SHIRAISHI Yukihide

Tungsten has a high melting point, low resistance, and excellent chemical resistance, and is used as an industrial material for lamp electrodes (filaments) and electrodes for large-scale integrated circuits. Since trace components in the material have a significant effect on the performance and reliability of the device, it is extremely important to determine the concentration of the components in order to evaluate the material properties. In this study, a separation and preconcentration method using a flow injection (FI) system has been developed for the analysis of trace elements in tungsten by AAS. A cation exchange resin column was used for separation and preconcentration. The spike and recovery tests of trace amounts of iron in tungsten were performed by the proposed FI system, and good recoveries were obtained without interference from the tungsten matrix. The proposed system has a 7-fold higher enrichment factor with a sample volume of 3.7 mL and a detection limit of 9 ppb (equivalent to 3.7 µ g g―1 in a solid sample), which enables highly sensitive analysis. The amount of waste fluid per sample analysis is extremely small (27 mL), and the relative standard deviation of 50 ppb iron solution measured five times repeatedly is 2.7 %, which enables accurate analysis. The system is capable of rapid analysis, taking only 6 minutes per sample, and the amount of liquid waste is less than one-tenth that of conventional method, thus reducing the burden on the environment. In this report, iron was selected as the target analyte, but this system is also expected to be applied to highly sensitive analysis of components that can be adsorbed on cation exchange resin.

Chromium has diverse oxidation states, the charges of +3 and +6 for chromium occur the most commonly within chromium compounds. Trivalent chromium (Cr(III)) is not toxic and is essential for living organisms. On the other hand, hexavalent chromium (Cr(VI)) is known to has the strong ability to oxidize and to be a carcinogen. Therefore, it is important selectively to determine of Cr(VI) for the analysis of chromium due to the difference of toxicity between Cr(III) and Cr(VI). 1, 5-Diphenylcarbazide (DPC) is a reagent which selectively reacts with Cr(VI) to color violet complex. We have developed a simple and sensitive analysis of Cr (VI) using a micro fluidic paper-based analytical device (μPAD) with the DPC colorimetric reaction. The fabrication of μPADs was carried out by melting wax with an oven after the pattern was printed with a wax printer. The detection spots were dropped DPC solution and dried. Then, the sample solution was dropped into the sampling spot and wicked to the detection spots. μPAD was scanned with a scanner, the color intensity for the detection spots was analyzed by an image analysis software. The RGB intensity of the images was analyzed, and the highest sensitivity was obtained when G-intensity was used. The detection limit of this device for the Cr(VI) analysis was 26.2 μg/L, the sensitivity for present method has been enhanced compared to the previous method (30 mg/L).