In order to measure a low-concentration sample without increasing the sensitivity of the measuring instrument, the target component in the sample should be concentrated*. If you are asked about the method of "concentration", you will probably imagine that it is "concentrated by boiling down to remove moisture". This is only valid for very manageable environmental samples with few coarse components and components that do not evaporate. For seawater samples, that doesn't work. It is easy to imagine that a large amount of salts will be concentrated and the matrix effect will be enormous. We have to come up with a method to selectively concentrate only the target component. In environmental analytical chemistry, a great deal of effort has been devoted to the concentration of target components, and various methods have been devised and improved. Here is an example.
