Why are plastic containers used instead of glass in the ULR Total Hardness test?


Dokument-ID TE7044


Veröffentlichungsdatum 27.05.2017
Why are plastic containers used instead of glass in the ULR Total Hardness test?
Plastic containers and the mltra low range total hardness test.
Hach Method 8374 is a low level test and operators should address every possible source of error and contamination in order to obtain precise and accurate results. The development work for this method showed that glass containers often gave erratic results and more precise numbers were obtained when plastic was used. Presumably, this was due to hardness being leached from the glass or maybe just from trace hardness absorbed on the glass. The erratic behavior can be obtained with plastic ware also, but normally this stabilizes rather quickly when the test is run a couple of times in the same container. The instructions are clear on how to treat labware in order to get precise results (refer to the method links below). The use of the pour-thru cell was actually somewhat questionable for the reasons stated above. The cell windows and the glass funnel are possible sources of contamination. It has been determined that it is reliable to run the test with the glass pourt-thru cell and funnel.

There are two key points in the procedure that an operator should adhere to for best results:
  1. Proper pretreatment of the labware and then dedicating that lab ware to the ULR hardness method only
  2. Eash 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. 

8374 Chlorophosonazo Rapid liquid, Pour-Thru Cell Chlorophosphonazo Colorimetric

8374 Chlorophosphonazo Colorimetric, Solution Pillow

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