text: The success of this method is critically dependent upon the manner in which the sample is manipulated. At all stages, steps must be taken to ensure that oxygen is neither introduced to nor lost from the sample. Furthermore, the water sample must be free of any solutes that will oxidize or reduce iodine.
  Instrumental methods for measurement of dissolved oxygen have widely supplanted the routine use of the Winkler test, although the test is still used to check instrument calibration.