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How to monitor the composition of water?
The composition of saltwater is crucial information for a saltwater aquarist, without which achieving success in maintaining the aquarium is impossible. When setting up an aquarium, we try to fill it with a salt solution that mimics natural saltwater. However, over time, the composition of the water can change, often unexpectedly and not always in a good way. That’s why it’s important to regularly check the water. How do you do that? I’ll answer that question now.
The most accurate method to determine the elemental composition of saltwater and RO/DI in saltwater aquariums is atomic emission spectrometry, simply called ICP (Inductively Coupled Plasma).
Most of you have heard of ICP-OES, and maybe some of you have also heard of ICP-MS. Both techniques allow you to study the quantity and quality of elements in the water. This article will explain the differences between these techniques.
What is the difference between ICP-OES and ICP-MS?
The names are quite complicated:
ICP-OES – Inductively Coupled Plasma Optical Emission Spectroscopy
ICP-MS – Inductively Coupled Plasma Mass Spectrometry
Source: https://ifdesign.com/de/winner-ranking/project/icpms-20402050/636336
ICP-OES works by measuring the light emitted by excited atoms and ions in the plasma. On the other hand, ICP-MS is a more advanced analytical technique that also uses plasma to excite atoms, but it measures the mass of ions, not the intensity of emitted light.
You can find more information about analyzing saltwater using the ICP-OES method here.
Both techniques, ICP-OES and ICP-MS, stem from a branch of analytical techniques that use plasma to excite atoms and ions in samples. The basic principle of operation in both cases is the same – utilizing inductively coupled plasma for elemental analysis.
However, they differ in the detection method, which determines the range of applications of the device. This allows for matching the appropriate technique to specific analytical needs.
Stages of sample analysis
It’s important to note that water analysis using ICP-OES or ICP-MS is an analytical method belonging to the group of destructive methods. This means that the sample analyzed is destroyed at one of the stages of analysis, and there is no possibility of recovering the analyzed water.
In essence, both techniques have a common part related to the analysis of the analyte (e.g., seawater), with the differences mainly concerning the detection stage. The choice between them depends on specific needs regarding sensitivity, precision, and analysis costs. In the table below, the stages of seawater analysis using ICP-OES and ICP-MS are briefly presented.
ICP-OES | ICP-MS | |
Analyte (e.g., seawater) | First, the sample is sprayed and introduced into the plasma, which is a hot, ionized gas. | |
Excitation of atoms / ion generation | In the plasma, atoms and ions are excited, resulting in the emission of light at characteristic wavelengths. | The plasma ionizes the atoms in the sample, creating ions of various masses. |
Detection | The detector analyzes the emitted light, measuring the intensity of light at different wavelengths. This intensity is proportional to the concentration of elements in the sample. | The detector measures the amount of ions of different masses, allowing for the determination of the concentration of individual elements and their isotopes. |
Is ICP-MS more accurate than ICP-OES?
ICP-MS definitely has a more complicated analysis process compared to ICP-OES, requiring specialized knowledge. Undoubtedly, the detection limits are lower for ICP-MS than in ICP-OES, allowing for the quantitative determination of elements at concentrations below 0.1 μg/L. The diagram below shows the detection ranges of ICP-OES and ICP-MS.
In simple terms, ICP-OES is a sensitive technique with a linear range and a reasonable detection limit suitable for concentrations from ppm to ppb (μg/L). So, it covers the range necessary in saltwater aquariums. On the other hand, ICP-MS allows for the determination of even lower concentrations (less than 1 ppb) and isotopes*.
Which analytical technique is used in saltwater aquariums?
Despite some laboratories also offering seawater analysis using ICP-MS, ICP-OES remains the most popular and commonly used technique for seawater analysis.
In my opinion, ICP-OES is and will remain the most common method for seawater analysis. Using ICP-MS in saltwater aquariums is like using the Hubble telescope to search for a lost button on the floor. Does it make sense? It depends on the individual needs of the aquarists, but from a chemist’s perspective, not really.
Summary
ICP-OES is sensitive enough to accurately determine element concentrations at levels necessary for maintaining a healthy saltwater aquarium. Information about element concentrations in water at the ppb (μg/L) level is sufficient. Of course, when someone requires the highest precision and sensitivity in analysis, especially where monitoring trace elements at very low levels is necessary, ICP-MS is a better choice.
The ultimate choice depends on specific needs, budget, and the goal of monitoring water parameters in the saltwater aquarium.
* Isotopes are variations of the same chemical element that have the same number of protons in the atomic nucleus (the same atomic number) but differ in the number of neutrons.
About author
Magdalena Metzler
Privately, I am a mother and a lover of nature and sport. My main interest is quantum chemistry, which hides a whole lot of unsolved mysteries and connections, which is extremely exciting from a scientific point of view.
In my scientific career, I have conducted international projects focused on innovative solutions for many branches of business, e.g. automotive, construction, and now, of course, marine aquaristics.
Working at Reef Factory gave me a passion for marine aquaristics, which I can develop every day, building a chemistry department and creating products that will help aquarists take care of tanks and ensure the highest safety of animals. One of the most exciting memories of working at Reef Factory is the commissioning of the ICP-OES spectrometer, which analyzes the elemental composition of seawater. The method of analysis in ICP is based on an analytical technique, which is a combination of my passion for quantum chemistry and marine aquaristics.
I hope you find my articles on ReefPedia interesting and helpful! Happy reading :))