ENVIRONMENTAL LABORATORY 35


Method optimization for separation of ammonium ions


In the analysis of industrial wastewater, a point of concern is the interference of high concentrations of sodium ions compared to only trace amounts of ammonium ions and the proximity of their elution times. To optimize the method with regard to this separation, 18-Crown-6 was added to the eluent. Crown ethers are hollow, ring-shaped compounds comprising of carbon, hydrogen and oxygen and have an inclusive effect on certain cations such as ammonium and potassium ions due to the oxygen atoms located on their interior. They can selectively increase the retention of these cations due to strong interaction with the stationary phase.


However, since the retention time of potassium ions is more strongly affected than ammonium ions, a series of experiments was carried out, gradually increasing the quantity of 18-Crown-6 in the eluent, to determine optimum conditions for both analytes. Fig. 4 shows a conceptual graph of changes in elution behavior depending on the amount of crown ether added, and the diagram in fig. 5 plots concentration of 18-Crown-6 against retention time of the 6 cations in the mixture.


Conclusion


This article compared the usefulness of eluent suppression in the determination of NH4


cations in industrial wastewater by


in the presence of interference by sodium ions. Good separation and accurate quantification were achieved, even for samples containing significantly more sodium than ammonium ions.


+ References [1] Application News No. L521, Shimadzu Corporation, 2017


Figure 5: Graph visualizing the effect of 18-Crown-6 addition on retention of 1: Li, 2: Na, 3: NH4, 4: K, 5: Mg and 6: Ca ions.


Eluent: 3 mmol/L oxalic acid plus 0 to 5 mmol/L 18-Crown-6.


ion chromatography. It also discussed method optimization by addition of 18-Crown-6 ether to the eluent to improve separation of NH4


Biography


Dr. Gesa Johanna Schad graduated with a diploma in chemical engineering from the Technical University NTA in Isny, Germany in 2004 and an MSc in pharmaceutical analysis from the University of Strathclyde in Glasgow, UK in 2005. She worked until 2006 as a consultant in HPLC method development and validation in an analytical laboratory of the FAO/IAEA in Vienna, Austria. She gained her doctorate for research in pharmaceutical sciences at the University of Strathclyde in 2010 and was employed as a HPLC specialist in the R&D department at Hichrom Ltd. in Reading, UK from 2009. Since 2013, she has worked as a HPLC product specialist and since 2015 as HPLC Product Manager in the analytical business unit of Shimadzu Europa in Duisburg, Germany.


Contact: shimadzu@shimadzu.eu


Figure 4: Chromatograms showing the effect of 18-Crown-6 addition on retention of 1: Li, 2: Na, 3: NH4, 4: K, 5: Mg and 6: Ca ions.


Eluent: 3 mmol/L oxalic acid plus 0 to 5 mmol/L 18-Crown-6.


Author Contact Details


Dr. Gesa Schad, Shimadzu Europa GmbH • Duisburg, Germany • Tel: +49 203 76870 • Email: shimadzu@shimadzu.eu • Web: www.shimadzu.eu Yukari Oka, Shimadzu Corporation • Kyoto, Japan


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