S/N Ratio according to E.Ph. 2.2.46

[Sahav]

Hi,

according to E.Ph. 2.2.46, S/N ratio is calcualed using a "range of the background noise in a chromatogram obtained after injection or application of a blank, observed over a distance equal to 20 times the width at half-height of the peak in the chromatogram obtained with the prescribed reference solution and, if possible, situated equally around the place where this peak would be found. "

For us, having to take 20 times the width at half-height of the peak is sometimes very challenging, due to interference peaks etc.

Is this huge window really justified?
And how could we work around this, not to get into troubles during audits?

Thank you very much.

Sahav

[krickos]

Hi

As from edition 6.4 of Ph Eur effective from 1st of April 2009, the "window" is reduced from a factor 20 to a factor 5.

This should reduce this issue significantly. At my work we historiclly worked around the problem by inserting a justification/exception in a SOP with examples (early eluters, "non removeble" interferances in blanks etc).

Cheers Chris

[Sahav]

Thank you very much for this helpful comment!

I could not find any reference in the USP on how exactly to determine the signal-to-noise ratio.

Is there any other US guideline which would detail this calculation?

Thank you very much!

Regards,

Sahav

[wrighty]

The change in the number of points is interesting. Would that affect the validity of software that calculates the S/N ratio based on the exisitng method?

[krickos]

The change in the number of points is interesting. Would that affect the validity of software that calculates the S/N ratio based on the exisitng method?

Would be surprised if that was the case, the few softwares I have used you set the time span for measuring the noise (h) manually, so hopefully you just have to adjust that.