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Hướng dẫn lựa chọn máy đo ôxy

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Selection Considerations

  • Submersible or BOD probes. Submersible probes are ideal for field use while the BOD probes, available for certain meters, are more appropriate for laboratory use.
  • Waterproof housing. Meters range from indoor use, to splashproof, to submersible.
  • Automatic barometric pressure compensation. The solubility of oxygen decreases with an increase in altitude (or reduction of atmospheric pressure). Some meters have a built-in barometer to make this adjustment automatically.
  • Manual barometric pressure compensation. Meters allow you to enter the barometric pressure manually.
  • Salinity adjustment. As the salinity of the solution increases, the solubility of oxygen decreases. Meters may allow the user to enter the salinity value of their liquid, then compensate accordingly.
  • Temperature compensation. As the temperature of a solution increases, the oxygen solubility decreases. Meters may provide automatic temperature compensation to ensure accurate readings.
  • Memory capabilities. Meters may store readings in memory for downloading to a computer or a recorder.
  • Replaceable membranes/caps/modules. Replaceable membranes are generally more cost-effective but are more time-consuming. Membrane modules are ready-to-use but cost a little more.

Ten Good Lab Practices (when testing for dissolved oxygen)

  • Store your DO probe in a moist atmosphere to limit evaporation of the electrolyte solution.
  • Rinse probe membrane with distilled water after each test.
  • Calibrate the probe and meter at temperatures closest to the temperature of the sample.
  • Ensure that the probe is always submersed deep enough to cover the membrane and automatic temperature compensation element.
  • Stir your sample no less than 15 cm/min to avoid oxygen starvation at the membrane.
  • Use a zero oxygen solution to calibrate your meter.
  • Remember that oxygen measurements are pressure/altitude dependent.
  • Know your sample's salinity since it affects your reading.
  • Polarographic probes require 15 to 30 minutes to polarize—be sure to allow for that time.
  • Remember when changing membranes to remove all air bubbles from under the membrane surface.

Dissolved Oxygen Probe Technology

  • Galvanic probes include a sensor with two dissimilar metals to produce a current required for measurement. The sensor has zinc or lead anode, silver cathode, and potassium hydroxide electrolyte. Galvanic probes do not require warm-up time.
  • Polarographic probes have polarographic sensors with silver anode surrounded by gold or platinum cathode. This type of probe is also called the "Clark cell". Power is supplied by the meter or other external battery source. Requires 15 to 30 minutes warm-up time.

Refence source:  http://www.coleparmer.com/TechLibraryArticle/682