Background
Test Method
Cautions & Safety Information
Sampling
Test Procedure
Using the Comparator
Click here for more information about Dissolved Oxygen
Oxygen is one of the most important elements of our atmosphere. It is necessary to the metabolic processes of virtually all life. For this reason, dissolved oxygen (D.O.) is an important indicator of the quality of a body of water.
In the process of respiration, plants and animals exchange gases with the atmosphere. Animals take in oxygen and exhale carbon dioxide, while plants take in carbon dioxide and excrete oxygen as a by-product of photosynthesis. Any factor that would disturb this system could be devastating to aquatic life.
Untreated emissions from sewage treatment plants are often responsible for oxygen depletion. The organic composition of this waste requires a great deal of oxygen as it decomposes. This being the case, areas near municipal sewage treatment facilities are often monitored for their dissolved oxygen levels.
There are some other factors that have an effect on the dissolve oxygen content of a body of water. The temperature of the water affects the water's capacity for holding dissolved oxygen. As the temperature of water increases, the concentration of dissolved oxygen decreases. As a result, there is a seasonal fluctuation in dissolved oxygen concentration in a body of water.
Wind currents also play an important role in aeration of bodies of water. As wind blows across a water surface, oxygen is mixed into the water. On windless nights, oxygen depletion can be so severe that it can cause substantial fish kills.
Turbulence is yet another way oxygen is added to water. As water runs its course in a stream or river bed, oxygen is mixed in as the water flow is agitated by obstructions such as rocks, fallen trees, and waterfalls. A great deal of variation in dissolved oxygen concentration can be seen along the course of a stream or river.
Aquatic and terrestrial environments do not have the same ability to hold oxygen. If an equal volume of air and very cold water were compared, the air would hold over 95% more oxygen than the water. As the temperature of the water increases, its capacity to hold dissolved oxygen rapidly decreases. Because water is less efficient in its ability to hold oxygen, respiration and organic degradation easily deplete the concentration of dissolved oxygen in water. The only way to avoid complete anoxia is for oxygen to be replenished from the atmosphere and from the biological activity in the aquatic environment.
The trophic state of a body of water is an important indicator of the status of aquatic living conditions. Trophic state is a measure of the amount of nutrients contained in the water. The amount of nutrients in the water will determine how much life can be sustained in the aquatic environment, therefore affecting the amount of oxygen being used or released in the water. There are two classifications of trophic state: eutrophic or oligotrophic. An eutriphic lake is on which has a fluctuating D.O. content and is always rich in nutrients. The fluctuations in D.O. content is due to activity and inactivity of the life in the body of water. An oligotrophic lake is one which is always rich in oxygen content but is poor in plant nutrients. The oxygen content is constant because there isn't much variation in life activity causing serious depletion.
Although standards for dissolved oxygen vary, it has been found that a concentration of D.O. of less than 4ppm (parts per million) is stressful to most forms of aquatic life. The ideal range for an adequate gamefish population (bass, pike, walleye) is about 8 to 15ppm.
The Snap Test utilizes the technology of the most advanced testing methods in a simple procedure. The chemistry used eliminates the interferences and atmospheric corrections (temperature, pressure, and salinity) of other testing methods.
The reagent utilized, indigo carmine, is commonly known for its use in determining dissolved oxygen in alkaline solution. Since many substances interfere with the alkaline solution used, this kit avoids the interference by using indigo carmine in acidic solution.
This test kit is useful in detecting dissolved oxygen in concentrations of 0-12ppm.
Read the MSDS (material safety data sheet) before performing this test procedure.
If this product is used as directed, the user will not come in contact with the chemical reagents. If contact does occur, flush skin or eyes with water. If swallowed, call a physician
As an added precaution, we recommend that the user wear safety glasses when performing this test.
To dispose of used test ampoules place in small container provided by instructor.
It is very difficult to obtain a sample which truly reflects its dissolved oxygen content. This is because the high oxygen content of our environment will cause the oxygen content of the sample to approach the saturation level. The activity of living organisms may also cause rapid oxygen depletion. It is important to be aware of these problems and when possible take steps to minimize their effects. For example, when dipping into a water source or pouring water, there should be as little agitation as possible.
When using samples containing solid waste, solids in the sample should be allowed to settle before conducting the test.
Important Note: The ampoules contain a dye which will deteriorate upon prolonged exposure to light. They will remain usable indefinitely only if stored in the dark.
1. Fill the sample cup provided in the kit to the 25ml mark with your sample.
2. Place the tapered tip of the test ampoule into one of the four depressions in the bottom of the sample cup. Snap the tip by squeezing the test ampoule toward the side of the cup (fig. 1). The sample will fill the ampoule and begin to mix with the reagent inside. NOTE: A small gas bubble will remain in the ampoule to facilitate mixing.
3. Remove the fluid filled test ampoule from the cup. Keeping the open end downward, cover the tip of the ampoule with a finger. NOTE: Although the end of the Snap Test ampoule is not sharp, we recommend you cover the end with a piece of tissue or tape before shaking contents.
4. Mix the contents of the ampoule by inverting it several times (5), allowing the bubble inside to travel from end to end.
5. Wipe all liquid from the exterior of the tube and wait two minutes. NOTE: After mixing, the ampoule tip may be left uncovered during the development period and while making color comparisons.
6. After waiting two minutes, use the comparator to determine the level of dissolved oxygen in the sample.
The comparator should be illuminated by a strong white light from directly above. Place the filled test ampoule between the color standards for viewing (fig. 2). It is important that you compare your ampoule by placing it on both sides of the standard tube before concluding that it is darker, lighter, or equal to the standard. NOTE: Store the comparatore in the dark when not in use.
Normally encountered levels of iron, copper, chromate, nitrite, nitrate, sulfite, sulfide, chlorine, hypochlorite, hardness, salinity, dissolved gases, acids, or alkalis will not interfere with the dissolved oxygen determination in freshwater, seawater, or municipal wastewaters.
No correction is required for temperature, barometric pressure, or salinity.
Excessive alkalinity (pH more than 10), occurring in certain industrial wastes, can cause the ampoule contents to appear green. If you observe this, add 10% hydrochloric acid to the sample to neutralize it, and repeat the test procedure.
Excessive acidity will cause low test results. If pH of the sample is less that two, neutralize with 2% sodium hydroxide solution and then repeat the test procedure.
Colored or turbid samples will obscure color comparison.
Source: (WARD'S Natural Science Establishment, Inc.)
