Signal to noise ratio

Hey, 
I have many questions.
how the noise is read in empower 3 for HPLC? Is it usp-noise or peak-to-peak noise when the blank injection is selected?
Because in my belief usp noise and peak to peak noise must result in same values but in reality they don’t.
Also, does empower 3 cancels drift and calculates noise where the drift is seen? 
Finally, how the software read noise if there is a signal in the vicinity of the main peak and the range from half-height multiplier product by the peak width at the half height is large enough to encompass the mentioned signal?

Comments

  • There is a lot of information on this topic when you google it.
    https://help.waters.com/help/en/support/library-details.html?documentid=TECN134884650
    Here is a document from waters that might have the answers for you.
  • Hey @Jovvor,
    thank you for your response. Let me give you an example. There is a peak with the height of 1578 microvolts, and the USP noise given by empower 3 is 0.000082. When you calculate s/n based on 2*(Height-0.5*usp noise)/usp noise it results to 37.48.
    when I print the compound peak and the baseline range of the blank on paper, the height of the peak is about 0.0016 mAu (or around 18.6 cm), and the peak to peak noise of the blank injection is 0.00004 mAu (or around 0.4 cm) if you consider 0.0016 as h and 0.00004 as H, then S/N based on 2*h/H would result to 80 which is very different compared to 37.48. I’m trying to understand this discrepancy and don’t see any logical explanation for this in technical notes.
  • I used approximates for values acquired on the paper print but my approximates are very close to what I’m watching on paper.