About

Dissolved oxygen (DO) analysis measures the amount of gaseous oxygen (O2) dissolved in an aqueous solution. Dissolved oxygen is one of the most important parameters in aquatic systems. DO is required for metabolism by aerobic organisms and also influences inorganic chemical reactions. Understanding of the solubility and dynamics of oxygen distribution is essential to interpreting both biological and chemical processes within water bodies. Oxygen enters water by diffusion from the surrounding air by aeration (rapid movement) and as a product of photosynthesis. The amount of oxygen (or any gas) that can dissolve in pure water (saturation point) is inversely proportional to the temperature of the water; the warmer the water, the less dissolved oxygen is present.

In aquaculture, dissolved oxygen is arguably the most important parameter of water quality. Most aquatic species require a minimum of 3 mg/L (ppm) dissolved oxygen, but 8 to 10 mg/L (ppm) is preferable.

The HI97732 uses an adaptation of the Standard Methods for Examination of Water and Wastewater , 23rd edition, azide modified Winkler method to measure dissolved oxygen concentrations up to 10.0 mg/L (ppm). When reagent is added to a sample containing DO, the sample turns a yellow hue; the greater the concentration, the deeper the color. The associated color change is colorimetrically analyzed according to the Beer-Lambert Law. This principle states that light is absorbed by a complementary color, and the emitted radiation is dependent upon concentration. For dissolved oxygen determination, a narrow band interference filter at 466 nm allows only blue light to be emitted and passed through the sample cuvette. The sample will produce a yellow color, with an intensity proportional to the concentration of dissolved oxygen. The absorbance of blue light increases as the intensity of yellow light increases resulting in less transmittance of light hitting the silicon photodetector.