Improving Water Testing Accuracy with Ion Chromatography
How IC is helping us provide more accurate, reliable, and insightful environmental solutions.
by Melissa John, Research Scientist
Ion chromatography (IC) is an analytical chemistry technique to analyze ions and polar molecules via liquid chromatography. This is a separation technique that uses a liquid mobile phase to separate components of a mixture, based on their interaction with a stationary phase. IC is highly versatile, working across a wide range of analytes, including both inorganic and organic ions. This makes it applicable in various sectors such as environmental monitoring, food and beverage quality control, industrial processing, and pharmaceutical/biopharmaceutical analysis. Ion Chromatography has become essential in many fields due to its precision, sensitivity, and versatility. It provides highly accurate data, making it a valuable tool for environmental research involving wastewater treatment and lake management.
What Is Ion Chromatography?
This technique works by utilizing the principle of ion exchange- the interchange of ions between an insoluble solid and a solution in contact with it. This principle is used for separation and purification processes, such as water softening. IC applies this principle as analytes (ions) of interest are injected into the system and pass over a column containing an ion-exchange resin. The ions ‘stick’ to the resin due to its charge. A liquid (eluent) that contains similarly charged ions is passed over the column and competes with the analytes of interest. The samples ions are ultimately displaced and move along with the eluent as it travels through the column.
This process varies depending on the charge of the ion of interest. Therefore, there are two types of IC: anion-exchange and cation-exchange. These different modalities are used depending on the ions being analyzed. Anion-exchange chromatography is used when the molecule of interest is negatively charged, while cation-exchange is for positively charged ions.
Figure 1: IC Schematic created in https://BioRender.com
How Ion Chromatography Works?
Figure 2: Chromatogram- ions are determined by retention time (x-axis) and the area of the peaks represent the ionic quantities.
This analysis works in a multi-staged process. Firstly, eluent (the mobile phase) flows through the system, pushed by the system’s pumps. Depending on the charge of the ion of interest, different eluents are needed for ion displacement. Anion (negatively charged) columns utilize a basic eluent, such as hydroxide or carbonate-bicarbonate, while cation columns utilize acidic eluents, such as methanesulfonic acid (MSA). This equilibrates the system to ensure that the column resins are in the correct state for desired separation.
As the eluent continuously flows, the sample is injected and pumped through the column. These ions adsorb to the column and are displaced by the eluent at different times depending on their affinity to the resin. After the ions and eluent leave the column, they go through a suppressor, which enhances the detection of the ions and suppresses the conductivity of the eluent. As the ions emerge from the suppressor, they are measured through a conductivity detector, which produces a signal based on their ionic properties. These signals produce peaks which can then be analyzed through a data collection system.
What is Ion Chromatography Used For?
While ion chromatography has many applications across various sectors, at Aquafix we are utilizing this technique for water quality analysis. While traditional methods such as colorimetry have served us in the past, IC provides superior sensitivity, accuracy, and reproducibility. This enhanced analytical performance yields higher-quality data, which is critical for our lake management services.
Our recent focus has been on phosphate detection, as concentrations exceeding 5 ppb can promote algal blooms and negatively impact aquatic ecosystems. IC allows for precise quantification of phosphate at trace levels.
Beyond phosphate, IC enables us to analyze key compounds relevant to wastewater treatment. One such application is the quantification of volatile fatty acids (VFAs) in anaerobic digestion processes. Accumulation of VFAs can disrupt system stability, inhibit biogas production, and cause pH imbalance that may lead to complete system failure. With IC, we can better understand how to manage these compounds for optimal digester performance.
Another application is the possible detection of quaternary ammonium cations (quats), which can severely disrupt wastewater systems, possibly leading to permit violations. Identifying both the type and concentration of these compounds during an upset provides valuable insight into toxicity sources, enabling targeted corrective actions and improved system resilience.
Ion Chromatography is a critical analytical tool that continues to play a vital role in science and industry. Its precision, range of applications, and flexibility make it extremely beneficial for researchers, scientists, and professionals working with complex matrices. At Aquafix, IC has significantly improved our ability to monitor and understand water quality at a deeper level, allowing us to provide the best services we can.
About the Author
Melissa John is a Research Scientist for Aquafix and holds a bachelor’s in environmental sciences. Melissa is the newest member to the Aquafix lab team and has been familiarizing herself to wastewater microscopy.