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| | | Supreme Being
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| | This may be old hat on the Lab section forum, because I'm mostly on the Operations section. Anyway we are setting up a new lab and the Ph's and ammonia probes are reading erratic. We have pinpointed the source of the problem as being the magnetic stirrer. Steady readings are gotten off of the stirrer. Has anyone else faced this problem? What do you do about it? Is it a faulty stirrer, and should I send it back? |
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| | | Supreme Being
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| | Jerry, I have seen it before a long time ago before the electronics are as good as they are now. I guess its possible that the stirrer is inducing voltage in something somewhere that it should not be. Could be a faulty stirrer , but it could be inadequate shielding or grounding on the probes and cabling. Given that you have the same problem on two probes , its probably not them unless perhaps they are the same brand and have a similar design issue. I am sure one of the lab people will have a comment. Regards TerryF |
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| | | Supreme Being
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| You might also be stirring the beaker too vigorously, so that the probe is seeing air gaps.
Jeff Naumann
(310) 540-0045
FAX (310) 540-0337
http://www.jeffnaumannassociates.com/ |
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Supreme Being
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| | You might be transferring heat from the stirrer to the sample. Is the top warm? If so, put a thin piece of styrofoam on top. |
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| | | Supreme Being
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| Check if your stirrer is also equipped with heating function and ensure that heating function is switched off plus if the magnetic beads are washed thoroughly. One large size magnetic bead moving gently is better than smaller jumping beads.
sabir |
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| | | Supreme Being
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| | The stirrer is not heated and .we are using a stir bar. |
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| | | Forum Newbie
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Last Login: 9/23/2008 11:31:10 AM
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| | This may or may not be your problem. In water samples that have a high dissolved carbon dioxide content, the dissolved CO2 keeps the pH low. Any stirring or sample warming causes the sample to off-gas and the pH will rise rapidly. No real solution here except to keep that stir bar spinning as slowly as absolutely possible and to take your readings quickly. The pH will not become stable, it will slowly rise as the sample off-gases from super-saturated down to saturation. |
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