Discussion Category:  UHPLC Detectors

PDA Noise vs. TUV Noise

We are attempting to transfer a method developed using a TUV detector on a Waters Acquity system to a simular system with a PDA. Signal to Noise seems to fail on the PDA due to higher noise. Just wondering if anyone had observed a difference betweent the detectors?
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Asked by

old_phart
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Bob Kafato
What are the Signal to Noise specifications of each detector? Is everything else the same configuration, like the column, pump, injector and plumbing? So many variables. If the PDA has similar specs to the TUV and all else is the same, then how about the flow cell volume on the PDA vs the TUV?
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Ben.W
Hi Mr Old_Phart! ; ) A difference in signal to noise between the two detectors is normal due to differences between their optics and electronics. From the spec sheet, the Acquity TUV manages pretty low noise of 6 µAU compared with the Acquity PDA with noise specs of 10 µAU. The pass / fail threshold may need to be re-determined for this detector change. Does this help explain why the signal noise is failing with the detector change? The flow cells are the same length of 1cm assuming they are both analytical... Thanks, Ben Empower at MVC [url=http://]www.mvc-consult.com[/url]
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Bob Kafato
With noise specs that close, I would think the difference then is due to plumbing issues or mobile phase and not the detector. We need more data on the problem.
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old_phart
Thanks Bob and Ben, Yes I agree that the differences in detector specs do not account for the signal differences we are seeing. We observe a several fold (3-6 or so) difference in noise; signal seems to be about the same on both instruments. And I agree it is likely plumbing or hardware other than the detector. I have requested Waters to bring in a TUV and test it on our instrument, if the problem disappears then it IS the detector, or at least our PDA, if the problem persists, then it has to be with the system. The instrument is under a service plan and Waters will need to investigate the differences. Thanks to both, I wanted to confirm if it was something others had seen as I have not personally used a system with the TUV.
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Ben.W
No problem. It is worth considering that although the specs are both very small, the TUV noise is almost half that of the PDA - in ideal conditions, this could give the TUV nearly twice the signal to noise for the same sample. Also how are a you calculating signal to noise? It is worth checking the noise value by eye and doing a quick manual calc to confirm the signal to noise is in the right ball park and the correct value for noise is being used. Other than that... it could be the hardware. Thanks, Ben Empower at MVC [url=http://]www.mvc-consult.com[/url]
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