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BOD sample toxicity
Posted: Thursday, November 10, 2011 1:41 PM
Joined: 11/10/2011
Posts: 1


Can someone tell me if this sample shows sample toxicity?

                Seed Volume(mL)  Dil (%)  DOi(mg/L)  DOf(mg/L) SCF

Seed ctr 1     3                    ---        8.98         5.66          1.11

Seed ctr 2     5                    ---        9.03         3.42          1.12   

                                                                                   BOD (mg/L)

GGA              3                    2          8.99          2.72        146

Sample A       2                    2          8.96          4.86        94

                   2                    2          8.96          5.03        85

                   2                    2          8.98          4.99        88

                   2                    5          8.90          4.99        55

                   2                    5          8.90          4.98        55

                   2                    5          8.91          4.94        54

                   2                    10        8.84          2.32        43

                   2                    10        8.84          2.36        43

                   2                    10        8.85          2.23        44

Thank you for your help!


Perry Brake
Posted: Friday, November 11, 2011 10:55 AM
Joined: 12/17/2010
Posts: 23

To the best of my knowledge, there is no definition of "interference" other than a vague statement that, as dilution increases, so does the BOD result.  I don't think anyone would say that your data shows definite signs of interference because you haven't done enough dilutions (2, 5, and 10%), and your most dilute bottles (2%) are not dilute enough.


If you were to dilute the entire sample by a factor of 10 and run those same dilutions (2, 5,and 10%) and the BOD results from those additional dilutions  jumped from, say, 100, to 300, to 800 for the most dilute bottle, then you could say without much doubt that there is interference.  I recommend at least seven different dilutions, with the most dilute including a dilution of the entire sample, when trying to prove interference.  


Not that you asked, but your data shows outstanding precision, so good that you are wasting your time in running each dilution in triplicate.  If you average the nine bottle for Sample A, you get 62.3...if you consider only one bottle, say the middle one, in each dilution set, your average would be 61.0, so why run the three identical bottles for each dilution. 


On the other hand, your GGA result is more than just a little bit low...but I think you know that!