Journal
TALANTA
Volume 77, Issue 1, Pages 66-72Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.talanta.2008.05.058
Keywords
Ammonia; Trace analyses; Optical sensor; Fluorescent pH-indicators; Cellulose esters
Categories
Funding
- Austrian Science Fund in the framework of the Austrian Nano Initiative
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Even though monitoring of dissolved ammonia is acutely important for environmental studies, fish farms and for industrial surveillance, no system for the performance of online measurements at the concentrations needed exists so far. For many applications it is necessary to detect dissolved ammonia concentrations at sub mg/l-levels, because ammonia is reported to be toxic for aquatic organisms above 25 mu g/l. We present new ammonia sensitive materials consisting of fluorescent pH indicators embedded into different cellulose esters. The low pK(a) value of the indicators and the high solubility of ammonia in the cellulose polymers lead to detection limits below 1 mu g/l and a dynamic range between 5 and 1000 mu g/l. Response times at these trace concentration levels are in the order of 20-30 min. The sensors are suitable for fresh and sea water monitoring by an additional silicon layer preventing the interference of protons and salinity. The fluorescent indicators Eosin ethylester and 2',7'-dichlorofluorescein methylester (DCF) were investigated to achieve sensors with a dynamic range matching the target concentrations. Sensors with improved performance were obtained by employing cellulose ester nanospheres with incorporated Eosin ethylester. The simple sensor design has a high potential to be applied in miniaturized optical measurement system for online ammonia detection. (C) 2008 Elsevier B.V. All rights reserved.
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