Research Topics' Summary

[Development of Analytical Methods for Trace Elements in Environmental, Biological, and Industrial Samples]

In this laboratory, students are divided into four main subjects and do research by exchanging their ideas. The common theme in the four main subjects is gnot only total concentration of each element but also itfs chemical spices in environmental, biological, and industrial samplesh.

A. Transportation of trace elements in the environment
This subject is intended to clarify cycling of trace elements in atmosphere, hydrosphere, biosphere, and geosphere. Target samples include airborne particulate matter, fly ash, automobile exhaust particles, rain water, river water, lake water, seawater, sediments, and so on.
1. Real time monitoring of airborne particulate matter
When airborne particulate matter (APM) was collected on a filter (filter-collection data), only average concentrations of elements in APM could be determined during a sampling period. Therefore, we developed the system to determine multi-elements in single APM particles by introducing APM into plasma directly (real-time monitoring data). From real-time monitoring data, we could elucidate sources of APM. We will open in public the real-time monitoring data on our homepage.

Long-term monitoring data (filter-collection data) from May 1995 to December 2013

Real-time monitoring data on 14th October 2013, 23th October 2014, 27th April 2015, 3rd August 2015, 16th November 2015, 13th October 2016, 6th December 2016

2. Speciation analysis of halides in river water and tap water
Speciation analysis of iodine was conducted from up-stream to down-stream of the Kanda River. We have detected iohexol and iopamidol, which are used for X-ray contract agents, at down-stream from Ochiai sewage treatment plant. Tap water of Korakuen Campus of Chuo University is supplied from Asaka Purification Plant after ozone purification treatment. We have detected not only iodide (I-) and iodate (IO3-) but also trace amount of iohexol and iopamidol in tap water.

B. Role of trace elements in living system
Thirty percent of human enzymes contain metals and they take an important role in life as an active center. The purpose of this group is to clarify the role of trace metals in animals and plants. Target samples include blood, organs, urine, and feces in animals, and root, stem, and leaf in plants.

1. Elucidation of selenium metabolism
This research is a joint research with Juntendo University. Mouse breeding is conducted at Juntendo University. Se-82, which is a stable isotope, enriched selenite or selenomethionine was injected intravenously into mice, and after that the distribution of Se-82 in mouse body and selenium spices are traced at different times. From the experimental results, it was clarified that Se is mainly distributed in liver and kidney, and high concentration was found in plasma and red blood cell. For the elucidation of Se metabolism, Se containing proteins are identified and quantified, and time dependent change of Se spices produced in the body was investigated.
2. Molecular mechanisms of metal transports and accumulations in plants
Plants acquire essential metal elements from soils. However, excessive accumulation of metals induce several physiological and biochemical stresses, resulting in severe growth inhibition. We are aiming to elucidate the mechanisms of metal transports and accumulations in plants at molecular levels, and develop biotechnologies to produce plants which are tolerant to environmental stresses. In current research projects, we are trying to discover novel genes causing extreme metal tolerance traits from the mutants and natural species of Brassicaceae family using both ggenome scienceh and ganalytical scienceh approaches. Our efforts will contribute to the improvement of crop production in poor and/or polluted soils, and also the soil clean-up technology using plants (so called gphytoremediationh). The other research topics we are also on-going include the evolutional adaptation to mineral environments in plants and the development of analytical methods to identify metalloproteins with new functions in plants.

C. Determination of trace metals in pure materials

Determination of trace elements in semiconductor materials is necessary for the improvement and the assurance of the production quality. Target samples include silicon carbide (SiC) and gallium nitride (GaN).
1. Determination of trace elements in SiC and GaN
High purity ceramics such as silicon carbide (SiC) and gallium nitride (GaN) are used in semiconductor industry, and the measurement of impurity is required. For the determination of trace elements in solid samples usually the solid samples are liquefied by dissolving them using acids. However, SiC and GaN are very difficult to dissolve by using acids. Therefore, an alternative method, in which trace elements in SiC and GaN are determined without dissolvation, is developing.

D. Development of new analytical methods

The above described A, B, and C groupes are application oriented researches. To achieve the researches, new analytical methods are developed.
1. Speciation analysis
New methodology to identify and quantify metalloproteins is developing. After metalloproteins are triptic digested, and produced peptides are identified by electrospray ionization mass spectrometry (ESI-MS). However, quantification of peptides is difficult by ESI-MS. Therefore, inductively coupled plasma-mass spectrometry (ICP-MS), which has superior quantification to ESI-MS, was used for capillary HPLC-ICPMS to determine sulfur in peptides. Taking yield of triptic digestion and absorption on column into account, finally metalloproteins are quantified.

2. Laser ablation ICP-MS
Metalloproteins are separated by using sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE), which has a wide spread use in the field of biochemistry. After that, laser ablation ICP-MS is used to survey metalloproteins in the separated bands without digestion. We also used LA-ICPMS for the determination of trace elements in pure semiconductor materials.

3. On-line micro column preconcentration
Concentration of REEs in river water and seawater is very low at ppt level. It is difficult to determine directly even if high sensitive ICP-MS is used. Therefore, pre-concentration is required. In this laboratory, on-line column ICP-MS with a chelate resin was developed for pre-concentration. During the pre-concentration process, coexisting matrix can be removed. Using the developed method, REEs in Kanda River water from upper stream to down stream, and REEs in Tokyo Bay seawater were determined. A positive anomaly of Gd was observed after Ochiai sewage treatment plant. It was clarified that the positive anomaly of Gd is caused by contrast medium used for magnetic resonance imaging (MRI).

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