Atsushi Uzawa

On-line preconcentration of phosphate onto molybdate form anion exchange column

In this paper, we describe an automated flow injection system for measuring the concentration of phosphate based on a fluorescence quenching reaction between Rhoadamine 6G and phosphomolybdate with a preconcentration column, which was packed with a molybdate-form ion exchange resin to collect and preconcentrate the phosphate in the sample solution. Rhodamine 6G was chosen because the reaction with phosphomolybdate was fast and did not require heat. For the construction of a stable flow injection system, an aqueous methanol solution was used as the cleaning reagent to overcome the precipitation of ion-associated complexes between Rhodamine 6G and phosphomolybdate or Rhodamine 6G and molybdate. For the preconcentration and collection of the phosphate ions in a water sample, a preconcentration column, which was packed with a molybdate-form ion exchange resin, was combined with the proposed flow injection system and applied to natural water samples containing low concentrations of phosphate.

Effect of Cobalt as a Chemical Modifier for the Determination of Lead by Electrothermal Atomic Absorption Spectrometry Using a Tungsten Furnace

The effectiveness of cobalt as a chemical modifier was investigated for the determination of lead by electrothermal atomic absorption spectrometry using a tungsten furnace. A 10 µl aliquot of the 0.1% m/v cobalt modifier (CoCl 2 in 1 M HCl) was dropped onto a tungsten metal board and pre-heating was carried out at 1200 °C. After the addition of a solution containing lead, followed by charring at a temperature of 1000 °C, the absorbance of lead was measured at an atomization temperature of 2400 °C. The loss of lead by volatilization could be suppressed at charring temperatures up to 1250 °C by the addition of the cobalt modifier. The relative standard deviation at the 0.06 mg l -1 lead level was less than 3% ( n =5) and the detection limit (S/N=3) was 0.07 ng.

Square-wave polarographic determination of lead in sea water after coprecipitation enrichment with zirconium hydroxide.

Square-wave polarographic determination of lead in sea water after coprecipitation with zirconium hydroxide was investigated. A square-wave polarograph of Shimadzu type PR-50 and Shimadzu type SWP-50 were used and anode was mercury pool in electrolytic cell. Zirconium oxychloride containing 30 mg of zirconium is added to 1000 ml of sea water and pH is adjusted to 8.1 with ammonia water (1: 2). After filtered, the precipitate is then dissolved in 25 ml of 4 M hydrochloric acid. The solution is diluted to 50 ml with distilled water. An aliquot is submitted to the polarographic determination. The polarogram is recorded over the range from-0. 20 V to-0.60 V vs. Hg-pool. The results are as follows: (1) Coprecipitation of lead in sea water was quantitative when the pH was adjusted to 8.1. (2) Lead in sea water was determined to be 3.78 ppb. (3) Effect of diverse ions was examined, and arsenic (III), tin (IV), thallium (I) were found to interfere with the polarographic determination of lead.