The Hach Lange kit goes from 0-1000mg/L.
Hach Lange say their LOD is around 6ppm and the LOQ is 21ppm.
Does anyone know how they will determine the LOD and LOQ for these kits?
I understand that one would determine 3xstd(blank) to get the LOD, however because these are test vials, you need to blank initially with the blank you made. Would I then just read the blank after blanking with it?
A problem with these vials is that if I do blank with the blank and read it back it gives me zero as it should. But when you move the test vial slightly in the spec, the values no longer reads zero. this is because the glass vial is not optically the same at all points (and it is round which cause light scattering). I cant just keep moving the vial around and taking any reading I want.
Thank you very much.
If your blanks read zero you need to determine the standard deviation of repeated analysis of a low concentration standard. I would prepare a standard with a COD around 20 mg/L and determine seven replicates of this.
The varying values of your blank should be accounted for, so for the LOD I would make the LOD measurements of the blanks by zeroing the detector with blank, then removing and rotating the vial (say 1/3), Inserting back into instrument and record value. Repeat this step (without re-zeroing) until you have the number of data points required.
See attachment for EPA method - and MDL requirement.
http://water.epa.gov/scitech/methods/cwa/bioindicators/upload/2007_07_10_methods_method_410_4.pdf
this is also very uselful. thank you for taking the time to reply! its greatly appreciated
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