Potential of gas chromatography-atmospheric pressure chemical ionization-time-of-flight mass spectrometry for the determination of sterols in human plasma.

The application of Gas Chromatography (GC)-Atmospheric Pressure Chemical Ionization (APCI)-Time-of-Flight Mass Spectrometry (TOF-MS) is presented for sterol analysis in human plasma. A commercial APCI interface was modified to ensure a well-defined humidity which is essential for controlled ionization. In the first step, optimization regarding flow rates of auxiliary gases was performed by using a mixture of model analytes. Secondly, the qualitative and quantitative analysis of sterols including oxysterols, cholesterol precursors, and plant sterols as trimethylsilyl-derivatives was successfully carried out. The characteristics of APCI together with the very good mass accuracy of TOF-MS data enable the reliable identification of relevant sterols in complex matrices. Linear calibration lines and plausible results for healthy volunteers and patients could be obtained whereas all mass signals were extracted with an extraction width of 20 ppm from the full mass data set. One advantage of high mass accuracy can be seen in the fact that from one recorded run any search for m/z can be performed.

Local tuning of CoPt nanoparticle size and density with a focused ion beam nanowriter.

Ultra-small CoPt nanoparticles (NPs) with a mean diameter of 1.3 nm (around 100 atoms) were deposited on a thin 5 nm self-supported amorphous carbon membrane. The effects of focused irradiation with a newly developed Ga(+) ion source were studied by transmission electron microscopy. While the overall coverage of the NPs remained constant, the mean diameter and the density of the NPs evolve in the dose range from 5 x 10(13) to 1 x 10(15) ions cm(-2). The local tuning of the size and density of CoPt NPs by means of ion irradiation could be used in magnetic data storage applications.