An improvement in the small-volume technique for determining thorium-234 in seawater
- 海洋环境－已发表论文 
The recently developed 2-5 L small-volume MnO2 coprecipitation method for determining Th-234 in seawater has provided a new way to substantially increase, both temporally and spatially, the sampling resolution of Th-234 and Th-234-based particulate organic carbon export estimates in the upper ocean. In this study, we further optimize the technique by reducing reagent quantities and the use of an additional water bath heating step. This optimization allows the filtration of the MnO2 precipitate onto a 25-mm diameter, 1.0 mu m pore size QMA filter to be completed within < 30 min for unfiltered waters from the South China Sea. In addition, we have modified the MnO2 purification procedure to allow for alpha spectrometric measurements of Th-234 recoveries. Results from recovery experiments suggest that reagent amounts can be reduced to 0.0375 mg KMnO4 and 0.1 mg MnCl2 center dot 4H(2)O per liter of sample, while still maintaining high Th-234 recovery. This study further confirms that the addition of a yield monitor is necessary for the application of the small-volume method. (c) 2006 Elsevier B.V. All rights reserved.