Colorimetric water analysis: mature, practical and accurate
Monitor the dissolved oxygen in the high-pressure boiler system
New data shows that the level of traffic pollution in Glasgow has risen by nearly a third...
Fixed solutions for protecting people and assets in oil and gas
Cost-effective and sustainable instrumentation and sensor storage
Realize data security in environmental monitoring system
Hidden motives: China, Taiwan and semiconductors
The article can be downloaded for free. Unlock articles to show more content, diagrams, and images.
Ion monitoring in wastewater using non-suppressed ion chromatography system for cation analysis
Introduction Ammonia present in industrial wastewater will be a toxic threat to aquatic organisms and ultimately to humans when it is converted into nitrate. The National Pollutant Discharge Elimination System (NPDES) permit program authorized by the US Clean Water Act requires monitoring of ammonium cations to understand the amount of ammonia dissolved in water. Ion chromatography with conductivity detector is an ideal tool for selective and sensitive determination of inorganic ions. However, since the eluent also contains ions that increase the level of background noise, an ion suppressor located between the column and the detector can be used to neutralize the eluent through ion exchange. When using a suppressor, at least six calibration points are required, because the response to conductivity decreases as the ammonium ion concentration increases, resulting in poor linearity of the calibration curve. IC systems without cation suppression will not show this effect, and accurate quantification can be achieved even with only a few calibration points. This article compares the calibration curves created using suppressor and non-suppressor systems, and introduces an example of measuring cations contained in industrial wastewater using no cation suppressor.
Calibration curves with and without ion suppression Figure 1 and Figure 2 show the calibration curves for quantification of ammonium ions in the concentration range of 0.5 to 20 mg/L using ion chromatography with and without ion suppression, respectively.
Both graphs were created using the same analysis conditions listed in Table 1. It can be seen from the two figures that the non-suppression system (Figure 2) provides good linearity within the calibration range, while the curve obtained with ion suppression is non-linear (Figure 1). When an ion exchange suppressor is used, the eluent is converted into water without pH buffering capacity, which results in the suppression of the dissociation of target ions. At the same time, the pH value of the eluent flowing into the conductivity detector increases, and the ammonium ions also increase. In other words, the balance relationship expressed in Equation 1 shifts to the left [1].
Therefore, when the concentration of ammonium ions in the sample solution increases, the response of the conductivity detector decreases, resulting in a non-linear calibration curve. This effect is not seen in a system without eluent suppression. Although a suppressor can be used or not to obtain the same level of quantitative value, as long as the calibration curve is accurately created, since the linear calibration curve allows reliable linear approximation, the non-suppressor system provides accurate quantification and fewer calibration points.
Industrial wastewater analysis Industrial wastewater is filtered through a special membrane filter for ion chromatography with a pore size of 0.2 μm, and then analyzed using an ion chromatography system without an ion suppressor. It can be seen from the analysis conditions described in Table 2 that 2 mmol/L of 18-Crown-6 was added to the eluent to ensure sufficient separation of sodium ions and ammonium ions. The quantitative results of the cations in the samples are listed in Table 3; Figure 3 shows the corresponding chromatograms. Even if the content of sodium ions in the sample is significantly higher than that of ammonium ions, good separation and accurate quantification can be achieved.
Method optimization of ammonium ion separation In the analysis of industrial wastewater, one concern is the interference of high concentrations of sodium ions compared with only trace ammonium ions and their similar elution time. To optimize this separation method, 18-Crown-6 was added to the eluent. Crown ethers are hollow cyclic compounds composed of carbon, hydrogen, and oxygen. Because oxygen atoms are located inside, they can contain certain cations (such as ammonium and potassium ions). Due to the strong interaction with the stationary phase, they can selectively increase the retention of these cations. However, since the retention time of potassium ions has a greater impact than the retention time of ammonium ions, a series of experiments were conducted to gradually increase the amount of 18-Crown-6 in the eluent to determine the best conditions for the two analytes. Figure 4 shows a conceptual diagram of the change in elution behavior with the amount of crown ether added, as well as the graph in Figure 3. Figure 5 plots the relationship between the concentration of 18-Crown-6 and the retention time of the 6 cations in the mixture.
Conclusion This article compares the usefulness of eluent suppression in the determination of NH4 cations in industrial wastewater by ion chromatography. It also discussed the method optimization of adding 18-Crown-6 ether to the eluent to improve the separation of NH4+ in the presence of sodium ion interference. Achieve good separation and accurate quantification, even if the sodium ion content in the sample is significantly higher than the ammonium ion.
References [1] Application News No. L521, Shimadzu Corporation, 2017
Biography Dr. Gesa Johanna Schad graduated from NTA University of Technology in Isny, Germany in 2004 with a diploma in chemical engineering, and in 2005 received a master's degree in pharmaceutical analysis from the University of Strathclyde in Glasgow, UK. She has been a consultant until 2006 when she performed HPLC method development and validation at the FAO/IAEA Analytical Laboratory in Vienna, Austria. She received a PhD in Pharmaceutical Science Research from the University of Strathclyde in 2010 and has been an HPLC expert in the R&D department of Hichrom Ltd. in Reading, UK since 2009. Since 2013, she has been an HPLC product expert and since 2015, she has been the HPLC product manager of Shimadzu Europa's analytical business unit in Duisburg, Germany. Contact: shimadzu@shimadzu.eu
The article can be downloaded for free. Please log in to read this article or create an account.
In this edition of business news-Alphasense celebrates the 25th anniversary of the development of sensor technology-Biral strengthens its development team with a new chief engineer-Fugro improves laboratory capabilities...
Analytica Anacon India and IndiaLabExpo-new date
Nepal Laboratory-New Date
National Biodiesel Conference and Expo
International Labmate Limited Oak Court Business Center Sandridge Park, Porters Wood St Albans Hertfordshire AL3 6PH United Kingdom
Phone +44 (0)1727 858 840 Fax +44 (0)1727 840 310 Email info@labmate-online.com
Copyright © 2021 Labmate Online. all rights reserved.