USGS-OWQ: NFM 6.2.1-Amp: Dissolved-oxygen concentration, field measurement by amperometric method
|
Official Method Name
|
Dissoved-oxygen measurement, amperometric method |
|---|---|
|
Current Revision
| June, 2006 |
|
Media
|
WATER |
|
Instrumentation
|
Membrane Electrode |
|
Method Subcategory
|
Inorganic |
|
Method Source
|
|
|
Citation
|
|
|
Brief Method Summary
|
Dissolved-oxygen measurement in natural water must be made at the time of sampling. The amperometric method specifies use of a temperature- and pressure-compensated amperometer that is field calibrated in accordance with section 6.2.1B of the source citation. Corrections are made for DO solubility at the given temperature and salinity. For surface-water measurements, the DO determination must be made in situ; refer to TWRI Book 9 Ch. A6.0 and Ch. A4 for isokinetic and nonisokinetic sampling methods. For ground-water measurements, the measurement must be made either downhole (in situ) at the given sampling interval, or within an air-tight flow-through chamber (cell) to which the sample is pumped directly from the downhole sampling interval; refer to TWRI Book 9 Ch. A6.0 and Ch. A4.2 for downhole and flow-through-chamber sampling methods. |
|
Scope and Application
|
This method covers the measurement of dissolved oxygen (DO) concentrations in surface water and ground water using a field-calibrated membrane sensor and temperature-compensating amperometric instrument . Standard USGS surface-water measurements represent the median or mean in-situ value of a reach cross section. Standard USGS ground-water measurements are made either in situ or within a flow-through cell to exclude contact of the sample with air. |
|
Applicable Concentration Range
|
1.0 to 20 mg/L |
|
Interferences
|
Measurement is affected by salinity and temperature. Degassing, mineral precipitation, and other chemical, physical, and biological reactions can cause rapid and substatial changes in dissolved-oxygen concentration. |
|
Quality Control Requirements
|
Field calibration is mandatory. Sensor must be clean and free of air bubble(s). |
|
Sample Handling
|
Measurements in surface water must be made in situ. Measurements in ground water are made either in situ (downhole) or in source water pumped directly (in-line) to a flow-through cell, with sample temperature maintained constant from source to cell and excluding bubbles or other source of air. |
|
Maximum Holding Time
|
zero holding time |
|
Relative Cost
|
Unknown |
|
Sample Preparation Methods
|
not applicable |
