Water quality testing is crucial for a variety of industries, from fish farming to wastewater management. Various dissolved oxygen test kits are available to perform these tests efficiently. One of the most important and informative tests is the dissolved oxygen test. Several methods and tools can be used to perform a dissolved oxygen test, all of which offer valuable insights into a water sample’s oxygenation level.
What is Dissolved Oxygen Test?
The Dissolved Oxygen (DO) test measures gaseous oxygen dissolved in water or other liquids. Dissolved gases like oxygen are vital for biological and chemical processes in water. Oxygen enters water from the air or through aeration, a process of rapid water stirring. Water plants also produce oxygen as a byproduct of photosynthesis, similar to how they enrich the atmosphere on land.
DO levels in water are influenced by temperature, pressure, and salinity. Higher temperatures break molecular bonds, lowering DO levels. Conversely, lower temperatures increase DO levels in water.
Pressure, meaning atmospheric pressure, weighs down on water and causes greater DO concentration — in other words, DO concentration might be lower in a mountain lake than in another lake at sea level.
Salinity measures the salt concentration in water. Salt dissolves in water more easily than oxygen. High salt concentration makes it difficult for oxygen to dissolve. Therefore, higher salinity usually means lower dissolved oxygen levels.
Why is Dissolved Oxygen Test Important?
Maintaining consistent dissolved oxygen (DO) levels is crucial for aquatic life. High DO levels can cause “gas bubble disease” in fish. This disease creates tiny bubbles in the gills, eyes, and fins, potentially leading to lethal tissue damage. Conversely, low DO levels can create “dead zones,” where aquatic life can’t survive. Conducting DO tests is key to planning for a healthy aquatic environment, whether in rivers or aquariums.
Methods for Measuring Dissolved Oxygen Test
Researchers use three main methods to measure dissolved oxygen, which they can perform both in the field and in the lab, although executing some methods accurately on-site is more challenging than others.
Sensor/Electroanalytical Method
Probably the most popular method of measuring dissolved oxygen is by using dissolved oxygen meters and sensors. Some sensors have analog output to quickly log data for further analysis and others are even designed to remain in water to record data over extended periods.
There are two main types of dissolved oxygen test sensors: optical DO sensors and electrochemical DO sensors. Optical sensors measure DO levels using blue light and luminescent dyes. The concentration of dissolved oxygen inversely affects luminescence lifetime. This means higher DO levels result in less light returning to the sensor.
Electrochemical DO sensors come in two types: galvanic and polarographic. They use electrodes and electrolyte solutions to measure water’s oxygen levels. Oxygen reacts with the solution, creating an electrical current. This current’s measurement reflects the oxygen concentration in the water.
Colorimetry
This test, called the colorimetric method, measures dissolved oxygen (DO) through color intensity from chemicals. It uses either indigo carmine or rhodazine D methods. The indigo method suits oxygen levels from 0.2 to 15 mg/L. However, substances like ferric iron, ferrous iron, nitrate, and sodium hydrosulfite may affect its accuracy. The more oxygen in a sample, the darker the blue color appears.
Rhodazine D measures oxygen in parts per billion (ppb), unlike the usual parts per million (ppm). However, chlorine, ferric iron, cupric copper, and other oxidizing agents can interfere. When the oxygen concentration is high, the sample turns a deep, vibrant pink.
Colorimetry provides a quick, straightforward, and affordable way to preliminarily assess dissolved oxygen levels. However, other substances in the water and external factors like temperature, pressure, and turbidity can affect its accuracy. Furthermore, you must conduct these tests quickly, evaluating results within 30 seconds of mixing the reagent.
Titrimetric Method/Iodometry in Dissolved Oxygen Test
Also known as the Winkler method, titration, or iodometry, represents the most traditional approach to conducting a dissolved oxygen test. It performs best with samples in a lab setting. This method leverages the oxidizing property of dissolved oxygen to yield some of the most accurate and precise results among DO tests. Researchers can choose from seven variations of the Winkler method if they have prior knowledge of additional elements in a sample.
In iodometry, a titration method, you use a titrant of known concentration to measure the unknown concentration of dissolved oxygen (DO) in a sample. The Winkler method, the titration technique for determining DO, monitors the appearance and disappearance of iodine to signal the process’s end, allowing for the measurement of DO levels.
The Dissolved Oxygen (DO) Test is a crucial analysis in water quality monitoring, assessing the amount of oxygen dissolved in water. Oxygen is essential for aquatic life and is an indicator of a water body’s ability to support its ecosystem. The test measures oxygen levels using chemical, electrochemical, or optical sensors, providing insights into the water’s health. Low DO levels can indicate pollution and poor water quality, affecting aquatic organisms. Regular DO testing is vital in environmental monitoring, wastewater treatment, and aquaculture, ensuring water bodies are healthy and capable of sustaining life, maintaining ecological balance, and supporting human needs.
Find Dissolved Oxygen Test Kit and More at Certified MTP
Certified Material Testing Products carries all the water quality testing meters and test kits you need to perform dissolved oxygen tests and keep tabs on your water or other fluids. Get dissolved oxygen meters, turbidity sensors, pH probes and more in our high-quality selection.
