Water quality can be characterized by three parameters: hydrology, physico-chemistry and biology. Here, we present methods to establish water quality based on the amount of dissolved oxygen, and nitrogen level
Dissolved oxygen (DO) is the amount of gaseous oxygen dissolved in water. Oxygen diffuses into water from the surrounding air, by aeration and as a by-product of photosynthesis. Dissolved oxygen levels are used as an indicator of water quality.
In this lab, we use a colorimetric method to measure the dissolved oxygen levels in the water sample. The dissolved oxygen test utilizes indigo carmine. In an acidic solution, oxygen oxidizes the yellow-green leuco form of indigo carmine to form a brightly colored blue dye. The resulting blue color is proportional to the dissolve oxygen levels in the water sample.
Figure 1. First image - The darker the blue in the tubes, the higher the dissolved oxygen concentration. Second image - Indigo carmine reaction.