Proper collection of water for ICP-OES analysis - how to do it?

Introduction

Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) is one of the most accurate tools for determining the elemental composition of seawater. The results of such analysis are crucial for marine aquarists, providing them with information about the condition of the entire aquarium ecosystem and offering guidance on resolving potential issues that may arise in the aquarium.
ICP-OES analysis is characterized by its high sensitivity and accuracy; therefore, proper sample collection is a critical step in the process. Analytical chemists often emphasize that the most significant impact on the quality and reliability of the results comes from the sample collection stage. In this article, we will present several tips on how to collect a sample from an aquarium to ensure that the results obtained in the laboratory accurately reflect the actual condition of our tank.

When to collect samples for ICP-OES analysis? 

If you have performed maintenance work in the aquarium or changed the water, we recommend waiting at least 12 hours before collecting a sample for ICP-OES analysis. Any work related to cleaning the aquarium, equipment, changing the layout, or introducing new inhabitants can cause a temporary increase in the concentration of some elements due to, for example, disturbing sediments at the bottom of the aquarium or using glues. Such a condition is temporary, and a sample taken at this moment will certainly not reflect the actual quality of the water in the aquarium. Similarly, in the case of feeding and element supplementation, a good solution is to wait at least 2 hours before collecting a sample. This will allow the water in the tank to mix properly and uniformly distribute the supplements and substances contained in the food.

How to properly collect a water sample from an aquarium?

1. Always try to collect water from the same spot. 
2. Open the vial. 
3. Wash the vial and cap three times in aquarium water (remember not to touch the inside of the cap with your fingers). 
4. Submerge the vial and cap under the water surface. 
5. Holding the cap and vial under the water, screw it closed – this way, you will avoid collecting impurities present on the surface of the water (such as a protein film). 
   
   
6. The vial should be full so that there is no air inside – this ensures greater chemical stability of the sample.
   
   

Essential information for correct Interpretation of results

Remember that the effectiveness of the recommendations you receive along with the analysis result depends on the information you provide about your aquarium. A common mistake is to report the “gross” capacity of the aquarium—that is, the volume derived from its external dimensions. To correctly calculate the dosages of supplement solutions, you should use the net volume. The net volume is the actual amount of water in the tank, taking into account the amount of rock, the level of tank filling, and the volume of water in the sump.

Common mistakes when collecting water samples from an aquarium? 

Performing maintenance tasks such as changing water, removing sediments, re-gluing rock or coral, directly before collecting a sample. Feeding the stock or supplementing directly before collecting a sample. Using hand cosmetics directly before collecting a sample (particularly important due to the high content of zinc in hand creams and balms). Directly touching the inside of the vial or cap. Collecting a sample along with sediment. Leaving air in the vial with the water sample.

Summary 

ICP-OES analysis is a powerful tool for creating the correct conditions in an aquarium. However, it is important to remember that due to the sensitivity of the method, the stage of collecting a sample for analysis is particularly crucial, and errors during this process can lead to falsification of the analysis result and incorrect assessment of the state of the ecosystem in the aquarium.