Dear Mohammed Yousffi,
I just calculated the amount of possible endotoxin in your sample.
The amount of 18 ppb is 18 ng/mL of total carbon. Assuming endotoxin is
about 10% weight of the total carbon, the concentration of endotoxin in
your sample is 1.8 ng/mL. The potency of purified endotoxin is about
5-10 EU/ng, but in this case, endotoxin is naturally occurred endotoxin.
Assuming the potency of the endotoxin is 1 EU/ng, the endotoxin activity
in your sample can be 1.8 EU/mL. So it was possible that you observed
0.65 EU/mL endotoxin in a water sample with 18 ppb TOC.
I know it is too much assumption, but if the sample contains mostly
endotoxin, endotoxin can be detected in a sample that shows under the
detection limit of TOC. The LAL test detects ppt order of endotoxin.
I am sorry for not providing any useful information to solve your
It is just for your information.
Masakazu Tsuchiya, Ph. D.
Senior Research Scientist
Endotoxin and Microbial Detection
E-mail: [log in to unmask]
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From: The Pharmaceutical Microbiology Forum Email List
[mailto:[log in to unmask]] On Behalf Of Mohammad Yousffi
Sent: Thursday, October 08, 2009 10:47 AM
To: [log in to unmask]
Subject: [PMFLIST] Endotoxin In RO system but TOC is low
Can someone explain to me why you would see high Endotoxin (0.65 Eu/mL)
in a USP purified RO water system (With RO membranes and an EDI system)
when the TOC is low (~ 18 ppb)?
We installed new membranes as part of our Preventative maintenance and
initially we saw high TOC (>300 ppb) and then it dropped after draining
the storage tank. Now its in normal range but we see high Endotoxin in
Thanks in advance!
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