Document Type : Original Article
Authors
1
Department of Chemistry Education, Faculty of Teacher Training and Education, Universitas Khairun
2
Department of Chemistry Education, Faculty of Teacher Training and Education, Universitas Khairun,
3
Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Negeri Padang, Padang
4
Department of Chemistry, Faculty of Medicine, Hamamatsu University School of Medicine, Hamamatsu
5
Department of Chemistry and Biomolecular Science, Faculty of Engineering, Gifu University, Gifu
Abstract
This paper proposes an ion chromatographic method for determining cationic nitrogen species (ammonium-NH4 and methylammonium-MeNH4) and anionic (nitrite-NO2 and nitrate-NO3) in raw spinach (Ipomoea aquatica) samples. The system was based on non-suppressed and suppressed conductivity for determining cationic and anionic nitrogen species. The cationic species was determined on Metrohm C150/4.0 column using a 2.5 mM nitric acid as the eluent. In contrast, the anionic species was determined on Metrohm Supp A 250/4.0 column using 6.0 mM sodium carbonate and 0.5 mM sodium hydrogen carbonate as a mixture eluent. Excellent peak resolution and completed each (cationic or anionic) determination in 10 min. Limits of detection (signal-to-noise ratio: S/N=3) were estimated at 0.068, 0.091, 0.011, and 0.016 mg/L for ammonium, methylammonium, nitrite, and nitrate, respectively. The RSD (relative standard deviation) were less than 3% for retention time, peak area, and peak height. The coefficient correlation with peak heights versus the concentration range is linear, with r2 ≥ 0.999. The method has been applied to the Indonesian water spinach (Ipomoea Aquatica Forsk) and land spinach (Ipomoea Reptans Poir) samples collected and purchased in the local traditional market, fresh food supermarket, and spinach plantation in Ternate City, North Maluku. As observed, the composition of nitrogen species concentration differed in each spinach leaf and stem from collected samples. However, the nitrate concentration was higher in the spinach leaves than in the stems from all samples, while the ammonium concentration was slightly higher in the spinach stems than in the leaves. As for methylammonium and nitrite, their concentrations were under the limit of detection in all samples studied.
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