High detection sensitivity achieved with cryogenic detectors in combination with matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry

Cryogenic detectors directly measure the impact energy of any impinging particle independent of its velocity. Thus a very high, mass-independent, detection efficiency is expected from their application in TOF-MS. The cryogenic detector applied here is based on a superconducting phase-transition thermometer and was implemented in a dual reflector time-of-flight mass spectrometer (N-geometry). A dilution series using standard sample preparation procedures shows that the detection limit for insulin (Mr: 5,734) can be decreased by several orders of magnitude, down to 0.5 amol on the MALDI target. Detection limits for rhM-CSF beta (Mr: 49,032) and for polyclonal IgG (Mr: ca 150,000) in the high femtomole and low picomole range, respectively, were established.     

Experimental evidence of absolute and convective instabilities in optics

Experimental evidence of convective and absolute instabilities in a nonlinear optical system is given. In optics, the presence of spatial nonuniformities brings in additional complexity. Hence, signatures characterizing these two regimes are derived based on analytical and numerical investigations. The corresponding noise-sustained and dynamical patterns are observed experimentally in a liquid crystal layer subjected to a laser beam with tilted feedback.     

Full automation of derivatization--solid-phase microextraction-gas chromatography-mass spectrometry with a dual-arm system for the determination of organometallic compounds in aqueous samples

The determination of organometallic compounds in aqueous samples by in-vial derivatization and headspace solid-phase microextraction (SPME)-gas chromatography (GC)-mass spectrometry (MS) has been fully automated using a Twin PAL dual-arm robotic system. Linearity, accuracy, sensitivity for a series of n-methyl, n-ethyl, and n-phenyl metal substituted chloride compounds of tin, lead, and mercury were investigated. The automated method was compared to similar manual methods and improved precision, speed and throughput was achieved. By originally programming the Twin PAL dual-arm system with the supplier's software (Cycle Composer, Version 1.5.0) the arms on the robot were only able to work in sequence. However, in order to have a flexible system and exploit time efficiently the robotic arms must work simultaneously. This was accomplished by programming the robot with the new software package called Cruise Control 4-2 for Twin PALs. Compared to Cycle Composer, Cruise Control 4-2 enhanced the speed and throughput of the automated system further. In addition, with a built-in crash prevention protocol and an improved user interface a more user-friendly system was obtained.     

Absolutely continuous spectrum of Stark operators

We prove several new results on the absolutely continuous spectra of perturbed one-dimensional Stark operators. First, we find new classes of perturbations, characterized mainly by smoothness conditions, which preserve purely absolutely continuous spectrum. Then we establish stability of the absolutely continuous spectrum in more general situations, where imbedded singular spectrum may occur. We present two kinds of optimal conditions for the stability of absolutely continuous spectrum: decay and smoothness. In the decay direction, we show that a sufficient (in the power scale) condition is |q(x)|≤C(1+|x|)^?1/4?ε; in the smoothness direction, a sufficient condition in Hölder classes isq∈C^1/2+ε(R). On the other hand, we show that there exist potentials which both satisfy |q(x)|≤C(1+|x|)^?1/4 and belong toC^1/2(R) for which the spectrum becomes purely singular on the whole real axis, so that the above results are optimal within the scales considered.     

Excitation of a van vleck-weisskopf gas by a resonant microwave pulse

A simple calculation of the response of a gas submitted to a resonant microwave pulse is proposed. In particular the often neglected importance of the “in-phase with the field” component of the induced electric dipole is pointed out and checked experimentally.     

A family of degenerate differential operators

Certain second-order partial differential operators, expressed as sums of squares of complex vector fields, are shown not to beC ^∞ hypoelliptic even at a point, rather than merely in an open set. The proof is based on an asymptotic analysis of a family of ordinary differential operators depending on a complex parameter. Research supported by the National Science Foundation.     

Fluoro-ketones VIII. Synthesis of some fluoroquinoxaline compounds from fluoroketones

The reaction between a perfluoroalkylether ,β-diketone or perfluoroalkyletherketoester and o-phenylenediamine yielding quinoxaline compounds was studied in detail. The various intermediate compounds leading to the formation of the quinoxalines were examined by NMR, MS, GC/MS and IR. 2,3-Perfluoroalkylether substituted quinoxaline is the major product of the reaction. In addition however, the formation of a minor product 3-perfluoro-alkylether-2(1H)-quinoxalinone, indicates an alternate reaction path.     

Infrared laser optogalvanic spectroscopy of molecules: Doppler free and double resonance effects

The use of CO₂ and N₂O lasers extends the range of applicability of the infrared laser optogalvanic spectroscopy of molecules recently demonstrated by Webster and Menzies. Doppler free spectroscopy increases the resolution by a factor of about 20 and microwave double resonance enables to observe rotational transitions with extremely small absorption length.