Does the flow-through-cell use a Photo DO method?

The flow-through-cell has the option, depending on the manufacturer, of either being a Polarographic cell or an Optical DO Probe. They both have advantages. The Polarographic, or Clark cells, that we are all pretty familiar with are less expensive and fairly easily maintained.  Unfortunately, they have a greater requirement for calibration and you need to change the DO membrane and solution from time to time.  Optical DO Probes have much greater stability. They hold their calibration for a much longer period of time.  However, they are considerably more expensive – they can easily be three times the cost of a standard DO sensor.  Also, Optical DO Probes have a tendency to be larger.  So the volume of the flow cell using an Optical DO Probe generally will also be larger.  For example with flow cells that use Polarographic or Clark cells the volume of the flow cell will often be in the range of 100-150 milliliters of total volume.  The advantage of this is as the well is purged, even at low rates, we are getting exchange of water in the flow cell fairly rapidly and repeatedly. With a larger volume we would have to take the readings further apart in order to make sure that we have completely flushed off the cell between readings.  But either one will work.