SOP No. EM-21 Page 1 of 2

Measurement of Dissolved Oxygen in Water Samples

Revision: #9 Replaces: 2/19/14 Effective: 9/3/19

1. Purpose and Scope: Sampling of any water body which supports aquatic life must be

accompanied by a measurement of the dissolved oxygen (DO) content. These measurements

help to evaluate the capacity of the water to support life. All visible aquatic species require a

minimum DO to survive, which varies with the species. When DO decreases, species become

stressed and mortality results at extremely low DO concentrations. This SOP describes how to

collect, handle, and measure DO from surface water samples using the Hach AccuVac DO test

kit. If you have previously used a DO meter or a Hach Powder Pillow test kit to measure DO

and are proficient in their use, you may continue to use one of these two methods, if available.

This method can be used in place of previously implemented methods to measure DO. Any

instructions on surface water sampling and documentation found in the Environmental

Monitoring Plan (EMP) supersedes instructions contained in this SOP.

2. Supplies Required: To request sampling supplies, contact the monitoring supplies 

coordinators, Lisa Mosser (305) 278 4902, or Richard King (305) 278 2905, Center for Plant 

Health Science and Technology, Miami, or email the Environmental Monitoring Supplies 

Checklist to lisa.k.mosser@usda.gov or richard.a.king@usda.gov.

2.1 “grab sampler” (a wide-mouth plastic container firmly attached to a 6-foot pole) 

2.2 AccuVac Dissolved Oxygen Test Kit - Hach Company 

2.2.1 AccuVac test ampules for high range concentrations of DO (0-15 mg/l) 

2.2.2 AccuVac color comparator

2.2.3 40 ml plastic beaker (supplied in kit) 

2.2.4 Zeroing vial 

2.2.5 Plastic ampule breaker

2.2.6 Blue ampule cap

2.3 field log book 

2.4 environmental monitoring forms (APHIS Form 2060) 

2.5 thermometer

3. Measuring DO in a Surface Water Sample with a Hach AccuVac DO test kit. Directions

for using the test kit are supplied with each test kit, and should be carefully followed. Directions

are reiterated in this document as well. The chemicals needed for measuring DO have been

individually packaged in a sealed (under vacuum), glass vial.
SOP No. EM-21 Page 2 of 2

Measurement of Dissolved Oxygen in Water Samples

Revision: #9 Replaces: 2/19/14 Effective: 9/3/19

3.1 Collect a “grab” water sample with the wide-mouth container affixed to the end of 

a pole. Minimize the agitation of water during the collection process so as not to 

introduce oxygen via air bubbles. 

3.2 After collecting water, dispense 40 ml into the small plastic beaker provided in 

the test kit and 10 ml into the zeroing vial provided. 

3.3 The sample in the zeroing vial serves as a blank control. Place this vial in the left 

top opening of the AccuVac color comparator. 

3.4 Use the ampules provided in the kit (dissolved oxygen range between 1-15 mg/l). 

Place the ampule breaker into the beaker containing the 40 ml sample. Place the 

AccuVac ampule in the ampule breaker and push down on the ampule with firm, 

steady pressure to break the tip. The ampule has been sealed under a vacuum, so 

once the glass tip is broken the ampule automatically fills with the water sample. 

The ampule can also be filled by simply breaking the glass tip against the side of 

the beaker well below the water surface. 

3.5 Once the ampule is filled with the water sample, and without inverting the 

ampule, immediately place the blue ampule cap over the tip of the ampule. 

Capping the ampule tip prevents contamination of the sample with atmospheric 

oxygen. If atmospheric oxygen is accidentally introduced into the sample it could 

result in an erroneously high DO measurement.

3.6 Shake the ampule for 30 seconds. Allow two minutes for color development 

inverting the ampule occasionally to ensure thorough mixing. 

3.7 Shake the ampule again for 10-15 seconds and place the ampule in the right top 

opening of the AccuVac color comparator. 

3.8 Rotate the color disc until the color matches in the two openings. Read the 

dissolved oxygen concentration in mg/l through the scale window. Record the 

results in the field book. 

3.9 Collect another grab sample and measure the temperature of this water with a 

thermometer. Do not use the water initially collected for the DO since the 

temperature may have changed to match that of the air.

3.10 The water may be discarded on the ground. The test ampule should be disposed 

of in the same manner as broken glass. Rinse out all equipment with pond water 

or distilled water. Upon return to the office, glassware should be washed, rinsed 

with tap water and allowed to dry.