Kaori Shigeta

We have applied a micro droplet generator (μDG) for sample introduction of single selenized yeast cells into a sector field ICP-MS, which was operated in a fast scanning mode with sampling rates of up to 10 kHz, to measure single cells time resolved with 100 μs integration time. Selenized yeast cells have been used as a model system for preliminary investigation. The single cells to be measured have been embedded into droplets and it will be shown that the time duration of a single cell event always is about 400 to 500 μs, and thus comparable to the time duration of a droplet without a cell. A fixed droplet generation rate of 50 Hz produced equidistant signals in time of each droplet event and was advantageous to separate contribution from background and blank from the analytical signal. Open vessel digestion and a multielement analysis were performed with washed yeast cells and absolute amounts per single cell were determined for Na (0.91 fg), Mg (9.4 fg), Fe (5.9 fg), Cu (0.54 fg), Zn (1.2 fg) and Se (72 fg). Signal intensities from single cells have been measured for the elements Cu, Zn and Se, and histograms were calculated for about 1000 cell events. The mean elemental sensitivities measured here range from 0.7 counts per ag (Se) to 10 counts per ag (Zn) with RSD's from 49% (Zn) to 69% (Se) for about 1000 cell events.

A micro-droplet generator (μDG) sample introduction system was coupled to a sector field ICP-MS instrument to investigate the analytical figures of merit with respect to single cell analysis. The sector field instrument was operated for the first time in a fast scanning mode (E-scan) with the shortest time resolution of 100 μs to measure the single droplet time resolved and using the original detector in a pulse counting mode without modification of the existing electronics. For reduction of the droplet diameter a triple pulse mode of the droplet generator was applied and a droplet diameter down to 23 μm has been achieved for this investigation with a 100% transport efficiency of droplets. Signal duration times of single droplets of less than 500 μs have been measured. Overall detection efficiencies in the range of 10−3 counts per atom have been achieved and absolute limits of detection range between 120 ag for Fe and 1.1 ag for Mg as a mean value from 1000 droplet events.

Se-containing proteins play an important role in human metabolic processes such as antioxidant action. However, speciation analysis of Se-containing proteins in biological samples is challenging because of their small amounts. In order to determine selenoprotein P (Sel-P) in human plasma, separation performance was compared between size exclusion chromatography and affinity chromatography. It was found that affinity chromatography showed better separation performance for Sel-P. Micro-affinity chromatography coupled with low flow ICP-MS was developed, which enabled separation analysis of Sel-P in sub-μl samples. Standard solution flow rate ranges for low sample consumption and total consumption nebulizers were investigated. Moreover, the stability analysis for each nebulizer with the change in composition of the mobile phase was investigated. Finally, using the developed micro-affinity chromatography coupled with the low flow ICP-MS, Sel-P and the other Se-containing proteins in sub-μl samples of human plasma were determined.

A new 4alpha-aryltetralin-type lignan called burseranin (1) and a known analogous lignan picropolygamain (2) were isolated along with known triterpenes, lupeol and epi-lupeol from the methanol extract of stems of Bursera graveolens, which showed a remarkable inhibitory activity against human HT1080 fibrosarcoma cells. The whole structure of 1 was established based on combined spectral studies and the absolute structure for 2 was first confirmed by CD spectral evidence. In addition, cytotoxic activities of the stem (methanol) extract and its components are evaluated in this paper.