Sometimes the source of a pollutant can be identified by changes in pollution concentration between different sampling locations. High nutrient loading in a stream downstream from a sewage treatment plant may actually be due to fertilizer runoff from agricultural concerns upstream. Many of the tests we run are color development tests. A reaction is set up where the analyte of interest will react with other chemicals to form a product with a specific color. By measuring the intensity of the color, we can infer the concentration of the analyte.
Titrations are tests where a substance reacts with something else in specific proportion.
When we add something to a solution until it stops reacting, we can tell how much of the substance of interest was there. Many tests are done electrochemically with probes. Probes, sometimes called electrodes, measure the conductivity of a solution that is inside the probe. If we cover the end of the probe with a membrane that allows only one chemical to pass through, any change in the electric potential inside the probe will be due to that chemical. By comparing the probe response to standards of known concentration we can figure out the quantity of a chemical.