How do you perform an air calibration of a DO probe?

Place the probe in water-saturated air (calibration sleeve with a little water) at stable temperature, confirm pressure and salinity settings, wait for a stable reading and accept the 100% calibration.

Compare electrochemical and optical DO sensors.

Electrochemical (Clark) sensors use a membrane, electrolyte and cathode; they consume oxygen, need stirring, polarisation time and regular membrane changes. Optical sensors use a luminescent dye, do not consume oxygen, need no stirring and less maintenance, but the sensor cap must be replaced periodically.

How would you check the residual oxygen in a nitrogen-purged solution without errors from air?

Measure in a closed flow cell or sealed vessel, fill without bubbles, keep air out of the sample path, use a recently zero-checked sensor and let the reading stabilise. Any contact with air raises the reading quickly at low levels.

Titration & electrochemistry

Dissolved Oxygen Meter

Measures the amount of oxygen dissolved in a liquid using an electrochemical or optical (luminescence) sensor. Used for water systems, fermentation, nitrogen-purged formulations and environmental testing.

Pharmaceutical
Biotech
Environmental
Food & beverage
Aquaculture
Power generation

Photo of a Dissolved Oxygen Meter — Photo: Nuno Nogueira (Nmnogueira), CC BY-SA 2.5 (cropped), via Wikimedia Commons

LEARN & PRACTICE

Test your DO meter knowledge

Multiple-choice questions

Pick an answer to see whether you are right and why.

Q1. What happens to the solubility of oxygen in water as temperature rises?
basic
Q2. What are the two calibration points of a DO meter?
basic
Q3. Why must barometric pressure be entered into a DO meter?
intermediate
Q4. Saturation DO at 25 °C and 1013.25 hPa is 8.26 mg/L. What is the expected value at 985 hPa?
intermediate
Q5. Readings from a Clark-type sensor fall when the sample is not stirred. Why?
intermediate
Q6. What is the working principle of an optical DO sensor?
basic

Viva questions

Think of your answer first, then open it to compare.

1. How do you perform an air calibration of a DO probe?
Place the probe in water-saturated air (calibration sleeve with a little water) at stable temperature, confirm pressure and salinity settings, wait for a stable reading and accept the 100% calibration.
2. Compare electrochemical and optical DO sensors.
Electrochemical (Clark) sensors use a membrane, electrolyte and cathode; they consume oxygen, need stirring, polarisation time and regular membrane changes. Optical sensors use a luminescent dye, do not consume oxygen, need no stirring and less maintenance, but the sensor cap must be replaced periodically.
3. How would you check the residual oxygen in a nitrogen-purged solution without errors from air?
Measure in a closed flow cell or sealed vessel, fill without bubbles, keep air out of the sample path, use a recently zero-checked sensor and let the reading stabilise. Any contact with air raises the reading quickly at low levels.

In LimsPulse · Calibration Management

Keep every DO meter in control: usage logs, calibration and maintenance schedules, and automatic blocking of overdue instruments.

See how