Fe, Co, and Ni ultrafine particles (UFP) were prepared by a gas evaporation method in an inert atmosphere. The different preparing conditions of the Fe, Co, and Ni UFP included inert gas pressures and kinds were investigated by means of x-ray diffraction, transmission electron microscopy (TEM), and magnetic measurements with low or high temperatures. The experimental results show that coercivities Hc of the Fe, Co, and Ni UFP, depending on particle sizes, obey a single-domain theory. The maximum Hc was 450, 1000, and 1500 Oe, respectively, for Ni (310 Å), Fe (210 Å), and Co (200 Å) at room temperature. The coercivities came up to high in the low temperatures. The saturation magnetizations Ms of the Fe, Co, and Ni UFP decreased with small particle sizes. A face-centered structure of Co UFP (200–300 Å) was confirmed by x-ray diffraction. Some Fe UFP in the shape of balls (200–400 Å) observed in the TEM may be an amorphous structure.

The diagnostic fragmentation of N-oxides resulting from loss of the oxygen atom (MH+ --> MH+-O) in electrospray and atmospheric pressure chemical ionization (APCI) mass spectra was investigated. When the temperature of the heated capillary tube was elevated, the ratio of the intensity of the [MH+ -16] fragment to the precursor ion (MH+) increased. This 'deoxygenation' process was associated with thermal activation and did not result from collisional activation in the desolvation region of the API source. Although the extent of 'deoxygenation' is compound-dependent, it can provide evidence for the presence of an N-oxide in a sample and can be used to distinguish N-oxides from hydroxylated metabolites (Ramanathan et al. Anal. Chem. 2000; 72: 1352). To demonstrate the practical application of thermal fragmentation of N-oxides, liquid chromatography (LC)/APCI-MS was used to distinguish an N-oxide drug from its hydroxylated metabolite in an unprocessed rat urine sample, despite the fact that the drug and its metabolite were not fully resolved by HPLC.

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