Calculation of S/N

[Sunjay]

Dear All,

Can someone tell me what is the right way to calculate Signal to noise? the software calculates the noise by ASTM method and by 6SD method. If we uses noise by ASTM method the S/N is high and passing but by 6SD method it is low.

Can u please help?

Regards

[HW Mueller]

JW Dolan, LC.GC Europe, January 2006, page 12. Dolan averages the noise somewhat, others don´t.

[Sunjay]

Dear Sir,

thankx for information.

We r using the Agilent software for the calculationof signal/noise. The noise is coming in two modes i.e. ASTM and 6SD and there is large difference between two results.

So which is the method acceptable to regulatory ASTM or 6SD? and what is the difference between two.

Pls help and expain, as by one method (6SD) S/N fails the limit and by oher (ASTM) it passes the limit of 10.

Regards

[Mark Tracy]

Unfortunately, your noise specification did not specify the noise measurement method. You probably will have to track down the original data or authors to find out. Then amend the SOP to include that information.

The reason that your software offers two different algorithms is because there is no agreement on the "right" way to do it. Opinions vary.

[Dan]

Sunjay,

There are three different ways to measure noise in the chromatogram (4 if you count standard deviation):

1) 'peak-to-peak' noise (Np-p)

2) 'peak-to-valley' noise (Np) (This is also called "peak noise").

3) RMS (root mean square) noise

An electronic system such as the Agilent CDS is most likely measuring RMS noise as that is an easy to do electrical measurement.

I don't remember how the ASTM method works.

Np-p = 2 X Np

and

N(RMS) = ~0.7 Np


As Mark noted, you need to know how the noise is being determined. That way you can see why there are differences. Check with your vendor.

The best guidance that I can think of is ICH Q2(R1). Please see this link:

http://www.ich.org/LOB/media/MEDIA417.pdf

I have usually used Np-p to determine the S/N, but, on occasion, I have used the standard deviation. It all depends on your SOP or validation protocol. The important thing is to document the technique for the noise measurement in the validation protocol and report and in the method.

Regards,

Dan

[Sunjay]

http://www.chem.agilent.com/cpdocs/a10424.pdf

This is link for Agilent document.

In the waters the S/N is low as compared to Shimadzu/Agilent.

In Shimadzu ASTM method is used and in Agilent noise is appearing on c'gram in all the three methods. By using ASTM method S/N is high (about 5 time) as compared to Waters.

Regards