• Journal of Radiation Protection and Research
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• v.29 no.2
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• pp.73-90
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• 2004

The Reg. Guide 1.109 model was reviewed against its applicability to calculating radionuclide concentrations in agricultural products for operating nuclear facilities and an improved method was proposed. The model was so modified that the radionuclides deposited since the start of operation could be considered in assessing the root uptake. Translocation factors were introduced in the equation for calculating the concentrations in edible parts due to direct plant deposition. Values specific to Korea were set up for the input parameters of the modified model. The concentrations of $^{54}Mn,\;^{60}Co,\;^{90}Sr\;and\;^{137}Cs$ in rice seeds, Chinese cabbage and radish root were calculated for various hypothetical deposition histories using the Reg. Guide 1.109 model and the modified model with parameter values in the guide and those specific to Korea put in alternately. Through comparisons among the results, it could be expected that the use of the modified model with the input of parameter values specific to Korea would result In a more resonable and realistic assessment.

• Analytical Science and Technology
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• v.9 no.4
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• pp.336-344
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• 1996

The extraction of trace cobalt, copper, nickel, cadmium, lead and zinc in urine samples of organic and alkali metal matrix into chloroform by the complex with a dithizone was studied for graphite furnace AAS determination. Various experimental conditions such as the pretreatment of urine, the pH of sample solution, and dithizone concentration in a solvent were optimized for the effective extraction, and some essential conditions were also studied for the back-extraction and digestion as well. All organic materials in 100 mL urine were destructed by the digestion with conc. $HNO_3$ 30 mL and 30% $H_2O_2$ 50 mL. Here, $H_2O_2$ was added dropwise with each 5.0 mL, serially. Analytes were extracted into 15.0 mL chloroform of 0.1% dithizone from the digested urine at pH 8.0 by shaking for 90 minutes. The pH was adjusted with a commercial buffer solution. Among analytes, cadmium, lead and zinc were back-extracted to 10.00 mL of 0.2 M $HNO_3$ from the solvent for the determination, and after the organic solvent was evaporated, others were dissolved with $HNO_3-H_2O_2$ and diluted to 10.00 mL with a deionized water. Synthetic digested urines were used to obtain optimum conditions and to plot calibration-eurves. Average recoveries of 77 to 109% for each element were obtained in sample solutions in which given amounts of analytes were added, and detection limits were Cd 0.09, Pb 0.59, Zn 0.18, Co 0.24, Cu 1.3 and Ni 1.7 ng/mL, respectively. It was concluded that this method could be applied for the determination of heavy elements in urine samples without any interferences of organic materials and major alkaline elements.

• Clean Technology
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• v.28 no.4
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• pp.269-277
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• 2022

With the recent development of the biological enzymatic reaction industry, lactic acid (LA) can be mass-produced from biomass sources. In particular, a catalytic process that converts LA into acrylic acid (AA) is receiving much attention because AA is used widely in the petrochemical industry as a monomer for superabsorbent polymers (SAP) and as an adhesive for displays. In the LA conversion process, NaY zeolites have been previously shown to be a high-activity catalyst, which improves AA selectivity and long-term stability. However, NaY zeolites suffer from fast deactivation due to severe coking. Therefore, the aim of this study is to modify the acid-base properties of the NaY zeolite to address this shortcoming. First, base promoters, Ca ions, were introduced to the NaY zeolites to tune their acidity and basicity via ion exchange (IE) and incipient wetness impregnation (IWI). The IWI method showed superior catalyst selectivity and stability compared to the IE method, maintaining a high AA yield of approximately 40% during the 16 h reaction. Based on the NH₃- and CO₂-TPD results, the calcium salts that impregnated into the NaY zeolites were proposed to exit as an oxide form mainly at the exterior surface of NaY and act as additional base sites to promote the dehydration of LA to AA. The NaY zeolites were further treated with KOH before calcium impregnation to reduce the total acidity and improve the dispersion of calcium through the mesopores formed by KOH-induced desilication. However, this KOH treatment did not lead to enhanced AA selectivity. Finally, calcium loading was increased from 1wt% to 5wt% to maximize the amount of base sites. The increased basicity improved the AA selectivity substantially to 65% at 100% conversion while maintaining high activity during a 24 h reaction. Our results suggest that controlling the basicity of the catalyst is key to obtaining high AA selectivity and high catalyst stability.