What could be the cause of inconsistent results using the ultra low range hardness chlorophosphonazo colorimetric methods?
Inconsistent results with the ultra-low range hardness chlorophosphonazo method
For best results, confirm proper pretreatment of the labware, and it is recommended to dedicate that labware to the ultra-low range (ULR) hardness method only. Wash the sample cell or pour-thru cell well with high purity water to eliminate all traces of CDTA from the previous sample. Carry-over of CDTA to the next sample will cause low results. Labware should always be covered or stored in a dust-free environment when not in use.