Reading dissolved oxygen (DO) in water involves using specific measurement techniques that quantify the amount of oxygen gas dissolved within the water sample.
Methods for Measuring Dissolved Oxygen
According to the provided information, there are three primary methods available for measuring dissolved oxygen concentrations in water:
- Colorimetry
- A sensor and meter
- Titration
Modern techniques commonly employ either an electrochemical or optical sensor, which are used with a meter.
Let's look at each method in more detail:
1. Titration (Winkler Method)
This is a classic chemical method.
- It involves adding a series of chemicals to the water sample.
- These chemicals react with the dissolved oxygen.
- The reaction forms a compound that is then "titrated" (reacted) with a known solution until a distinct color change occurs (the endpoint).
- The amount of the known solution used directly correlates to the amount of dissolved oxygen in the original sample.
2. Colorimetry
Colorimetry is another method that relies on a chemical reaction to determine DO levels.
- Chemical reagents are added to the water sample.
- These reagents react with dissolved oxygen to produce a colored compound.
- The intensity of the color produced is proportional to the concentration of dissolved oxygen.
- A colorimeter or spectrophotometer is used to measure the color intensity and translate it into a DO concentration reading.
3. Sensor and Meter Methods
These methods utilize electronic probes or sensors connected to a meter to provide a direct reading of dissolved oxygen. These are considered the modern techniques for DO measurement.
- Electrochemical Sensors: These sensors measure changes in electrical properties (like current or voltage) that occur due to the presence of oxygen diffusing across a membrane. The electrical signal is converted by the meter into a DO concentration.
- Optical Sensors: These sensors use fluorescence or luminescence principles. They measure how light changes in the presence of oxygen. The sensor material interacts with oxygen, altering its light-emitting properties, which the meter detects and relates to the DO concentration.
These sensor-based methods often allow for faster measurements and can be more suitable for field use or continuous monitoring compared to chemical methods like titration.
Here's a summary of the methods:
| Method | Principle | Typical Application |
|---|---|---|
| Titration | Chemical reaction to an endpoint | Laboratory (Historical) |
| Colorimetry | Chemical reaction forming colored compound | Field or Laboratory |
| Sensor & Meter | Electrochemical or Optical detection of oxygen | Field, Laboratory, Online |
By employing one of these methods – whether through chemical reactions like titration or colorimetry, or via modern electrochemical or optical sensors used with a meter – the concentration of dissolved oxygen in water can be accurately read and determined.
