ENGINEERING SCIENCE DEPARTMENT
Water and Environmental Technology Program
Name _________________
SPRING TERM
Aquatic Chemistry II, WQT-134
Laboratory
Dissolved Oxygen
Purpose: In this lab you will use a Hach dissolved oxygen probe and a Luminescent Dissolved
Oxygen (LDO) probe, to perform an assessment of the dissolved oxygen content of a
water/waste water sample. Dissolved oxygen analysis measures the amount of gaseous oxygen
(O2) dissolved in an aqueous solution. Oxygen gets into water by diffusion from the surrounding
air, by aeration (rapid movement), and as a waste product of photosynthesis. Oxygen is one of
the most important tests that can be used to determine the quality of water. Dissolved oxygen
content can be used as an indication of the effects of waste on a body of water, purity of water,
and suitability of the water for fish and other organisms. For example, dissolved oxygen levels
of 4 to 5 mg/L are considered borderline for extended survival of aquatic plants and animals.
Ideally, most game fish, require levels of 8 to 15 mg/L. Conditions which affect the dissolved
oxygen level include: flow rate, photosynthesis, aerobic respiration, elevation, clarity,
temperature, sludge deposits, and water depth. Because plants are not producing oxygen during
the night, but oxygen is still being used for respiration at that time, dissolved oxygen
concentrations will be the lowest within a waterbody just before sunrise. The colder the water,
the greater capacity it has to hold oxygen. Atmospheric pressure effects the amount of oxygen
dissolved in water. At higher elevations, less oxygen can be dissolved in water. Oftentimes,
warm turbid water will have lower DO levels. In addition, nutrient rich water has a greater
opportunity for plant growth. With more plants, there will be more photosynthesis, but also more
respiration. This means that dissolved oxygen concentrations may be very low in the morning,
and very high in the afternoon. In this investigation, you will measure and analyze the dissolved
oxygen (DO) concentration in your unknown water samples.
Factoids/Conversions
 Dissolved oxygen content for aquatic life = ~10 mg/L
 Dissolved oxygen content to stress aquatic life = ~<5 mg/L
 21% DO level at sea level
 An atmosphere is considered oxygen deficient when the oxygen level drops below 19.5%
DO
 As temperature goes down, dissolved oxygen goes up.
 Solubility of dissolved oxygen also decreases as salinity increases.
 Solubility of dissolved oxygen into water increases with pressure
Advantages
 No pretreatment necessary for well or potable water samples
 Ease of use accuracy at 1.5%, 0-20 mg/L

LDO probe (0-60 mg/L) no membranes and superior accuracy +/- 0.1 mg/L at <8 mg/L
+/- 0.2 mg/L at >8 mg/L, +/- 10% reading >20 mg/L, resolution 0.01 mg/L
Disadvantages/Interferences
 Probe can short circuit and drifts
 Frequent, recalibration
Sample collection: Collect 1 liter sample with no headspace.
SUPPLIES/SAFTEY
Lab Materials:
1. Hach Ion Sension 6 Dissolved Oxygen Meter
2. Hach LDO probe and sensor
3. Beakers 125-, 250 mL
SUMMARY PROCEDURE
Dissolved Oxygen LDO Probe HQ 10
MEASUREMENT
1. Place the LDO probe into the sample
2. Press the Blue I button to turn the probe on.
3. Press the Blue Check Mark to take a reading the value will fluctuate and the display will
show “Stabilizing…mg/L…” The lock ion will appear after the measurement is complete.
This may take awhile. Record the value as __________mg/L and hit the O2 % button to
record the O2 percentage.
4. Repeat this procedure
Step-by-step Procedure
Dissolved Oxygen Multi Sensor Probe HQ40d18
MEASUREMENT
5. Place the LDO probe into the sample
6. Press the GREEN/RIGHT key under Read
7. The display will show “Stabilizing…” and a progress bar will fill from 0 to 100% as the
probe stabilizes in the sample. The lock ion will appear after the measurement is
complete.
8. Repeat this procedure
Dissolved Oxygen Hach Ion Sension 6 Dissolved Oxygen Meter
Step-by-step Procedure
Dissolved Oxygen
Calibration Using the Hach Sension6 Series Dissolved Oxygen
1. Please follow along with the instruction book.
2. Fill the module cap 2/3 full with dissolved oxygen electrolyte filling solution
3. Hold the probe in a vertical position with the tip down.
4. Measure 150 ml of sample in a 250 ml beaker with a magnetic stir bar
5. Turn on the meter by pressing I/O button.
6. Press the CAL key Cal? Numerically enter the barometric pressure and elevation. Press
the Enter key.
7. The salinity value of 0/00 will be shown. Press the Enter key. The display will show
100%
8. Press the Enter key, stabilization will occur. The meter will return to the read mode.
Press the EXIT key to leave calibration and take a measurement. Press the CONC %
button to get from % to mg/L.
Department of Engineering Science
Water & Environmental Technology
Environmental Chemistry II, WQT 134
Dissolved Oxygen
Analyzed by
Date
Facility Name
Sample Temperature___________________
Sample pH __________________________
1.
Reported sample dissolved oxygen (DO ) concentration :
sample location
DO concentration
mg/L
sample location
DO concentration
mg/L
sample location
DO concentration
mg/L
sample location
DO concentration
mg/L