• Journal of Environmental Science International
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• v.4 no.1
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• pp.91-103
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• 1995

The reaction rate, equilibrium, and flow injection analysis methods were fundamentally evaluated for the determination of aqueous ammonia. The selected indophenol blue method was based on the formation of indophenol blue in which ammonium ion reacted with hypochlorite and phenol in alkaline solution. In the optimized reaction condition, the reaction followed 1st order reaction kinetics and the final product was stable. The absorbance measurements before and after the equilibrium were utilized for the reaction rate and equilibrium methods. The reaction rate methods, based on the relative analytical signals for the possibility of eliminating interferents, were shown to have good linear calibration curves but the detection limit and the calibration sensitivity were poorer than those in the equilibrium method. The detection limits were 32-49 pub and 24 pub for the reaction rate and equilibrium methods, respectively In the flow injection analysis, the absorbance was measured before the equilibrium reached and thus resulted in 30% reduction of calibration sensitivity. However, the detection limit was 11 ppb, indicating that the peak-to-peak noise for the blank was remarkably improved. Compared to the manual methods, the optimized experimental condition in a closed reaction system reduced the blank absorbance and the inclusion of ammonia from the atmosphere was prevented. In addition, highly reproducible mixing of sample and reagents and analytical data extracted from continuous recording showed excellent reproducibility.

• Bulletin of the Korean Chemical Society
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• v.30 no.9
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• pp.2032-2038
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• 2009

The amount of phenol and NaOH for the colorimetric determination of ammonia in Korean standard methods (KSM) is found to be highly excessive compared to the standard methods of several other countries. The absorbance of indophenol formed by the Berthelot reaction for ammonia analysis was measured under the various reaction conditions classified in experiment groups 1, 2, 3, 4 and KSM and American standards methods (ASM), and the relationships between the absorbance of indophenol and concentration of ammonia were compared. The amount of phenol can be reduced to 10 g (current 25 g in KSM) and NaOH can be reduced to 1.76 g (current 11 g in KSM) for the preparation of 200 mL phenate solution, and the absorbance sensitivity increased. The concentration of the phenol and NaOH correlatively affect the pH of the solution, which is a critical variable in achieving the maximum sensitivity and rapid and stable color development.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.12
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• pp.667-675
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• 2016

Nanoscale zero-valent iron (nZVI) has been effectively applied for environmental remediation due to its ability to reduce various toxic compounds. However, quantification of nZVI reactivity has not yet been standardized. Here, we adapted colorimetric assays for determining reductive activity of nZVIs. A modified indophenol method was suggested to determine reducing activity of nZVI. The method was originally developed to determine aqueous ammonia concentration, but it was further modified to quantify phenol and aniline. The assay focused on analysis of reduction products rather than its mother compounds, which gave more accurate quantification of reductive activity. The suggested color assay showed superior selectivity toward reduction products, phenol or aniline, in the presence of mother compounds, 4-chlorophenol or nitrobenzene. Reaction conditions, such as reagent concentration and reaction time, were optimized to maximize sensitivity. Additionally, pretreatment step using $Na_2CO_3$ was suggested to eliminate the interference of residual iron ions. Monometallic nZVI and bimetallic Ni/Fe were investigated with the reaction. The substrates showed graduated reactivity, and thus, reduction potency and kinetics of different materials and reaction mechanism was distinguished. The colorimetric assay based on modified indophenol reaction can be promises to be a useful and simple tool in various nZVI related research topics.

• Korean Journal of Microbiology
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• v.24 no.2
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• pp.133-140
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• 1986

Extracts of CO-autotrophically grown cells of Acinetobacter sp. 1 were shown to use thionin, methylene blue, or 2,6-dichlorophenol-indophenol, but not NAD, NADP, FAD, or FMN, as electron acceptors for the oxidation of CO under strictly anaerobic conditions. The CO dehydrogenase (CO-DH) in the thes bacterium was found to be an inducible enzyme. The enzyme activity was determined by an assay based on the CO-dependent reduction of thionin. Maximal reaction rates were found at pH 7.5 and $60^{\circ}C$, and the Arrhenius plot revealed an activation energy of 6.1 kcal/mol(25.5kJ/mol). THe $K_m$ m/ for CO was $154{\mu}M$. Known metalchelating agents tested had no effects on the CO-DH activity. No divalent cations tested affect the enzyme activity significantly escept $Cu^{2+}$ which suppressed the activity completely. The enzyme was inhibited by glucose and succinate. The same extracts catalyzed oxidation of hydrogen gas and formate with thionin as electron acceptor. The CO-DH of Acinetobacter sp. 1 was to have no immunological relationship with that of Pseudomonas carboxydohydrogena.