Biomedical subjects

U Dressler

Publications and source records attributed to U Dressler.

7 recordsLinked to original sources

PubMed2001

Characterization and stabilization of the unstable fixed points of a frequency doubled Nd:YAG laser.

We demonstrate the successful stabilization of type II chaos of a multimode, intracavity frequency doubled, diode-pumped Nd:YAG (neodymium-doped yttrium aluminum garnet) laser in experiment using an adaptive proportional feedback control. The two orthogonal polarized infrared intensities are fed back to the injection current of the pump diode. The stability properties of the stabilized unstable fixed points are investigated and exploited to explain the performance of our control scheme and to determine suitable measurement signals for the feedback control.

Journal Article↗

PubMed2000

Detection of THCCOOH in hair by MSD-NCI after HPLC clean-up.

Regular consumption of cannabis can easily be detected by examination of hair for tetrahydrocannabinol, cannabinol, and cannabidiol. Although several studies have demonstrated that after contamination with smoke or treatment with THC containing shampoos THC is not detectable, or only in small traces, the detection of 11-nor-9-carboxy-delta 9-tetrahydrocannabinol (THCCOOH) should be offered to prove the consumption and metabolisation of THC. Up to now this confirmation was only available using tandem MS techniques combined with negative chemical ionisation. A new method using a normal quadrupole GC/MS is described. The lack of expensive instruments has to be paid for by a costly and time consuming extraction and clean-up. After the sample has been digested by 2 M NaOH at 95 degrees C and the neutralised liquid has been extracted with a mixture of n-hexane and ethyl acetate the dried residue is reconstituted in acetonitrile-methanol-0.01 M sulfuric acid (49:21:30, v/v/v) and the cannabinoids separated by HPLC. Each fraction is collected over 1 min. Another extraction with n-hexane-ethyl acetate is followed by evaporation, derivatisation, and GC/MS determination. The calibration with THCCOOH spiked hair led to a LOD of 0.3 pg/mg and a LOQ of 1.1 pg/mg.

Chromatography, High Pressure Liquid↗

PubMed1995