Journal
ANALYTICA CHIMICA ACTA
Volume 434, Issue 2, Pages 209-216Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/S0003-2670(01)00851-0
Keywords
ammonia; indophenol blue; pH; buffering capacity
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Magnesium ions in brackish water or sea water complex with the citrate reagent (CIT) and thus interfere with the indophenol blue spectrophotometric method for ammonia measurement by altering the final pH of the color solution. The complex system, possibly Mg(CIT)(-) + OH- double left right arrow Mg(OH)(CIT)(2-), shows buffer characteristics and can be identified by acid-base titration. A maximum capacity of ca. 40 mu eq pH(-1) ml(-1) was found at pH 10.2 when [Mg2+] was 0.045 M. To compensate for this capacity. extra alkali reagent should be added to sea water samples for the optimal IPB color reaction. For samples with a wide salinity range, the results still need to be corrected empirically either for pH. [Mg2+] or salinity. (C) 2001 Elsevier Science B.V. All rights reserved.
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