ICP

An Analysis of ICP-OES

Many water quality problems can’t be directly observed, and often have similar symptoms — so how do we make proper changes? The answer will always be water testing. For the everyday parameters, home titration tests are still our most valuable method. However, knowing your system to an intimate degree requires an even closer look. Decoding the mystery of aquarium chemistry has become much easier with the availability of affordable trace element testing done specifically for the aquarium hobby.

ICP, an abbreviation for Inductively Coupled Plasma, is one method for looking at elements that can’t be measured with titration kits or elements present only in trace amounts. There are a few types of ICP methods, but the one used by all commercially available aquarium water testing services is called ICP-OES, or Optical Emission Spectroscopy. It is a natural fit for seawater analysis for the following reasons:

• Simultaneous analysis of multiple elements, eliminating the need for large samples or repeated testing
• Easy-to-read output
• Less chemical or ionization interference, allowing for analysis of high-matrix samples (samples that contain many elements)
• High sensitivity — can read trace concentrations to 10 ppb or lower for some elements
• Large number of measurable elements — elements that are difficult to analyze in other methods, such as Zr, Ta, rare earth elements, P and B, can be easily analyzed with ICP-OES

The sample of water you send in to an analysis company is usually diluted before it is sent into the ICP machine. When introduced into the ICP system, it is nebulized (sprayed into a very fine mist), mixed with argon gas, and then superheated up to a toasty 10,000 Kelvin (for reference, this is almost double the temperature of the surface of the sun). This separates all of the component atoms into highly excited states. It takes an extreme amount of energy to keep these atoms in excitation, so they quickly settle back to their ground states. During this settling process, each element emits photons in unique wavelengths that are observed by a spectrophotometer. This data is then compiled and analyzed by a spectroscopist. The element type is determined based on the position of the photon rays, and the content of each element is determined based on the rays’ intensity.