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

Document ID

Document ID TE7044

Version

Version 3.0

Status

Status Published

Published Date

Published Date 08/14/2018
Question
Why are plastic containers used instead of glass in the ULR Total Hardness test?
Summary
Plastic containers and the ultra low range total hardness test.
Answer
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 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.
However, the pour thru cell has been proven to be reliable for hardness testing.


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. 
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