Analysis of testosterone and dihydrotestosterone from biological fluids as the oxime derivatives using high-performance liquid chromatography/tandem mass spectrometry

A sensitive liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method for the simultaneous quantitative analysis of dihydrotestosterone (DHT) and testosterone (T) from biological fluids has been developed. Commercially available deuterated analogues were used as internal standards. Steroids were extracted from serum or testicular fluid with hexane/ethyl acetate, evaporated to dryness, and treated with hydroxylamine to form their oxime derivatives. Upon chromatographic separation, the compounds were quantified using selected reaction monitoring (SRM). For T, the [M+H](+) ion at m/z 304 and the fragment ion at m/z 124 were used as the precursor and product ions. For DHT the ion cluster [M+H+ACN](+) at m/z 347 and the dissociated ion [M+H](+) at m/z 306 were used as the precursor and product ions, respectively. The limits of detectability on-column were in the sub-femtomole range for both compounds and the intra-day coefficient of variation (CV) for analysis from serum was less than 7% for both compounds. Given its high reproducibility, sensitivity, and relative simplicity, this assay should be of use in determining androgen levels in biospecimens, particularly in settings where sample quantity or steroid concentration are low.     

Scanning force microscopy on the Si(111)7×7 surface reconstruction

Scanning force microscopy images of the Si(111)7×7 surface reconstruction are presented which are taken in the contact mode in ultrahigh vacuum. Topographic and lateral force data are acquired simultaneously. A special treatment of the sensing tip with PTFE helps to overcome the strong adhesion and wear effects that normally occur on this particular surface.     

Application of thermospray liquid chromatography-mass spectrometry to the simultaneous quantification of tracer concentrations of isotopically labelled carbamazepine epoxide and steady-state levels of carbamazepine and carbamazepine epoxide

A thermospray high-performance liquid chromatography-mass spectrometry method for the separation and quantification of tracer concentrations of isotopically labelled carbamazepine epoxide ([15N, 13C]CBZE) in the presence of steady-state levels of the anticonvulsant carbamazepine (CBZ) and its epoxide metabolite (CBZE) has been developed. The technique does not require derivatization, demonstrates little or no thermal degradation of the analytes, provides increased specificity not available from conventional high-performance liquid chromatography, and has a detection limit of 500 pg for CBZE on-column. The method, incorporating d4-CBZ and d4-CBZE as internal standards, allows precise and accurate determination of the analytes with good reproducibility and stability.     

Die akzessorische Irrationalität der Gleichung fünften Grades

Ohne Zusammenfassung Herrn Professor Andreas Speiser zum siebzigsten Geburtstag gewidmet     

用蒙特卡罗方法计算光通过薄层随机分布粒子的散射

本文利用蒙特卡罗方法计算准直光束通过薄层随机分布粒子散射的透射和反射光强,并和输运理论的扩散近似结果做了比较。当散射接近各向同性时两者符合良好。当散射明显地成为各向异性时,蒙特卡罗方法的结果是合理的,而输运理论的扩散近似失效。