expected if the configurational rearrangements are dominated by reptation. In the diblock-triblock mixtures, in which the diblock butadiene segments are free at one end but anchored at the other and therefore incapable of reptation, there was no contribution to relaxation from the dangling butadiene segments of the diblock component; this would be expected if there are no relaxation mechanisms alternative to reptation for these very long semiattached species within the experimental time scale.     

Balance equation formulation and memory effects in retarded high field semiconductor transport

The role of the finite, non-zero collision duration in high electric fields is examined for its effect on transient and overshoot response of carrier velocity and energy. A quantum kinetic equation approach is used to develop modifications of the balance equations obtained in a drifted Maxwellian approach for treating high-field transport. These result in corrections which require convolution integrals to be evaluated on the short-time scale.     

On the existence and detection of Bloch oscillations in superlattices

While many predicted superlattice behaviors depend on the presence of Bloch oscillations, the existence of such oscillations remains problematical. Here, we consider procedures by which their existence within a superlattice could be detected. We first set upper and lower bounds on the necessary fields. We then demonstrate that while a negative differential mobility is expected, no resonant peak occurs in this mobility at the Bloch frequency. However, we provide two ways of directly observing Bloch oscillations. In the first, we note the existence of structures in the dc velocity-field characteristic when an externally applied RF field has a frequency which is harmonically related to the Bloch frequency. The second approach is to measure the velocity fluctuation noise spectra, which should have a peak at the field-tunable Bloch frequency.     

Theoretical and empirical approaches to understanding the effect of phosphonate groups on the thermal degradation for two chemically modified PMMA

The influence of phosphonated groups on thermal degradation and flammability has been investigated in the case of two chemically modified PMMA. Thermogravimetric analysis as well as pyrolysis combustion flow calorimetry have been used to define the efficiency of phosphorus in both condensed and vapor phases. A theoretical study was also performed to determine the contribution of phosphonated groups to the effective heat of combustion, residue content and heat release capacity. Empirical and theoretical approaches agreed to highlight that PMMA modified with monophosphonated comonomer is more efficient in both condensed and vapor phases in terms of flammability and char formation. These results were attributed to the ability of phosphonate groups to interact with ester groups and also to the weakness of the P–C–N bonds. Moreover, this study proposes a method for designing the chemical environment of phosphonate group in polymers to achieve better flame retardancy.