YSI's ProODO® handheld meter and ProOBOD® laboratory probes use optical, luminescent DO to determine dissolved oxygen values. The probes measure dissolved oxygen by emitting a blue light of the proper wavelength that causes the dye in the sensing element to luminescence, or glow red. Oxygen dissolved in the sample continually passes through the diffusion layer to the dye layer, affecting the luminescence of the dye both in intensity and lifetime. With the optical sensors, there are no electrodes to clean or solutions to change.
There are several factors that can affect dissolved oxygen (DO) readings, such as improper probe care and laboratory practices. However, improper calibration is a widespread issue. As a general rule, the data collected is only as accurate as the calibration made prior to data collection. The effects of an improperly calibrated instrument can result in erratic readings, including unstable, jumpy, or odd values.
For biological oxygen demand (BOD), it can also result in DO values of blank water being “higher” on day five than on day one. At some point, most labs experience some issue with their BOD results, from blanks coming out too high to poor GGA results.
YSI’s ODO technology uses optical, luminescent DO to determine dissolved oxygen values. The instruments use “smart” sensor technology which stores calibration data within the sensor. The instruments are designed to hold calibrations over long periods of time and to be easily calibrated as needed. With the optical sensors, there are no electrodes to clean or solutions to change.
The technology can be found in the company’s ProODO® handheld meter and ProOBOD® laboratory probe.
Based on usage, calibrations can be stable for up to one year and are stored in each sensor. In addition, free YSI Data Manager Software (included with the instruments) allows users to configure just one or multiple instruments.
The company encourages an air-saturated calibration procedure for DO probes and instruments. Compensating for altitude or barometric pressure is also important and all of YSI’s instruments have the capability of compensating.
The ProODO field probe and OBOD laboratory probe both work in the same manner. The probes measure dissolved oxygen by emitting a blue light of the proper wavelength that causes the dye in the sensing element to luminescence, or glow red. Oxygen dissolved in the sample continually passes through the diffusion layer to the dye layer, affecting the luminescence of the dye both in intensity and lifetime.
The sensor measures the dye’s luminescence as it is affected by the presence of oxygen with a photodiode (light detector) in the probe. It then compares that reading to a reference. This is an advantage of optical sensors as they have greater stability and are less susceptible to drift than traditional electromechanical sensors.
Although YSI recommends verifying an instrument’s calibration on a regular basis, optical sensors can hold their calibration for many months (and potentially as long as a year). Optical sensing elements on the ProODO and ProOBOD are warranted for a year but may last longer. The company advises keeping the sensing element clean and stored in a moist environment between uses to obtain the longest usable life possible and to be ready to take measurements quickly.
YSI’s ODO luminescent sensor has no flow dependence making it an excellent choice for applications where stirring is difficult or undesirable. No flow dependence also reduces the possibility of operator error due to inadequate stirring, ensuring high quality data. However, YSI advises that stirring, or movement, of the optical DO sensors does improve the sensor response time.
To learn more about the DO and BOD probes, visit ysi.com/proODO and ysi.com/proOBOD. For more about Dissolved Oxygen, go to ysi.com/weknowDO.
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