This document provides a history and overview of optical dissolved oxygen measurement techniques. It discusses: - Traditional Winkler titration and electrochemical methods for measuring dissolved oxygen. - The development of optical dissolved oxygen measurement using luminescence lifetime, which was optimized for environmental monitoring in 2006. - The advantages of optical sensors over electrochemical sensors, including longer lifetime, greater stability, and suitability for high fouling environments. - Details of optical sensor operation, calibration procedures, accuracy, certifications, and some example deployment applications.

1. Optical Dissolved Oxygen:
Fundamentals and Applications
GAWP – Athens, GA
Scott Kindelberger
17 November 2015

2. A Brief History
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• Winkler Titration (1888)
• Slow, highly subjective result
• Sample transport to lab
• Toxic glassware cleaning reagent

3. A Brief History
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• Electrochemical (1956)
• Most widely used method

4. A Brief History
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• Optical (Luminescence Lifetime)
• Method optimized for environmental monitoring (YSI, 2006)
• Theoretical (1939)
• Practical (1984)

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• Oxygen diffuses across membrane,
and is consumed at the electrode
A Little Deeper: Electrochemical DO
• This generates a small current
More oxygen
= More Current
= Higher Signal
Oxygen (mg/L)
Current(mA)

6. The Problem with Membranes…
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• Electrolytes + Membranes
• 1-4 week lifetime
• Easily damaged (3/1000 inch thick)
• Large calibration drifts

7. The Problem with Membranes…
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8. Light at the End of the Tunnel…
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• No electrolytes, membranes
• 1-2 year lifetime ($200)
• Thermal / Physical shock resistant calibration
• Calibration stability on order of months
• Screw-on cap

9. So What’s the Big Deal?
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• Durable, can be wiped
• Essential in high fouling environments
• RELIABLE long-term data

10. 4 day deployment, July 2010
Water Temp 82 °F
6 day deployment, Jan 2013
Water Temp 54 °F
Biofouling Issues

11. Other Deployments
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Hydroelectric
Monitoring Wells
High-fouling

12. So What’s the Big Deal?
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• Equal or Higher Accuracy
• Work BETTER at low DO
• Impervious H2S
• +/- 1.0%, or 0.1mg/L
• 0 – 500% Range

13. Calibration / Check
• Water-saturated air
• Semi-closed environment
• Wait 15 minutes, calibrate
• Saturate with airstone
• Reading should be ~100%

14. Drawbacks..
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• Expense.. About 2x as membrane
• Equilibration times
• High turbidities..

15. Method Certifications..
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• US-EPA : 1002-8-2009
• ASTM (International): D888-09
• Standard Methods: 4500-O-G
• CFR: 40 CFR 136

16. • Thank you for your time and attention!
• Questions?